WEATHERABILITY OF ENHANCED-DEGRADABLE PLASTICS
by
Anthony L. Andrady
Research Triangle Institute
Research Triangle Park, NC 27709
Contract No, 68-02-4544
Work Assignment Manager
Walter E. Grube, Jr.
Waste Minimization, Destruction and Disposal Research Division
Risk Reduction Engineering Laboratory
Cincinnati, Ohio 45268
RISK REDUCTION ENGINEERING LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
The material has been funded wholly or in part by the United States
Environmental Protection Agency under contract 68-02-4544 to Research Triangle
Institute. It has been subject to the Agency's review and it has been approved for
publication as an EPA document. Mention of trade names or commercial products does
not constitute endorsement or recommendation for use.
11
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FOREWORD
Today's rapidly developing and changing technologies and industrial products and
practices frequently carry with them the increased generation of materials that, if
improperly dealt with, can threaten both public health and the environment. The U.S.
Environmental Protection Agency is charged by Congress with protecting the Nation's
land, air, and water resources. Under a mandate of national environmental laws, the
agency strives to formulate and implement actions leading to a compatible balance
between human activities and the ability of natural systems to support and nurture life.
These laws direct the EPA to perform research to define our environmental problems,
measure the impacts, and search for solutions,
The Risk Reduction Engineering Laboratory is responsible for planning,
implementing and managing research, development and'demonstration programs to
provide an authoritative, defensible engineering basis in support of the policies,
programs, and regulations of the EPA with respect to drinking water, wastewater,
pesticides, toxic substances, solid and hazardous wastes, and Superfund-related activities.
This publication is one of the products of that research and provides a vital
communication link between the research and the user community
This publication is a result of co-funded research between the Office of Research
and Development and the Office of Solid Waste. The purpose of this project was to
assess the performance of several enhanced degradable plastic materials under a variety
of different exposure conditions.
E. Timothy Oppelt, Director
Risk Reduction Engineering Laboratory
in
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ABSTRACT
The main objective of this study was to assess the performance and the asociated
variability of several selected enhanced degradable plastic materials under a variety of
different exposure conditions. Other objectives were to identify the major products
formed during degradation and to assess the preliminary toxicity of such products, arid to
determine the effect of the enhanced degradable plastic material on the quality of
recycled products.
Several commercially available materials, including both photodegradable and
biodeteriorable plastics were chosen for inclusion in this study. Exposure scenarios
consisted of outdoor direct exposure, soil burial, and marine and freshwater exposure.
Laboratory exposure scenarios consisted of accelerated weathering and lab accelerated
soil burial.
Results of this study showed the elongation at break and the energy to break to
be the test parameters most sensitive to weathering induced changes.
IV
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CONTENTS
Disclaimer
Foreword
Abstract
jv
Figures
Tables
Acknowledgement ............................................ xvii
1. Introduction .......................................... 1-1
2. Exposure Methods ..................................... 2-1
3. Spectral Sensitivity of Enhanced Photodegradable Plastics ....... . 3-1
4. Weathering of Enhanced Degradable Plastics ................. 4-1
5. Other Effects of Weathering ................ . ............. 5-1
6 Preliminary Toxicity Studies .............................. 6-1
7. Preliminary Recycling Study .............................. 7-1
8. Conclusions and Recommendation .......................... 8-1
Appendices
A Sample Log for Outdoor Exposure
B Sample Log for Weathero-Ometer Exposure
C Sample Log for Lab Accelerated Exposure
D Table of Daily High, Low, and Average Temperatures, Rainfall, and Total Global
Radiation for Cedar Knolls, NJ
E Table of Daily High, Low, and Average Temperatures, Rainfall, and Total Global
and UV Radiation for Chicago, IL
F Table of Daily High, Low, and Average Temperatures, Rainfall, and Total
Global and UV Radiation for Seattle; WA
H Table of Daily High, Low, and Average Temperature, Rainfall, and Total Global
and 'UV Radiation for Wittmann, AZ
I Table of Daily High, Low, and Average Temperatures and Rainfall for Research
Triangle Park, NC
J Tensile Data for Activation Spectra Samples
K Tensile Data Summaries for All Polymers and Locations
L Conversion of Solar Radiation Data for a Horizontal Surface to a Tilt Angle of 45
Appendices are not included in this document, limited quantities are available from
Lynnann Kitchens, US EPA Center Hill Research Facility, 5995 Center Hill Road,
Cincinnati, OH 45224
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List of Figures
Number Page
1.2.1 A flow chart for consumer plastic products: production, use, and ;
disposal ' 1-23
2.3.1 Duplicate exposure protocol for an exposure for n weeks with weekly
sampling of set 1 ; 2-6
2.4.1 Spectral transmittance of sharp-cut filters 2-16
2.4.2 Spectral band for incremental UV radiation of filters 5 and 6 2-18
2.4.3 Specimen arrangement for Weather-Ometer® exposure of activation
spectra samples 2-22
2.5.1 Experimental set up for WVTR measurements 2-25
2.8.1 Typical sample flow 2-37
3.1.1 (Ethylene carbon monoxide) copolymer (6P): percent elongation at
break as a function of short wavelength cut-off-Set 1 - 77°C - inner
plus outer strips 3-14
3.1.2 (Ethylene carbon monoxide) copolymer (6P): percent elongation at
break as a function of short wavelength cut-off-Set 1 - 77°C - inner
strips only 3-15
3.1.3 (Ethylene carbon monoxide) copolymer (6P): percent elongation at '
break as a function of short wavelength cut-off-Set 2 - 60°C 3-16
3.1.4 Spectrum of sunlight filtered through window glass 3-17
3.1.5 Low density polyethylene containing added metal compound pro- ;
oxidants (PG): percent elongation at break as a function of short
wavelength cut-off -.preliminary exposure 3-18
3.1.6 Low density polyethylene containing added metal compound pro- •
oxidants (PG): percent elongation at break as a function of short
wavelength cut-off - 295 hours - filter sets A and B 3-19
3.1.7 Activation spectrum for yellowing of polystyrene foam 3-20
3.1.8 Polycaprolactone/LLDPE (PCL): percent elongation at break as a ;
function of short wavelength cut-off of filter 3-21
4.1.1 Elongation at break vs. exposure time for duplicate exposures of 6P
samples outdoors in Miami, FL 4-45
a. Enhanced degradable material
b. Control material
VI
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List of Figures (continued) ;
Number , .. Page
4.1.2 • Elongation at break vs. exposure time for duplicate exposures of PG
samples outdoors in Chicago, IL 4-46
a. Enhanced degradable material
b. Control material
4.1.3 Change in mass after tumbling friability test vs. exposure time for
duplicate exposures of PS foam outdoors in Cedar Knolls, NJ 4-47
a. Enhanced degradable material
b. Control material
4.1.4 Variation of selected tensile parameters with duration of exposure for '
outdoor exposure 4-48
a. 6P - Miami, FL - stress at break 4-48
b. 6P - Miami, FL - elongation at break 4-48
c. 6P - Miami, FL - energy to break 4-49
d. 6P - Miami, FL - modulus 4-49
e. 6P - Seattle, WA - stress at break 4-50
f. 6P - Seattle, WA - elongation at break : 4-50
g. 6P - Seattle, WA - energy to break 4-51
h. 6P - Seattle, WA - modulus 4-51
i. PG - Miami, FL - stress at break 4-52
j. PG - Miami, FL - elongation at break 4-52
k. PG - Miami, FL - energy to break 4-53
1. PG - Miami, FL - modulus 4-53
m. PG - Seattle, WA - stress at break • 4-54
n. PG - Seattle, WA - elongation at break 4-54
o. PG - Seattle, WA - energy to break 4-55
p. PG- Seattle, WA - modulus 4-55
4.1.5 Elongation at break vs. exposure time for outdoor, marine-floating,
4-56
a.
b.
c.
d.
e.
f.
g-
h.
i.
k!
1.
m.
n.
o.
P-
q-
r.
Vll
6P - Cedar Knolls, NJ - outdoor
6P - Chicago, IL - outdoor
6P - Miami, FL - outdoor
6P - Miami, FL - marine floating
6P - Seattle, WA - outdoor
6P - Seattle, W A - marine floating
6P - Wittmann, AZ - outdoor
6P - Kerr Lake, VA - fresh water floating
PG - Cedar Knolls, NJ - outdoor
PG - Chicago, IL - outdoor
PG - Miami, FL - outdoor
PG - Miami, FL - marine floating
PG - Seattle, WA - outdoor
PG - Seattle, WA - marine floating
PG - Wittmann, AZ - outdoor
PG - Kerr Lake, VA - fresh water floating
ADM - Cedar Knolls, NJ - outdoor
ADM - Chicago, IL - outdoor
4-56
4-56
4-57
4-57
4-58
4-58
4-59
4-59
4-60
4-60
4-61
4-61
4-62
4-62
4-63
4-63
4-64
4-64
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List of Figures (continued)
Number
4.1.5
s.
t.
u.
V.
w.
X.
y.
z.
aa.
bb.
cc.
dd.
ee.
ff.
gg-
4.1.6
a.
b.
c.
d.
e.
f.
g-
h.
i.
J-
k.
1.
m.
n.
0.
p.
q-
r.
s.
t.
u.
V.
w.
X.
y.
z.
aa.
bb.
cc.
Elongation at break vs. exposure time for outdoor, marine-floating,
and marine-sediment exposures (continued)
ADM - Miami, FL - outdoor
ADM - Miami, FL - marine floating
ADM - Seattle, WA - outdoor
ADM - Seattle, WA - marine floating
ADM - Wittmann, AZ - outdoor
ADM- Miami, FL - marine sediment
ADM - Seattle, WA - marine sediment
ADM - Kerr Lake, VA - fresh water floating
PCL - Miami, FL - outdoor •
PCL - Miami, FL - marine sediment
PCL - Seattle, WA - marine sediment
PCL - Kerr Lake, VA - fresh water floating
BP - Miami, FL - outdoor
BP - Miami, FL - marine sediment
BP - Kerr Lake, VA - fresh water sediment
Semi-logarithmic plot of elongation at break vs. exposure time for
outdoor, marine-floating, and marine sediment exposures ,
6P - Cedar Knolls, NJ - outdoor
6P - Chicago, IL - outdoor
6P - Miami, FL - outdoor
6P - Miami, FL - marine floating
6P - Seattle, WA - outdoor
6P - Seattle, WA - marine floating
6P - Wittmann, AZ - outdoor
6P - Kerr Lake, VA - fresh water floating
PG - Cedar Knolls, NJ - outdoor
PG - Chicago, IL - outdoor
PG - Miami, FL - outdoor
PG - Miami, FL - marine floating
PG - Seattle, WA - outdoor
PG - Seattle, WA - marine floating
PG - Wittmann, AZ - outdoor
PG - Kerr Lake, VA - fresh water floating
ADM - Cedar Knolls, NJ - outdoor
ADM - Chicago, IL - outdoor
ADM - Miami, FL - outdoor
ADM - Miami, FL- marine floating :
ADM - Seattle, WA - outdoor
ADM - Seattle, WA - marine floating
ADM - Wittmann, AZ - outdoor
ADM - Miami, FL - marine sediment ".
ADM - Seattle, WA - marine sediment
ADM - Kerr Lake, VA - fresh water floating
PCL - Miami, FL - outdoor
PCL - Miami, FL - marine sediment
PCL - Seattle, WA - marine sediment
: Page
....;4-65
....4-65
.... 4-66
....'4-66
....'4-67
.... 4-67
.... 4-68
>4-68
....4-69
....14-69
....4-70
;4-70
.... 4-71
.... 4-71
.... 14-72
....4-73
....4-73
.... 4-73
....'4-74
.... 4-74
.... 4-75
....4-75
.... 4-76
.... :4-76
.... 4-77
,...4-77
....4-78
....•4-78
.... 4-79
....4-79
.... 4-80
.... 4-80
,...;4-81
....4-81
....4-82
,...'4-82
....4-83
,...:4-83
....4-84
4-84
....4-85
4-85
,...4-86
,... 4-86
,...4-87
Vlll
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List of Figures (continued)
Number . ;,. page
4.1.6 Semi-logarithmic plot of elongation at break vs. exposure time for
outdoor, marine-floating, and marine sediment exposures (continued)
dd. PCL - Kerr Lake, VA - fresh water floating 4-87
ee. BP - Miami, FL - outdoor " 4-88
ff. BP - Miami, FL - marine sediment • 4-88
gg. BP - Kerr Lake, VA - fresh water sediment 4-89
4.1.7 Change in mass (as measured by tumbling friability) with duration of
exposure for polystyrene foam exposed outdoors .' 4-90
a. Cedar Knolls, NJ 4-90
b. Chicago, IL 4-90
c. Miami, FL '. 4-91
d. Seattle, WA 4-91
e. Wittmann.AZ 4-92
4.1.8 Semi-logarithmic plot of tumbling friability data versus duration of
exposure for polystyrene foam exposed outdoors 4-93
a. Cedar Knolls, NJ 4-93
b. Chicago, IL '. 4-93
c. Miami.FL 4-94.
d. Seattle, WA 4-94
e. Wittmann, AZ 4-95
4.1.9 GPC data for PS plotted as reciprocal degree of polymerization vs.
duration of exposure 4-96
a. Outdoor - Chicago, IL 4-96
b. Outdoor - Miami, FL „ 4-§6
c. Marine floating - Miami, FL 4-97
d. Marine floating - Seattle, WA 4-97
4.1.10 Marine-floating exposure of LDPE control and (ethylene-carbon
monoxide) copolymer in Miami, FL ' 4-98
a. 6P-35days 4-98
. b. 6PC-35days 4-98
c. 6P-49days 4-99
d. 6PC-49days 4-99
4.1.11 Marine floating exposure of LDPE control and (ethylene-carbon
monoxide) copolymer in Seattle, WA 4-100
a. 6P-35days 4-100
b. 6P-42days , 4-100
c. 6PC-42days • 4-101
d. 6P-45days 4-101
e. 6P-52days 4-102
f. 6PC-52days 4-102
g. 6P-59days 4-103
IX
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List of Figures (continued)
Number ; Page:
4.1.12 Marine floating exposure of LDPE control and LDPE/MX material in
Miami, FL 4-104
a. PG-39days ! 4-104
b. PG-42 days ......'.: 4-104
c. PG - 49 days 4-105
d. PGC-49days '.'.'.'.'.'.'.'.'. 4-105
e. PG-61 days 4-106
f. PGC-61 days '.'.'.'.'.'.';. 4-106
g. PG-68 days :.4-107
4.1.13 Marine floating exposure of LDPE control and LDPE/MX material in
Seattle, WA .4-108
a. PG-35 days ;4-108
b. PG-42days 4-108
c. PGC-42days '4-109
d. PG - 45 days 4-109
e. PG-52days 4-110
f. PGC-52days !.:4-ll()
g. PG-59 days .! 4-111
4.1.14 Marine sediment exposure of LDPE control and LDPE/starch/MX
material in Seattle, WA 4-112
a. ADM-35 days 4-112
b. ADM - 42 days 4-112
c. ADMC-42days '..'.'.'.'.'.'.'.'.'.'.'. 4-113
d. ADM-59 days 4-113
4.1.15 Marine floating exposure of polystyrene foam and photodegradable
polystyrene foam in Seattle, WA 4-114
a. PS- 14days 4-114
b. PSC- 14days ' 14-114
4.1.16 Total solar radiation (45° south) versus the duration of exposure ,4-115
a. Cedar Knolls, NJ 4-115
b. Chicago, IL 4-116
c. Miami, FL 4-117
d. Seattle, WA 4-118
e. Wittmann.AZ 4-119
4.1.17 Degradation rate versus the average temperature and average solar
radiation at exposure site 4-120
a. (Ethylene-carbon monoxide) copolymer 4-120
b. Plastigone (LDPE//MX) film 4-121
c. ADM (LDPE/Starch/MX) film 4-122
d. Expanded polystyrene foam (Polysar material) 4-123
x
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List of Figures (continued)
Number . Page
4.1,18 Semi-logarithmic plot of elongation at break versus the total radiation at
exposure site: composite data for all outdoor locations .' 4-124
a. (Ethylene-carbon monoxide) copolymer 4-124
b. PG (LDPE/MX) film 4-125
c. ADM (LDPE/starch/MX) film 4-126
d. • Expanded polystyrene foam (Polysar material) 4-127
4.1.19 Elongation at break versus duration of exposure for outdoor soil burial
at Research Triangle Park, NC 4-128
a. ADM/ADMC materials 4-128
b. PCL/LLDPE materials 4-129
c. BP materials 4-130
4.1.20 Outdoor soil burial of Biopol (BP) at Research Triangle Park, NC 4-131
a. 22 days 4-131
b. 24 days • 4-131
c. 27 days : .....4-132
• d. 36 days " 4-132
e. 38 days 4-133
f. 41 days • 4-133
g. 43 days 4-134
h. 45 days 4-134
i. 48 days 4-135
4.2.1 Elongation at break versus the duration of exposure for Weather-
Ometer® exposure 4-136
a. 6P/6PC 4-136
b. PG/PGC 4-137
c. ADM/ADMC 4-138
4.2.2 Change in mass (as measiired by tumbling friability) versus the
duration of exposure for Weather-Ometer® exposures of
photodegradable polystyrene foam 4-139
4.2.3 Elongation at break versus the exposure temperature for Weather-
Ometer® exposure (50 hours) for 6P, PG, and ADM samples 4-140
4.2.4 Change in mass (as measured by tumbling friability) versus exposure
temperature for Weather-Ometer® exposure (50 hours) of
photodegradable polystyrene foam 4-141
XI
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List of Figures (continued) ;
Number :Page
5.1.1 Molecular weight distribution (as measured by GPC) of exposed
polystyrene foam , • 5-24
a. PS - Outdoor - Chicago, IL ! 5-24
b. PSC - Outdoor - Chicago, IL 5-24
c. PS - Outdoor - Miami, FL 5-25
d. PSC - Outdoor - Miami, FL ; 5-25
e. PS - Marine floating - Miami, FL 5-26
f. PSC - Marine floating - Miami, FL 5-26
g. PS - Marine floating - Seattle, WA 5-27
h. PSC - Marine floating - Seattle, WA ; 5-27
i. PS - Weather-Ometer® i 5-28
5.2.1 Water vapor transmission data for LDPE/MX samples weathered in :
Miami, FL 5-29
5.2.2 Change in WVTR with weathering time for PG (LDPE/MX) samples ; 5-30
5.2.3 Water vapor transmission data for PCL (LLDPE/PCL blend) unaged |
film and a film exposed to an aerobic biotic environment (40 days) ...: 5-31
5.2.4 Water vapor transmission data for unexposed and weathered ADM
(LDPE/starch/MX) films ' 5-32
5.2.5 Gas (COz) sorption curves for weathered PG (LDPE/MX) films \
exposed in Weather-Ometer® ", 5-33
5.2.6 Gas (CO2) sorption curves for weathered 6P (ethylene-carbon •
monoxide) copolymer films exposed in a Weather-Ometer® 5-34
5.2.7 Difference in short-time gradient in sorption curves for aged and ;
unaged PG samples '. 5-35
5.2.8 Difference in short-time gradient in sorption curves for aged and
unaged 6P samples • 5-36
5.2.9 Effect of Weather-Ometer® exposure upon the COi permeability for
PG material ; 5-37
5.2.10 Effect of Weather-Ometer® exposure upon the CO2 permeability for 6P
material \ 5-38
5.3.1 A TGA tracing of LDPE/starch/MX film containing -6% starch 5-39
5.3.2 A TGA tracing of an LDPE control film 5-40
XII
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List of Figures (continued)
Number page
5.3.3 Percent weight loss versus known starch content of ADM
(LDPE/starch/MX) films in TGA experiments 5-41
5.3.4 Percent weight loss versus weight fraction of ADM (LDPE/starch/MX)
film in mixtures of ADM and control LDPE 5-42
5.3.5 A TGA tracing of an ADM (LDPE/starch/MX) film exposed outdoors
for 20 weeks showing variability in 140°C-260°C range 5-43
6.1 Concentrations of test solutions used in toxicity experiments 6-3
NOTE:
Any reference to "degradable" polymers in the figure or table captions means
"potentially degradable" and is not a conclusion that the material has been demonstrated as
being enhanced degradable according to any standard test method.
xni
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List of Tables
Number
1.5.1 Proposed Definitions of Environmental Breakdown Processes and
Enhanced Degradable Plastics
2.2.1. Identification, Sources, and Code Names of Plastic Film Materials
Used in the Study.
Page
1-11
2-4
2.3.1 Sample Exposure Matrix for Natural Weathering ; 2-8
2.3.2 Sample Identification for Outdoor Exposure 2-9
2.3.3 Sample Identification for Marine Exposure > 2-12
2.3.4 Sample Identification for Freshwater Exposure at Kerr Lake, VA '< 2-13
2.3.5 Sample Identification for Soil Burial Exposure at Research Triangle ;
Institute ^2-14
2.5.1 Instron Test Parameters Used for Testing Exposed Samples 2-21
2.6.1 Test Conditions for Acute Fathead Minnow (Pimephales promelas) \
Toxicity Tests ;2-30
2.6.2 Test Conditions for Ceriodaphnia dubia survival and Reproduction
Test (Conforming to EPA/600/4-89/001) \ 2-32
2.7.1 Pre-exposure of Degradable Plastics for Recycling Study \ 2-33
2.7.2 Composition of Extruded Films Prepared for Preliminary Recycling
Study :2-35
3.1.1 Photodegradation Data for (ethylene-carbon monoxide) Copolymer
[6-Pack Rings (6P)] Exposed 117 Hours (Set 1) at 77°C : 3-2
3.1.2 Photodegradation Data for (ethylene-carbon monoxide) Copolymer i
[6-Pack Rings (6P)] Exposed 219 Hours (Set 2) at 60°C ; 3-4
3.1.3 Photodegradation Data for Plastigone Material (PG) Exposed 94.5
Hours at 77°C i 3-6
3.1.4 Photodegradation Data for Plastigone Material (PG) Exposed 295
Hours at 77°C ' 3-7
3.1.5 Yellowness Index Data for Polystyrene Foam (PS) Exposed 189 ,
Hours in Atlas 6500 Watt Borosilicate Filtered Xenon Arc ;
Weather-Ometer® at60°C 3-9
i
3.1.6 L, a, and b Values for Polystyrene Foam Samples : 3-10
xiv
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List of Tables (continued)
Number .. . Page
3.1.7 Photodegradation Data for Polycaprolactone/LLDPE (PCL)' Exposed
129 Hours at 60°C 3-12
3.1.8 Spectral Sensitivity of Plastic Materials 3-13
4.1.1 Table of Slopes Based on Plots of Selected Tensile Parameters of 6P
and PG Exposed Outdoors in Miami, FL and Seattle, WA,
According to Equation 4-1 ' 4-3
4.1.2 Table of Regression Coefficients (Slopes and Intercepts) Based on
Plots of Tensile Elongation at Break Data for Outdoor Exposure
Experiment 4-8
4.1.3 Yellowness Index and L, a, b Values for Polystyrene Foam Exposed
Outdoors , 4-12
4.1.4 Tumbling Friability Results for Polystyrene Foam Samples Exposed
Outdoors 4-19
4.1.5 Number Average Molecular Weight of Polystyrene Foam Exposed
Outdoors, as Determined by Gel Permeation Chromato-
graphy (GPC) 4-24
4.1.6 Table of Regression Coefficients Based on Plots of Tumbling Friability
and GPC Data for Polystyrene Foam Exposed Outdoors 4-25
4.1.7 (a) Analysis of Variance for ADM Soil Burial Samples 4-29
(b) Analysis of Variance for ADMC Soil Burial Samples 4-30
(c) Analysis of Variance for PCL Soil Burial Samples '.. 4-31
(d) Analysis of Variance for LLDPE Soil Burial Samples 4-32
(e) Analysis of Variance for BP Soil Burial Samples 4-33
4.1.8 Table of Regression Coefficients Based on Plots of Tensile Elongation
at Break Data for Soil Burial Exposures 4-34
4.1.9 Extents of Degradation for Natural Weathering 4-36
4.2.1 Table of Regression Coefficients Based on Plots of Tensile Elongation
at Break and Tumbling Friability for Weather-Ometer® Exposure 4-39
4.2.2 Acceleration Factors Obtained for Weather-Ometer® Exposures as
Compared to Outdoor Exposures 4-40
4.2.3 Polystyrene Foam Yellowness Index Values for Weather-Ometer®
Exposure 4-41
4.2.4 Tensile Test Data for Laboratory Accelerated Soil Burial Samples 4-43
5.1.1 Gel Permeation Chromatography Results for Polystyrene Foam 5-3
xv
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List of Tables (continued)
Number • ;Page
5.1.2 Gel Permeation Chromatoeraphy Results for Polycaprolactone Fraction
of PCL/LLDPE Blend : 5-6
5.2.1 Water Vapor Transmission Test Data (LDPE/MX Samples) ' 5-8
5.2.2 Water Vapor Transmission Test Data (LLDPE/PCL Blend Samples) '5-10
5.2.3 Water Vapor Transmission Test Data (ADM Samples) J5-12
5.2.4 Water Vapor Transmission Test Data (LDPE/Starch/MX Samples) '5-13
5.2.5 Carbon Dioxide Permeation Data for 6P and PG Films 5-15
5.2.6 Comparison of Transport Parameters and Tensile Modulus of
Photodegradable Films Weathered in Weather-Ometer® 5-16
5.3.1 TGA Data for ADM (LDPE/Starch), LDPE Mixes, and ADM (2) Films :
with Different Starch Contents '5-18
5.3.2 Effect of Environmental Exposure on Starch Content of ADM Samples ... :5-20
6.1.1 Chronic Toxicity Test Data Summary for (ethylene-carbon monoxide)
Copolymer Material (6P and 6PC). Test Organism: Ceriodaphnea
dubia , 6-5
6.1.2 Acute Toxicity Test Data Summary for (ethylene-carbon monoxide)
Copolymer Material (6P and 6PC). Test Organism: Pimephales ;
promelas ; 6-6
6.2.1 Chronic Toxicity Test Data Summary for Polystyrene [(styrene-vinyl |
ketone) copolymer blends] Copolymer Material (PS).
Test Organism: Ceriodaphnea dubia ; 6-8
6.2.2 Acute Toxicity Test Data Summary for (polystyrene/(styrene-vinyl
ketone) blends) Copolymer Material (PS):
Test Organism: Pimephales promelas ; 6-9
6.3.1 Chronic Toxicity Test Data Summary for LDPE/starch/MX (ADM film) !
Material (ADM). Test Organism: Ceriodaphnea dubia 6-10
6.3.2 Acute Toxicity Test Data Summary for LDPE/Starch/MX (ADM)
Material. Test Organism: Pimephales promelas 6-11
7.2.1 Composition and Tensile Properties of Unexposed Films Containing
Recycled Degradable Plastics ; 7-2
xvi
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ACKNOWLEDGEMENT
This report was prepared under the coordination of Walter E. Grube, U.S.
Environmental Protection Agency (EPA), Risk Reduction Engineering Laboratory,
Cincinnati, Ohio. This report was prepared by Dr. Anthony Andrady, Research Triangle
Institute (RTI), Research Triangle Park, North Carolina. Contributing researchers from
RTI include Dr. Jan E. Pegram, Dr. Shuji Nakatsuka, Dr. Naraporn Rungsimuntakul,
Dr. Yelena Tropsha, Song Ye, William Woodard and Dr. Norma D. Searle.
XVII
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SECTION 1.0
INTRODUCTION
1.1 BACKGROUND
The use of plastics in packaging and in other consumer applications invariably leads
to a growing fraction of post-consumer plastic waste in the municipal solid waste stream
and in urban litter. The United States presently generates about 160 million tons of munic-
ipal solid waste annually, of which about 8 percent by weight is plastics [Franklin Associ-
ates, 1988; USEPA, 1991]. On a volume basis, however, the value is higher, about 20-25
percent [Modern Plastics, April 1990]. Since litter is generally perceived more readily in
terms of volume, the latter figure is probably of greater relevance. The proliferation of
plastic waste is related to the useful lifetimes (or the periods of utility) of the consumer
plastic products. Disposable plastic products with short useful lives, such as packaging,
therefore constitute nearly one third of the plastic waste in the municipal solid waste stream
[USEPA, 1990]. The large fraction of packaging materials designed for single use (fast
food containers, plastic cups, plastic bags, food wrappers, beverage bottles and bottle
caps) further exacerbates the situation. Even those packaging products designed for multi-
ple use do not have useful lifetimes comparable to those of durable plastic goods.
The present interest in plastic waste is driven not merely by aesthetic considerations
but also by ecological and economic concerns. The available volume of landfill space is
rapidly depleting hi most regions of the country [USEPA, 1988; USEPA, 1989]. Land-
filling is by far the primary means of solid waste disposal, and the growing shortage of
available volume of landfills in the United States will have a serious effect on future waste
disposal practices. A particularly visible fraction of post-consumer plastic waste is urban
litter. The unacceptability of litter, particularly the plastic litter, on purely aesthetic grounds
has been discussed since the early seventies when the problem of waste plastics first sur-
faced [GuiUett, 1973; Jensen et al., 1974].
Over the recent years a growing body of scientific data suggesting that plastic waste
may be hazardous to wildlife has been gathered. This is especially true in marine environ-
ments where many instances of entanglement of several species in plastic debris such as
netting and six.-pack rings have been reported. Sea lions [Loughlin, 1986] and fur seals
[Henderson, 1985; Bonner,1982] are particularly susceptible to entanglement in plastic
waste. Not only do these species concentrate about vessel routes (possibly because of food
waste discharged from ships), but the young animals are specifically attracted by floating
colored plastic material, increasing the probability of encounter with debris [Laist, 1987].
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Entangled animals may on occasion free themselves, but the episode, at least in some
species, may result in changes in feeding habits and slower growth rates [Feldkamp,
1985]. Entanglement can also be permanent, with the animal swimming about with a "col-
lar" of plastic restricting its growth and eventually leading to its death by asphyxiation.
At least fifty species of marine birds are known to ingest plastics [Day, 1980]. While
the effects of ingesting plastic waste, including virgin resin pellets, are not definitely'
known, ingestion is believed at least to reduce the urge to feed. Turtles [Balazs, 1985],
too, ingest plastic, particularly floating plastic bags probably mistaken for jellyfishes, a
staple of these species. Large amounts of plastics have been observed in the stomach con-
tents of turtles drowned and washed ashore. '.
1.2 RATIONALE FOR ENHANCED DEGRADABLE PLASTICS AND IMPACT
ON WASTE MANAGEMENT
Plastics are perceived to be persistent and non-degradable unlike other constituents of
the solid waste stream, particularly nature's own polymers such as cellulose, chitin, and
proteins. Rates of degradation of natural materials such as plant and animal tissue might be
a reasonable guide to ecologically "acceptable" rates of environmental degradation. If syn-
thetic thermoplastic materials can be designed to break down into innocuous products in
the environment at rates matching or exceeding the rates for naturally occurring polymeric
materials, the synthetic material would presumably be equally environmentally acceptable.
Enhanced degradable plastics technology strives to accelerate the breakdown of plas-
tic material by chemical modification of the polymer, synthesis of new thermoplastics
which are environmentally degradable, and incorporation of additives into commodity plas-
tic materials to achieve faster breakdown. Several different classes of such plastics have
evolved over the years, and these claim enhanced degradability in sunlight, under soil, in
sea water (or marine sediment), and under composting conditions.
From a practical standpoint this category of materials might be expected to have the
following impacts on solid waste management.
(a) Litter reduction. The lifetime of litter will be reduced, thus reducing the cost of litter
collection and disposal. In this role the degradable plastics can bring about the same
benefits as source reduction, if the lifetime of litter will be shortened to an extent to
make collection unnecessary.
(b) Marine plastic waste. There is no mechanism by which plastic waste is removed
from the marine/estuarine environments. Collection and disposal is often impractical.
In the absence of alternative strategies, the degradable plastics might play a role in
addressing this need.
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(c) Composting. Mechanical sorting of the solid waste prior to composting is both costly
and time consuming. If plastic films and containers can be left in the composting
stream, it represents a substantial cost saving. Enhanced degradable plastics may
therefore be desirable in a composting operation. The same is true of anaerobic
digestion processes as well.
(d) Landfills and sewers. These essentially anaerobic environments do not affect plas-
tics. Consequently even natural products such as food wastes and yard wastes as
well as cellulosics undergo very slow breakdown under landfill conditions (Rathje,
1987). Containment of organic waste capable of ready degradation in an enhanced
degradable plastic material might in some instances hasten the plastic's breakdown in
a landfill.
Figure 1.2.1 summarizes the fate of plastics waste and the impact of Enhanced
Degradable Plastics on current solid waste management practices. The present emphasis in
the area of municipal solid waste disposal is heavily placed on landfilling. Mainly due to
economic factors, future disposal strategies are likely to rely more heavily on incineration,
composting, and anaerobic treatment. Recycling, while certainly a helpful strategy, is
essentially a means of extending the useful lifetime of the plastic by a limited extent and is
not a means of disposal. It may, however, move the plastic material from the packaging
category into one which has a longer period of utility, easing the burden on the waste
stream. Success in recycling depends to a great extent, unfortunately, on large-scale,
consistent public participation as well as on identification of markets of adequate size for
the recycled product
1.3 BARRIERS TO WIDER ACCEPTANCE OF ENHANCED DEGRADABLE
PLASTICS
While several enhanced-degradable plastic formulations are currently available in the
market, their use in large-volume applications remains limited. The six-pack ring material
made of (ethylene - carbon monoxide) copolymer and the agricultural mulch films using
different photodegradable polymer technologies are about the only large-volume applica-
tions at the present time.
The slow growth and acceptability of the technology might be directly attributed to
lack of information on the nature, performance, and limitations of this technology. Specifi-
cally, there are several key issues which have not been fully resolved. In most cases, then-
resolution requires scientific information not as yet available from either the manufacturer
or from other sources. Due to the limited resources of smaller companies, and also to the
perceived small market size for their degradable plastics products, the manufacturers often
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cannot afford to carry out the studies required to fully explore this technology. These
issues are listed below.
Issue I: Confusions in Terminology
There is no consistent terminology to accurately describe a given category of :
enhanced degradable plastics. The technical literature on the subject often uses inaccurate
and make-shift descriptive terms. Manufacturer's trade literature does the same, using
terms which may potentially mislead the consumer.
A primary concern is the extent to which the environmental disintegration of .a product
needs to be accelerated before the plastic material may appropriately be described as being
enhanced degradable (or controlled lifetime). For instance, even the addition of regular-
compounding ingredients and the processing of the resin itself can (and often do) increase
its degradability. Such cursory increases, however, should not qualify the material as an
enhanced-degradable plastic. A well defined enhancement factor for different types of
enhanced-degradable plastics, compared to a control plastic, needs to be eventually estab-
lished to adequately define the term. '
The related issue is that of classification. The main confusion seems to arise from the
inconsistent use of the "bio" and "photo" prefixes and careless use of the term "degrada-
tion". The naming of a given technique is best based on the primary, predominant mecha-
nism and not on the resulting secondary processes. (Thus, the rapidly disintegrating six-
pack yokes currently in use are correctly called enhanced photodegradable materials.. On
extensive photodegradation, the polyethylene might be rendered increasingly biodegrad-
able. Since this is incidental and secondary, a "bio" or even "photo/bio" prefix is not
appropriate.)
Issue II: Performance: Litter and Municipal Solid Waste i.
Adequate performance of degradable plastics must invariably be defined in terms of
enhancement of degradation relative to that of a typical stabilized compound of the same
plastic. The two key aspects of performance are: (a) the degree of enhancement achieved
with a given degradable plastic in a specific product under given exposure conditions, and
(b) the variability of actual lifetimes (relative to the average controlled lifetime) that might be
expected during field performance. Fear of premature failure is perhaps a key factor which
stands in the way of transferrir ' "gradable plastics technology to most applications. This
concern needs to be complete!, iressed before any large-scale use of degradable plastics
might be expected. ;
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Enhanced degradable plastics may show both geography-dependent and seasonal
variations in performance. Claims made for some degradable polyethylenes of continued
degradation in landfills following an initial exposure to light have not been verified. Rates
and variability of environmental deterioration of starch-containing systems need to be veri-
fied and completely investigated.
It is also important for the user to be assured that a pre-determined controlled lifetime
will not overlap with the useful life of the product leading to premature failure during use.
Some degree of variability is to be expected in the controlled average lifetimes. However,
such scatter must not only be manageable and small, but the average lifetime selected must
be sufficiently longer than the maximum expected useful life of the product
Issue III: Performance: Marine Environment
Any strategy adopted to address the plastic waste problem must also address the
marine/estuarine environment as well. While recent legislative developments, such as
United States ratification of MARPOL Annex V, may discourage the discharge of plastics
into the world's oceans, a significant amount of discharge might still be expected due to
non-compliance, accidental gear losses, and input from land-based sources [CMS, 1990].
This is particularly true of regions with high levels of maritime activity.
None of the currently available enhanced degradable plastics, however, have been
demonstrated to perform equally well under both outdoor (land) and marine/estuarine
conditions. Except for some preliminary data on enhanced photodegradable six-pack
material made of (ethylene-carbon monoxide) copolymer, no relevant data exists in the
technical literature.
Adequate performance of a given enhanced degradable plastic material under outdoor
weathering need not necessarily guarantee similarly acceptable performance under marine
exposure. Plastics at sea are maintained at lower temperatures compared to those on land,
in spite of severe solar irradiation, and can become progressively shielded from sunlight
due to surface fouling. Unique microbial environments experienced by plastics at sea (both
floating and submerged) might be expected to modify any biodegradation behavior of plas-
tics as well. Thus both classes of degradable plastics (photo- and biodegradable) may per-
form differently on exposure at sea compared to that on land. These differences, where
they exist, must be established for different classes of products.
Issue IV: Toxicity of Degradation Products
While there is little chemical basis upon which to expect the majority of products of
enhanced degradation to be significantly different from those of regular plastic products,
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the issue has not been completely addressed. In the case of enhanced photodegradable
plastics, the small amounts of additives (or low levels of matrix modification) may lead to
some degradation products not typically found in the case of regular polymers.
The rates and extents at which these additional products are released into the ;
environment during weathering and thek toxicities are not known at this time. Further-
more, even the usual breakdown products common to both enhanced degradable and regu-
lar plastics will be generated at a faster rate by the enhanced degradable plastic material.
The consequent effects of higher levels of such chemical products on the soil microehvi-
ronments have not been studied.
Issue V: Effect of Degradable Plastics on Recycling
The recycling of post-consumer plastics is expected to become increasingly important
as a future solid waste management strategy. Reusable plastic resin for low-value applica-
tions can be derived from uniform, high-volume, easily separable post-consumer plastic
products. Polyester soft-drink bottles as well as polyethylene milk jugs are currently
recycled, successfully. While the recycling of commingled post-consumer plastics is:tech-
nically feasible, a remarketable base resin cannot often be cost-effectively obtained. The
mix can, however, be extruded into profile which might be used as synthetic lumber, auto-
stops, and other specific products. '
Inadvertent mixing of low levels of enhanced degradable plastic items into a recycling
stream of well-identified products (such as soda bottles) is extremely unlikely. Bottles for
carbonated beverages are currently not rendered enhanced degradable. Even if a degradable
plastic bottle does enter the market, the chances are that it will be easily identifiable and
separated during the pre-cleaning operation. The product would probably be designed in
such a manner that it would be easily identified as a degradable plastic product.
The same is not true of commingled streams of plastics where cleaning of individual
items is too expensive, and some degradable material may easily find its way into the
recycling stream. Reliable estimates of the fraction of degradable plastics likely to be found
in the municipal waste stream are not available. j
The key question is - does the inclusion of degradable plastics in a commingled
stream significantly affect the weatherability of the extruded recycled product (usually syn-
thetic lumber posts and panels)? Technical literature does not show any experimental data
either supporting or refuting the claim sometimes made that even a small amount of degrad-
able plastic will be disastrous to the quality of re-extruded material. :
However, it must be pointed out that the recycled extruded products from commin-
gled plastics tend to be very thick and dark colored material. Environmentally degradable
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plastics generally cannot function in products other than thin films or laminates. Light -
induced enhanced degradation of such a thick product is likely to be minimal and will be
limited exclusively to surface layers.
1.4 GOALS AND THE SCOPE OF WORK
The basic objectives (a major goal A and three minor goals) of this research program
effort might be summarized as follows.
A. To study the performance and the associated variability of several selected
Enhanced Degradable Plastic [EDP] materials under a variety of different expo-
sure conditions.
B. To better understand the underlying factors governing enhanced degradability in
EDP systems.
C. To study the major products formed during the enhanced degradation of EDP
materials and to assess the preliminary toxicity of such products.
D. To study the effects of including small fractions of partially degraded EDP
materials in a recycling stream on the quality of recycled products.
These broad objectives cover a wide area of experimentation which cannot be
exhaustively studied within the period of performance and the available resources. The dif-
ferent goals shown above have all been achieved, though to different extents. The state-
ment of work, given below, identifies the specific research areas addressed during the pre-
sent effort.
1.4.1 Goal A
(a) To determine the relative rates of disintegration of different types of Enhanced
Degradable Plastics [EDP] on exposure to outdoor environments at different
geographic locations in the US.
(b) To determine the relative rates of disintegration of selected EDP materials
exposed outdoors in air and at sea.
(c) To determine the relative rates of disintegration of enhanced biodegradable plas-
tics under exposure to soil.
(d) To determine the rate of disintegration of selected EDP materials under acceler-
ated laboratory exposure conditions.
(e) To study the improvement of outdoor exposure methodology with the develop-
ment of "Duplicate Exposure" protocol.
1.4.2 Goal B
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(a) To study activation spectra of the enhanced photodegradable plastics to identify
the spectral regions most effective in bringing about light-induced degradation.
(b) To study the temperature dependence of photodegradation in enhanced :
photodegradable polymers.
(c) To develop a rapid method for determining the starch content in starch/LDPE
blend materials.
(d) To study the effect of enhanced degradation on the water vapor and gas perme-
ability of selected EDP materials.
1A3 Goal C ;
(a) To determine the volatile photodegradation products formed on exposure'of
enhanced photodegradable polymers to light.
(b) To carry out a preliminary1 assessment of any toxicity related to degradation
products formed on exposure of selected EDP plastics to the outdoor environ-
ment. '.
(c) To study the effect of photodegradation on possible changes in leachability of
metal components from the polymer matrices.
1.4.4 Goal D
To carry out preliminary experiments to determine the range of mix compositions to
be considered in a future recycling study.
1.5 REVIEW OF DEFINITIONS
The research and technical literature on Enhanced Degradable Plastics [EDP's] shows
a variety of definitions for terms such as "photodegradability", "biodegradability," and
"degradable plastics". These definitions are inconsistent and sometimes vague, resulting in
conclusions which are not clear. Unfortunately, most work carried out on degradable plas-
tics therefore tends to be somewhat poorly defined and not standardized, making it difficult
to make inter-laboratory comparisons of data.
The need for good definitions is also felt by those attempting to develop various
pieces of legislation relating to plastics solid waste management A recent GAO report
[GAO, 1988] highlighted this lack of agreement on definitions of the basic terms and stan-
dard test procedures for assessing enhanced degradability and found the federal govern-
ment and the private sector to be making only limited efforts to develop the required stan-
dards for EDP materials.
Definitions in the most recent literature include those currently under development and
approval by the ASTM Committee D-20, subcommittee on "Environmentally Degradable
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Plastics", D20.96. The subcommittee is currently in the process of drafting definitions and
test procedures for "Degradable Plastic" materials. The definitions developed thus far
include the following key terms. Each term has two definitions: a broader general defini-
tion and a specific definition.
Degradable Plastic ~
(General) Plastic materials that disintegrate under environmental conditions in a reason-
able and demonstrable period of time.
(Specific) Plastic materials that undergo bond scission in the backbone of a polymer
through chemical, biological, and/or physical forces in the environment at a rate
which is reasonably accelerated, as compared to a control, and which leads to frag-
mentation or disintegration of the plastic.
Related terms such as "photodegradable plastics" and "biodegradable plastics" also
have such pairs of definitions. These definitions have not as yet been adopted by the
ASTM.
Andrady [Andrady, 1991] has proposed a set of working definitions for these terms
which allow the demarcation between EDP materials which chemically degrade as opposed
to those where the plastic component physically breaks down. This set of definitions is
adequate for the purpose of this study and is given below.
Definitions Used in the Study
The term "Degradable Plastics" is strictly a misnomer suggesting the existence of
non-degradable plastics; all polymers are of course environmentally degradable. In the
case of most synthetic organic polymers, the rate of biologically-mediated degradation in
the environment is too slow to be of any practical consequence. It is more appropriate to
use the term "enhanced degradable plastics" or "rapidly degradable plastics" for those
plastics designed (or selected) for relatively faster breakdown in the environment.
It is convenient to first define "Disintegration" as a broad overall description of the
loss in properties and embrittlement of plastic materials exposed to the environment. This
is consistent with the general usage of the term as well as with its use in the ASTM general
definition of Degradable Plastics given above.
Disintegration: The loss of integrity, embrittlement, or breakdown of a material on
exposure to the environment.
The term "deterioration" is next defined rather narrowly as a sub-set of "disintegra-
tion", to mean breakdown primarily due to non-chemical causes. This term has unfor-
tunately been used in the literature to mean different phenomena [Eggins et al, 1980].
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Deterioration: Disintegration of a material predominantly due to physical changes.
(e.g.. damage to materials due to freeze-thaw cycles, damage from thermal
expansion, dissolution, damage from rodents, and insect attack on plastics)
A second sub-set of "disintegration" is "degradation" as defined below. The two
classes of disintegrations are mutually exclusive as defined. However, both processes
could occur concurrently. In any event the primary, predominant process is used for the
purpose of definition.
Degradation: Disintegration of a material predominantly due to chemical processes.
(light-induced degradation of polymers, hydrolysis, microbial attack on poly-
mers.)
Note that degradation alters the chemical nature of the polymer while deterioration,
does not A degraded polymer will generally show an altered average molecular weight
and changes in functional group chemistry, while in a deteriorated polymer, the individual
fragments after disintegration retain about the initial intrinsic properties of the original
polymer. The reader is cautioned that the above terms are used rather loosely and in a
widely different sense from above in the literature [Modern Plastics, 1990; Barenberg et
al., 1990]. Both Deterioration and Degradation might be further classified according to the
agency bringing about the disintegration. Table 1.5.1 illustrates the use of the above ter-
minology with the various types of breakdown. Some of the more important ones are dis-
cussed below.
1. Photodegradable polymers: The primary predominant mechanism of degrada-
. tion on exposure to the environment is via light-induced (chemical) processes.
Two classes of such polymers are widely used: (a) Polymers such as (ethylene-
carbon monoxide) copolymer which use the absorbed solar radiation primarily for
direct bond scission reactions (direct photolysis); and (b) polymer systems where
light initiates thermo-oxidative reactions.
This latter group of plastics is classified as "photodegradable " under the present
scheme, but light is used merely to initiate the degradation process.
2. Biodegradable polymers: The degradation is brought about by the activity of
microorganisms. Polymers such as poly(e-caprolactone) fall into this category.
The bio-degradation process may occur in several stages: biotransformation of
polymer to oligomeric species or small molecules, consequent biotransformation
of non-polymer products into simple chemical compounds, and finally mineral-
ization of these compounds into carbon dioxide, ammonia, and water.
3. Biodeteriorable material: The plastic material undergoes deterioration as a
result of microbial activity on the material. Starch/LDPE blends are an example of
i
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this class of material. On exposure to a biotic environment, the microorganisms
.degrade the starch component but do not utilize or chemically affect the polymer
fraction. Weakening of the material due to loss of the starch component eventu-
ally causes embrittlement of the composite material.
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Table 1.5.1. Proposed Definitions of Environmental Breakdown Processes and
Enhanced Degradable Plastics. !
DEGRADATION .
A disintegration caused
predominantly by chemical
changes
/ •
DISINTEGRATION
Breakdown (size reduction)
of material into small fractions,
including embriiltement
\
DETERIORATION
A disintegration caused *
predominantly by physical
changes
PHOTODEGRADATION
Light-induced
BIODEGRADATION
Brought about by living animals,
plants, particularly microbes
OXJDATIVE DEGRADATION
Caused by thermooxidative
reactions
HYDROLYSIS
Caused by reaction with water
BIODETERIORATION
Brought about by living animals'
and plants
DISSOLUTION
(Hydrodeterioration) Brought
about by water
' THERMAL DETERIORATION
Caused by freeze-thawing or
thermal cycling forces
Examples
a
b
c
d
e
f
g
Product ,
Ecolyte
ECO resin
Plastigone :
Biopol - ICI
*"""
ADM, ;
Ecostar ;
PCL/PE - !
Union Carbide
Belland
i
a Polymers with ketone groups in main chain or as a side chain.
b Metal-compounds additives for PE ;
c Poly(hydroxybutyrate valerate) '
d Metal-compounds and inorganic pigments in polyolefins ;
e Acid catalyzed hydrolysis of cellulose
f Starch-polymer composites; biodegradable polymer - other polymer composites
g Soluble acrylic copolymers; soluble poly(vinyl alcohol) films
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4. Water soluble plastics: Plastics such as soluble poly(vinyl alcohols) do not repre-
sent a case of "degradation," as sometimes incorrectly stated, but only a water-
induced deterioration.
1.6 SUMMARY OF CURRENTLY COMMERCIALIZED ENHANCED
DEGRADABLE (EDP) TECHNOLOGIES
A variety of techniques described in the patent and scientific literature fall under the
definition of "Enhanced Degradable Plastics" as defined above. However, all such systems
have not been commercialized or have not been successful after commercialization. The
intent of this section is not to present a technical review of the research literature on degrad-
able plastics but to provide a general description of the mechanisms responsible for
enhanced degradability (or enhanced deteriorability) in some of the common EDP systems.
Discussion is limited to those EDP systems selected for the experimental part of this
study. A description of the actual EDP film materials used in the study is provided in
Section 2.1.
!-6.1 Ethylene-carbon Monoxide Copolymers (PHnTODPrre APART .K)
Copolymerization of ethylene with carbon monoxide allows the introduction of low
levels of ketone functionalities into the main chain of the polymer [Hartley and Guillet,
1968; Heskins and Guillet, 1968; Heskins and Guillet, 1970; Guillet, 1972]. The pro-
duct, a low density polyethylene containing usually 1 percent of the ketone repeat unit, is
generally referred to as ECO copolymer and is able to absorb ultraviolet radiation in sun-
light and undergo photolysis reactions. Enhancement of the degradation is obtained due to
the presence of a significant amount of carbonyl chromophores in the form of keto groups
in the polymer. ;The photooxidation of regular polyethylene on exposure to sunlight also
results in the formation of ketone functionalities. However, the main mechanism of chain
scission is different for ECO copolymers and regular polyethylene material.
Success of the ECO copolymer system is due to the ability of these ketones to
undergo n-jc* transitions absorbing relatively long wavelength solar radiation (313 nm)
[Hartley and Guillet, 1968]. The chain scission process occurs via classical Norrish I and
Norrish n mechanisms [Guillet and Norrish, 1955], though the Type II reaction predomi-
nates under ambient temperatures [Hartley and Guillet, 1968]. At ambient temperatures the
difference between the quantum yield of the Type H and Type I reactions is about 100-fold
[Guillet, 1973]. The Type n reaction, an intramolecular elimination reaction with a low
activation energy of about 1 kcal/mole, results in chain scission yielding a methyl ketone
and vinyl unsaturated chain end. Norrish I and n reactions for ethylenes with ketone func-
tionalities in the main chain as well as on a side chain are shown below.
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o
II
>. CH2 + -C CH:
O T ^ CHf ^CH2 ^CHf"
CH;
X.
.II
O
II
CH C^
GH CHf CHf
Norrish I and n Reactions Leading to Degradation of Polymer ;
ECO copolymers are manufactured in the U. S. by several resin manufactures ;and are
almost exclusively used in the fabrication of six-pack ring connectors in the packaging
industry. The success of this particular application as a large-volume user of photodegrad-
able plastics is to a large extent due to regional legislation in more than seventeen states
requiring photodegradability in six-pack carriers. Public Law 100-556, Degradable Plastic
Ring Carriers Law, will encourage even stronger growth for this material. ITW-HiCone
Division trade literature on photodegradable carrier material claims a loss of approximately
75 percent of its structural integrity within days and embrittlement in a matter of weeks.
The manufacturer has carried out several exposure studies, both in the United States and in
Europe, which show the ECO copolymer used in six-pack rings to embrittle within a 5-8
week period.
1.6.2 Polymers with Ketone Functionality on a Side Chain [PHOTODEGRADABLE] ;
(a) Polyethylene
Ketone groups on a side chain of the polymer can also be effective as chromophores
in bringing about Norrish I and n photolysis of polymers. Copolymerization with vinyl
ketone has been extensively used to synthesize enhanced degradable polyethylenes [Li and
Guillett, 1980], polystyrene [Heskins et al, 1976], and o.ther polymers [Amerik and
GuUlet, 1971]. ;
With the carbonyl group located on the side chain, only the Norrish n type reaction
causes chain scission, while the Type I reaction yields a free radical on the macromolecule.
This radical may, however, initiate oxidation via reaction with oxygen followed by hydro-
gen abstraction. While the quantum yield for the Type n reaction in ethylene/methylvinyl
ketone polymers is not high, the material is claimed to undergo facile embrittlement on
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exposure to light. Generally , a small number of scission events cause a large decrease in
the strength of the polymer. The approach has been demonstrated for polystyrene as well.
This technique has been developed to the point of commercialization, and a master-
batch compound of the modified polymer (containing 2-5 percent ketone content) is avail-
able for use in polyethylene and polystyrene resins. Appropriate amounts of the master-
batch blended (in a ratio of 1:9 to 1:20) with the base unmodified resin render the blends
enhanced photodegradable. The extent of such enhancement depends on the level of
masterbatch incorporated into the resin and also on the level of pigment, if any, in the for-
mulation.
(b) Polystyrene
Vinyl ketone/styrene copolymers undergo photodegradation in a manner similar to the
etliylene copolymers discussed above. The general mechanism [Heskins et al., 1976] and
the quantum yield [Dan and Guillet, 1973] have been reported for such systems.
1.6.3 Low Density Polyethylene Containing Added Metal-compound Pro-oxidants
[PHOTODEGRADABLE] (A polymer which undergoes catalyzed
photoinitiated oxidative degradation)
The ability of transition metals to accelerate both thermal autoxidation and photoiniti-
ated autoxidation of polyolefins is well known [Alter, 1960; Reich and Stivala, 1971]. The
mechanism primarily involves the catalysis of the hydroperoxide dissociation reaction
which initiates the oxidation. Some likelihood of the metal ion participating in the propaga-
tion/termination steps also exists.
Particularly interesting is the use of transition metal thiolates, particularly dithiocar-
bamates. Some of these, such as the nickel complex, show outstanding antioxidant effects,
while others, such as the iron complex, are unstable and act as prooxidants in polyolefins.
The difference in stabilizer activity of metal dithiocarbamates is due mainly to their
invariable light stability [Scott, 1984]. Some of the metal dithiocarbamates act as thermal
stabilizers (or act as neutral additives) during processing and as antioxidants during early
exposure to light but thereafter are themselves photodegraded into pro-oxidant species.
This results in polyethylene/MX systems (where MX refers to dithiocarbamate or other
organic compound of iron or manganese) which, when exposed to light, undergo enhanced
photodegradation after a delay or a "lag time". During processing, shelf life, use,
1-15
-------
radical
' species
ROOM
RH
RO,
Termination: radical combination
and the lag-time, the metal dithiocarbamate is believed to stabilize the polymer by reacting
with hydroperoxides in a reaction yielding non-radical products [Gilead and Scott, 1982].
Early weathering photodegrades the dithiocarbamate, liberating the metal, which can
catalyze the initiation by hydroperoxide decomposition.
R2NC
Fe
[ROOH]
hi)
R2NC=S + SO3 + Fe:
3 +
R2NC
N./J
s
II
Fe + R2N;C-S
This reaction produces ferric ions which are efficient hydroperoxide decomposers in
an initiating reaction. The redox catalysis [Amin and Scott, 1974] reaction involvedls well
known. This latter reaction can occur in the absence of light and is probably the basis of
the manufacturer's claim that, once initiated, the degradation process will continue in the
dark in air [Gilead et al., 1981; Gilead, 1978]. ;
Fe2+ + ROOH
Fe3+ + RO' + OET
Fe3+ + ROOH
«=- Fe2+ + RO2« + H+
1-16
-------
The delay period can be altered, and therefore controlled to some extent, by changing the
amount of metal dithiocarbamate used in the polymer. A later improvement of the technol-
ogy uses a second, more stable, metal dithiocarbamate as an additional additive. Varying
the relative proportion of the parr of ditMocarbamates is claimed to allow close control of
the outdoor lifetime of the film [Gilead, 1984]. The commercial product, in the form of a
plastic film containing the relevant metal compounds, has been successfully used in agricul-
tural mulch fiObtns [Gilead, 1978; Gilead, 1990].
1.6.4 LDPE/starch Systems With or Without Added Pro-oxidants
PBIODETERIORABLE] or [PHOTODEGRADABLE/BIODETERIORABLE]
(a) Starch/Polyethylene Blends
Biodegradation of polyethylene under soil exposure is well known to be extremely
slow, and the reported evidence for any biodegradation at all is based on radiotracer studies
indicating a breakdown of a few percent over several years [Albertsson, 1978; Albertsson
and Banhidi, 1980]. Incorporating starch grains as an organic filler into a polyethylene or
other polymer matrix was observed to enhance the breakdown of the polymer in biotic
environments as early as 1974, when the first patent was issued to Griffin [Griffin, 1974].
The plastic material so prepared was essentially a very slowly biodegradable thermoplastic
material filled with a readily biodegradable naturally occurring polysaccharide. Starch con-
sists of 17-21 percent amylose fraction, a linear polysaccharide consisting of up to 1000
glucose residues, and 73-82 percent amylopectin, a branched chain polysaccharide fraction.
Blending in a hydrophilic filler (and an unsaturated fatty acid) at levels high enough to
obtain a significant difference in disintegration rates, without sacrificing the mechanical
properties of the rilled polymer, is the major challenge in this approach. This is generally
achieved by using a small enough particle size of starch to optimize dispersion and a novel
silicone (or other polymeric) treatment of the starch grains to improve the starch/polymer
interphase properties. The addition of an unsaturated vegetable oil which readily autoxi-
dizes is claimed to further enhance the disintegration of the system, particularly under warm
exposure conditions such as compost environments.
On exposure to a biotic environment, the starch fraction of the composite material can
readily undergo ready biodegradation. This would depend on the accessibility of the starch
to soil microbes and/or extracellular amylases secreted by the microbes. Biodegradation of
starch creates voids within the plastic matrix which weaken and deteriorate the plastic film.
The matrix may contain a readily auto-oxidizable hydrocarbon blended with the polyolefin.
1-17
-------
The above approach was first described by Griffin [Griffin, 1978] and is marketed by
St. Lawrence Starch Company. A modified version of this technology is marketed under
the trade names Polygrade II and Polygrade HI. The modified approach based on tech-
nology licensed from Archer Daniels Midland Company uses untreated starch and a pro-
prietary prodegradent compound. Manufacturers often add metal compound pro-oxidants
into the mix to make the material more photodegradable, thereby making it more versatile.
The pro-oxidant promotes photoinitiated autoxidation as mentioned earlier and also cat-
alyzes the thermooxidative breakdown of plastics under the higher temperatures found in
composting. Where both biological and light-initiated processes work simultaneously, the
latter mechanism is expected to work relatively faster.
The original concept for this type of material was patented by Griffin [Griffin, 1978],
and both manufacturers currently marketing the product use the same general composition.
The main difference between the two commercially available product lines appears to be in
the choice of additives which cause rapid autoxidation.
(b) Starch Chemically Bonded to Polyethylene ;
The loss of useful mechanical properties of the blend at even moderate levels of starch
in the polymer limits the use of the above approach. This can be avoided to some extent by
more intimate mixing of the starch with polymer and even possible partial reaction of the
two materials. A varient of the starch/polymer blend technology developed in US DA labo-
ratories by Otey [Otey, et al., 1977] uses a copolymer of polyethylene containing pendent
carboxylic acid groups which are able to react with starch molecules. The starch itself is
pregelatinized, intimately mixed, and partially reacted with the polymer. The resulting
'blend" is claimed to be processable into films and molded objects which display a high
degree of biodeteriorability due to the relatively high levels of starch that can be incorpo-
rated into the matrix. >
While the idea has been patented [Otey, 1979] and some developmental work is under
way, the product has not as yet been commercialized. :
1.6.5 Polyethylene/ e-Polycaprolactone Blends [BIODETERIORABLE]
- L—L——~ - - - - J ' t
This approach is essentially similar to that discussed under 1.6.4 above in that it uses
a blend of a non-degradable polymer and a degradable polymer. In place of starch, which
is a biopolymer, this system uses polycaprolactone, a readily biodegradable synthetic
polymer. Unlike starch, polycaprolactone can be easily blended with polyethylene and
polypropylene without affecting the mechanical properties of the blend.
1-18
-------
Environmental degradability of e-polycaprolactone under bio tic conditions has been
reported by Potts [Potts et al., 1972] and others [Fields, et al. 1974; Benedict et al., 1983],
Fungi in particular are able to fully degrade this polymer [Benedict et al., 1983]. For
instance, Penicillin species acting on a polycaprolactone sample of Mn = 25,000 reduced
the organic carbon content of the growth medium to near zero in 15 days under laboratory
exposure conditions [Tokiwa et al., 1976].
The manufacturer's trade literature on Tone P-767 polycaprolactone shows tensile test
data for film samples 0.125 in. in thickness. Under aerobic soil burial exposure, the test
samples embrittled (elongation at break< 5 percent) within 4 months and lost 42 percent of
weight within 12 months. The temperature for the exposure is unspecified. The literature
also shows data on marine degradation [based on Andrady, 1989] of
polyethylene/polycapro-lactone blends. Film samples of 10 or 20 percent by weight of
E-polycaprolactone in polyethylene lost 70-80 percent of initial elongation at break on expo-
sure to marine sediment at a coastal Miami location for a 9 month period. As in the case of
starch/polymer composites, the deterioration of these blends is controlled by the accessi-
bility of the polycaprolactone to the relevant enzymes.
1.6.6 Biopol Thermoplastic Biopolvmer
Under certain growing conditions, bacteria and algae are known to synthesize
polyesters which are stored in the form of granules within the cell and utilized as a source
of energy as needed by the microrganism. The aliphatic polyester, poly(3-hydroxy-
butyrate), is an example of such a polyester.
By controlling the feedstock and growth conditions closely, ICI researchers were able
to induce a common soil bacterium, Alcaligenes eutrophus, to produce up to 80 percent (of
dry biomass weight) of the polyester, which could be easily extracted to obtain a biode-
gradable thermoplastic material [Lloyd, 1987]. Incorporation of a valerate comonomer
(5-20 %) reduces the crystallinity of the polyester, leading to improved properties. An
aqueous extraction process is used to obtain a copolymer with moderate molecular weights.
While the material cost is high at the present time, given high levels of production,
this polymer might be available at a cost comparable to that of engineering thermoplastics.
1-19
-------
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i
Albertsson, A. -C. and Z. G. Banhidi, J. Appl. Polym. Sci., 25, 1655 (1980).
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Amerik, Y., and Guillet, I.E., Macromolecules, 4, 375 (1971).
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Andrady, A. L. "Outdoor and Laboratory Weathering of Plastics Formulated for Enhance-
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Andrady, A. L. and J. E. Pegram, "Research and Development on Enhanced Degradable
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Balazs, G. H. Impact of Ocean Debris on Marine Turtles: Entanglement and Ingestion. in:
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Department of Commerce, Honolulu, Hawaii (1985). . ;
Barenberg, S. A., J. L. Brash, R. Narayan, and A. Redpath, "Degradable Materials: Per-
spectives, Issues, and Opportunities", CRC Press, Florida (1990).
Benedict, C. V. , W. J. Cook, P. Jarrett, J. A. Cameron, S, J. Huang, and J. P. Bell, J.
Appl. Polymer Sci., 28., 327 (1983).
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Bonner, W. N. and T. S. McCann. Neck collars on fur seals, Arctocephalus gazella, at
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CMS (Center for Marine Conservation), "Cleaning North America's Beaches, 1989 Beach
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Dan, E. and I.E. Guillet, Macromolecules, & 230 (1973).
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birds. Unpubl. M. S. thesis, Univ. of Alaska, Fairbanks, 1980. :
Eggins, H.O.W. and T. A. Oxley, Int. Biodet. Bull., 16(2), 53 (1980).
Feldkamp, S. D., The effects of net entanglement on the drag and power output of a
California sea lion, Zalophus californianus. Fish. Bull. £3(4), 692-695 (1985).
Fields, R. D, F. Rodriguez, and R. K. Finn, J. Appl. Polyrn. Sci., 18, 3571 (1974).
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GAO, "Degradable Plastics. Standards Research and Development", 1988. Report to the
Chainnan, Committee on Governmental Affairs, U.S. Senate. Sept. 1988
GAO/RCED 88-208 US General Accounting Office).
Gilead, D., "Plastics that self distract", Chemtech, May 1978, pp 299-301.
Gilead, D. and Scott, G. Time-controlled stabilization of polymers. In "Polymer Stabiliza-
tion," Vol. 5, Ed. G. Scott, Applied Science Publishers. London, 1981, pp. 71-
103.
Gilead, D. and G. Scott, In Development in Polymer Stabilization, N. S. Allen (Ed), .
Chapter 4 (1982).
Gilead, D. and G. Scott., Controllable Degradable Polymer Compositions, British Patent
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Gilead, D. Polym. Degradation and Stab., 29, 65-71 (1990).
Griffin, G.J.L., Synthetic Resin-Based Compositions. United States Patent 4,125,495
(1978) Coloroll, Ltd.
Griffin, G. "Biodegradable Fillers in Thermoplastics", American Chemical Soc., Adv. in
Chem. Ser., 134, Washington D.C. (1974).
Guillett, J. E. and R.G.W. Norrish, Proc. Roy. Soc. (London), A233. 153 (1955).
Guillett, J. E. Pure Appl. Chem., 30, 135 (1972).
Guillett, J. E. Polymers with Controlled Lifetimes, In "Polymers and Ecological Prob-
lems", J. E. Guillett (Ed.), Plenum Press (1973).
Hartley, G. H. and J. E. Guillett. Macromolecules, 1, 413 (1968).
Henderson, J. R. and M. B. Pillos. Accumulation of net fragments and other marine
debris in the northwestern Hawaiian Islands (abstract only), in R. S. Shomura and
H. O .Yoshida (eds.), Proceedings of the Workshop on the Fate and Impacfof
Marine Debris, 27-29 November 1984, Honolulu Hawaii. U. S. Dept. Commerd.,
NOAA Tech Memo. NOAA-TM-NMFS-SWFS-54, 1985.
Heskins, M. and J .E. Guillett. Macromolecules, 1, 97 (1968).
Heskins, M. and J. E. Guillett, Macromolecules, 3, 224 (1970).
Heskins, M., T. B. McAnney, and J. E. Quillet, In "Ultraviolet-induced Reactions in
Polymers", S. S. Labana (Ed.), ACS Symposium Series No. 25, New York (1976).
Jensen, J. W., J. L. Holman, and J. B. Stephenson. "Recycling and Disposal of Waste
Plastics" in "Recycling and Disposal of Solid Wastes", T. F. Yen (Ed.), Ann Arbor
Science Publishers, Ann Arbor, MI (1974).
Laist, D. W. Overview of the biological effects of lost and discarded plastic debris in the
marine environment. Mar. Pollut. Bull, 18(6B), 319-326 (1987).
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Li S K.I. and J. E. Guillet, Photochemisry of Ketone Polymers V., J. Polym. Sci.,
Polym. Chem. Ed., i&, 2221 (1980).
Lloyd, D. R. Proceedings of the Symposium on Degradable Plastics, Washington, DC,
1987, pp. 19-21. ;
Loughlin, T. R., P. Gearin, R. L. DeLong, and R. Merrick. Assessment of net entangle-
ment on northern sea lions in the Aleutian Islands, 25 June - 15 July, 1985. NWAFC
Processed Rep. 86-D2. NOAA, NMFS, NWAFC, Seattle, WA. 1986. ;
Modern Plastics, "Dimensions" in "Waste Solutions". A supplement to 4/90 issue of
Modern Plastics, April 1990, p. 12. ;
Otey, F.H. and R.P. Westhoff, Biodegradable Starch-Based Films. Department of ;
Agriculture, Washington, DC (1977).
Otey, F. H. and R. P. Westhoff, U. S. Patent #4,133,784 (1979). ;
Potts, J. E., R. A Clendinning, W. B. Ackartand W. D. Niegisch, Am. Chem. Soc.,
Polym. Chem. Preprints, 13, 629 (1972).
Rathje, W. L. andD. C. Wilson, "Archaeological Techniques Applied to Characterization
of Household Discards", paper presented at 3rd International Symposium on
Resource Management, new York, February 11-14,1987. i
Reich, L. and S. S. Stivala, "Elements of Polymer Degradation", McGraw Hill, New York
(1971).
Scott, G., British Polymer 1, 1_6_, 271 (1984). ;
Tokiwa, Y., T. Ando, and T. Suzuki, J. Fermentation Technol., 5_4, 603 (1976). ;
USEPA, 1991. U. S. Environmental Protection Agency. "Characterization of Municipal
Solid Waste", U. S. Environmemal Protection Agency Office of Solid Waste,
Washington, DC.
USEPA, 1990. U. S. Environmental Protection Agency. "Methods to Manage and Control
Plastic Wastes, U. S. Environmetnal Protection Agency Office of Solid Waste,
Washington, DC.
USEPA, 1989. U. S. Environmental Protection Agency. The Solid Waste Dilemma: An
agenda for action. EPA/530-SW-89-019, US EPA 1988. U. S. Envixonmetnal Pro-
tection Agency Office of Solid Waste, Washington, DC.
USEPA, 1988. U. S. Environmental Protection Agency. Report to Congress: Solid
Waste Disposal in the United States. EPA/530-SW-88-01 IB, Washington, DC,
1988.
1-22
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Post-consumer
Recycling
Plastic Products
for Consumer Use
Enhanced
Degradation
Aerobic/anaerobic
Composting
Landfill or
Sea Disposal
Incineration
Resource Recovery
Recycling
POST-CONSUMER PLASTIC WASTE MANAGEMENT OPTIONS
Andrady, 1991
Figure 1.2.1. A flow chart for consumer plastic products: production, use, and disposal
(MSW: Municipal Solid Waste).
1-23
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-------
SECTION 2.0
EXPOSURE METHODS
2.1 SAMPLE SELECTION AND ACQUISITION
The number of different types of degradable plastics investigated in this study was
limited by the available resources. As such, a representative set of sample types had to be
selected from the commercially available (or fully developed) technologies. The following
criteria were used in making the selections.
(a) The most-used consumer packaging material which utilizes enhanced degradable
plastics technology is the six-pack ring holder. State level legislation and anticipated
national legislative interest in the product also made it a key material to be included in
the study.
(b) Given the time scale of the study, which included less than six months of exposure
duration, enhanced photodegradable materials are likely to be the more profitable
class of enhanced degradable plastics to study. Therefore the main selections
included three photodegradable plastics, one photodegradable/biodeteriorable plastic,
and one which was biodeteriorable. On the basis of literature data, photodegradable
materials were expected to be more likely to undergo measurable changes in mechani-
cal properties during the short duration of exposure.
(c) An attempt was made to include different classes of resins as well as different tech-
nologies for imparting enhanced degradability in the study. Therefore, both poly-
ethylene and polystyrene were included. The latter was expanded extruded polysty-
rene foam widely used in single-serve food and packaging applications.
(d) Polymer/starch blends are an important class of enhanced degradable plastics which
have drawn public as well as technical interest. The photo/bio-disintegrating material
was included in the study, as it represented a plastic/starch blend and in addition
claimed photodegradability, which allowed both processes to be studied.
Based on these considerations the following test materials were selected for the study.
In each case the manufacturer of the material and/or the relevant packaging product was
contacted. In the case of polyethylenes, including blends, approximately 1 mil thick films
were requested for use in the study. In the case of six-pack ring material and polystyrene
foam material, however, thicker sheets of the material typically used in the product were
requested. The samples were labelled with the appropriate code and stored at ambient tem-
perature. A list of the sample types is given below.
2-1
-------
Classification:
Source:
Code:
Control:
(Ethylene-carbon monoxide) copolymer containing ~ 1 percent of the CO comonomer
units. The sample was obtained as sheets (some sheets partially cut into sample
strips).
[Enhanced photodegradable plastic material]
Illinois Tool Works (HiCone Division). i
6P !
Low density polyethylene of comparable thickness. Code : 6PC
Polystyrene blended with (styrene - vinyl ketone) copolymer, as an expanded,;
extruded sheet. The amount of the photoactive copolymer in the blend was approxi-
mately 10 percent
Classification: [Enhanced photodegradable plastic material] ;
Source: PolysarInc.,Leominister, MA :
Code: PS \
Control: Sheets of regular expanded extruded polystyrene. Code: PSC
Low density polyethylene containing metal prooxidant compounds.
Classification: [Photodegradable film]
Note: Photoinitiated thermooxidation is the degradation mechanism.
Plastigone Company, Miami, FL
PG
i
Low density polyethylene sheet with no prooxidant additive. -
Code: PGC ;
Source:
Code:
Control:
Low density polyethylene/starch (6 percent) blends containing metal compound
prooxidants.
Classification: [Biodeteriorable /Photodegradable film]
Note:
Source:
Code:
Photoinitiated thermooxidation is the degradation mechanism. Some
biodeterioration due to loss of starch is also expected.
Archer-Daniels Midland Company
ADM
2-2
-------
Control: Low density polyethylene film with no prooxidant additive.
Code: ADMC
5. Linear low density polyethylene/polycaprolactone (20 percent) blends.
Classification: [Biodeteriorable film]
Source: Union Carbide Company
Code: PCL
Control: Linear low density polyethylene film. Code: LLDPE
6. Poly(hydroxybutyrate valerate) film.
Classification: [Biodegradable film]
Source: ICI Americas Co.
Code: BP
Control: None used
NOTE: This sample type was used only in a limited number of exposures
due to cost and sample limitations.
2.2 SAMPLE CONTROL AND IDENTIFICATION
The various types of plastics for the study, their manufacturers, and the.code names
used to identify them are listed in Table 2.2.1. The samples will be referred to by their
code names, e.g., 6P for (ethylene-carbon monoxide) copolymer, throughout this report.
These samples were dispatched from RTI to various locations for the different types of
exposure required by the study: direct weathering, marine floating and marine sediment
exposure, and laboratory-accelerated weathering (Weather-Ometer®). Outdoor and labora-
tory-accelerated soil burial were conducted at RTI.
The large numbers of samples exposed at the various outdoor weathering sites
necessitated the development of a sample tagging system able to withstand severe outdoor
exposure to identify each sample to prevent inadvertent mislabeling by the exposure ser-
vice. Small metal punches of various shapes were used to stamp the plastic films before
sending them for exposure. Each sample type and each exposure location were represented
by a different shape. Conventional labels were also used, allowing two independent means
of sample identification.
Samples were returned to RTI as soon as possible after each sampling interval. Upon
receipt of a sample, the punch code was checked to see if it had been properly labeled.
Each sample was then assigned a code which identified the material type (code names from
Table 2.2.1); type of exposure (O = outdoor direct weathering, F = marine floating, M = '
marine sediment, FW = freshwater, S = soil burial, W = Weather-Ometer®, LA = lab
accelerated soil burial); exposure site; and duration of exposure. The exposure logs are
2-3
-------
Table 2,2.1. Identification, Sources, and Code Names of Plastic Film Materials
Used in the Study.
Description of Material
Manufacturer
Code. Name
Ethylene/carbon monoxide
copolymer with 1%
CO-monomer (Used
in 6-pack rings for
beverage cans).
Polyethylene 6-pack ring
material (Control for 6P)
Low density polyethylene
films conL ting pro-
prietary metal com-
pounds
Low density polyethylene
film (Control for PG)
Low density polyethylene
film containing 6-7% by
weight cornstarch, and
proprietary metal com-
pounds
Low density polyethylene
film (Control for ADM)
Expanded, extruded poly-
styrene foam with
ketone groups (10%)
Expanded, extruded
polystyrene foam
Linear low density poly-
ethylene/polycapro-
lactone (20%) blend
Linear low density polyethy-
lene film (Control for
PCL)
Biopol film (polyhydroxy-
butyl valerate)
Illinois Tool Works
HiCone Division, IL
Illinois Tool Works
HiCone Division, IL
Plastigone Company, FL
Plastigone Company, FL
Archer Daniels Midland
Company, IL
Archer Daniels Midland
Company, IL
Polysar, Inc., MA
Polysar, Inc., MA
Union Carbide Company,
NY
Union Carbide Company,
NY
Imperial Chemical Industries
6P
6PC
PG
PGC
ADM
ADMC.
PS
PSC
PCL
LLDPE
BP
2-4
-------
given in Appendices A, B, and C and show a complete record of the information pertaining
to sample exposure. These logs were also used to keep a record of the tensile testing per-
formed on the exposed samples.
2.3 FIELD EXPOSURE METHODS
2.3.1 Rationale for Use of Duplicate Exposures
Outdoor exposure under natural weathering conditions is best suited for studying
permanence properties of plastics to the extent that it is typical of the exposure received by
the material in use. Attempts at acceleration of weathering in the laboratory by resorting to
higher temperature, more intense light, spectrally altered light, and cycling result in very
large deviations from the actual outdoor conditions. Consequent uncertainty as to the simi-
larity of underlying chemical processes resulting in degradation of the exposed material in
outdoor and accelerated conditions can often make the latter data difficult to interpret. The
more the exposure condition deviates from natural outdoor conditions, the higher is the
likelihood that the mechanisms are not typical of those taking place under natural exposure,
and therefore less reliable is the test data.
The main difficulty associated with natural weathering is of course the very long
durations of exposure required to collect meaningful data for most commodity plastics. In
the case of enhanced degradable plastic materials, however, the duration of exposure to
embrittlement is relatively short, and, unlike the case of regular plastics, data can easily be
obtained from natural weathering studies. The main drawbacks are the large variations in
temperature, sunlight, and rainfall generally obtained with natural weathering. The non-
uniformity of outdoor exposure conditions is well known to lead to variability in weather-
ing test results. Unlike the case of establishing permanence properties of regular plastic
films, the outdoor exposure of enhanced degradable plastic films requires a much shorter
period of exposure, often 2-3 weeks outdoors. As such, the short term (day to day) fluc-
tuation in key factors such as average temperature, rainfall, and the available sunshine, is
likely to affect the variability of test data to a greater extent in the case of exposures of a few
weeks compared to longer exposures of months or years. In an attempt to overcome this
difficulty a "duplicate exposure" protocol was developed during this work. This protocol,
however, was only used in selected exposure sites due to cost constraints.
Figure 2.3.1 illustrates the basis of the "duplicate exposure" procedure. An exposure
experiment is initiated with a set of n samples exposed outdoors. Essentially, each time a
sample is removed from the original set of plastic films, it is replaced by a fresh sample of
the identical plastic film. Thus, two complete sets of samples are available for testing at the
2-5
-------
end of the test period; one with 1,2 ntn week of exposure and another with ntn, (n-
!)&, ].st week of exposure. Thus for any given duration of n weeks of exposure, the
procedure yields two samples collected in chronologically reverse order. With no drastic
changes in weathering conditions both sets should yield very similar data. Inconsistent
data between the two sets would suggest non-uniform exposure conditions during the short
duration of exposure. ;
SETl
SET 2
E:
ADD
REMOVE
TOTAL
ADD
REMOVE
TOTAL
KPOSURETIME
n
0
n
1
0
1
0
1
n-1
1
0
2
0
1
n-2
1
0
3
0
1
n-3
1
0
4
• • •
• • •
• • •
• * *
• O •
• • «
0
1
2
1
0
n-3
0
1
1
1
0
n-2
0
1
0
0
n-1
n-1
l 1 I I ill
0 1 2 3 • • • n-2 ii-1 n
Weeks
Figure 2.3.1 Duplicate exposure protocol for an exposure for n weeks with weekly sam-
pling of set 1. ;
While this duplicate exposure protocol is straightforward, its novelty made it difficult
to implement in the field. In several of the sample sets, the exposure procedure was not
correctly carried out by the field technicians. However, in the cases where the protocol
was properly followed, good data showing little or no drastic changes in the factors
responsible for weathering were obtained.
2.3.2 Outdoor Exposure ;
The following samples were exposed outdoors at five geographic locations:
(a) (ethylene-carbon monoxide) copolymer (6P),
(b) low density polyethylene/MX (PG), ;
(c) low density polyethylene/starch/MX (ADM), and
(d) expanded polystyrene foam (PS).
(MX repre& ts proprietary metal complexes.) The five locations were Cedar Knolls,
NJ; Chicago, IL; Miami, FL; Seattle, WA; and Wittmann, AZ. In addition, samples of
polycaprolactone/linear low density polyethylene blend (PCL) and poly(hydroxybutyl
2-6
-------
valerate) (BP) were exposed outdoors in Miami, FL. Control samples of plastic films were
exposed simultaneously with the degradable materials in most exposure experiments.
Table 2.3.1 shows the sample matrix for outdoor direct weathering, as well as for marine
and soil burial exposures. Data for daily average, minimum, and maximum temperature,
daily rainfall, and total global and UV radiation for the exposure sites are reported in
Appendices D through H.
Outdoor exposure studies were carried out from June 19 to September 30, 1990 in
general accordance with ASTM G7. The samples were exposed on racks to direct sunlight
facing 45° south and were backed with unpainted plywood. The exposed samples were
placed in opaque paper envelopes and returned to RTI from the exposure service as quickly
as possible after sampling for testing. The samples were not exposed to any light in the
interim period between exposure and testing. To prevent any misidentification, samples
were coded using small punches of various shapes prior to sending them to the exposure
services.
In certain cases, duplicate sample sets were exposed. Duplicate exposure was carried
out by replacing a sample from the original set with one from the duplicate set at each
sampling interval. Upon removal of the final sample from the orginal set, the entire dupli-
cate set was removed. A detailed discussion of the rationale for exposing duplicate sets is
given in Section 2.3.1. Table 2.3.2 identifies the sample materials, locations, duplicate
sets, and scheduled sampling intervals for outdoor exposure. Actual sampling intervals are
shown in Appendix A.
2.3.3 Marine Exposure
Two types of marine exposure were utilized for the degradable plastic materials;
photodegradable materials were exposed floating in sea water, while biodegradable materi-
als were exposed to bottom sediment at a depth of about 10 feet. The two locations for
marine exposure were Miami (Biscayne Bay), FL, and Seattle (Puget Sound), WA. For
floating exposures, the rectangular samples were attached by nylon monofilament lines to a
plastic frame attached to styrofoam floats so that sample level was unaffected by tidal con-
ditions. Water depth was always at least 15 feet. Excess nylon line was provided so that
the samples were always freely floating. Biodegradable samples were affixed to 8" x 12"
fiberglass-reinforced polyester frames, which kept the samples flat. The frames were
bolted to plastic piping and placed on the bottom of about 10 feet of water at a coastal expo-
sure site. After sampling, the plastic pieces were wrapped in newspaper, enclosed in a
plastic bag, and returned to RTI for testing. Prior to testing at RTI, the wet samples were
dried at ambient temperature under a fume hood for at least 24 hours.
2-7
-------
,
e
•c
S
C3
L«4
Location
U
2
&T
H
b^
o
C?
g^
• »— t
fe
**^
•a
OJ f>
CO
^
'§ j
§
**
O
fd
u
oo
"o
C
be ^™*
U_i *^^
3
•o
6
•8
o
U
1
1
0
IX,
O
tL<
O
O
o
(Ethylene-carbon ,-p
monoxide) copolymer
1
O
O
fc
0
o
o
o
OH
§
CO CO CO
12
o o
o"
o
M
fri 5j 5j
d °" °^ °"
o o
o o
LDPE/Starch/MX ADM
Polystyrene Foam PS
LLDPE/PCL Blend PCL
Biopol BP
to
CL ^3
3 OO
§** aa fa O O.
P § &S1
tu 55 o x
-------
Table 2.3.2 Sample Identification for Outdoor Exposure.
Initial Number Samples
Code
6P
6P
6P
6P
6P
PG
PG
PG
PG
PG
PS
PS
PS
PS
PS
Location
Cedar Knolls,
NJ
Chicago, IL
Miami, FL
Seattle, WA
Wittmann, AZ
Cedar Knolls,
NJ
Chicago, IL
Miami, FL
Seattle, WA
Wittmann, AZ
Cedar Knolls,
NJ
Chicago, IL
Miami, FL
Seattle, WA
Wittmann, AZ
Sample Set
Original
Original
Original
Duplicate
Original
Original
Original
Duplicate
Original
Duplicate
Original
Duplicate
Original
Original
Duplicate
Original
Duplicate
Original
Duplicate
Original
Duplicate
Original
Original
Duplicate
Degradable
15
15
15
15
20
15
20
20
20
20
20
20
20
20
20
20
20
20
20 ,
20
20
20
20
20
Control
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
Sampling Frequency
Degradable
3 days
3 days
3 days
3 days
Twice/week
1st 4 weeks;
then every 7 days
3 days
3 days
3 days
3 days
3 days
3 days
3 days
Twice/week
1st 4 weeks;
then every 7 days
3 days
3 days
7 days
7 days
7 days
7 days
7 days
7 days
7 days
7 days
7 days
Control
6 days
6 days
6 days
6 days
7 days
6 days
6 days
6 days
6 days'
6 days
6 days
6 days
7 days
6 days
6 days
14 days
14 days
14 days
14 days
14 days
14 days
14 days
14 days
14 days
- continued-
2-9
-------
Table 2.3.2 (continued)
Sampling Frequency
Code
ADM
ADM
ADM
ADM
ADM
Location
Cedar Knolls,
NJ
Chicago, IL
Miami, FL
Seattle, WA
Wittmann, AZ
Sample Set
Original
Duplicate
Original
Duplicate
Original
Duplicate
Original
Original
Duolicate
Degradable
15
-
15
15
15
15
15'
Control
10
10
10
10
10
10
i .
10
10
Degradable
3 days
-
3 days
3 days
3 days
Twice/week
1st 4 weeks;
then every 7 days
3 days
iControl
; 6 days
; 6 days
6 days
I 6 days
; 6 days
: 6 days
; 7 days
i
6 days
! 6 days
PCL Miami, FL
Original
20
10
7 days
14 days
BP
Miami, FL
Original
12
7 days
2-10
-------
Pertinent weather conditions for marine exposure, i.e., air and water temperatures,
are included in Appendices F and G. Table 2.3.3 identifies the samples and conditions for
marine exposure.
2.3.4 Freshwater Exposure
Exposure to a fresh water environment was carried out at Kerr Lake in Boydton, VA
at the United States Army Corps of Engineers maintenance facility.
Floating samples were exposed affixed to a floating platform fabricated of PVC pipes
and held afloat by two plastic buoys. Samples were attached in a manner to allow them to
freely float on water at all times. The depth of water at the exposure location was about
8-10 feet. Test samples exposed to the lake bottom environment were mounted on fiber-
glass frames which held the film flat and allowed an area of approximately 6" x 8" to be
exposed to the water/sediment Frames were attached to several nylon ropes in such a way
as to allow the frames to be placed flat on the lake bottom.
Samples (identified in Table 2.3.4) were removed at appropriate intervals, placed in
plastic bags, and transported to RTI for testing. All samples were dried under ambient
conditions prior to tensile testing.
2.3.5 Soil Burial Exposure
Samples to be tested for biodegradability (or biodeteriorability) were exposed to field
sqil burial conditions at Research Triangle Institute (NC). The exposure site was an above-
ground wooden enclosure, approximately 3 feet in depth and 15' x 15' in area, filled with
unfumigated, unfertilized standard sieved soil. The soil mixture could drain freely from the
enclosure into the ground. The entire area was enclosed by fence to prevent animals from
interfering with the exposure. Rectangular sample pieces were buried vertically in num-
bered plots, with the top of the material at least one inch below the surface of the soil. The
soil burial was carried out in triplicate, using three separate blocks of the soil burial enclo-
sure. Samples were randomized within each block. The material codes and sampling fre-
quencies for soil burial exposure are given in Table 2.3.5. Climatic data for the Raleigh-
Durham, NC area are given in Appendix I.
2.4 LABORATORY EXPOSURE METHODS
2.4.1 Weather-Ometer® Exposure
Accelerated weathering studies were carried out in general accordance with ASTM
G 26 (Operating Light-Exposure Apparatus (Xenon-Arc Type) With and Without Water
2-11
-------
Table 2.3.3 Sample Identification for Marine Exposure.
Initial Number Samples
Code
6P
6P
PG
PG
PS
PS
ADM
ADM
ADM
ADM
PCL
PCL
Location
Miami, FL
Seattle, WA
Miami, FL
Seattle, WA
Miami, FL
Seattle, WA
Miami, FL
Seattle, WA
Miami, FL
Seattle, WA
Miami, FL
Seattle, WA
Sample
Set
Floating
Floating
Floating
Floating
Floating
Floating
Floating
Floating
Sediment
Sediment
Sediment
Sediment
Degradable
20'
20
20
20
20
10
15
15
15
15
20
15
Control
10
10
10
10
10
10
10
8
10
8
10
8
Sampling Frequency
Degradable
3 days
7 days
3 days
7 days
7 days
7 days
3 days
7 days
7 days
7 days
14 days
Every 2 weeks
until 9 weeks;
then
weekly
Control
6; days
14 days
6 days
14 days
14 days
7|days
6. days
14 days
14 days
14 days
i
28 days
Every 4 wks
until 10 wks;
then
every 2 wks
BP
Miami, FL Sediment
12
1 day
2-12
-------
Table 2.3.4 Sample Identification for Freshwater Exposure at Kerr Lake, VA.
Sample
Code
Exposure
Type
Initial Number Samples
Sampling Frequency
Degradable Control Degradable Control
6P
PG
PCL
BP
Floating
Floating
Floating
Sediment
7
9
4
5
4 days
2 days
14 days
2-3 days
7 days
2-13
-------
Table 2.3.5 Sample Identification for Soil Burial Exposure at Research Triangle Institute.
Sample Initial Number Samples
Code -^ , , ,
Degradable
ADM 30 (10x3)
PCL 60 (20x3)
BP 45 (15x3)
Control
30 (10x3)
30 (10x3)
-
Sampling Frequency
Degradable
14 days
14 days
7 days
Control
28 days
28 days
. - .
for Exposure of NonmetalHc Materials). Samples (rectangular films or sheets) of !
(ethylene-carbon monoxide) copolymer (6P), low density polyethylene/MX (PG), low
density polyethylene/starch/MX (ADM), and expanded polystyrene foam (PS) were '
exposed for durations of 50,100, 150, 200, and 250 hours. (MX refers to transitional
metal compound pro-oxidants.) Controls for each sample type (with the exception of 6P)
were exposed for 100, 200, and 250 hours. The following conditions were used: ;
Apparatus: Xenon Arc Weather-Ometer® ;
Black Panel Temperature: 63+/-3°C :
Cycle: 102 minutes light/18 minutes light and ;
water spray :
Relative Humidity: 50 +/- 5% :
Prior to exposure, samples were conditioned for a minimum of 24 hours at 23°C and
50% 'ative humidity. After exposure, samples were returned to RTI for testing.
To study the effects of temperature, the four sample types (6P, PG, ADM, and PS)
were exposed for a constant time (50 hours) at several temperatures under the following
conditions:
Test Method: ASTMG26
Apparatus: HERAEUS XENOTEST® 1200 •
Light Source: Xenon Arc
Black Panel Temperature: 65, 70, 75, 80, and 85°C '
Duration: 50 hours i
Cycle: 102 minutes light/18 minutes light and :
water spray i
Relative Humidity: 50 +1-5%
Filter: Borosilicate Natural Sunlight Suprax
Radiation: 14.5 MJ/m2 (300-400 nm) !
2-14
-------
2.4.2 Accelerated Laboratory Soil Exposure
The biodeteriorable samples (PCL and ADM) and corresponding controls were sub-
jected to accelerated soil burial under controlled laboratory conditions. Rectangular pieces
of film approximately 8" x 10" in size were placed in a specially prepared soil mixture con-
tained in Rubbermaid® plastic containers. Each box contained approximately 3.2 kg soil,
and four film samples were initially placed into each container. A total of 8 sheets each of
PCL and ADM were exposed, along with 4 sheets of each control. Thus, a total of 6 plas-
tic containers were necessary for the experiment. For consistency, one large batch of soil
mixture containing additives to provide microbes and nutrients was made up and divided
among the six containers. The contents of the mixture were:
1. "Black Kow" Brand Topsoil - (6 x 3155) g
2. Garden soil (source: outdoors at RTI) -1% of weight of topsoil
3. Urea - 0.1 % of total weight of plastic samples
4. K2HPO4 - 0.05% of total weight of plastic samples
5. Water - 20% of the saturation value of the topsoil (in this case, 1735 mL)
The containers were incubated in a controlled-temperature room at 37°C. The initial
sampling intervals were every 3 days for the degradable films and every 6 days for the
controls, but testing of the inital samples showed that longer exposure durations would be
needed to achieve measurable degradation. The actual sampling frequencies are given in
Appendix C.
2-4.3 Evaluation of Spectral Sensitivity: Determination of the Activation Spectrum
of a Material by the Sharp Cut-on Filter Technique
(a) Filter Set
The set of filters covering the ultraviolet region consisted of 12 or 13 glass filters with
cut-on wavelengths (5% transmittance) ranging from 265 nm to 375 nm. The filters were
normally 2" x 2", but other sizes up to 6" x 6" can be used. A combination of Hoya and
Schott filter glasses were used to fabricate filters with the required transmission character-
istics. The spectral transmittance curves of the first six filters in the set are shown in Figure
2.4.1.
In fabricating the filters, types of glass which provide a spectral shift between filter
pairs of approximately 10 nm at 40% transmittance when ground to appropriate thicknesses
are generally selected. The exact thickness to which each filter is ground is governed by
2-15
-------
en
cc
tu
o
o
8
es
O
o
o
O)
o
00
o
CO
o
in
o
m
2-16
-------
the incremental ultraviolet transmitted by the shorter wavelength filter of the pair. The
thicknesses are adjusted so that the incremental ultraviolet is nearly the same for all filter
pairs. Because of the large tolerance in transmission characteristics of each glass type
necessitated by variations in the melt, the thickness required for each type varies with the
melt.
(b) Determination of Incremental Ultraviolet Between Filter Pairs
The area in Figure 2.4.1 between the curves of filters 5 and 6 represents the addi-
tional portion of the ultraviolet transmitted by filter 5 compared with that transmitted by fil-
ter 6. The spectral curve in Figure 2.4.2 is a plot of A% transmittance for the filter pair.
Similar spectral curves spaced about 10 nm peak to peak were obtained for the other pairs
.of filters.
The area of the spectral curve above A 10% transmittance is referred to as the incre-
mental ultraviolet (Figure 2.4.2). This is the radiation transmitted by filter 5 which is
mainly responsible for the incremental degradation in the specimen exposed behind filter 5
compared with the degradation in the specimen exposed behind filter 6. The area can be
determined from transmission spectra by any suitable technique such as by the use of a
planimeter, by counting squares if plotted on grid paper, or by cutting out the area and
weighing it. The measured areas of the spectral curves of the different filter pairs above
A 10% transmittance are used to determine the normalization factors.
(c) Normalization Factors
Although the filter thicknesses are adjusted to provide nearly equal areas above the A
10% transmittance level for all filter pairs, the areas are not identical. Therefore, normal-
ization factors are used to adjust the measured incremental degradation caused by each
spectral region so that the activation spectrum represents the relative effect of equal spectral
portions of the ultraviolet.
The normalization factor for each filter pair is calculated by dividing the average of the
measured areas by the area measured for each filter pair. Since degradation is usually not a
linear function of radiant exposure, the filter set is designed so that the maximum adjust-
ment required is less than 15%.
(d) Activation Spectrum
The activation spectrum is a plot of the relative extent of degradation caused by differ-
ent spectral portions of the radiation of the source. In the sharp cut filter technique, the
adjusted incremental degradation of the pairs of specimens exposed behind each pair of
adjacent filters in the set is plotted in bar graph form versus the spectral band pass of the
filter pair.
2-17
-------
Ob*
OOt-
08C
09C
I
h
c
z
Li
_i
W
>
in
o
o
in
n
02C;
ooc
035
03Z
•o
c
• r-(
.fi
CO
E"
2-18
-------
The spectral band pass defined by a pair of filters is the spectral range at A 20%
transmittance, approximately half the maximum A% transmittance. Thus, for the filter pair
5-6 of the set illustrated in Figures 2.4.1 and 2.4.2, the maximum A% transmittance is 42%
at 326 nm and the spectral range at A 20% transmittance is from 317 to 337.
(e) Exposure
Samples were exposed in an Atlas 6500 watt borosilicate-filtered xenon arc Weather-
Ometer® using the filter sets described above. Several preliminary exposures using a vari-
ety of filters were carried out for each sample type, and the information was used to select
the proper exposure times for activation spectra determination. Figure 2.4.3 schematically
illustrates the specimen arrangement during exposure.
Exposure frame
Exposure frame
Filter
(2" x 2")
N\\%\\\\
\ S \
\ \ \
""»fi. f S S S / f .
\S\\SN\N
SSSfSfS,
SSSNS-SNX
SfSSSSSS,
\N\S\\NS
Sample Strips
(- 1/2" x 7")
Overhead View
Side View
Figure 2.4.3. Specimen arrangement for Weather-Ometer® exposure of activation spectra
samples.
(f) Testing
With the exception of polystyrene foam, all exposed samples were tested on an
Instron Model 1122 using a crosshead speed of 500 nm/min and a gauge length of 40 mm.
Yellowness Indices of exposed polystyrene foam were measured according to ASTM
D1925 using a Macbeth 1500 colorimeter with integrating sphere for reflectance
2-19
-------
measurements. The specular component of light was excluded and the ultraviolet i
component included in the measurements. The specimens were backed with white ceramic
tile. On the basis of CDS standard illuminant C, Yellowness Index (YI) was calculated
from the tristimulus values X, Y, and Z using the equation below (see also Section 2.5.2):
YT 100 (1.28X- 1.06Z) ;
YI = ;(2-l)
2.5 OTHER TEST METHODS ;
2.5.1 Tensile Properties
Tensile testing of plastic films after field, Weather-Ometer®, and lab accelerated soil
">
burial exposure was carried out according to ASTM D882 (Tensile Properties of Thin
Plastic Sheeting). Method A of the test procedure, which employs a constant rate of igrip
separation, was used. The instrument used was an Instron Model 1122 connected toi a
computerized data acquisition system with a Sintech Testworks software package to allow
for statistical analysis of the data. At least five test pieces of each sample type were tested
unless deterioration of the film due to exposure did not allow five pieces to be cut. To pre-
pare test pieces, films were cut into 1/2-inch strips using a TMI Twin-Blade Cutter Model
22-34-03. Thickness values (to the nearest 0.001 mm) of films were obtained prior to
exposure using a Digitrix n Digital Micrometer. Thickness values are reported in
Appendices J and K, which summarize all tensile data obtained. Instron parameters for the
various sample types are shown in Table 2.5.1. As per the test method, test parameters
were chosen based on the properties of each sample material.
Tensile testing for determination of activation spectra of 6P, PG, and PCL was! car-
ried out as described above except that gauge length was 4.0 cm instead of 5.0 cm. j
2.5.2 Yellowness Index \
Yellowness Index (YI) and L, a, b, values for polystyrene foam samples were:
determined in accordance with ASTM standard D1925-70 by reflectance measurements
using an X-Rite 968 colorimeter. A standard calibration tile, whose percent reflectance was
measured between wavelength 400 nm and 700 nm against CPPA calibrated Japanese Opal
Glass EW-24 with the exclusion of specular light, was used as the white standard. Both
for the opal glass standard and for the test samples, the UV component of the incident light
(98%) was included but the specular component of the reflected light was excluded during
2-20
-------
Table 2.5.1. Instron Test Parameters Used for Testing Exposed Samples.
Test Parameter
Material
Full Scale
Load
(kgl
Crosshead Gauge
Speed Length
(mm/min)
Clamp
Jaw Face
Size
6P
6PC
PG
PGC
ADM
ADMC
PCL
LLDPE
BP
20
2
2
2
2
500
500
500
500
50
50
50
50
50
100
Pneumatic;
50PSI
Pneumatic;
50PSI
Pneumatic;
50PSI
Pneumatic;
50PSI
Pneumatic;
50PSI
1 x 1.5
1x1.5
1 xl.5
1 x 1.5
1x1.5
2-21
-------
the measurement The yellowness index (YI) was based on CIE standard illuminant Dgo
and CIE 10° standard observer viewing (CIE-SO) and was obtained from the tristimulus
values of X, Y and Z relative to the source C using the equation 2-1.
VT 100 (1.28X- 1.06Z)
ii —
"L", "a", and "b" parameters were also calculated from the tristimulus values. The
following equations were used for the purpose. i
X2-2)
a = 500 [ (--)1/3 - (--)173 1 (2-3)
b = 200 [ (--)l/3 . (--)l/3 ] (2-4)
1 n ^n
The tristimulus values Xn, Yn, and Zn define the color of normally white object-color
stimulus. This is given by the spectral radiant power of a standard illuminant (C.I.E. illu-
minant C, in this case) reflected into the observer's eye by the perfectly reflecting diffuser.
Under these conditions, Xn, Yn, and Zn are the tristimulus values of the standard illumi-
nant with Yn equal to 100. i
Several values of YI obtained from different sections of exposed sheet were used to
obtain the mean value of yellowness index. Reproducibility of measurement was generally
better than ±0.50 units.
2.5.3 Tumbling Friability
For polystyrene foam samples exposed outdoors, degradation was measured ih gen-
eral accordance with the Test Method for Tumbling Friability of Degradable Polystyrene
Foams, which is currently under consideration by subcommittee D20.96 as a standard
ASTM test method. This method determines the mass loss of a foam sample as a result of
the abrasion and impact produced by a laboratory tumbling device. It was suitable for the
samples subjected to outdoor weathering and to laboratory-accelerated weathering, but it
could not be used for samples exposed to marine conditions, where fouling caused by
I
marine growth greatly affected sample weight.
The tumbling apparatus was a cubical box of oak wood (3/4 in thick) with inside
dimensions of 190 x 197 x 197 mm. One of the 190 x 197 -mm faces was a hinged lid
2-22
-------
which was gasketed to prevent passage of dust. One of the 197 x 197-mm faces was
attached to an axis (the axis was normal to the center of the face) which allowed rotation of
the box at 60 ± 2 rpm. Two sets of 24 cubes (3/4 ± 1/32 in) of white oak wood were pre-
pared. Each set of cubes was preconditioned by tumbling for 6000 revolutions. The two
sets were numbered from 1 to 24 so that at the end of each test, a given cube could be
removed and replaced with the correspondly-numbered cube from the other set In this
way, the cubes were continually rotated, and cube wear was eliminated as a variable.
. Each test required 12-1" x 1" squares cut from the foam sample. All cut samples were
conditioned overnight at 50% relative humidity in a dessicator at 23°C before testing. The
humidity level in the dessicator was maintained by a saturated KSCN solution.
Since all the unexposed polystyrene foam samples were of uniform thickness, initial,
values (before exposure) of mass of a 1" x 1" square were determined for both the degrad-
able and the control PS foam by cutting and weighing 50 squares of each. These averages
were used in all tumbling friability calculations as initial mass. For degradable foam, a 1" x
1" square weighed 0.1031 g with a standard deviation of 0.0018 g; a square of the control
material weighed 0.1039 g with standard deviation of 0.0039 g.
Before each day's testing, the apparatus was calibrated by setting the speed control
and counting the number of revolutions per 60 seconds. (This calibration was done with
the 24 wooden cubes in the box.) The count was repeated twice and the three values
entered in the calibration log book. For an average speed above or below 60 ± 2 rpm, the
speed was readjusted and calibration repeated. Based on the average speed, the time
required to give exactly 600 revolutions was calculated and used for all testing for that day.
For each test, 24 wooden blocks and 12 foam test squares were placed into the box and
the lid secured. The box was rotated for 600 revolutions, after which the wooden cubes
were removed and the polystyrene emptied onto a 1/4" mesh screen placed over a collection
pan. The screen was gently tapped to cause dust and large particles to pass through, and all
large pieces which did not pass the screen were collected and weighed to the nearest
0.0001 g.
Mass loss was calculated with the following equation:
Mass Loss (%) = [(Mi - M2)/Mi] x 100 (2-5)
where MI was the original mass before exposure (equals 12 x the initial values discussed
above) and M2 was the weight recorded after the tumbling friability test
2.5.4 Gel Permeation Chromatography
Gel permeation chromatography (GPC) was used to obtain molecular weight mea-
surements for selected foamed polystyrene sheets (PS) and polycaprolactone/ polyethylene
2-23
-------
blend films (PCL). Chloroform solutions (0.2% w/w) of PS samples were prepared
directly from the exposed samples. For PCL samples, the polycaprolactone fraction was
extracted by stirring the film in chloroform at ambient temperature for at least 24 hours.
The chloroform solutions of polycaprolactone were then diluted to give the required con-
centration for GPC analysis. All solutions (particularly those of the marine floating sam-
ples, which were covered with foulants) were filtered prior to injection into the GPC.
The chromatography system used consisted of a Waters Associates pump (Model M-
6000A), a Waters Associates differential refractometer (Model R401), and five Ultra-
sytragel® columns (Millipore) with pore sizes of 500,103,104, 105, and 106 A. The
mobile phase was HPLC-grade chloroform at a flow rate of 0.9 mL/min. The attenuation
setting on the refractometer was 2X. Eight monodisperse polystyrene standards were used
in calibration. . ;
Data from the chromatograms were entered into a computer program which calculated
molecular weights and molecular weight distribution based on the coefficients for each
polymer for the Mark-Houwink equation and on the elution volume of the polystyrene
standards.
GPC results were obtained for the following PS samples: outdoor exposure in
Chicago and Miami, marine floating exposure in Miami and Seattle, and Weather-Ometer®
exposure. For PCL, GPC results were obtained for outdoor soil burial exposure and for
marine sediment exposure in Miami.
2.5.5 Water Vapor Transmission
The area of exposed film samples available for the water vapor transmission rate
[WVTRJ determination was small, so a smaller area than the standard sample area of at
least 3000 sq.mm (ASTM E 96) was used in the test. The methodology described is there-
fore a modified test method. :
Measurements of WVT were made using a modified "cup method", where the film
sample was attached over the mouth of a cylindrical glass dish (5.0 cm diameter and 58 ml
in volume) containing about 20 g of calcium oxide (Aldrich Chemicals), using a rubber
o-ring. The weight of the dish with attached film was accurately determined with a balance
readable to 0.1 mg. Two to four replicate dishes were used for each determination. The
weighed dishes were placed in a dessicator containing deionized water and kept in aniair
oven at 37°C. Figure 2.5.1 depicts the experimental set-up for WVTR measurements. At
appropriate intervals the dishes were removed, cleaned free of adhering water droplets on
the outside, and weighed. Samples were generally weighed every 2-4 days for a period of
10 days. Thicknesses of the films were measured using a recording micrometer (Digitrix
2-24
-------
n, Japan Micrometer Manufacturing Co.). The slope of a plot of the weight gain versus
the duration of exposure to saturated water vapor yielded the WVTR of the film,
In the case of samples exposed outdoors for long periods of time, the material was
too brittle to be folded over the outside rim of the glass dish and secured with the o-ring.
This led to development of micro-cracks along the fold. For these samples, a smaller dish
with a diameter of 2.1 cm was used and the film sample .was glued on to the mouth of the
37°C Oven
Glass cup
Figure 2.5.1 Experimental set up for WVTR measurements.
dish using rubber cement. Weight gains of photodegraded plastic film samples were moni-
tored for a period of 22 - 25 days.
2.5.6 Thermogravimetry
A therrnogravimetric method was developed for rapid determination of the starch
content of polyethylene/starch blends.
A Perkin Elmer model TGS-2 Therrnogravimetric System, with a 4-system micropro-
cessor temperature control unit and a TADS data station, was used. The samples of plastic
films were cut into discs (5 mm in diameter). Several discs cut from different areas of the
film sample were placed together in an aluminum sample pan and set in the sample holder
of the equipment. Initial weight of the sample was recorded and generally found to be 6 -
10 mg. The sample in the pan was heated from 50°C to 450°C in a helium atmosphere at a
heating rate of 10°C/min. The weight of sample (with pan) was monitored as a function of
temperature.
2-25
-------
Under these conditions a distinct loss in weight was obtained at about 280°C - 340°C
that was attributed to degradation of starch. The loss in weight and the initial sample
weight were then used to determine the percent starch in the sample. In the case of samples
exposed in soil environments, the film was washed free of surface debris and dried prior to
being tested.
2.5.7 Gas Transport Properties ;
A gravimetric sorption technique was used to obtain transport parameters for the
plastic films. A recording electrobalance (Cahn 2000, Cahn Instruments Inc.) was used to
monitor the increase in weight of a sample placed in a carbon dioxide atmosphere due to
sorption of the gas by the polymer previously held in vacuo. The weight increases were
directly recorded on floppy disc using a simple data acquisition system consisting of an
A-D board and an IBM XT computer. The balance assembly was insulated, protecteb from
air current, and maintained at constant temperature 30 ± 2°C in a lagged wooden box,
A sample of the film material (approximately 200 mg for PG samples and 170 mg for
6P material) was placed in an aluminum pan and placed in the sample holder of the
microbalance. The sample chamber was evacuated to 0.01 torr and maintained under vacuo
for 24 hours to remove any dissolved gas from the polymer matrix. Dry carbon dioxide at
a pressure of 760 mm Hg was introduced into the chamber, and the data collection was car-
ried out at the rate of a reading every 5 or 10 seconds. Sensitivity of the balance was
0.5 fig. Data collection was continued until a constant weight was recorded. !
Sorption data obtained in the above described experiments can be conveniently plotted
as amount of gas absorbed by the plastic versus time. Solubility, S, is calculated using the
equilibrium weight gain at too, MOO, as follows.
x 29.47 (2_6)
(WQ/P)
where MW is the molecular weight of carbon dioxide (44 g/mole), p is the density of j film
(0.93 g/cc for LDPE), WQ is the weight of film sample, and P is the applied pressure1 of
gas. MOO is the final maximum weight of the sample after gas sorption. During initial
stages of gas sorption the time dependence of the weight gain by the sample was given by
the following equation. !
4 / Dt
Me
2-26
-------
where /is the thickness of the sample, and D is the diffusion coefficient of carbon dioxide
in the film sample. The diffusion coefficient was calculated from the initial slope, k, of the
plot of (M/Moo) versus square root of time.
k2/2TC
D= 16 (2-8)
Permeability constant P was obtained as the product of solubility and diffusivity
P = S * D (2-9)
2.6 TOXIOTY 3VETHQDOLOGY
2.6.1 Extraction Procedures
Thin plastic sheets such as (ethylene-carbon monoxide) copolymer, the Plastigone
material, and the ADM plastic material were ground by a Wiley mill and passed through
0.032-in mesh. The grinding was facilitated by dipping the plastic sheets in liquid nitro-
gen. The foamed polystyrene sample was ground by a blender. The ground plastics were
leached by the water extraction procedure as follows:
1. ' Add 80 g of ground plastic to a container,
2. Add 4 L of deionized water,
3. Measure and record initial pH of the plastic/water mixture,
4. Stir the mixture continuously for 24 hours at 18 to 27°C,
5. Filter the extract with porcelain funnel using Whatman Filtering Paper No. 1,
6. Measure and record the pH of the filtrate,
7. Test filtrate for toxicity.
2.6.2 General Laboratory Toxicity Testing Procedures
1. Prior to mixing toxicity test dilutions, dissolved oxygen (DO), pH, total residual
chlorine, conductivity, and salinity of the sample were measured and recorded. For
DO values of an extract sample <40% saturation, the sample was aerated with single-
bubble aeration until the DO was >40% saturation. Aeration rate and duration were
recorded. For pH values below 6.0 or above 9.0, the pH was generally adjusted to
pH 7.0 with base or acid. The type, strength, and volume of acid or base added were
recorded.
2. For cases where dechlorinated water was used as diluent, the total residual chlorine
was measured as nondetectable prior to using a given batch for testing.
2-27
-------
3. All containers, glassware, and materials coming into contact with the test solution
were cleaned and dried. Each test container and other glassware were labeled :as to
the test concentration, replicate number, and test identifier or experiment ID number..
4. For definitive tests at least 5 test concentrations and a control were tested. Ideally,
the test concentrations should produce extreme effects in the high concentrations
(assuming the sample is toxic), moderate or partial effects in the intermediate concen-
trations, and no effects in the low concentrations. At least 2 replicates for each' test
concentration were used.
5. Appropriate volumetric glassware was used for preparing the test concentrations
(Class A volumetric flasks, graduated cylinders, and pipets). The total volume of the
glassware used was not more than 2 times the volume being measured. The glass-
ware used and volumes of effluent/stock solution and diluent measured for each test
concentration were recorded.
6. Prior to introducing the test organisms, temperature, pH, and conductivity (and salin-
ity for saltwater testing) of (at a minimum) the control, intermediate, and high test
concentrations were measured. Dissolved oxygen was measured in one replicate of
all concentrations. These parameters were measured at least every 24 hours foi: the
test duration, more frequently (hourly) for a low initial DO of the high concentration.
For tests in which the DO of any container fell below 40% saturation for warm water
species or 60% saturation for cold water species, all test chambers were provided
single-bubble aeration (approximately 100 bubbles/min.) for the remainder of the test.
Alkalinity and hardness were measured in the control and high concentration prior to
test initiation.
7. Test organisn ;-re randomly assigned to the test containers. One to five test iorgan-
isms were seq . atially placed in each container starting with the control and ending
with the highest concentration. This was repeated until the appropriate number of test
organisms were added to each container. During transfer, organisms were released
under the surface of the water, and the volume of culture water transferred with the
organism was minimal (<0.5 ml).
8. All containers were checked for the proper number of organisms and to ensure that
the organisms were not harmed in the transfer process. j
9. The number of live organisms in each test container was recorded every 24 hours for
the test duration. Dead organisms were removed when noted. General behavior of
the organisms was also noted.
2-28
-------
2-6-3 Static or Static Renewal (48 or 96 H) Fathead Minnow Toxicitv Tests
1. The test temperature was 20 ± 2°C,
2. All test fish were 1-90 days old at the start of the test. The range of ages in each test
did not exceed 3 days.
3. The test volume and test chamber size was based on test organism size. Organism
loading did not exceed 0.8 g/L.
4. Steps 1 through 9 in General Laboratory Toxicity Test Procedures (G.I) were fol-
lowed.
5. All test solutions were renewed at 48 hours: A duplicate set of chambers was used,
fresh solutions prepared, and organisms carefully transferred to corresponding test
chambers just as when initiating the test.
6. U. S. EPA computer program for analysis of acute toxicity test data was used.
2.6.4 H.I Ceriodaphnia dubiaSurvival and Reproduction Test
1. The test temperature was 25 ± 1 °C.
2. The test chambers were 30 ml plastic beakers, and the test volume was 15 ml.
3. The samples were filtered through a 60 jim plankton net.
4. Neonate Ceriodaphnia dubia <24 hours old and released during the same 8 hour
period were used as test organisms.
5. Generally 6 or 7 test concentrations, including a control, were used. Ten organisms
were exposed to each concentration, one per test chamber. The test consisted of 60
or 70 beakers.
6. Stock solutions (200 ml) of each test concentration were prepared using the appro-
priate volumetric glassware. BMI Ceriodaphnia culture water (20% DMW mixed
with a pond water) was used as diluent All stock solution containers were labeled
with concentration and test I.D.#.
7. The temperature of the stock solutions was adjusted to 25±1°C. Temperature, dis-
solved oxygen, conductivity, and pH in the control, low, intermediate, and high con-
centration stock solutions were recorded. Dissolved oxygen concentration of any
stock solution of less than 40% saturation necessitated the aeration of all stock solu-
tions prior to the start of the test. Alkalinity and hardness of the control and high
concentration were measured.
8. Test chambers were labeled with concentration, test I.D.#, and replicate #. Stock
solutions were distributed to appropriate test chambers (15 ml each chamber).
Ceriodaphnia dubia food (0.1 ml) was added to each chamber along with 0.05 ml
Selenastrum food.
2-29
-------
Table 2.6.1 Test Conditions for Acute Fathead Minnow (Pimephales promelas)
Toxicity Tests. '
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Temperature (°C)
Light quality:
Light intensity:
-
Photoperiod:
Size of test vessel:
Volume of test solution:
Age of fish:
No of fish/rep.
No. of replicate test vessels per
concentration:
Total no. organisms per
concentration:
Feeding regime:
Aeration:
*
Dilution water:
Test duration:
Effect measured:
20°C±2° :
Ambient laboratory illumination
50-100 foot candles (ft c) (ambient ;
laboratory levels)
16 h light/24 h
500-1000 ml
500-1000 ml :
1-90 days
10 (not to exceed 0.8 g fish per liter of
test solution) :
2
20 !
None
None, unless DO concentration falls
below 40% of saturation, at which
time single-bubble aeration should
be started.
Dechlorinated water or other ;
approved water.
Definitive test 48 or 96 h (static or static
renewal test)
Mortality^ - no movement (LC50)
9. One organism was transferred to the 0% "A" replicate test chamber using a polyethy-
lene disposable pipet (bore ize 3 mm). During transfer, the organism was released
below the surface of the test solution and as little culture water as possible was 'trans-
ferred with the organism (less than 0.3 ml).
10. One organism from a given brood was transferred to each "A" replicate test chamber
as described above (one pipet was used to transfer control animals only). When all
"A" test chambers contained one organism, organisms from another brood were
transferred to the "B" replicates. Organisms were transferred in this manner until all
test chambers contained one organism. Each test chamber contained one organism
from a brood size greater than 8.
11. Replicates of each concentration were randomly placed in rows.
12. Test solutions were renewed daily with the appropriately collected and mixed sam-
ples. Two-hundred ml stock solutions were prepared, their temperature adjusted, and
water chemistry analyses performed. Starting with the control (0%), organisms were
transferred to clean beakers containing 15 ml of fresh test solution containing Q. 1 ml
2-30
-------
Ceriodaphnia food and 0.1 ml Selenastrum food (only adults were transferred, off-
spring were discarded after counting). The number of living adults and the number
of offspring produced by each female were then recorded. Water chemistry analyses
were performed after organisms were counted and transferred in one randomly
selected chamber from the control, low, intermediate, and high test concentrations
(this was recorded as "before renewal").
13. The test ended at 7 days or when 60% of the control organisms had had 3 broods,
and each female must have averaged > 15 offspring.
14. Seven day NOEC and LOEC values for survival and reproduction were calculated
using computer programs for analysis of chronic toxicity test data as per
EPA/600/4-89/001.
Toxicity testing was carried out by Biological Monitoring, Inc. of Blacksburg, VA,
using water extracts of plastics prepared at Research Triangle Institute.
2-31
-------
Table 2.6.2 Test Conditions for Ceriodaphnia dubia Survival and Reproduction Test
(Conforming to EPA/600/4-89/001).
1. Test Type:
2. Temperature (°C)
3. Light quality:
4. Light intensity:
5. Photoperiod:
6. Size of test vessel:
7. Volume of test solution:
8. Renewal of test concentrations:
9. Age of test organism:
10. Nc. ... test organisms per
chamber:
11. No. of replicate chambers
per treatment:
12, Feeding regime:
13. Aeration:
14. Dilution water:
15. Dilution factor:
16. Test duration:
17. Effects measured:
18. Effluent concentrations:
19. Test acceptability:
20. Sampling requirements:
Static renewal
25±1°°C
Ambient laboratory illumination
10-20 |iE/m2/2, or 50-100 ft c (ambient
laboratory levels)
16 h light, 8 h darkness :
30ml
15 ml
Daily (for N. Carolina Methodology,*
2X) ;
<24 h; and all released with an 8 hour
period
1
10
Feed 0.1 ml each of food suspension;
Selenastrum per test chamber daily.
None ;
Moderately hard standard water, 20%
DMW receiving water, other surface
water, or ground water with hard-
ness similar to receiving water.
Approximately 0.3 or 0.5.
7 days or until 60% of the controls have 3
broods. :
Survival and reproduction
Minimum of 5 and a control for definitive
tests. :
80% or greater survival and an average of
15 or more young/surviving females
in the control solutions. At least
60% of surviving females in con-
trols should have produced their
third brood. '
For on-site tests, samples are collected
daily, and used within 24 hours.
For off-site tests, a minimum of 3
samples are collected. Maximum
time to first use of a sample is 36
hours. ;
2-32
-------
2.7 PRELIMINARY RECYCLING STUDY
2.7.1 Sample Preparation
Four of the degradable materials were chosen for the recycling study: (ethylene-car-
bon monoxide) copolymer (6P), low density polyethylene/MX (PG), low density
polyethylene/starch/MX (ADM), and expanded polystyrene foam (PS). Samples of these
degradable plastics were pre-exposed to outdoor weathering in Miami, FL, for selected
exposure durations and were then mixed with virgin resin to extrude new films. Pre-expo-
sure was carried out in general accordance with ASTM G7 (direct sunlight, samples backed
on racks at 45° South), with exposure dates given in Table 2.7.1 below:
Table 2.7.1 Pre-Exposure of Degradable Plastics for Recycling Study
Sample Code
6P
6P
6P
PG
PG
PG
ADM
ADM
ADM
PS
PS
PS
~~~#of
Sample
Pieces*
27
27
27
66
66
66
56
56
56
10
10
10
Exposure
Duration
(days)
5
9
15
5
9
14
5
9
15
5
9
14
Exposure
Dates
8/2-8/7/90
8/2-8/11/90
8/2-8/17/90
7/19-7/24/90
7/19-7/28/90
7/19-8/2/90
8/2-8/7/90
8/2-8/11/90
8/2-8/17/90
7/19-7/24/90
7/19-7/28/90
7/19-8/2/90
rotal Solar
Radiation
(MJ/m2)
61
114
190
74
153
225
61
114
190
74 '
153
225
Total Solar
UV Radiation-
300 -385 nm
(MJ/m2)
3
6
9
4
8
11
3
6
9
4
8
11
*These were the number of sample pieces required to give 80-100 g of sample for
each exposure duration.
To prepare for extrusion, the exposed films were ground (6P, ADM) or chopped
(PG, PS) into small pieces. Grinding was done using a Wiley mill; the samples were
mixed with dry ice to keep them brittle enough to be cut by the blades of the mill. PG
samples were too thin and flexible to be ground by this method; they were cut into small
pieces with a paper cutter. PS samples were made into an aqueous slurry and chopped into
small pieces using a household blender.
2-33
-------
2.7.2 Extrusion
Various levels of the pre-exposed samples were blended with virgin resin and
extruded into thin films. The compositions of the extruded films are given in Table 2.7.2.
The virgin resin used for 6P, PG, and ADM was a medium density polyethylene powder
(particle size <0.032") with melt index of 0.54; for PS, crystal polystyrene of melt flow
1.7 was used. The polystyrene virgin resin was in pellet form and had to be ground to
pass 40 mesh prior to extrusion.
All pre-exposed films were micro-pelletized prior to extrusion using a single strand
pelletizing die 0.062" in diameter. A Micro-pelletizer was used to make pellets roughly
0.02" in diameter and 0.02" long.
Blends (50 g) of virgin resin and exposed material were prepared according to the
ratios given in Table 2.7.2. Extrusion was carried out using a Microtruder of 1/4" 24:1
L/D ratio with a 1/2 HP DC drive and digital temperature controllers. The' feed section was
water cooled, and screw RPM varied from 20 to 175. Temperatures were:
Barrel Zone 1: 300°F
Barrel Zone 2: 375°F
Barrel Zone 3: 425°F
Die: 425°F
A slit die was used to extrude films 2" wide and approximately 1.5 mils thick. :
2.8 QUALITY OF DATA
Figure 2.8.1 shows the typical sample flow for all types of weathering experiments,
both natural and accelerated exposures. Various steps were taken at each stage of sample
handling to insure the highest possible data quality. These steps included proper sam'ple
identification and record-keeping, care in handling and preparing samples for exposure and
testing, use of standard test protocols when at all possible, and statistical analysis of the
data to determine its significance. An internal audit was conducted by the RTI Quality
Assurance Officer, Doris Smith; her report is shown in Exhibit A.
(a) Sample Identification and Record-Keeping
*
When received from the manufacturer, all plastic materials (both enhanced degradable
and controls) were assigned a code name generally consisting of several letters. These
codes have been identified in Sections 2.1 and 2.2 of this report. These code names iwere
consistently used throughout the study to refer to the samples. To prevent inadvertent
mislabeling by the exposure service, small metal punches of various shapes were used to
2-34
-------
Table 2.7.2. Composition of Extruded Films Prepared for Preliminary Recycling Study.
Film
Code
6P-0
6P-1
6P-2
6P-3
6P-4
6P-5
6P-6
6P-7
6P-8
6P-9
6P-10
6P-11
6P-12
PG-0
PG-1
PG-2
PG-3
PG-4
PG-5
PG-6
PG-7
PG-8
PG-9
PG-10
PG-11
PG-12
ADM-0
ADM-1
ADM-2
ADM-3
ADM-4
ADM-5
ADM-6
ADM-7
ADM-8
ADM-9
ADM-10
ADM-1 1
ADM-12
Percent of
Pre-exposed
Material
0
5
10
20
5
10
20
5
10
20
5
10
20
0
5
10
20
5
10
20
5
10
20
5
10
20
0
5
10
20
5
10
20
5
10
20
5
10
20
Amount of Virgin
Resin * (g)
50.0
47.5
45.0
40.0
47.5
45.0
40.0
47.5
' 45.0
40.0
47.5
45.0
40.0
50.0
47.5
45.0
40.0
47.5
45.0
40.0
47.5
45.0
40.0
47.5
45.0
40.0
50.0
47.5
45.0
40.0
47.5
45.0
40.0
47.5
45.0
40.0
47.5
45.0
40.0
- continued
2-35
Amount of Pre-
exposed Material
(g)
0.0
2.5
5.0
10.0
2.5
5.0
10.0
2.5
5.0
10.0
2.5
5.0
10.0
0
2.5
5.0
10.0
2.5
5.0
10.0
2.5 ,
5.0
10.0
2.5
5.0
10.0
0.0
2.5
5.0
10.0
2.5
5.0
-10.0
2.5
5.0
10.0
2.5
5.0
10.0
-
Exposure Time for
Pre-exposed
Material**(days)
-
0
0
0
5
5
5
9
9
9
15
15
15
-
0
0
0
5
5
5
9
9
9
14
14
14
-
0
0
0
5
5
5
9
9
9
15
15
15
-------
Table 2.7.2. (continued)
• Film
Code
PS-0
PS-1
PS-2
PS-3
PS-4
PS-5
PS-6
PS-7
PS-8
PS-9
PS-10
PS- 11
PS-12
Percent of
Pre-exposed
Material
0
5
10
20
5
10
20
5
10
20
5
10
20
Amount of Virgin
Resin* (g)
50.0
47.5
45.0
40.0
47.5
45.0
40.0
47.5
45.0
40.0
47.5
45.0
40.0
Amount of Pre-
exposed Material
(g)
0.0
2.5
5.0
10.0
2.5
5.0
10.0
2.5
' 5.0
10.0
2.5
5.0
10.0
Exposure Time for
Pre-exposed
Material**(days)
-
0
0
0
5
5
5
9
9
9
14
14
14
* Virgin resin for 6P, PG, and ADM films was medium density polyethylene and for PS was
crystal polystyrene.
**
Outdoor exposure was carried out at 45° South in Miami, Florida.
2-36
-------
^<
"^ — ~%
RTI Exposure:
{soil burial, lab
accelerated
soil burial)
.. __..., J
^-
Manufacturer
\
O
^
r
n 1
J
"^^
-
r"-Cut. "\
» Measure TnicRness
* Punc^i Code
» Log into Spmadshest
^^
Contracted Exposure
Services:
(direct weathering, marine
floating, and sediment,
accelerated weathering)
* Assign Code Name
*log Actuaf Exposure Dates
r Storage of Exposed
' and Tested Sampfes
Figure 2.8.1 Typical sample flow.
2-37
-------
EXHIBIT A: Internal Audit Report.
TO: Shri Kulkarni
FROM: Doris Smith
DATE: July 19, 1990
Systems Audit Report: Exposure Assessment Work Assignment Number 11-60.
Accelerated Environmental Exposure, Laboratory Testing, and !
Recyclability of Photo/Bio-degradable Plastics.
The QAPP for this work assignment states that four major stucly
components will be reviewed during this study: :
-Results of preliminary studies,
-Sample exposure in the field,
-Measurement systems, and
-Data processing.
.1
A systems audit was conducted July 10 and July %&, 1990 to review the
first 2 study areas. A checklist was prepared and used for the systems
audit. The participants were
Dr. A. L. Andrady, Preliminary Experiments and Subtask 1,
Literature Review, \
Dr. J. Pegram, Subtask 2, Outdoor Exposure. \
The review focus was determining that the objectives of the preliminary
experiments and literature review were met, and reviewing the sample
documentation and custody records for outdoor exposure experiments.
Results:
The recordkeeping for this work assignment is excellent, and ;samples are:
tracked using a computer spreadsheet system designed for this study. ;
Dr. Pegram is responsible for sample custody and tracking, arid she
reviews all data from the samples. I suggested that she record her
reviews in some manner, such as initialing data sheets, or adding the
review to the spreadsheet.
The preliminary experiments fulfilled the objective of providing data to
determine the timing of the outdoor exposure experiments. Corrective
action was required in only one case where an experimental material was
found to have an unexpectedly short shelf life. I
No data were reviewed as a part of this audit. \
Copy: " ;
Dr. A. L. Andrady • :
2-38
-------
stamp the plastic films before sending them for exposure. Each sample type and each
exposure location were represented by a different shape. These shapes were identifiable
even after weathering of the sample. As samples were removed from field exposure racks,
field sites, or from Weather-Ometers®, each sample was labeled. A paper label was sta-
pled onto dry samples. Wet samples were placed in a plastic bag which was labeled on the
outside with a marker pen.
After exposure, each sample was assigned a name which included the material code;
type of exposure (O = outdoor direct weathering, F = marine floating, M = marine sedi-
ment, FW = freshwater, S = soil burial, W = Weather-Ometer®, LA = lab accelerated soil
burial); exposure site; and duration of exposure. An example of a sample name would be
6P/O-Mi/3DY, which completely identifies the material with respect to type, location, and
duration of exposure: (ethylene-carbon monoxide) copolymer exposed to outdoor direct
weathering in Miami for three days.
Computer spreadsheets were used to keep a record of the number of samples sent for
exposure, the dates samples were sent and received, actual dates of exposure, and testing
of the exposed samples. These spreadsheets were updated each time a sample was received
from the exposure service. Notes of .any abnormalities were also entered into the spread-
sheets. Back-up copies of the spreadsheets were kept on separate disks. Printouts of the
spreadsheets are given in Appendices A, B, and C.
(b) Exposure
Samples were prepared for exposure at RTI by.cutting the plastic films into approxi-
mately 8" x 10" sheets (except for 6P samples, which were received from the manufacturer
in sheets which could be easily cut into 3-1/2" x 6" pieces which contained 6 1/2" strips of
material). All sample pieces were consistently cut with the machine direction of the film
along the 8" side so that strips for tensile testing would all be parallel to the machine direc-
tion and thus be comparable for a given material at various exposure times. The material
and exposure location for each individual piece were then identified using the punch code
system. Average thickness measurements of each type of material were taken prior to
exposure arid the values used for all subsequent stress-strain calculations. It was necessary
to use unexposed thicknesses because marine exposure causes build-up-of a foulant layer
on the surface of the film and makes it impossible to obtain accurate thickness values.
Thickness measurements were made to the nearest 0.001 mm using a digital Digitrix II
micrometer connected to an EDP-1000 QC printer with statistical capabilities. At least ten
measurements were taken for each average value determined.
2-39
-------
To determine suitable sampling intervals, preliminary exposures were carried out at
one location (Miami) for direct weathering for four of the sample types and for marine
sediment exposure for two of the sample types. Results for tensile testing of the exposed
materials were used to choose sampling frequencies and intervals for the main exposure
experiment. In all
-------
(c) Testing
While different tests might have been carried out by several researchers, sample cus-
tody was handled by a single person (Dr. Pegram). All samples, before and after expo-
sure as well as after testing, were managed by her.
Two major types of testing were carried out to determine degradation/deterioration of
exposed-samples: tumbling friability for polystyrene foam and determination of tensile
properties by Instron for all other sample types. As described in Section 2.5.3, the pro-
cedure for tumbling friability testing is currently under consideration by an ASTM sub-
committee for acceptance as a standard test method. The proposed draft procedure, kindly
provided by the subcommittee, was followed for this test. The test apparatus was con-
structed according to the instructions in the method, using the specified materials. It was
calibrated daily to determine the proper time to give the exact number of rotations per test.
A computer log of the daily calibration was kept on record at RTT. Data summaries for
tumbling friability, as well as a record of which samples had been tested, were kept on
computer spreadsheets, including back-up files.
Tensile properties of the plastic films were measured according to ASTM D882,
Tensile Properties of Thin Plastic Sheeting. This method applies to materials less than 1.0 -
mm in thickness. Method A of the procedure, Static Weighing - Constant-Rate-of-Grip
Separation Test, was followed. As stated previously, the average thickness of each mate-
rial prior to exposure was used for stress-strain calculations. Test pieces 1/2" in width
were cut after exposure using a TMI twin-blade cutter which gave smooth, consistent edges
and sample widths. Cut edges of the samples were routinely examined, and those which
were not perfectly smooth were discarded. All samples were cut so that machine direction
of the film was parallel to the direction of pull on the Instron. Samples were conditioned
for 24 hours prior to testing in the standard laboratory atmosphere of 23 °C and 50% rela-
tive humidity. Instron testing was also conducted under these conditions. The hydropho-
bicity of these plastic samples minimized the effects of conditioning on the test results.
The Instron machine was calibrated daily using a 2-kg weight to set the load range.
Gauge length was also checked before each use of the machine. Conditions for gauge
length and rate of separation of the grips were determined according to the test method. As
per the test method, at least five pieces were tested for eacji sample except in those cases
where embrittlement or sample loss due to'deterioration did not allow five pieces to be cut.
Observations were made during testing as to whether the sample gave a clean break, tore,
broke at the grip, or showed abnormal behavior. In most cases, samples which broke at
the grip gave similar tensile results to those which broke between the grips, so these data
were retained. (See Section 8.3 of ASTM D882.) Those data points which were abnor-
2-41
-------
mally low due to tear failure, holes, or other anomalies were marked to be excluded from
the statistical analysis. Computer printouts of the complete tensile data showing all indi-
vidual results, comments, omitted data points, and statistical analyses of data were too
voluminous to be included in this report but are on file at RTI. The data are also stored on
floppy disks. ;
(d) Tested Samples :
After testing, samples were stored under dark conditions at ambient temperatures at
RTI. The samples were identified by code name and were available for additional testing,
e.g., Yellowness Index measurements and GPC for polystyrene foam, TGA, toxicity test-
ing, and other methods discussed in this report.
All the exposed samples will be retained for a reasonable period of time at RTT.
(e) Statistical Analysis of Data ;
As stated above, at least five pieces of each sample were tested for all Instron work
except where loss of sample prevented it. Based on values for percent elongation at break.,
data points were omitted in cases of extremely low values, which were attributed to failure
at a tear or hole in the sample and thus were not indicative of the tensile properties of the
polymer material. Values for mean, standard deviation, and the number of test pieces
included in the analysis are given in the summaries of tensile data in Appendix K. These
numbers can be used to calculate confidence intervals for the mean values and thus deter-
mine whether significant differences exist between enhanced degradable and control mate-
rials for comparable conditions at a given duration of exposure. Relatively large values for
standard deviation are inherent in the testing of exposed plastic materials due to the vari-
ability of the polymer material itself as well as to variations in exposure conditions within a
given film sample, especially in marine exposure due to fouling. :
For soil burial exposure, where the profile of the microbial population can vary
widely even at the same geographic location, a randomized block experiment was carried
out in which triplicate samples were buried in each of three different blocks. Analysis of
variance of the data for soil burial showed the block effects to be insignificant and the
treatment effects (variation of exposure times) to cause significant differences in values for
elongation at break.
In conclusion, the basic methodologies proposed in the Quality Assurance Project
t
Plan of January 1990 were closely followed. System audits relating to (a) preliminary
studies, (b) field exposure, (c) measurement systems, and (d) data processing were carried
out as proposed in Section 4.2 of the QA plan. In the case of Subtask 3, Degradation of
Products of Plastics, the actual work carried out was less than planned due to resource
2-42
-------
limitations. The proposed protocol for trapping and concentrating volatiles on Tenax
cartridges was not used.
2-43
-------
-------
SECTION 3.0
SPECTRAL SENSITIVITY OF ENHANCED PHOTODEGRADABLE PLASTICS
3.1 ACTIVATION SPECTRA
The activation spectrum of a material identifies the wavelengths in a specific light
source responsible for its photodegradation. A specially designed set of sharp cut-on filters
was used to determine the relative effect of various spectral regions in the ultraviolet portion
of the white light spectrum, between about 270 to 400 nm, on polymer degradation. Each
spectral region was defined by the difference in transmittance of a pair of cut-on filters.
A separate sample of the same material was exposed behind each of the filters in the
set for the same duration of time. The extent of degradation of the exposed material was
then defined using an appropriate test method. The degradation caused by each of the
spectral regions was based on the difference in degradation in the two samples exposed
behind each pair of filters that defined a spectral region. It was plotted in bar graph form
versus the spectral band pass of each filter pair to give the activation spectrum.
3.1.1 Ethvlene-Carbon Monoxide Cooolvmer (ECO Copolvmer - Code 6P)
Data were obtained for a set of ECO copolymer film samples exposed for 117 hours
behind filters in a preliminary experiment The temperature of these samples during expo-
sure was maintained at 77°C (set 1). Table 3.1.1 shows the data summary for percent
elongation at break for these samples. (Detailed results on tensile testing of all activation
spectra samples are given in Appendix J.) Only the elongation at break is considered, as
this measure was found to be the most sensitive tensile property to degradation.
Separate results are shown for the inner two strips of the exposed specimens to study
the possibility that the outer positions (strips A & D in Figure 2.4.3) may have been
shielded by the edge of the frame; however, no difference in wavelength sensitivity was
noted when the inner position data was evaluated separately. However, the scatter in data
is significantly lower for the later set of data (see Figure 3.1.1 compared to 3.1.2).
An activation spectrum was not plotted for data on ECO copolymer samples because
extensive degradation occurred within a very narrow spectral region of the borosilicate-fil-
tered xenon arc radiation. Based on percent elongation at break, the data suggested that
wavelengths below 330 and 340 nm were mainly responsible for the degradation.
Differences in elongation at break among samples exposed behind filters #9 through
#16 appeared to be within experimental variation. The lower elongation-at-break in these
specimens compared with the unexposed specimens indicates some photodegradation even
3-1
-------
Table 3.1.1 Photodegradation Data for (ethylene-carbon monoxide) Copolymer
[6-Pack Rings (6P)] Exposed 117 Hours (Set 1) at 77°C.
Percent Elongation at Break
Filter 5%
No.
Unexposed (3
00
2
3
4
5
6A
6B
7
8
9
10
11
12
13
14
15
16
Transmittance
(nm)
specimens)
238.2
262.5
280.2
295.0
303.5
313.2
318.0
322.5
328.1
337.9
339.7
352.4
359.1
360.5
367.5
373.0
406.8
Inner
Average
155
1751
54
125
48
101
214
162
214
593
632
693
626
513
459
734
2813
Strips Only
Standard
Deviation
9
-
10
5
50
27
4
63
22
94
59
5
58
32
149
131
207
All
Average
922
132
1652
572
100
55
113
166
107
1752
612
460
640
4932
5252
5042
738
3693
Strips
Standard
Deviation
21
28
15
9
31
52
31
56 !
10,
70;
70:
202
72:
234:
31
131
80
210
Exposure Filter Set A Only - 4 strips behind each filter; no air space between filters and
specimens. The latter were backed with black paper and cardboard.
1 Only one sample available for testing.
2 Three samples only.
3 The data for filter #16 was omitted because of abnormally low % elongation.
3-2
-------
at these wavelengths. A further indication that this radiation had little effect on these
samples is that most of them failed at the clamp during tensile testing. In contrast, those
specimens exposed to shorter wavelength radiation failed in the section exposed to the
radiation. There was a slight increase in degradation with decreasing wavelength of
irradiation by wavelengths shorter than about 330 nm (the wavelength at 10% transmittance
of filter 8). It was noted that nearly all samples behind filters #9 through #16 failed at the
clamp indicating that the central portion which was exposed to the radiation was not
extensively degraded by it.
The value of percent elongation at break used for the long-wavelength, flat part of the
curve is the average of data for filters #9 through #15, which is 606% for the inner strips
only and 567% for the inner and outer strips taken together. The data for inner strips only
was evaluated because of the possibility that a small portion along the edge of some of the
outer strips may not have been fully exposed to the source. However, the wavelength
sensitivity is the same as when combined data for the inner and outer strips are used.
Reduction in elongation at break was due almost entirely to the shorter wavelength
ultraviolet transmitted by filter #8 compared with the ultraviolet transmitted by filter #9.
Although the spectral band pass (at A 20% transmittance) for this filter pair was between
334 and 354 nm, the actinic wavelengths were probably at the short wavelength end of this
spectral band. Although filter #9 transmits a significant amount of radiation between 344
and 354 nm, the specimen exposed behind filter #9 was not degraded by the radiation it
transmits.
Figure 3.1.1 shows percent elongation at break as a function of short wavelength cut-
off for the 117-hour exposure data. The short wavelength cut-off is the wavelength corre-
sponding to 5% transmittance of the filter. Figure 3.1.2 is similar except that it is based on
the inner strips only. The curves in the two figures are very similar, indicating that the
specimens did not receive uneven exposure.
The data in Figure 3.1.2 clearly identify the transition from relatively low-damage to
high damage for samples exposed at A, < (344-354) nm and A, > (354 )nm. However, the
data is based on a maximum of 4-5 sample strips in each wavelength range. Further expo-
sures were carried out to confirm these findings. '
Two series of cut-on filters were used in a second experiment where ECO copolymer
films were exposed for 219 hours at 60°C; these data are summarized in Table 3.1.2 (set
2). Because of the large standard deviations among replicate specimens, the activation
3-3
-------
Table 3.1.2 Photodegradation Data for (ethylene carbon-monoxide) Copolyraer
[6-Pack Rings (6P)] Exposed 219 Hours (Set 2) at 60°C.
Filter
No.
5% Trans.
(nm)
Percent Elongation at Break ;
Filter Set A
Filter Set B Filter Sets A + B;
Average npvLrirm Average nl^w! Average
jLJcviaiion Deviation
Unexposed (5 specimens) 774
1
2
3
00
2
3
4
5
6A
6B
7
8
9
10
11
12
13
14
15
16
238.2
262.5
280.2
295.0
303.5
313.2
318.0
322.5
328.1
337.9
339.7
352.4
359.1
360.5
367.5
373.0
406.8
73
15
170
141
49
72
73
63
2751
812
95
190
97
877
8873
369
384
174
78
4
22
26
41
41
9
19
173
41
19
72
19
38
21
433
174
The averages for Filter Sets A and B were
because the two averages were very different
was
large.
These data points
The
774
_
7
6
40
78
92
148
170
9321
, 900
-
9923
9193
950
169
68
112
plotted
and the
for the combined averages were not
average for Filter Set B was
174
.
0
2
48
35
7
8
16
16
36
-
42
56
50
44
5
11
774
73
11
88
91
63
82
103
117
6042
856
952
5912
5062
913
5282
2192
2482
Standard
Deviation
174
78
5
' 91
65
38
29
42
60
376
1 59
19
443
449
56
395
320
186
separately instead of combining them
standard deviation of the corhbinecl data
plotted.
plotted for filters #1 1 and #12, and the average for Filter Set
A was plotted for Filter #14.
3-4
-------
spectrum could not be plotted as a bar diagram, and the wavelength sensitivity was evalu-
ated on the basis of the percent elongation at break values as in the previous experiment.
Figure 3.1.3 shows a plot of the data. The percent elongation at break used for the long
wavelength flat part of the curve is the average of data obtained for filters #9 through #14,
i.e. 913%. Table 3.1.2 indicates the data points which were combined averages for the
two filter sets and those which were plotted separately. Data from all exposure experimens
taken together clearly show a narrow, critical wavelength interval below which extensive
photodegradation of ECO copolymer occurs. The values of average ultimate extension
obtained for samples exposed at wavelengths in the critical region show a drastic and con-
sistent change. Based on the three sets of data (Set 1, Set 2 - Filter Sets A & B) this
transition in photodegradation was determined to occur at 328-338 nm and 323-328 nm.
Samples exposed to filters with 5 percent transmission at these pairs of wavelength for
equal duration showed a more than 5-foid difference in average ultimate extension.
Both experiments also indicated a moderate fall (compared to unexposed material) in
elongation at break, suggesting increased photodegradation at wavelengths greater than
373 nm (5 percent transmission). As the degradation process in (ethylene-carbon monox-
ide) copolymer under ambient conditions is relatively insensitive to temperature (see
Section 4.2.1.2), this might be due to a secondary minimum in the activation spectrum.
Further work is needed to establish this effect.
The sunlight spectrum, filtered through window glass, is not totally devoid of UV
radiation. Figure 3.1.4 shows such a spectrum. It is clear that small amounts of light in
the region between 320 nm and 345 nm are transmitted through clear float glass commonly
used in residential and store front glazing. Therefore, the data does not allow the
assumption that these materials will not degrade during behind-glass exposure. Since the
thickness and quality of glass, as well as spectral qualities of sunlight at a given location,
influence behind-glass degradability, exposure studies are needed to establish the
performance of degradable plastics in this regard.
3.1.2 Low Density Polyethylene Containing Added Metal Compound Pro-oxidants fPG)
Plastigone material (PG or LDPE/MX) was exposed for 94.5 hour behind one set of
filters as a preliminary experiment and for 295 hours behind two sets of filters. The data
for percent elongation at break for these exposure times are summarized in Tables 3.1.3
and 3.1.4.
Figure 3.1.5 shows the data from the preliminary exposure experiment. Unlike the
case of (ethylene-carbon monoxide) copolymer samples, which were 16 mils in thickness,
the LDPE/MX samples were thin and flimsy (1 mil thick). The outer sample strips adjacent
3-5
-------
Table 3.1.3 Photodegradation Data for Plastigone Material (PG) Exposed
94.5 Hours at 77°C.
Filter 5% Transmittance
No. (nm)
Percent Elongation at Break
Unexposed
Number of
Samples
Inner Strips Only
Standard
Average
Deviation
398
112
00
2
3
4
5
6A
6B
7
8
9
10
11
12
13
14
15
16
238.2
262.5
280.2
295.0
303.5
313.2
318.0
322.5
328.1
337.9
339.7
352.4
359.1
360.5
367.5
373.0
406.8
2
4
2
4
3
4
3
2
3
4
3
3
2
2
2
1
0
52
41
8
92
92
61
81
162
124
138
150
314
393
176
412
374
-
19
12
2
29
37
11
8
66
19
21
48
88
93
60
54
_
-
Exposure Filter Set A Only - 4 strips behind each filter; no air space between filters and
specimens. The latter were backed with black paper and cardboard.
1 Data for specimens that broke at the clamp, in most cases, was abnormally low. Data for
such samples was not included in the table.
3-6
-------
Table 3.1.4 Photodegradation Data for Plastigone Material (PG) Exposed 295 Hours at 77°C.
Percent Elongation at Break
Filter
No.
5% Trans. Filter Set A
(nm)
Unexposed
l
2
3
00
2
3
4
5
6A
6B
7
8
9
10
11
12
13
14
15
16
Data
Data
outer
Data
238.2
262.5
280.2
295.0
303.5
313.2
318.0
322.5
328.1
337.9
339.7
352.4
359.1
360.5
367.5
373.0
406.8
Average
398
51
50
60
59
59
96
131
109
181
273
347 !
287
355
4942
3103
•-
.5
Filter Set B
Filter Sets A + B
Standard Avprapp Standard Avprawi
Deviation Avera§e Deviation Avera£e
112
11
11
13
23
20
6
5
18
28.
44
-
217
81
-
146
-
398
-
42
53
63
101
91
156
136
136
332
-
290
329
3192
3443
3291
112
-
13
12
22
12
9
22
24
32
122
-
29
81
-
145
123
398
51
46
56
61
80
93
141
122
158
302
347 !
289
342
4062
3273
3294
Standard
Deviation
112
11
12
12
20
27
8
18
25
36
88
-
139
74
123
72
123
for inner strips only.
for only
one of the outer strips was used
strip of each of the sets had scratches and
used for
break in each
2 strips from
from each
of the two sets. The
inner and one
smudges and an opaque section.
each of the sets. The strip that
set was eliminated. In set B, one
had the
of the outer strips
lowest percent elongation at
had white, opaque marks on
the edge and a lengthwise scratch.
4
5
Only
the outer strips of Set
B were used for filter #15.
Data excluded.
3-7
-------
to the edges of the exposure frame and filter were easily marred, wrinkled, and stained.
The data shown was calculated using inner'film samples exclusively.
The data shows a gradual increase in elongation at break with wavelength region of
exposure expressed as the 5 percent transmission levels of the relevant filter pair. While
not as sharp as that obtained with (ethylene-carbon monoxide) copolymer, there is a well-
defined transition wavelength above which the elongation at break remains close to that for
unexposed material. The percent elongation at break value used for the long-wavelength,
flat part of the curve is the average of the data for the total of four strips used for filters #12
and #14, i.e., 403%. The data for filter 13 was too low to be included and the single data
point accepted for filter #15 was also not included. For the preliminary set of data, the
transition occurred in the 340-352 nm interval. The average elongation at break for films
exposed behind the relevant pair of filters varied by a factor of two. The gradual increase
in degradation in the wavelength region 260 nm - 352 nm is interesting. Significant levels
of photodegradation are obtained in a broad range of wavelengths in this region. Unlike
the ECO copolymer, where the light-absorbing chromophore (i.e. >C=O group) is well-
defined, the LDPE/MX system uses light as an initiating agent. Hydroperoxide photolysis
may occur over a wider range of wavelengths compared to carbonyl group excitation.
Hence the gradual increase is not surprising. ;
Figure 3.1.6 shows the data from repeat exposures using two different sets of filters
(A & B). Note that the temperature for the 295 hour exposure is 77°C (as opposed to! 60°C
for the 95 hour exposure). For a metal-compound catalyzed system, the oxidation might be
photo- and/or thermally initiated. Higher temperatures can contribute to increased sample
degradation. This might explain the slight shift of the curve in Figure 3.1.6 toward tonger
wavelengths. The percent elongation at break used for the long wavelength flat part of the
curve is the average of the data used for filters 9 through 15, i.e., 335%.
As with the ECO polymer, the LDPE/MX system shows maximum photodegradation
near the 340 nm band of the solar spectrum.
3.1.3 Foamed Polystyrene with Carbonvl Functionalities (PS)
An activation spectrum for yellowing of polystyrene foam was obtained for foam
samples exposed 189 hours. Table 3.1.5 summarizes the data. Table 3.1.6 shows the L,
a, b values from which Yellowness Indices were calculated.
The activation spectrum (Figure 3.1.7) shows that yellowing by the borosili-
cate-filtered xenon arc radiation is due mainly to wavelengths between about 310 nm and
345 nm. Wavelengths longer than 350 nm cause very little yellowing, while wavelengths
3-8
-------
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-------
Table 3.1.6. L, a, and b Values for Polystyrene Foam Samples.
Filter
00
2
3
4
5
6A
6B
7
8
9
10
11
12
13
14
15
YI
26.6
27.2
29.8
28.5
24.0
17.9
15.0
11.3
8.4
3.1
2.8
1.6
1.8
1.4
1.4
1.4
L
88.10
87.84
87.66
87.38
88.15
88.91
89.95
89.92
90.36
91.03
90.88
91.38
91.41
91.59
91.50
91.34
a
-4.21
-4.19
-4.36
-4.23
-3.89
-3.24
-2.95
-2.27
-1.72
-0.66
-0.55
-0.28
-0.27
-0.26
-0.21
-0.23
b
14.73
15.02
16.30
15.60
13.31
10.14
8.81:
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3-10
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shorter than about 300 nm tended to bleach the yellow color formed under longer
wavelength radiation.
3.1.4 LDPE/Starch Systems
The marked temperature-sensitivity of this material caused it to become embrittled at
even short exposure times; it was therefore not possible to determine its wavelength sensi-
tivity. Trial exposures resulted in extremely low values for percent elongation at break
which could not be differentiated with respect to the wavelength of radiation transmitted.
3.1.5 Polycaprolactone/Polvethylene Blend
This sample type is a biodeteriorable material which has no additives (or chemical
modification) to render it photodegradable. However, even the biodeteriorable or
biodegradable packaging can also end up as litter. It was therefore thought desirable to
investigate its activation spectrum as well. The samples of linear low density polyethylene
blended with 20% polycaprolactone (PCL) were exposed for 129 hours behind 2 sets of
filters. Again, large standard deviations between replicates prevented determination of an
actual activation spectrum in the form of a bar diagram. Data for percent elongation at
break are summarized in Table 3.1.7; graphs are shown in Figure 3.1.8. All of the aver-
age percent elongation at break values for specimens exposed behind filters #9 through #16
are within the range of values of the unexposed specimens. Therefore, wavelengths longer
than about 338 nm (the 5% transmittance of filter #9) do not appear to cause photodegrada-
tion. The destructive effect of the xenon arc radiation appears to be due primarily to wave-
lengths between about 328 nm and 338 nm. The percent elongation decreases from an
average of 545 to an average of 164 in this wavelength region. Wavelengths shorter than
the 5% transmittance of filter #8 contribute only a little more than 20% to the total destruc-
tive effect of the UV radiation. The average percent elongation at break of the 6 specimens
exposed behind filter #9 (545%) is the same as the average for all the specimens exposed
behind filters #9 and #11-#16, i.e., 542%, the value used for the long wavelength flat part
of the curve. The data for filter #10 was omitted from the average because only 3 speci-
mens were exposed and their average appears to be out of line with the other points on the
graph. The curve shows the activation region to be between 328 and 338 nm.
3.1.6 Summary of Results •
For polystyrene, the activation spectrum based on Yellowness Index measurements
showed maximum yellowing to be due to radiation between 320 and 345 nm. For the other
samples, activation spectra could not be obtained in the form of a bar diagram (conventional
3-11
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representation for activation spectra) due to large standard deviations for elongation at break
between replicate samples. Spectral sensitivities were thus evaluated based on elongation at
break as a function of short wavelength cut-off (5% transmittance of the filter).
Nevertheless, with all three types of samples examined, the change from relatively low
levels to high levels of light-induced damage was marked and occurred over a narrow range
of wavelengths. It is of interest to note that the main actinic region for the different types of
enhanced degradable plastics is essentially the same. The results are summarized in Table
3.1.8.
Table 3.1.8. Spectral Sensitivity of Plastic Materials.
Material
PCL
6P
PG
PS
Temperature
60°C
60°Cl
77°C1,2
77°C1,3
etrc1
770C1
-
Main Actinic Region
>328-338 nm
>323-328 nm
>328-338 nm
>328-338 nm
>328-338 nm
>340-360 nm
320-345 nm
Additional Actinic Effects
>3 10-328 nm
>31 0-328 nm
>3 10-328 nm
>300-328 nm
>300-340 nm
-
1 The temperature is based on measurement of the surface of specimens using
Omega label temperature monitor strips during exposure.
2 Inner strips only (of 4 strips in sample holder, the 2 inner strips)
3 Inner and outer strips
In the case of LDPE/MX material, a temperature-dependent shift in the actinic wave-
length region was observed. The higher temperature shifted the actinic region to longer
wavelengths. This can probably be explained by the fact that the longer wavelength, lower
energy, radiation is more effective in causing degradation when the energy supplied by heat
is greater. Previous studies on polycarbonate and aromatic polyesters have not exhibited a
shift in wave-length sensitivity with temperature; this behavior has only been observed with
the above samples.
Window glass may transmit as much as 54% of 330 nm and 75% of 340 nm radiation
incident on its surface. The activation spectra obtained in this study do not rule out the
possibility that the three types of photodegradable plastics studied undergo at least a small
amount of degradation in behind-the-glass exposure. The practical significance of such
amounts of disintegration must be established by experiment.
3-13 .
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SECTION 4.0
WEATHERING OF ENHANCED DEGRADABLE PLASTICS
4.1 NATURAL WEATHERING
For the purpose of this study, natural weathering refers either to direct weathering
(outdoor exposure at 45° facing South), marine floating exposure, marine sediment expo-
sure, freshwater exposure, or outdoor soil burial. Not all of the plastic types tested were
exposed to all types of natural weathering; in general, the photodegradable samples were
exposed to direct weathering and to marine and freshwater floating environments, while the
biodegradable samples were exposed to marine sediment and soil burial conditions (see
Table 2.3.1).
4.1.1 Outdoor Duplicate Exposure
The rationale for exposing duplicate sample sets at selected locations has been dis-
cussed in Section 2.3.1. Duplicate exposures were carried out only for direct weathering.
Figures 4.1.1, 4.1.2, and 4.1.3 show plots of the tensile elongation at break (4.1.1, 4.1.2)
or tumbling friability mass loss (4.1.3) for the samples versus exposure time for duplicate
sets of selected materials and exposure sites. Figure 4.1.1 illustrates tensile test data for
duplicate exposure of sample 6P in Miami, FL, and shows good agreement between the
original data and that for the duplicate set, especially for the degradable material (Figure
4.1.1.a). For the control material, the duplicate samples were inadvertently exposed for
longer durations than the original set, but the duplicate data continues the trend established
by the original data, as seen hrFigure 4.1.l.b.
Figures 4.1.2.a and 4.1.2.b illustrate exposure of sample PG in Chicago, IL and
show some disagreement in elongation at break at comparable times for the two sets. This
may in part be explained by the fact that for short exposure durations, the equivalent time
intervals for the two sets (original and duplicate) occurred at different months of the year;
e.g., the three-day sample from the original set was exposed in June, but the three-day
sample from the duplicate set was exposed in August. Values for solar radiation and tem-
perature would be different, especially in Chicago, for these two time intervals. The data
does in fact show that for the period of 6/19 to 6/22/90, total radiation (45°S) was 37.9
MJ/m2 and for 8/3 to 8/6/90 was 48.7 MJ/m2. In general, however, the data points for the
original and duplicate sets follow the same trend.
Duplicate exposure results for PS and PSC in Cedar Knolls, NJ, are shown in
Figures 4.1.3.a and 4.1.3.b. The degradation parameter shown in the figure is the frac-
4-1
-------
tional mass of sample remaining after the tumbling friability test. The data show excellent
agreement between original and duplicate sample sets, indicating no drastic changes in
weather during the period of exposure and thus good reliability of the results.
4.1.2 {Comparison of Various Tensile Parameters
Tensile testing of the plastic films (See 2.5.1.) resulted in values for breaking load
and elongation, stress at break (load divided by cross-sectional area of the sample), strain at
break (elongation divided by gauge length), modulus (initial slope of stress-strain curve),
and energy to break (total area under load-elongation curve). The computerized data
acquisition system connected to the Instron test machine enabled quick, accurate determina-
tion of the above parameters and others. It was, however, necessary to choose a single
parameter which could be used consistently to characterize degradation for all the types of
plastic films. Percent elongation (or strain) at break, a measure of brittleness, has been
used in previous studies [Andrady, 1990;- Pegram and Andrady, 1989] as an indicator of
film embrittlement and consequent tendency to break into small pieces. For the present
study, one goal of which was to formulate a mathematical model for rates of disintegration
of materials exposed to various conditions and locations, a parameter which was con-
venient to obtain and was well suited for facile mathematical treatment was required. The
four candidate parameters studied were stress at break, percent elongation at break, ehergy
to break, and initial modulus.
Figure 4.1.4 shows semi-logarithmic plots of these four tensile parameters versus
exposure time for outdoor exposure of two sample types, 6P and PG, and the relevant
controls in Miami, FL and Seattle, WA. The data could best be fitted by an equation of the
form:
logP = logA-Bt (4-1)
where P is the tensile parameter, t is the duration of exposure in days, and A and B are
constants. Table 4.1.1 summarizes the gradient (B) values and correlation coefficients for
the four sets of data. Both elongation at break and energy to break tended to have higher
values for correlation coefficient than the other two parameters, especially for the degrad-
able plastics. The ratio of parameter B for the degradable material to that of the control
material is also shown in the table. This ratio was especially useful in choosing a single
parameter for data analysis; it was consistently higher for elongation at break and energy to
break, suggesting these parameters to be the more sensitive to weathering-related changes
in the plastic.
4-2
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Modulus is an indication of a material's stiffness and may in fact generaUy increase to
a certain extent as a material degrades. For 6P samples exposed in Seattle.WA, this
increase was greater for the control material than for the enhanced degradable material.
Similarly, breaking stress or tensile strength sometimes increases slightly in the initial
stages of degradation due to crosslinking reactions or crystallization which may occur as
longer chains break down into lower molecular weight chains. This effect is observed in
Figures 4.1.4.a, e, i, and m. Although stress at break eventually does decrease at longer
exposure durations, this parameter does not show as great a relative change as energy to
break or elongation at break.
In terms of correlation coefficient and values for B ratio, both the energy to break and
percent elongation at break were equally sensitive parameters, but consideration of the ease
of obtaining values for the parameter would favor percent elongation at break.
Determination of energy at break would require' measurement of the entire area under the
stress-strain curve, which would be very difficult to carry out without an automated data
collection set-up. Percent elongation at break is simple to obtain directly from the load-
elongation or stress-strain curve. Therefore, percent elongation at break was chosen as the
tensile parameter to characterize the extent of degradation.
4-l-3 Discussion of Outdoor. Marine Floating, and Marine Sediment Exnnsnre
by Sample Type
4.1.3.1 Rate Parameters Based on Elongation at Break -
As discussed in 4.1.2, the degradation of all samples under exposure was charac-
terized using values for percent elongation at break. This included all samples except
expanded polystyrene foam, which was characterized by tumbling friability, Yellowness
Index measurements, and GPC. These results for polystyrene will be discussed in
4.1.3.2.
Figures 4.1.5.a through 4.1.5.gg illustrate the data for percent elongation at break
plotted against exposure time. Separate plots are shown for each exposure location, with
the degradable material and its corresponding control plotted on the same graph. In cases
where duplicate exposures were carried out, these data points are also included. Figures
4.1.6.a through 4.1.6.gg show the same data plotted on a semi-logarithmic scale with
curve fitting based on the equation:
log E = log A - Bt (4_2)
4-4
-------
Bd and Bc are B values for the degradable and control materials, respectively. The magni-
tude of Bd/Bc is a measure of the effectiveness of enhanced-degradable polymer in bringing
about accelerated disintegration and is called the "enhancement factor". Based on Figures
4.1.5 and 4.1.6 and on Table 4.1.2, each sample material will be discussed separately.
(a) {Ethylene-carbon monoxide) Copo.lymer - 6P
For (ethylene-carbon monoxide) copolymer (6P) samples, comparison of raw data
for percent elongation at break versus exposure time showed a very significant difference in
degradation rate between the degradable and the LDPE control film. This is evidenced by
the values for Bd/Bc shown in Table 4.1.2. The data are illustrated by Figures 4.1.6 (a) -
4.1.6 (h). The photodegradable plastic material showed extensive disintegration-on expo-
sure at all locations. With control samples, however, the 2-3 month exposure was often
too short to obtain a marked change in elongation at break. Good correlation between
elongation at break and duration of exposure was obtained at all exposure sites, especially
for the enhanced degradable material. Low values for correlation coefficient were obtained
at some exposure sites for the control material, but in these cases percent elongation at
break changed very little with increased exposure time. The only exposure sites where
measurable degradation of the control material occurred were Miami, FL, and Wittmann,
AZ, where average daily temperature and/or solar radiation would have been relatively
high.
Comparison of rate parameters (Table 4.1.2) for 6P at various sites showed that the
samples exposed in Wittmann, AZ, degraded at the fastest rate followed by those exposed
in Chicago, IL. Samples exposed outdoors at the other locations all showed similar degra-
dation rates which were significantly lower than that for the Wittmann, AZ site.
Samples exposed floating in sea water experienced much slower degradation rates
(comparison of B values) than samples exposed to direct weathering at the same location.
Both the enhanced-degradable and the control samples showed a decreased rate of disinte-
gration probably related to lower temperature of samples exposed floating in sea water.
The enhancement factors (Bd/Bc values) were greater for samples exposed floating in sea
water than for samples exposed to direct weathering.
(b) Plastigone Films fLDPE/MX^ - PG
For PG samples, the degradation rate of the enhanced degradable material was con-
sistently 3 to 4'times greater than that of the LDPE control material. The curve-fitting lines
in Figures 4.1.6 (i) - 4.1.6 (p) represent regression applied to the data points from the
original data set; points for duplicate sets are shown on the graphs, but separate regression
equations were obtained for the duplicates, as seen in Table 4.1.2. The B values show
4-5
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good agreement between duplicate se& of test samples for all exposure sites. As with 6P
samples, exposure in Wittmann, AZ, produced the fastest degradation rate in the PG films
The other locations produced comparable rates for direct weathering.
PG material also behaved similarly to 6P with regard to marine and freshwater float-
mg exposure; B values were lower for floating exposures than for direct weathering but
Bd/Bc ratios were generally higher for floating exposures. '
^ Archer Daniels Midland Co. Films (LOPE/Starch/MXI - ADM
. Figures 4.1.6 (q) - 4.1.6 (z) show the semi-logarithmic plots of data for ADM sam-
ples. In addition to its enhanced photodegradability, this material was also heat sensitive
and underwent slight degradation even when stored in darkness at ambient temperatures in
tiie laboratory. Tensile testing carried out on unexposed samples which had been stored in
darkness at ambient temperature for three months showed a decrease in percent elongation
at break from 89% to 33%. The original lot of ADM samples had been dispatched for
exposure approximately two months after receipt from the manufacturer and therefore had
probably degraded somewhat before actual exposure. For this reason, a second lot of
identical composition was requested from the manufacturer for repeat direct weathering at
selected outdoor exposure sites. The repeat exposures are shown as "Set H" in the figures
The original samples (Set I) are also included for comparison with the floating and marine '
sediment exposures, as these could not be repeated with fresh material.
Due to the extremely rapid degradation rate of ADM samples, duplicate exposures
could not be carried out on the enhanced degradable material; however, duplicates were
exposed for the control material at several sites. Comparison of Bd values for the original
and duplicate sets showed fair agreement.
Values for Bd for Set H were generally somewhat lower than B values for Set I but
were still much higher than the Bc values for the LDPE control material. Values for B^
for Set I exposure are shown in Table 4.1.2 and are generally higher than the ratio for both
the 6P and PG materials. For Sets I and n of the enhanced degradable material, direct
weathering in Wittmann, AZ resulted in the highest rate parameters for disintegration
The B value for floating exposure in Miami, FL could not be obtained due to lack of a
sufficient number of data points but appears to be high based on the two data points avail-
able. For exposure in Seattle, WA, the B^c ratio for marine floating exposure was simi-
lar to the ratio obtained for direct weathering.
In addition to being extremely sensitive to light and heat, the ADM material also
exhibited some degree of enhanced biodeterioration. A comparison of the Bd values for
marine-floating and marine-sediment exposure of the ADM films suggests the principal
mechanism of disintegration to be photodegradation rather than biodeterioration However
4-9
-------
the rates of disintegration of the films under sediment exposure are significantly faster than
those of control films indicating a small contribution to disintegration by the biodeteriora-
tion mechanism. ADM film samples exposed to marine sediment conditions in Miami and
Seattle were found to disintegrate 5 to 9 times faster than the control material (See Bd/Bc
values in Table 4.1.2.), although the B values themselves were lower for marine sediment
exposure than for direct weathering or floating exposure for both the enhanced degradable
and control materials.
(d) Polvcaprolactone Blends (LLDPE/PCL) - PCL '
Exposure of the polycaprolactone/LLDPE blend (PCL) was carried out under marine
sediment conditions in Miami, FL and Seattle, WA and under direct weathering in Miami,
FL. Plots of the tensile test data according to equation 4-1 are shown in Figures 4.1.6 (aa)
- 4.1.6 (dd). PCL was slightly more degradable than the control for direct weathering, but
for marine sediment conditions, values for Bd/Bc were slightly less than one, indicating no
significant acceleration in disintegration during this time scale. The PCL fraction of the
blend (20%) is known to be biodegradable; however, it may not biodegrade within the
exposure durations reported here. In addition, the polyethylene matrix may have limited
the access of microorganisms to the polycaprolactone domains.
(e) Biopol Films
Biopol [poly(hydroxybutyrate) films] showed very low degradability under direct
weathering but showed high values for B when exposed to sediment conditions in both
marine and freshwater (Figures 4.1.6 (ee)-4.1.6 (gg). There was no control material data
for Biopol for comparison of degradation rates; however, comparison of B^ values with Bc
values for polyethylene under marine sediment'exposure suggests an enhancement factor of
about 20.
4.1.3.2 Rate Parameters Based on Yellowness Index, Tumbling Friability, or GPC -
Three tests were used to characterize the degradation of expanded polystyrene foam;
two methods, tumbling friability testing and measurement of Yellowness Index, were used.
for samples exposed to direct outdoor weathering. These methods were unsuitable, how-
ever, for samples exposed to marine environments. Accumulation of marine foulant
species on the surface of foam sheets interfered with color measurements (Yellowness
Index) and mass determinations (required for tumbling friability testing). Marine floating
samples could, however, be characterized by gel permeation chromatography (GPC).
Table 4.1.3 shows the Yellowness Index values obtained for PS samples exposed to
direct weathering. Visual examination of the exposed samples showed the formation of a
brittle, yellow surface layer on the surface of sample exposed to sunlight. In general,
4-10
-------
Yellowness Index (YI) increased with exposure time for both the enhanced degradable and
control samples of polystyrene foams, with YI for the degradable material higher than for
the control for the same exposure duration. For longer exposure durations, YI leveled off
or even decreased. This was attributed to loss of the brittle yellow layer due to abrasion or
removal by wind or rain.
A study of the change in color might be attempted based on values of the parameters
"L", "a", and "b" (see Section 2.5.2). Typically, outdoor exposure did not drastically
affect the lightness, L, of the styrofoam. The parameters "a" and "b" both changed with
exposure, the former becoming more negative and the latter increasing with exposure time.
During early periods of exposure, "a" and "b" are almost linearly correlated. The change in
these parameters suggests a gradual change from light blue-white color of sample to a pro-
gressively darker yellow color. After a deep yellow color is achieved, the value of "b"
increases further with exposure time (with that of "a" remaining almost the same), indicat-
ing increased redness in color.
Interestingly, the same trend was observed with data for samples exposed in a
Weather-Ometer®. Both control and degradable polystyrene foam samples showed the
same behavior in Weather-Ometer® exposure as in a typical outdoor exposure site such as
Cedar Knolls, NJ. In both instances, "a" changed from about 0 to -4 and "b" from about 0
to 25. This agreement essentially supports the assumption that the chemical processes
giving rise to the colored species must be the same in both types of exposure.
The partial loss of the embrittled layer due to wind, rain, and abrasion, especially in
samples exposed for an extended period of time, precluded a detailed study of the devel-
opment of coloration on exposure.
Tumbling friability testing resulted in values for percent mass loss for the samples
exposed to direct weathering. These values are given in Table 4.1.4 and show a general
increase in mass loss with exposure duration, with the effect more pronounced for the
enhanced degradable material than for the control. Mass loss values were converted to per-
cent mass remaining after tumbling friability, and these values were used to obtain the plots
in Figure 4.1.7. Data for duplicate exposures are also shown on these graphs and tend to
overlap the data from the original exposures. The graphs in Figure 4.1.7 illustrate the exis-
tence of a "lag time" for the onset of measurable degradation by tumbling friability. This
lag time was always greater for the control material. The significance of this "lag time" and
the mechanism giving rise to it are not clear at this time.
4-11
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-------
Table 4.1.4. Tumbling Friability Results for Polystyrene Foam Samples Exposed
Outdoors.
Exposure Site Exposure Duration
(days)
Unexposed 0
Cedar Knolls, NJ 7
14
22
29
36
43
50
58
64
71
85
99
104
Cedar Knolls, NJ 5
(duplicates) 12
19
26
33
40
47
54
61
68
75
82
90
97
104
Chicago, IL 7
14
22
29
36
43
50
57
64
71
78
85
92
99
106
Mass Loss
Photodegradable
PS Foam
0.00
0.00
0.00
7.26
24.71
28.58
35.75
42.93
46.29
44.15
46.31
46.14
48.63
54.44
0.00
0.00
0.00
0.00
20.60
34.50
38.05
42.66
47.08
44.88
46.94
45.24
47.91
49.05
48.62
0.00
0.00
12.30
25.06
29.12
36.55
35.17
39.05
44.47
46.10
43.53
47.37
46.19
49.65
48.70
(%)
Control PS Foam
0.00
0.00
0.00
1.15
12.03
16.22
17.31
22.51
25.09
0.00
0.00
0.00
6.50
15.32
21.69
25.14
0.00
0.00
8.25
21.40
26.15
22.57
25.47
- continued -
4-19
-------
Table 4.1.4. (continued).
Exposure Site
Chicago, IL (cont.)
Chicago, IL
(duplicates)
Miami, FL
Miami, FL (duplicates)
Exposure Duration
(days)
113
120
127
134
141
28
35
42
49
56
63
70
77
84
91
98
105
112
119
127
134
7
14
21
28
35
42
49
56
63
70
77
84
91
98
103
5
12
19
26
33
40
47
54
Mass Loss
Photodegradable
PS Foam
47.74
47.73
52.40
55.67
55.01
0.49
0.00
0.00
16.01
32.05
36.15
41.21
48.09
47.23
47.03
47.98
47.46
47.73
51.01
-
52.49
0.00
0.00
17.00
24.19
33.96
40.10
41.06
41.43
46.10
52.59
51.41
64.18
57.28
58.96
63.82
0.00
0.00
8.92
30.79
33.40
40.80
38.91
41.66
(%)
Control PS Foam
26.86
26.97
28.30
/
0.00
0.00
0.00
6.29
19.92
22.09
22.49
0.00
0.00
4.32
23.08
35.52
35.70
36.99
40.63
5.57
0.73 :
10.47
- continued -
4-20
-------
Table 4.1.4. (continued).
Exposure Site
Miami , FL Duplicates
(continued)
Seattle, WA
Wittmann, AZ
•
Wittman, AZ
(duplicates)
Exposure Duration
(days)
61
68
75
82
89
96
7
14
21
28
35
42
45
52
59
66
73
79
87
94
101
7
14
22
29
36
43
50
57
64
71
78
85
92
99
113
120
7
14
21
28
35
42
49
56
Mass Loss
Photodegradable
PS Foam
42.64
52.13
56.02
57.19
59.66
66.82
0.00
0.07
_
6.25
35.91
38.36
36.76
42.28
44.04
43.03
43.97
47.72
46.92
45.07
47.92
0.00
24.51
33.80
-
47.58
46.99
48.55
49.63
57.06
53.52
55.21
57.27
56.49
74.39
72.69
0.00
0.00
19.32
37.85
47.03
50.16
48.69
52.72
(%)
Control PS Foam
14.00
26.67
36.41
7.02
0.49
3.82
13.69
27.51
23.86
31.66
24.26
0.00
0.00
17.70
30.77
36.80
42.56
35.15
42.49
0
0
0
18.17
- continued -
4-21
-------
Table 4.1.4. (continued).
Mass Loss (%)
Exposure Site Exposure Duration Photodegradable
-••—*v •«-— wj- t*.u.A_-ii A XAVI.WVIVC.A w. viu. u/j-W x~i , -« r\f-\ T-i
(days) PS Foam Control PS Foam
Wittman, AZ
Duplicates (continued) 63 55.56 3144
70 56.79
77 - 35.27
84 55.09
91 - 38.29
98 59.94
106 66.20 40.46
113 63.93
120 70.47 42.08
4-22
-------
Figure 4.1.8 shows curve-fitting for the tumbling friability data. The equation used
was the same as for the data based on percent elongation at break:
log M = log A - Bt (4-3)
where M is fractional mass remaining after tumbling friability, t is the duration of exposure
in days, and A and B are constants. To obtain the best straight lines, the points for expo-
sure durations less than the "lag times" discussed above were omitted. Good correlation
coefficients were obtained for all the polystyrene data. Values for the rate parameter, B,
show good agreement for duplicate data sets with the exception of Chicago, EL As with
tensile test data, the rate parameter (B) values obtained for control samples were always
smaller than those obtained for photodegradable foam material.
Marine floating samples exposed in Miami, FL and Seattle, WA, as well as samples
from selected outdoor exposure sites (Miami, FL and Chicago, EL), were characterized by
gel permeation chromatography (GPC). The molecular weights (number average) from
GPC are shown in Table 4.1.5. Molecular weight determinations are the best indicator of
degradation at a molecular level since they show actual breakdown of the polymer chains.
For example, tumbling friability data for direct weathering in Chicago, IL showed a "lag
time" of about 14 days before measurable mass loss, whereas GPC data showed over 50%
reduction in molecular weight after only 7 days of exposure. Brittleness of surface layer
apparently developed after significant molecular level degradation had taken place.
Analysis of GPC data was accomplished by converting molecular weight values to
degree of polymerization (DP) and using the following equation [Jellinek, 1967]:
l/DPt - 1/DPo = A + Ht (4-4)
where t is the duration of exposure in days. The value of H would increase for increasing
degradation rate. These plots are shown in Figure 4.1.9 and show good fit for all data
sets. The constant A should have a value of zero and was approximately zero for the con-
trol material but was somewhat higher for the degradable material. It is possible that the
degradable material at zero exposure time is already degraded to a slight extent due to "shelf
aging".
Table 4.1.6 summarizes the degradation rates obtained by both GPC and tumbling
friability for polystyrene foam. Comparison of the ratio of B values (from tumbling fri-
ability data) for degradable and control materials (B
-------
Table 4.1.5 Number Average Molecular Weight of Polystyrene Foam Exposed
Outdoors, as Determined by Gel Permeation Chromatography.
Exposure Site
Unexposed
Chicago, IL
Miami, FL
Miami, FL
Seattle, WA
Exposure Type Exposure
(days)
0
Outdoor 7
14
22
29
36
43
50
57
64
Outdoor 7
14
1 21
28
35
42
49
56
63
70
Marine Floating 7
29
35
43
58
Marine Floating 7
14
21
28
Molecular Weight x 10'3
Degradable PS
Foam
125
51.1
45.6
43.7
35.2
32.6
29.2
29.4
31.0
27.9
66.7
45.5
45.7
40.4
38.3
45.4
34.4
40.0
36.4
32.0
64.2
35.6
33.9
-
-
70.7
71.3
51.9
50.3
Control
PS Foam
144
102
72.1
63.2
52.5
95.3
81.7
59.6
74.5
_ i
-
_
72.3
68.9
126
120
103
96.1
4-24
-------
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4-25
-------
4.1.3.3 Comparison of Marine and Freshwater Exposure to Land Exposure
(Direct Weathering -
As discussed previously, samples placed in marine environments became fouled, or
covered with various types of marine foulant species, during exposure. The fouling is
illustrated in Figures 4.1.10 through 4.1.15, which show photographs of various sample
types after marine exposure. Fouling occurred on both photodegradable and control film*
samples. In general, the presence of surface foulants shields the sample from UV radiation
and slows the degradation rate. However, such shielding occurs unevenly due to the non-
uniform foulant layer on the sample surface. This unevenness in photodegradation is a
primary cause of the high scatter in tensile property data obtained with marine-exposed
samples. Various plastic materials have been shown [Pegram and Andrady, 1989] to
degrade more slowly in seawater than on land due to the cooling effect of the water and to
the shielding of foulants.
In agreement with previous studies, comparison of B values (Table 4.1.2) for direct
weathering to those for marine and freshwater floating shows slower rates in water for both
control and degradable materials for 6P, PG, and ADM samples. Values for Bd/Bc, how-
ever, are higher for floating samples than for samples exposed to direct weathering, indicat-
ing the enhancement effect to be greater in water than for direct weathering. The higher
values for this ratio for marine samples are attributed to extremely low degradation rates of
control materials (Bc) in water. While the degradation rates of both the control and degrad-
able plastic films slowed, as expected, in sea water, that of the latter slowed to a relatively
lesser extent. Polystyrene foam also shows higher values for the B ratio for floating expo-
sure as compared to direct weathering.
4.1.4 Effect of Geographic Location of Exposure on Rate Parameters
In all figures discussed, the elongation at break has been plotted versus the duration
of exposure in order to determine degradation rates. This is based on the assumption that
the samples receive a fairly constant average daily radiation at each exposure site. Figure
4.1.16 shows a plot of total solar radiation versus exposure duration for each location. The
plots are, in fact, linear, with the slope of each line a measure of each location's average
daily total solar radiation (All referrals to radiation measurements in this section are to
radiation received at a tilt angle of 45° South). Thus, for the period of exposure for this
study, degradation parameters may be plotted against either time or total radiation. The
average daily radiation would be expected to change from month to month for a given loca-
tion; the graphs in Figure 4.1.16 do appear to slightly decrease in slope toward the end of
4-26
-------
the study period (September), particularly for Chicago, IL; Cedar Knolls, NJ; and Seattle,
WA.
From the values of gradients in Figure 4.1.16, the locations can be ranked as follows
in order of average daily total radiation (high to low): Wittmann, AZ; Seattle, WA;
Chicago, IL; Miami, FL; and Cedar Knolls, NJ. To determine the correlation of degrada-
tion rate with radiation received, values for B (Table 4.1.2) were plotted versus average
daily total radiation, and also versus average daily temperature, at each location. Where '
more than five points are shown on a graph, duplicate exposures were included. These
graphs are shown in Figure 4.1.17 and show a somewhat better correlation of degradation
rate with temperature than with radiation. For example, the degradation rate of 6P in
Seattle, WA was lower than for any of the other sites, and even though Seattle, WA had a
high value for average daily total radiation, it had the lowest average daily temperature.
This is somewhat surprising in view of the fact that the 6P material, which is an (ethylene-
carbon monoxide) copolymer, photodegrades via a Norrish n pathway under ambient
conditions. Rates of Norrish n reactions are not particularly sensitive to temperature.
Miami, FL exposure, which generally resulted in relatively high degradation rates, received
lower average daily radiation than most sites but had a higher average daily temperature.
Apparently the rate of disintegration is influenced by. a combination of the two factors of
temperature and radiation.
Figure 4.1.18 shows a composite semi-log plot of percent elongation at break versus
total radiation for the exposure duration for all exposure sites for each plastic material.
Using the same equation for modeling as for Figure 4.1.6, moderately good correlation
coefficients were obtained for all materials. The data points which showed the poorest fit
to the equation were those for Miami, FL and Seattle, WA, where, as discussed above, the
effect of temperature should not be discounted. For example, in Figure 4.1.18.b, the data
for Seattle, WA could be shifted to the left (and therefore closer to the line predicted by the
equation) if the lower temperatures were accounted for by effectively decreasing the values
for total radiation. Similarly, the data points for Miami, FL could be shifted to the right by
effectively increasing radiation values to account for the higher average temperature in
Miami, FL.
4.1.5 Outdoor Soil Burial
Outdoor soil burial was carried out at Research Triangle Institute from March to
September, 1990. Samples expected to be enhanced-biodegradable/biodeteriorable, i.e.,
ADM, PCL, and BP, were exposed to .these conditions. Tensile elongation at break was
used to characterize the extent of disintegration of the materials. As described in Section
4-27
-------
2.3.5, exposure was carried out in triplicate by randomly distributing samples in each of
three different blocks at the soil burial testing site. This type of experimental design would
show whether differences in extent of degradation could be attributed solely to exposure
time or whether the effects of soil conditions, e.g., microbe population distribution,-mois-
ture content, growth of vegetation, etc., significantly affected degradation. These latter
factors will be referred to as block effects. Tables 4.1.7.a through 4.1.7.e show an analy-
sis of variance for each plastic material in which the sources of variation for percent elon-
gation at break are broken down into treatments (exposure times), blocks, and error.
Hypothesis testing for each material showed the block effects to be insignificant in each
case, with exposure time being the only significant variable. Average values for percent
elongation at break were therefore obtained from the three block values for each exposure
duration. These values were used to obtain the plots shown in Figure 4.1.19. Each page
shows a linear as well as a semi-log plot.
Values for B (empirical disintegration rate) are summarized in Table 4.1.8. Of the
three enhanced biodegradable materials, BP showed the highest degradation rate. Figure
4.1.20 shows photographs of BP samples taken after various durations of soil burial expo-
sure; tiny holes caused either by chemical degradation due to microbial action or by the
physical deterioration caused by insects, etc., are evident even in the early stages of expo-
sure. All BP samples were too weak for tensile testing by 29 days of exposure.
Based on comparison of B values, ADM was approximately twice as biodeteriorable
under soil burial conditions as its corresponding control material; PCL blend material,
however, was not significantly more deteriorated than the control. As discussed pre-
viously, the LLDPE matrix surrounds the polycaprolactone domains, limiting the PCL's
access to enzymes required for biodegradation (or to microbes themselves) in the short
time-scale of observation.
4.1.6 Comparative Extents of Degradation
The rate of disintegration of a plastic film or, sheet material is an important parameter
which characterizes the effectiveness of the material as an enhanced degradable plastic.
However, in screening a material for enhanced degradability and in analysis of limited
amounts of data which do not allow for the determination of such a rate, it is convenient to
refer to degradability (or disintegration) in terms of "time to embrittlement". Here the term
"embrittlement" is taken to mean the reduction of the tensile elongation at break to a value
of 5 perce or less. While a figure of 2 percent is sometimes used in the literature with
most types of common plastic films, the standard error associated with measuring the
4-28
-------
Table 4.1.7 (a). Analysis of Variance for ADM Soil Burial Samples.
Analysis of variance for tensile data: Randomized complete block design
Parameter used: Percent elongation at break
k = Number of treatments (exposure times) = 10
b = Number of blocks = 3
SST = I£yij2 -
SSA = STL2/b -
SSB = STj2/k -
Exposure Time
(weeks)
0
2
4
6
8
10
12
14
16
18
20
Total (T.j's)
T 2/bk
*•
T 2/bk
**
T_2/bk
1
89.2
67.3
50.3
65.1
52.3
23.1
28.7
19.4
13.1
11.1
419.6
Equations:
si2 = SSA/(k-l).
s22= SSB/(b-l)
s2 = SSE/(b-l)(k-l)
Blocks
2
89.2
70.0
56.3
57.6
62.3
25.9
36.0
24.1
21.1
7.0
449.5
SSA + SSB
fl = Si2/s2 '
f2 = s22/s2
3
89.2
71.0
51.6
58.6
56.7
20.5
32.7
25.1
20.3
7.3
433.0
+ SSE = SST
Total (Ti.'s) '
267.6
208.3
158.2
181.3
171.3
69.5
97.4
68.6
54.5
25.4
1302.1 (T )
,
Source of
Variation
Exposure Times
Blocks
Error
Total
Sum of Squares
' 18443.74
44.86
174.91
18663.51
Degrees of
Freedom
9
2
18
29
Mean Square
2049.30
22.43
9.72
Computed f
210.89
2.31
Critical values of f :
Exposure times: FI = Fa[k-l,(k-l)(b-l)J
Blocks: F2= Fa[b-l,(k-l)(b-l)]
Let a = 0.05
For Blocks:
Hq: 61 = 62 = 63 = 0 (block effects zero)
Critical region: F> f 95 (2,18)
F > 3.55
Computed f = 2.31;:.. accept Ho
For Exposure Times;
H'0: cq = OC2 = ... = (% = 0
Critical region: F> f 05 (9,18)
F> 2.46
Computed f = 210.89,:. reject Ho
4-29
-------
Table 4.1.7 (b). Analysis of Variance for ADMC Soil Burial Samples.
Analysis of variance for tensile data: Randomized complete block design
Parameter used: Percent elongation at break
k = Number of treatments (exposure times) = 8
b = Number of blocks = 3
SSB = n\j2/k -
Exposure Time
(weeks)
0
4
8
12
16
20
24
28
Total (T.j's)
T..2/bk sl
T..2/bk «2
T^2/bk S2
1
331.7
108.9
94.8
159.5
50.5
84.5
84.5
218.4
1132.8
Equations:
2 = SSA/(k-l)
2= SSB/(b-l)
= SSE/(b-l)(k-l)
Blocks
2
331.7
82.7
97.4
117.1
107.0
62.7
77.5
69.6
945.7
SSA + SSB
fj = S12/S2
f2 = s22/s2
3
331.7
131.3
105.2
165.5
96.0
73.9
91.3
85.0
1079.9
+ SSE = SST
Total •(Tj.'s)
995.1
322.9
297.4
442.1
253.5
221.1
253.3
373.0
3158.4 (T )
Source of
Variation
Exposure Times
Blocks
Error
Total
Sum of Squares
149296.21
2325.60
15827.27
167449.08
Degrees of
Freedom
7
2
14
23
Mean Square
21328.03
1162.80
1130.52
Computed f
18.87
1.03
Critical values of f:
Exposure times: FI = Fa[k-l,(k-l)(b-l)]
Blocks: F2= Fa[b-l,(k-l)(b-l)J :
Let a = 0.05
For Blocks:
H0: BI = 62 = 63 = 0 (block effects zero)
Critical region: F> f 05 (2,14)
F > 3.74
Computed f = 1.03;:.. accept H0
For Exposure Times:
Hq: oq = a2 = ... =
Critical region: F>
F>
Computed f = 18.87,
% = 0
f 05 (7,14)
2.76
: . reject H0
4-30
-------
Table 4.1.7 (c). Analysis of Variance for PCL Soil Burial Samples.
Analysis of variance for tensile data: Randomized complete block design
Parameter used: Percent elongation at break
k = Number of treatments (exposure times) = 15
b = Number of blocks = 3
SST = SZyj.2 . T
SSA=,£TL2/b -
SSB = IT :2/k - T 2/bk
•J
Equations:
s12 = SSA/(k-l)
s22= SSB/(b-l)
s2 = SSE/(b-l)(k-l)
SSA + SSB + SSE = SST
fl = si2/s2
Exposure Time
(weeks)
Blocks
Total (Ti.'s)
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
Total (T.j's)
717.3
466.5
508.3
468.6
433.4
511.6
501.4
417.4
441.3
553.8
354.8
352.9
359.3
389.0
466.7
6942.3
717.3
504.7
483.3
519.3
493.6
444.2
471.2
378.0
396.3
431.9
460.2
319.9
336.6
359.2
377.0
6692.7
717.3
456.9
332.6
522.3
412.5
449.9
467.9
469.2
401.0
450.7
347.5
402.1
323.6
447.6
374.1
6575.2
2151.9
1428.1
1324.2
1510.2
1339.5
1405.7
1440.5
1264.6 •
1238.6
1436.4
1162.5
1074.9
1019.5
1195.8
1217.8
20210.2 (T )
Source of
Variation
Exposure Times
Blocks
Error
Total
Sum of Squares
325086.45
4685.97
59144.85
388917.28
Degrees of
Freedom
14
2
28
44
Mean Square
23220.46
2342.99
2112.32
Computed f
10.99
1.11
Critical values of f:
Exposure times: FI =Fa[k-l,(k-l)(b-l)]
Let a = 0.05
For Blocks:
H0: BI = 82 = 83 = 0 (block effects zero)
Critical region: F > f 05 (2,28)
F > 3.34
Computed f = 1.11; :.. accept Ho
Blocks: F2 =Fa[b-l,(k-l)(b-l)]
For Exposure Times:
Critical region: F> f 05 (14,28)
F> 2.06
Computed f = 10.99,: . reject Ho
4-31
-------
Table 4.1.7 (d). Analysis of Variance for LLDPE Soil Burial Samples.
Analysis of variance for tensile data: Randomized complete block design
Parameter used: Percent elongation at break
k = Number of treatments (exposure times) = 8
b = Number of blocks = 3
SST = ££yij2 -
SSA = £TL2/b .
SSB = XT j2/k -
Exposure Time
(weeks)
0
4
8
12
16
20
24
28
Total (T.j's)
T^/bk si
T..2/bk s2
Tt>2/bk S2
1
698.1
368.9
375.7
488.4
156.7
301.6
302.1
330.1
3021.6
Equations:
2 = SSA/(k-l)
2= SSB/(b-l)
= SSE/(b-l)(k-l)
Blocks
2
698.1
395.3
387.9
476.8
367.2
312.9
341.5
363.4
3343.1
SSA + SSB +
fj = S12/S2
f2 = s22/s2
3
698.1.
694.8
391.3
520.3
341.7
314.9
412.9
357.1
3731.1
SSE = SST
Total Oh's)
2094.3 .
1459.0
1154.9
1485.5
865.6
929.4
1056.5
1050.6
10095.8 (T )
Source of
Variation
Exposure Times
Blocks
Error
Total
Sum of Squares
382543.63
31554.02
68564.25
482661.90
Degrees of
Freedom
7
2
14
23
MeanSqii2; :
54649.09
15777.01
4897.45 .
Computed f
11.16
3.22
Critical values of f:
Exposure times: FI =Fa[k-l,(k-l)(b-l)]
Let a = 0.05
For Blocks:
H0: 61 = 82 = 63 = 0 (block effects zero)
Critical region: F> f 05 (2,14)
F > 3.74
Computed f =3.22;:.. accept H0
Blocks: F2= Fa[b-l,(k-l)(b-l)]
For Exposure Times:
H0: cq =c<2 = ... =
Critical region: F>
F>
Computed f = 11.16,
^ = 0
f Q5 (7,14)
2.76
. reject HQ
4-32
-------
Table 4.1.7 (e). Analysis of Variance for BP Soil Burial Samples.
Analysis of variance for tensile data: Randomized complete block design
Parameter used: Percent elongation at break &
k = Number of treatments (exposure times) = 8
b = Number of blocks = 3
SST =
- T 2/bk
SSA = £TL2/b - T 2/bk
SSB =
- T 2/bk
Equations:
si2 = SSA/(k-l)
s22= SSB/(b-l)
s2 = SSE/(b-l)(k-l)
SSA + SSB + SSE = SST
Exposure Time
(days)
0
7
14
20
22
24
27
29
Total (T j's)
' ..'..', ' ,',•!, ss=a
"
Source of
Variation
Exposure Times
Blocks
Error
Total
— — —
1
60.0
20.3
11.6
8.5
,3.7
5.9
3.7
3.8
117.5
g^-^.-.J..Jig===!B— —-——-—
Sum of Squares
7751.52
15.90
128.08
7895.50
^SSSSfS~^~^f~^^™^-^~S~^^^^^~.a.
2
60.6
8.0
6.4
4.3
11.2
3.1
4.2
4.6
102.4
====================
' n , SaasSBSSSaSSSSS
Degrees of
Freedom
7 ,
2
14
23
. 3
60.6
12.8
10.6
4.8
4-0
4.5
4.7
3.5
105.5
.1— ... : .
— — ™™.- •— isassssss
Mean Square
1107.36
7.95
9.15
Total (Ti4's)
181.2
41.1
28.6
17.6
18.9
13.5
12.6
11.9
32JL4 (T .)
Computed f
121.04
0.87
Critical values of f:
Exposure times:
Blocks:
Let a = 0.05
For Blocks:
= Fa[b-l,
For
Times:
Hq: BI = 62 = 63 = 0 (block effects zero)
Critical region: F > f 05 (2,14)
F> 3.74
Computed f = 0.87;:.. accept H0
Ho: aj = c<2 = ... = ccj^ = 0
Critical region: F> f 95 (7,14)
F> 2.76
Computed f = 121.04,:. reject H0
4-33
-------
Table 4.1.8 Table of Regression Coefficients (Slopes and Intercepts) Based on Plots of
Tensile Elongation at Break Data for Soil Burial Exposure.
Equation: log (% elongation) = log (A) - Bt where t = exposure time in days
Degradable Polymer . Control Polymer
Polymer Code A B (x 1Q3) A B (x 103) AB (x 10*) Bd/Bc
ADM/ADMC 98.0 7.0 213 3.5 3.5 2.0
PCL/LLDPE 544 0.9 571 1.3 -0.4 0.7
BP 41.0 38.3 - - . ..
4-34
-------
elongation at break of a near-embrittled material is too high to allow a clear distinction
between values of 2 and 5 percent.
With enhanced photodegradable film materials 6P, PG, and ADM, the durations of
exposure used were long enough to obtain embrittlement of the samples. After a certain
number of weeks, each exposure location reported samples too embrittled to be collected
for testing. Table 4.1.9 shows the time scale to embrittlement for the different exposure
locations as the exposure duration. In the case of 6P samples, for instance, Wittmann, AZ
exposure resulted in embrittlement after one week of exposure, while in Seattle, WA, the
same material required an exposure as long as 8.5 weeks for embrittlement. In fact, the
different locations might be ranked in terms of the length of exposure to embrittlement. For
the three materials assessed on the basis of elongation at break, the following rankings
were obtained:
6P AZ>IL>FL>NJ>WA
PG AZ>IL>NJ>FL>WA
ADM AZ>IL>NJ>FL> WA
The rankings are very similar for all materials, unlike the rankings based on the rate
parameter B.
In the case of marine and freshwater exposures, the process of degradation is gener-
ally slower, and the samples were not always embrittled at the maximum duration of expo-
sure. These durations were estimated on the basis of a few preliminary experiments and
were not long enough to obtain embrittlement of all samples exposed. Each of the sample
types embrittled in the marine floating exposure conducted in Miami, FL, with the ADM
material degrading the fastest However, only the ADM film reached the embrittlement
point in the Seattle, WA exposure. PG and 6P samples had extensibilities of 11 and 14
percent, respectively after a maximum of about 14 weeks of exposure. Freshwater lake
exposures were of a limited duration, and the samples did not reach embrittlement.
Of the enhanced biodegradable and biodeteriorable samples, BP degraded extensively
in the time scale of observation. The BP films were embrittled at the end of the test period
in both soil and marine sediment environments. While embrittlement was not obtained in
the nearly 2 weeks of exposure in fresh water, the sample had an elongation at break of
only 14 percent at the end of this period. While not designed for enhanced photodegrad-
ability, the BP film did break down well under outdoor exposure as well and yielded an
elongation at break of 18 percent within 8.5 weeks of exposure.
None of the PCL (polycaprolactone/LLDPE blend) samples embrittled in the time
scale of observation. The disintegration of these samples evidently requires longer times
and could not be observed.
4-35
-------
Table 4.1.9 Extents of Degradation for Natural Weathering.
Material
Code
6P
PG
ADM
PCL
Exposure
Type*
O
MF
FF
O.
MF
FF
O
MF
MS
SB
O
MS
FF
SB
!xr "
^c^on (days)
Cedar Knolls, NJ
Chicago, IL
Miami, FL
Seattle, WA
Wittmann, AZ
Miami, FL
Seattle, WA
Kerr Lake, VA
Cedar Knolls, NJ
Chicago, IL
Miami, FL
Seattle, WA
Wittmann, AZ
Miami, FL
Seattle, WA
Kerr Lake, VA ,
Cedar Knolls, NJ
Chicago, IL
Miami, FL
Seattle, WA
Wittmann, AZ
Miami, FL
Seattle, WA
Miami, FL
Seattle, WA
RTI
Miami, FL
Miami, FL
Seattle, WA
Kerr Lake, VA
RTI
37
22
30
66
6
35
94
32
31
!22
34
i42
9
49
101
,21
9
9
13
14
3
3
14
65
14
126
63
147
101
56
196
Initial
Percent
Elongation
775
775
775
775
775
775
775
775
796
796
796
796
796
796
796
796
89
89
89
89
89
89
89
89
89
89
717
717
717
717
717
Final
Percent
Elongation
3
5
3
2
22
4
14
40
6
93
4
4
52
63
11
578
4
3
1
3
6
6
11
3
10
8
24
359
327
358
406
Embrittled?2
yes
.. yes
yes
yes
yes
yes
no
no
yes
yes
yes
yes
yes
yes
no
no
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
yes
no
no
no
no
- continued -
4-36
-------
Table 4.1.9 (continued).
Material
Code
BP
Exposure
Type1
O
MS
FS
SB
Exposure
Location
Miami, FL
Miami, FL
Ken- Lake, VA
RH
Exposure
Duration
(days)
58
12
12
29
Initial
Percent
Elongation
61
61
61
61
Final
Percent
Elongation
18
2
14
4
Embrittled?2
no
yes
no
yes
1 O = Outdoor; MF = Marine floating; FF = Freshwater floating; MS = Marine sediment;
SB = Soil burial; FS = Freshwater sediment
2 Embrittled: "Yes" indicates that the exposure duration given is the maximum for which
samples could be tested. Beyond this duration, the remaining samples were either
retrieved in pieces too small and brittle to be tested or could not be retrieved at all.
"No" indicates either that the entire sample set initially exposed could be retrieved and
tested or that the deadline for ending the exposure period was reached before the entire
set was sampled.
4-37
-------
4.2 LABORATORY-ACCELERATED WEATHERING
4.2.1 Weather-Ometer® Exposure
All enhanced photodegradable plastic materials (6P, PG, ADM, and PS) were
exposed to laboratory-accelerated weathering in a Xenon-Arc type Weather-Ometer® with
both exposure time and black panel temperature varied. The corresponding control samples
were also exposed under identical conditions. With the exception of PS foam samples,
which were subjected to tumbling friability testing, all exposed materials were tested by
Instron to determine percent elongation at break.
4.2.1.1 Rate Parameters--
Rate parameters for the samples exposed to accelerated weathering were determined
by using the same curve-fitting equation as for outdoor weathering. Figures 4.2.1 (a)
through 4.2.1 (c) show the linear and semi-log plots of the data, along with the curve-fit-
ting equations. For accelerated exposure of 6P, the enhanced degradable material was
inadvertently submitted for exposure in place of the control material, so values for elonga-
tion at break after Weather-Ometer® exposure for the control material were obtained from
literature supplied by the manufacturer of this product. Literature values from the same
source for the degradable material were found to overlap with the experimental values
obtained in this study; the literature values for control samples were therefore considered
acceptable substitutes for experimental values. These data points are shown in Figure
4.2,1 (a). Data shown in Figure 4.2.2 is based on the tumbling friability results for
polystyrene foam.
Rate parameters for Weather-Ometer® exposure based on these plots are summarized
in Table 4.2.1. The enhancement factors (Bd/Bc), shown in Table 4.2.1, are similar to
those given in Table 4.1.2 for 6P, PG, and ADM and in Table 4.1.6 for PS. These B val-
ues are hourly rates, and should be converted into daily rates for direct comparison with the
outdoor degradation rates. The B values based on elongation at break can be compared to
those for outdoor exposure in Table 4.1.2 to determine the acceleration factor for Weather-
Ometer® exposure. (For PS accelerated rate parameter can be compared to the values in
Table 4.1.6.) Weather-Ometer® rate parameters were from 2-5 times greater than outdoor
rate parameters for 6P, PG, and ADM for all exposure locations except Wittmann, AZ,
which had similar values to those for accelerated exposure. The following table (4.2.2)
shows values for the ratio of Bw (Weather-Ometer® rate parameter) to B0 (outdoor rate
parameter) for the enhanced degradable materials. These values shall be referred to as
4-38
-------
Q
•a
s_i
j*y^
4— >
i — 1 i — i
co ON TJ- I-H
cs ON •^>
ON 10 ' — i
C-; CO r-H O
od vo od cs
-
o O i-I
CO CS ON
CN ON ^H
f-H f-H f-H p
s
^g§^
VO Si S OH
ct; o Q So
VO OH < OH
05
is
o
.3
1
•d
D
05
O
Cu
X
||
-------
acceleration factors. Rate parameters for Set II of ADM outdoor exposure were used in the
calculations, as this was the material used in Weather-Ometer® exposure. The accelera-
tion of the rate of degradation in the Weather-Ometer® was much more pronounced for
polystyrene foam than for the other materials. Since the intensity and spectral quality of
light in the Weather-Ometer® (borosilicate-filtered xenon source) were not too different
from that encountered outdoors, this phenomenon must be attributed to higher temperature,
cycling, and/or humidity. Of these, temperature is likely to be a major factor. The tem-
perature-dependence of embrittlement times for polystyrene foam is not known. Perhaps a
high temperature dependence of the surface embrittlement phenomenon leads to the
observed dramatic acceleration of degradation under laboratory conditions compared to that
obtained outdoors. All samples collected during the experiment were not degraded to an
extent to preclude testing (or embrittled), although formation of an embrittled yellow sur-
face layer did occur during Weather-Ometer® exposure, as evidenced by the values for
Yellowness Index in Table 4.2.3.
Table 4.2.2. Acceleration Factors Obtained for Weather-Ometer® Exposures as Compared
to Outdoor Exposures.
6P
PG
ADM
PS
Cedar Knolls.
_NI
4.0
3.0
2.5
17
Chicago.
IL
2.4
3.1
2.9
22
Miami.
FL
3.0
2.1
2.3
12
:WA
5.2
2.8
-
20
Wittmann.
AZ
0.8
1.2
1.4
17
4.2.1.2 Temperature Dependence -
Figures 4.2.3 and 4.2.4 show the effect of increasing black panel temperature in the
Weather-Ometer® on the rate parameters of 6P, PG, and ADM for an exposure time of 50
hours. ADM appears to be the most temperature sensitive material at this exposure dura-
tion. 6P was relatively unaffected by temperature changes, although exposure for 50 hours
at even the lowest temperature (65°C) resulted in a breaking elongation value much lower
than for the unexposed material. This is not surprising, as the (ethylene-carbon monoxide)
copolymers are known to photolyze predominantly via Norrish n reaction, which is not
sensitive to temperature. Nevertheless, secondary oxidation of photolysis products, as
4-40
-------
.
CO
0
x
W
H>
to
a
9
-------
well as any concurrent, low levels of Norrish I reactions, will initiate free radical reaction
sequences which can be sensitive to changes in temperature.
Based on evaluation by tumbling friability, PS material did not significantly degrade
when exposed for 50 hours in the temperature range studied. This exposure duration was
apparently not sufficient to overcome the "lag time" for the onset of measurable (by tum-
bling friability) degradation discussed in Section 4.1.3.2. Had longer exposures been car-
ried out, the material was likely to have shown markedly high rates of breakdown based on
data discussed in Section 4.2.1.1.
4.2.2 Laboratory-Accelerated Soil Burial
The enhanced biodegradable plastic samples ADM and PCL were exposed to soil
burial under laboratory-controlled conditions at 37°C. Values for percent elongation at
break were measured and are reported in Table 4.2.4. These results show little change in
breaking elongation during the exposure, which was carried out for up to 70 days, and tend
to confirm the results of the outdoor exposure. Evidently, modifications to the accelerated
exposure procedure will be necessary in order to achieve measurable degradation within
this time scale. Such modifications may include raising the temperature, seeding, the soil
with a higher or different microbial population, improving soil aeration, or changing condi-
tions of moisture and pH. However, changes to exposure environment cannot be so dras-
tic as to induce biological/chemical processes not typical of outdoor, field exposure.
4-42
-------
Table 4.2.4 Tensile Test Data for Laboratory Accelerated Soil Burial Samples.
Material
Code
ADM
ADM
ADM
ADM
ADM
ADM
ADM
ADM
ADMC
ADMC
ADMC
ADMC
ADMC
PCL
PCL
PCL
PCL
PCL
PCL
PCL
PCL
LLDPE
LLDPE
LLDPE
LLDPE
LLDPE
Exposure
Time
(days)
0
3
7
10
15
22
36
70
0
7
15
36
70
0
3
7
10
15
22
36
70
0
7
15
36
70
Average Stress
at Break
(kg/cm2)
119
123
114
127
119
118
117
134
220
149
216
241
201
333
287
353
176 •
162
. 343
337
244
257
156
62
240
108
Stress Std. Dev.
(kg/cm2)
8
5
5
4
4
6
3
2
21
7
15
6
28
100
40
64
48
25
55
51
80
67
73
4
112
5
Average
Elongation
at Break (%)
176.3
139.2
160.1
156.9
165.5
199.4
178.3
168.2
183.5
171.8
167.8
169.9
107.7
717.3
664.0
683.7
406.4
449.0
748.1
761.4
678.3
698.1
422.9
323.4
670.8
366.7
Elongation
Std. Dev.
(%)
22.0
20.5
13.6
17.9
15.6
18.2
23.1
9.9
41.2
35.0
43.5
23.7
59.5
92.2
41.3
57.2
68.9
71.3
41.9
63.7
91.0
79.1
165.8
36.3
164.5
50.0
Number of
Samples
16
5
7
7
6
8
6
5
11
5
4
6
6
10
5
6
8
5
7
6
6
8
9
6
7
5
4-43
-------
REFERENCES
A. L. Andrady, Weathering of Polyethylene (LDPE) and Enhanced Photodegradable
Polyethylene in the Marine Environment, J. Appl. Polymer Sci, 39, 363-370
(1990).
J. E. Pegram and A. L. Andrady, Outdoor Weathering of Selected Polymeric Materials
under Marine Exposure Conditions, Polymer Degradation and Stability, 26., 333-345
(1989).
H.H.G. Jellinek, Appl. Polym. Symp., 4, 41-54 (1967).
4-44
-------
1000
Q
G
o
3
t>0
G
O
T—H
w
4—»
G
0>
O
fc
100
10
• Original Set
O Duplicate Set
10 20 30
Exposure Time (days)
40
Figure 4.1.1 (a) Elongation at break vs. exposure time for duplicate exposures of 6P
samples outdoors in Miami, FL - Enhanced degradable material.
3
§
G
O
f—)
w
f—i
8
100
10
w
}
o.
© Original Set
O Duplicate Set
0
20 40 60 80
Exposure Time (days)
100
Figure 4.1.1 (b) Elongation at break vs. exposure time for duplicate exposures of 6P
samples outdoors in Miami, FL - Control material.
4-45
-------
J.UUU
££\
4_>
cj
C
O
•j"-H
E 100
a
o
55
"3
I
10
> c © * ' '
: o § "o •
o
I
! 5 5* 1
I
ff :
8— '•" • -1— — ••—- ' .
• Original Set
O Duplicate Set
0
10 20
Exposure Time (days)
30
Figure 4.1.2 (a) Elongation at break vs. exposure time for duplicate exposures of PG
samples outdoors in Chicago, IL - Enhanced degradable material.
^rf 1UUU
100
G
0
53
4— >
c
0
^ 10
• i >— r- , -| , _
; * • * f o
5
§^§ *
? •
•
•
«
.
• 1 -. ••!_•.
• Original Set
O Duplicate Set
0
20 40 60
Exposure Time (days)
80
Figure 4.1.2 (b) Elongation at break vs. exposure time for duplicate exposures of PG
samples outdoors in Chicago, EL - Control material.
4-46
-------
•a
i
• \M> «-w\^w-«- ~i 1 n % , , , — _,___-
®°e '
! o@0
•°«c^o»o ^o c^o
®
) 20 40 60 80 100 12
© Original Set
O Duplicate Set
,0
.1
Exposure Time (days)
Figure 4.1.3 (a) Change in mass after tumbling friability test vs. exposure time for duplicate
exposures of PS foam outdoors in Cedar Knolls, NJ - Enhanced
degradable material.
IP
•a
§3
If-—f-^-Q—-®O—r©€V
.1
0 20 40 60 80 100
Exposure Time (days)
® Original Set
O Duplicate Set
120
Figure 4.1.3 (b) Change in mass after tumbling friability test vs. exposure time for duplicate
exposures of PS foam outdoors in Cedar Knolls, NJ - Control material.
4-47
-------
1000
1
•§,
CO
C/3
fi
00
• 6P
O 6PC
Exposure Time (days)
Figure 4.1.4 (a)
Variation of selected tensile parameters with duration of exposure for
outdoor exposure (6P - Miami, PL - stress at break).
1000
O
»~«
W
100-
101
« 6P
O 6PC
0
10 20 30 40 50
Exposure Time (days)
Figure 4.1.4 (b) Variation of selected tensile parameters with duration of exposure for
outdoor exposure (6P - Miami, FL - elongation at break).
4-48
-------
a
PQ
8
10000 i
1000-
100-
10-
© 6P
O 6PC
10
20 30
Figure 4.1.4 (c)
Exposure Time (Days)
Variation of selected tensile parameters with duration of exposure for
outdoor exposure (6P - Miami, FL - energy to break).
10000
© 6P
O 6PC
1000
Exposure Time (days)
Figure 4.1.4 (d) Variation of selected tensile parameters with duration of exposure for
outdoor exposure (6P - Miami, FL - modulus).
4-49
-------
1000 1
1
o
a
cd
e/5
C«
fi
00
• 6P
O 6PC
Exposure Time (days)
Figure 4.1.4 (e) Variation of selected tensile parameters with duration of exposure for
outdoor exposure (6P - Seattle, WA - stress at break).
1000
&
§
I?
o
20 40 60
Exposure Time (days)
® 6P
O 6PC
80
Figure 4.1.4 (f) Variation of selected tensile parameters with duration of exposure for
outdoor exposure (6P - Seattle, WA - elongation at break).
4-50
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10000 i
a
a 1000 -
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1000-a
100:
fi
00
® PG
O PGC
10 20 30 40 50 60
Exposure Time (days)
Figure 4.1.4 (i) Variation of selected tensile parameters with duration of exposure for
outdoor exposure (PG - Miami, FL - stress at break).
1000
-
03
rt
o
C3
10 20 30 40 50
Exposure Time (days)
© PG
O PGC
60
Figure 4.1.4 (j) Variation of selected tensile parameters with duration of exposure for
outdoor exposure (PG - Miami, FL - elongation at break).
4-52
-------
1000
W
© PG
O PGC
.1
0 10
Exposure Time (days)
Figure 4.1.4 (k) Variation of selected tensile parameters with duration of exposure for
outdoor exposure (PG - Miami, FL - energy to break).
10000
•g
O
1000
• PG
O PGC
0
10 20 30 40
Exposure Time (days)
Figure 4.1.4 (1) Variation of selected tensile parameters with duration of exposure for
outdoor exposure (PG - Miami, FL - modulus).
4-53
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1000
s
.o
PQ
C/3
CO
22
4— »
CO
100 d
« PG
O PGC
Exposure Time (days)
Figure 4.1.4 (m) Variation of selected tensile parameters with duration of exposure for
outdoor exposure (PG- Seattle, WA - stress at break).
1000
S
PQ
rt
o
o
s
« PG
O PGC
Exposure Time (days)
Figure 4.1.4 (n) Variation of selected tensile parameters with duration of exposure for
outdoor exposure (PG - Seattle, WA - elongation at break).
4-54
-------
1000
100:
101
••
© PG
O PGC
Exposure Time (days)
Figure 4.1.4 (o) Variation of selected tensile parameters with duration of exposure for
outdoor exposure (PG - Seattle, WA - energy to break).
10000
1
£
Cfl
1000
20 40 , 60
Exposure Time (days)
Figure 4.1.4 (p) Variation of selected tensile parameters with duration of exposure for
outdoor exposure (PG - Seattle, WA - modulus).
4-55
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ts 600
c
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rt
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200
a
o
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O 6PC
20 40 60
Exposure Time (days)
80
Figure 4.1.5 (a) Elongation at break vs. exposure time. (6P - Cedar Knolls, NJ - outdoor
exposure).
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s
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CJ
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Exposure Time (days)
80
Figure 4.1.5 (b)
Elongation at break vs. exposure time. (6P - Chicago, IL - outdoor
exposure). ;
4-56
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1
5-1
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a
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I 400
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• 6P Duplicate
O 6PC
Q 6PC DupUcate
Exposure Time (days)
Figure 4.1.5 (c) Elongation at break vs. exposure time. (6P - Miami, FL - outdoor
exposure).
cd
a
c
o
m
i**
8
600
400
200
0
© 6P
O 6PC
20
40
60
80
Exposure Time (days)
Figure 4.1.5 (d)
Elongation at break vs. exposure time. (6P- Miami, FL - marine floating
exposure) .
4-57
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6UU*
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W 600
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10
20
30
40
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Exposure Time (days)
Figure 4.1.5 (e) Elongation at break vs. exposure time. (6P - Seattle, WA - outdoor
exposure).
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Exposure Time (days)
120
Figure 4.1.5 (f) Elongation at break vs. exposure time. (6P - Seattle, WA - marine floating
exposure). :
4-58
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I
«
s
.2
cd
o
w
800,
600
400
8 200
0
,
© 6P
O 6PC
20 40 60
Exposure Time (days)
80
Figure 4.1.5 (g) Elongation at break vs. exposure time. (6P - Wittmann, AZ - outdoor
exposure).
800
t3 600
a
o
'i
g 200
fc
a,
6P
0
10
20
30
Exposure Time (days)
Figure 4.1.5 (h) Elongation at break vs. exposure time. (6P - Kerr Lake, VA - fresh water
floating exposure).
4-59
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o
8
w
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cd
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c3
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m
600
400
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S3
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H PG Duplicate
O PGC
Q PGC Duplicate
0 10 20 30 40 50
Exposure Time (days)
60
Figure 4.1.5 (i) Elongation at break vs. exposure time. (PG - Cedar Knolls, NJ - outdoor
exposure).
SUIM
Cu (
fc 600
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| 200
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H PG Duplicate
O PGC
a PGC Duplicate
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Exposure Time (days)
80
Figure 4.1.5 (j) Elongation at break vs. exposure time. (PG - Chicago, IL - outdoor
exposure).
4-60
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•a
0)
PQ
3 600
'd
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I 400
o
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W
O
200
OH
0
1V_JA
20 40 60 80
Exposure Time (days)
• PG
• PG Duplicate
O PGC
E PGC Duplicate
Figure 4.1.5 (k) Elongation at break vs. exposure time. (PG
exposure).
100
- Miami, FL - outdoor.
iUUU • « > 1 " i '
a^ ITT
PA SOOff 2
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O PGC
20 40 60
Exposure Time (days)
80
Figure 4.1.5 (1) Elongation at break vs. exposure time. (PG - Miami, FL - marine floating
exposure).
4-61
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800
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600
400
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1 £
*Ti2 i %?
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O PGC
10 20
Exposure Time (days)
30
Figure 4.1.5 (p) Elongation at break vs. exposure time. (PG - Kerr Lake, VA - fresh water
floating exposure).
4-63
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400
cq
~ 300
fi
0
W
I
onn
200
100
o
,
A i
© ADM I
A ADMIT
O ADMC
D ADMC Duplicate
0
20 40 60
Exposure Time (days)
Figure 4.1.5 (q) Elongation at break vs. exposure time. (ADM - Cedar Knolls, NJ - outdoor
exposure).
4UU
CD
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S
| 100,
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4 ADMIT
O ADMC
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20 40 60
Exposure Time (dk.ys)
80
Figure 4.1.5 (r) Elongation at break vs. exposure time. (ADM - Chicago, IL - outdoor
exposure).
4-64
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3
eS 300
o
If 2001;
o *
c
OH
0
g
*
0
{ $
B
® ADM I
A ADMH
O ADMC
B ADMC Duplicate
20 40 60
Exposure Time (days)
80
Figure 4.1.5 (s) Elongation at break vs. exposure time. (ADM - Miami, FL - outdoor
exposure).
*
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•a 40°
200
o
53
1 100,
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.
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0
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Exposure Time (days)
80
Figure 4.1.5 (u) Elongation at break vs. exposure time. (ADM - Seattle, WA - outdoor
exposure).
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a
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• ADM
O ADMC
0
20 40 60
Exposure Time (days)
80
Figure 4.1.5 (v) Elongation at break vs. exposure time. (ADM - Seattle, WA - marine
floating exposure). :
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• ADMI
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40
Figure 4.1.5 (w) Elongation at break vs. exposure time. (ADM - Wittmann, AZ - outdoor
exposure).
-^
-
: { :
1
i ~ x.
f\ O O
• ADM
O ADMC
0
100
Exposure Time (days)
200
Figure 4.1.5 (x) Elongation at break v§. exposure time. (ADM - Miami, FL - marine
sediment exposure).
4-67
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400
03
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c
o
200
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• ADM
O ADMC
0
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Exposure Time (days)
100
Figure 4.1.5 (z)
Elongation at break vs. exposure time. (ADM - Kerr Lake, VA - fresh
water floating).
4-68
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800
C^S f
8 1
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3 600
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© PCL
O LLDPE
0
20 40 60 80
Exposure Time (days)
100
Figure 4.1.5 (aa) Elongation at break vs. exposure time. (PCL - Miami, PL - outdoor
exposure).
800
« 700
CJ
•2 600
03
a
o
500
1
g 40°
300
§ JL
© PCL
O LLDPE
0
100
Exposure Time (days)
200
Figure 4.1.5 (bb) Elongation at break vs. exposure time. (PCL - Miami, FL - marine
sediment exposure).
4-69
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20 40 60 80 100
Exposure Time (days)
120
Figure 4.1.5 (cc) Elongation at break vs. exposure time. (PCL - Seattle, WA - marine
sediment exposure).
S
PQ
a
_o
03
800
700,
600
g 500
400
10 20
Exposure Time (days)
30
Figure 4.1.5 (dd) Elongation at break vs. exposure time. (PCL - Kerr Lake, VA - fresh water
floating exposure).
4-70
-------
100
80
I 60 f
C3
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E3 40
0)
§ 20
P*
10 20 30 40
Exposure Time (days)
50
Figure 4.1.5 (ee) Elongation at break vs. exposure time. (BP - Miami, FL - outdoor
exposure).
70
*
60f
50
PQ
d
I 40.
J 30
I 20
I 10
0
0
5 10
Exposure Time (days)
15
Figure 4.1.5 (ff) Elongation at break vs. exposure time. (BP - Miami, FL - marine sediment
exposure).
4-71
-------
cd
cs
o
2
(U
70
601
50
40
30
20
10
A
1- ,
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'
" S "
JK JL
o * *
i . . . .
0
5 10
Exposure Time (days)
15
Figure 4.1.5 (gg) Elongation at break vs. exposure time. (BP - Kerr Lake, VA - fresh water
sed:- it exposure).
4-72
-------
PQ
a
o
S3
O
1000 A:
T———f
100
10
a—fBrn™, ^V—^a.
r™—~fy—fy
© 6P
O 6PC
Figure 4.1.6 (a)
0 20 40 60 80
Exposure Time (days)
6P: y = 139.21 * 10A(-5.2012e-2x) RA2 = 0.826
6PC: y = 708.26 * 10A(-9.5306e-4x) RA2 = 0.367
Semi-logarithmic plot of elongation at break vs. exposure time. (6P -Cedar
Knolls, NJ - outdoor exposure).
1000,
a
<—
cd
§
O
W
a
100
10
-©
® 6P
O 6PC
0 20 40 60 80
Exposure Time (days)
6P: y = 246.43 * 10A(-8.7294e-2x) RA2 = 0.886
6PC: y = 647.89 * 10A(-4,3002e-4x) RA2 = 0.056
Figure 4.1.6 (b) Semi-logarithmic plot of elongation at break vs. exposure time. (6P
Chicago, IL - outdoor exposure).
4-73
-------
1000
@ 6P
• 6P Duplicate
O 6PC
n 6PC Duplicat(3
20 40 ; 60 80 100
Exposure Time (days)
6P: y = 184.01 * 10A(-6:9220e-2x) RA2 = 0.853
6PC: y = 952.72 * 10A(-1.3694e-2x) RA2 = 0.823
Figure 4.1.6 (c) Semi-logarithmic plot of elongation at break vs. exposure time. (6P
Miami, FL - outdoor exposure).
w
1000
100
10
Q
X
© 6P
O 6PC
0 20 40 60 80
Exposure Time (days)
6P: y = 157.35 * 10A(-4.5126e-2x) RA2 = 0.747
6PC: y = 665.17 * 10A(-5.1527e-4x) RA2 = 0.109
Figure 4.1.6 (d) Semi-logarithmic plot of elongation at break vs. exposure time. (6P
Miami, FL - marine floating exposure).
4-74
-------
a
o
1000
100
10
© 6P
O 6PC
0 10 20 30 40 50 60
Exposure Time (days)
6P: y = 96.735 * 10A(-3.9540e-2x) RA2 = 0.779
6PC: y = 822.94 * 10A(-4.2079e-3x) RA2 = 0.600
Figure 4.1.6 (e) Semi-logarithmic plot of elongation at break vs. exposure time. (6P
Seattle, WA - outdoor exposure).
1000
20
40 60 80
Exposure Time (days)
100
120
Figure 4.1.6 (f)
6P: y = 70.108 * 10A(-1.1019e-2x) RA2 = 0.424
6PC: y = 647.69 * 10A(-3.2978e-6x) RA2 = 0.000
Semi-logarithmic plot of elongation at break vs. exposure time. (6P
Seattle, WA - marine floating exposure).
4-75
-------
1000
C3
4— >
03
I?
o
_
4>
0
20 40 60
Exposure Time (days)
6P: y = 550.26 * 10A(-0.25680x) RA2 = 0.900
6PC: y = 1047.3 * 10A(-2.5055e-2x) RA2 = 0.929
Figure 4.1.6 (g) Semi-logarithmic plot of elongation at break vs. exposure time. (6P
Wittmann, AZ - outdoor exposure).
1000
s
a
o
•.a
03
bQ
C
O
s
4->
d
100
10
6P
0 10 20 30
Exposure Time (days)
y = 355.52 * 10A(-3.9229e-2x) RA2 = 0.687
Figure 4.1.6 (h) Semi-logarithmic plot of elongation at break vs. exposure time. (6P - Kerr
Lake, VA - fresh water floating exposure).
4-76
-------
1000
0
10
20 30 40
Exposure Time (days)
PG: y = 1032.7 * 10A(-4.9811e-2x) RA2 = 0.882
PGC: y = 612.51 * 10A(-1.2228e-2x) RA2 = 0.901
@ PG
B PG Duplicate
O PGC
Q PGC Duplicate
60
Figure 4.1.6 (i)
Semi-logarithmic plot of elongation at break vs. exposure time. (PG - Cedar
Knolls, NJ - outdoor exposure).
1000
PQ
bO
a
o
a
-------
1000
CQ
4_>
C3
&
O
W
4~J
§
I
P-4
0
20 40 60 80
Exposure Time (days)
PG: y = 959.75 * 10A(-7.1569e-2x) RA2 = 0.945
PGC: y = 917.20 * 10A(-2.1588e-2x) RA2 = 0.865
e PG
• PG Duplicate
O PGC
D PGC Duplicate
Figure 4.1.6 (k) Semi-logarithmic plot of elongation at break vs. exposure time. (PG
Miami, FL - outdoor exposure).
1000
S
PQ
a
o
WO
«
O
3
4->
s
I
Pi
0
Figure 4.1.6 0)
20 40 60
Exposure Time (days)
PG: y = 859.41 * 10A(-2.6596e-2x) RA2 = 0.939
PGC: y = 631.52 * 10A(-4.1660e-3x) RA2 = 0.414
Semi-logarithmic plot of elongation at break vs. exposure time. (PG
Miami, FL - marine floating exposure).
4-78
-------
1000
bO
C3
O
3
•s
0>
20 40 60 80
Exposure Time (days)
PG: y = 1004.1 * 10A(-5.3510e-2x) RA2 = 0.921
PGC: y = 586.92 * 10A(-1.6205e-2x) RA2 = 0.840
Figure 4.1.6 (m) Semi-logarithmic plot of elongation at break vs. exposure time. (PG
Seattle, WA - outdoor exposure).
•a
%
PQ
rt
o
W)
a
o
—
a
CD
O
I
1000,
100
10
100
© PG
O PGC
120
0 20 40 60 80
Exposure Time (days)
PG: y = 351.55 * 10A(-1.7733e-2x) RA2 = 0.753
PGC: y = 382.52 * 10A(-2.3899e-3x) RA2 = 0.113
Figure 4.1.6 (n) Semi-logarithmic plot of elongation at break vs. exposure time. (PG
Seattle, WA - marine floating exposure).
4-79
-------
1000
22
PQ
G
O
bfl
«
O
53
10 20 30
Exposure Time (days)
PG: y = 885.09 * 10A(-0.12231x) RA2 = 0.915
PGC: y = 607.31 * 10A(-3.2960e-2x) RA2 = 0.961
* PG
H PG Duplicate
O PGC
Q PGC Duplicate
Figure 4.1.6 (o) Semi-logarithmic plot of elongation at break vs. exposure time. (PG-
Wittmann, AZ - outdoor exposure).
1000
PQ
4— >
c«
g
§
—
s
100
© PG
O PGC
0 10 20 30
Exposure Time (days)
PG: y = 937.87 * 10A(-7,4701e-3x) RA2 = 0.612
PGC: y = 738.90 * 10A(-1.1908e-3x) RA2 = 0.438
Figure 4.1.6 (p) Semi-logarithmic plot of elongation at break vs. exposure time. (PG - Ken-
Lake, VA - fresh water floating exposure).
4-80
-------
cd
8
a
o
\d
cd
00
a
o
"
D
O
S-4
1000
1004
20 40
Exposure Time (days)
ADM I: y = 65.886 * 10A(-0.13726x) RA2 = 0.916
ADM H: y = 193.71 * lO^-?.7012e-2x) RA2 = 0.980
ADMC: y = 340.40 * 10A(-5.7249e-3x) RA2 = 0.573
® ADM I
4 ADMH
O ADMC
B ADMC Duplicate
Figure 4.1.6 (q)
Semi-logarithmic plot of elongation at break vs. exposure time. (ADM-
Cedar Knolls, N] - outdoor exposure).
1000
G
O
s
8
@ ADMI
A ADMH
O ADMC
Q ADMC Duplicate
Figure 4.1.6 (r)
20 40 60 80
Exposure Time (days)
ADM I: y = 67.514 * 10A(-0.14776x) RA2 = 0.940
ADM E: y = 176.15 * 10A(-6.6930e-2x) RA2 = 0.978
ADMC: y = 354.16 * 10A(-1.1136e-2x) RA2 = 0.816
Semi-logarithmic plot of elongation at break vs. exposure time. (ADM
Chicago, IL - outdoor exposure).
4-81
-------
1000
pp
c
o
4 t**4
*->
03
bO
§
• ADM I
A ADMIT
O ADMC
Q ADMC Duplicate
0
20 40 60
Exposure Time (days)
ADM I: y = 41.353 * 10A(-0.12929x) RA2 = 0.847
ADM H: y = 180.08 * 10A(-8.4751e-2x) RA2 = 0.914
ADMC: y = 370.65 * 10A(-9.0717e-3x) RA2 = 0.717
Figure 4.1.6 (s) Serai-logarithmic plot of elongation at break vs. exposure time. (ADM
Miami, FL - outdoor exposure).
1000
•
§
toJD
0
10 20 , 30
Exposure Time (days)
40
ADM I
O ADMC
Figure 4.1
ADM I: y = 89.200 * 10A(-0.38599x) RA2 = 1.000
ADMC: y = 251.83 * 10A(-8.1158e-3x) RA2 = 0.634
.6 (t) Semi-logarithmic plot of elongation at break vs. exposure time. (ADM
Miami, FL - marine floating exposure).
4-82
-------
1000 E
100
-------
1000
8
O
• i— i
4-J
ed
bO
a
i
o
© ADMI
A ADMH
O ADMC
D ADMC Duplicate
10 20 30
Exposure Time (days)
ADM I: y = 89.200 * 10A(-0.39074x) RA2 = 1.000
ADM II: y = 176.30 * 10A(-0.13989x) RA2 = 1.000
ADMC: y = 299.79 * 10-^(-2.4488e-2x) RA2 = 0.917
Figure 4.1.6 (w) Semi-logarithmic plot of elongation at break vs. exposure time. (ADM
Wittmann, AZ - outdoor exposure).
a
o
a
o
W
+->
8
I
P-4
1000
100
-------
1000
• ADM I
O ADMC
20 40 60 80
Exposure Time (days)
ADM I: y = 47.720 * 10A(-1.8235e-2x) RA2 = 0.714
ADMC: y = 130.65 * lO'X-S^nSe-Sx) RA2 = 0.163
Figure 4.1.6 (y) Semi-logarithmic plot of elongation at break vs. exposure time. ADM
Seattle, WA - marine sediment exposure).
1000 F
100 -
a
o
10
20 40 60
Exposure Time (days)
80
O ADM I
ADMC
100
ADM 1: y = 178.47 * 10A(-4.7004e-3x) RA2 = 0.952
ADMC: y = 256.32 * 10A(1.2l39e-4x) RA2 = 0.003
Figure 4.1.6 (z) Semi-logarithmic plot of elongation at break vs. exposure time. (ADM
Kerr Lake, VA - fresh water floating exposure).
4-85
-------
If
o
B
3
o
§
PH
1000,
100
10
• PCL
O LLDPB
0 20 40 60 80 100
Exposure Time (days)
PCL: y = 1034.3 * 10A(-2.7304e-2x) RA2 = 0.849
LLDPE: y = 1223.1 * 10A(-2.1475e-2x) RA2 = 0.802
Figure 4.1.6 (aa) Semi-logarithmic plot of elongation at break vs. exposure time. (PCL
Miami, FL - outdoor exposure).
1000
8
PQ
o
'$
toO
C
100
® PCL
O LLDPE
0 100
Exposure Time (days)
PCL: y = 499.50 * 10A(-1.1951e-3x) RA2 = 0.257
LLDPE: y = 604.84 * lO'X-S.SSSOe-Sx) RA2 = 0.764
200
Figure 4.1.6 (bt, Semi-logarithmic plot of elongation at break vs. exposure time. (PCL
Miami, FL - marine sediment exposure).
4-86
-------
1000
cd
S2
ffl
C3
feO
fl
O
^— <
W
100
T——i-—-T——•v
0
© PCL
O LLDPE
0 20 40 60 80 100 120
Exposure Time (days)
PCL: y = 473.66 * 10A(-1.7112e-3x) RA2 = 0.342
LLDPE: y = 497.29 * 10A(-2.6985e-3x) RA2 = 0.511
Figure 4.1.6 (cc) Semi-logarithmic plot of elongation at break vs. exposure time. (PCL
Seattle, WA - marine sediment exposure).
1000
PQ
a
o
100 l-
0
PCL
10 . 20 30
Exposure Time (days)
y = 663.82 * 10A(-7.1150e-3x) RA2 = 0.745
Figure 4.1.6 (dd) Semi-logarithmic plot of elongation at break vs. exposure time. (PCL - Kerr
Lake, VA - fresh water floating exposure).
4-87
-------
cs
o
3
§
10
J__™»_
BP
10 20 30 40 50
Exposure Time (days)
y = 61.477 * 10A(-3.1064e-3x) RA2 = 0.653
Figure 4.1.6 (ee) Semi-logarithmic plot of elongation at break vs. exposure time. (BP
Miami, FL - outdoor exposure).
S
PQ
bO
a
o
W
I
BP
5 ' 10
Exposure Time (days)
y = 34.892 * 10A(-0.10171x) _RA2 = 0.856
Figure 4.1.6 (ff) Semi-logarithmic plot of elongation at break vs. exposure time. (BP
Miami, FL - marine sediment exposure).
4-i
-------
a
o
00
rt
o
W
•4— >
a
D
O
t-4
a>
100
10
05 10
Exposure Time (days)
y = 29.655 * 10A(-4.7742e-2x) RA2 = 0.438
© BP
15
Figure 4.1.6 (gg) Semi-logarithmic plot of elongation at break vs. exposure time. (BP - Ken-
Lake, VA - fresh water sediment exposure).
4-89
-------
1 .o &*»TSQ~q—®&a-
0.8
W)
I 0.7
s
-------
1.
0.8
too
c
•a
vo
0.6
0.2
D
O On
© PS
m PS Duplicate
O PSC
o PSC Duplicate
0 20 40 60 80 100 120
Exposure Time (days)
Figure 4.1.7 (c) Change in mass (as measured by tumbling friability) with duration of
exposure for polystyrene foam exposed outdoors - (Miami, FL).
too
1.
0.9
0.8
0.7
0.6
0.5
0
© PS
O PSC
20 40 60 80 100 120
Exposure Time (days)
Figure 4.1.7 (d) Change in mass (as measured by tumbling friability) with duration of
exposure for polystyrene foam exposed outdoors - (Seattle, WA).
4-91
-------
Q
0.8
I?
•a
0.6
,1 0.4
0.2
1 - ' - 1 - ' - r
0D ©
« PS
B PS Duplicate
O PSC
n PSC Duplicate
0 20 40 60 80 100 120 140
Exposure Time (days)
Figure 4.1.7 (e) Change in mass (as measured by tumbling friability) with duration of
exposure for polystyrene foam exposed outdoors - (Wittmann, AZ).
4-92
-------
I
I
04
© PS
• PS Dup
O PSC
a PSC Dup
0 20 40 60 80 100
Exposure Time (days)
120
PS: y = 0.89728 - lQ*(-2.&935e-3x) RA2 = 0.803
PS Dup: y = 0.92676 * 10A(-2.9269e-3x) RA2 = 0.700
PSC: y = 1.1287 * 10A(-1.6861e-3x) RA2 = 0.963
PSC Dup: y = 1.2780 * 10A(-2.2969e-3x) RA2 = 0.987
Figure 4.1.8 (a)
Semi-logarithmic plot of tumbling friability data versus duration of
exposure for polystyrene foam exposed outdoors - (Cedar Knolls, NJ).
•a
i
03
0
20 40 60 80 100 120
Exposure Time (days)
140
PS: y = 0.86780 * 10A(-2.1989e-3x) RA2 = 0.845
PS Dup: y = 1.0408 * 10A(-2.9193e-3x) RA2 = 0.733
PSC: y = 0.98004 * 10A(-1.1117e-3x) RA2 = 0.715
PSC Dup: y = 1.3766 * 10A(-2.1135e-3x) RA2 = 0.861
® PS
H PS Dup
O PSC
0 PSC Dup
Figure 4.1.8 (b) Semi-logarithmic plot of tumbling friability data versus duration of
exposure for polystyrene foam exposed outdoors - (Chicago, EL ).
4-93
-------
l q
bO
C
•a
•a
s
00
§3
© PS
n ps Dup
O PSC
Q PSC Dup
20
40
60
80
100
120
Exposure Time (days)
PS: y = 0.95497 * 10A(-4.1068e-3x) RA2 = 0.926
PS Dup: y = 0.99516 * 10A(-4.6193e-3x) RA2 = 0.938
PSC: y = 1.1630 * 10A(-2.9494e-3x) RA2 = 0.834
PSC Dup: y = 1.3083 * 10A(-3.3825e-3x) RA2 = 0.964
Figure 4.1.8 (c) Serai-logarithmic plot of tumbling friability data versus duration of
exposure for polystyrene foam exposed outdoors - (Miami, FL).
tkQ
«
•a
•a
I
04
00
© PS
O PSC
0 20 40 60 80 100 120
Exposure Time (days)
PS: y = 0.84067 * 10A(-2.4004e-3x) RA2 = 0.717
PSC: y = 1.0786 * 10A(-1.8944e-3x) RA2 = 0.661
Figure 4.1.8 (d) Semi-logarithmic plot of tumbling friability data versus duration of
exposure for polystyrene foam exposed outdoors - (Seattle, WA).
4-94
-------
bO
a
•a
• PS
• PS Duplicate
O PSC
• D PSC Duplicate
100 120 140
Exposure Time (days)
PS: y = 0.80825 * 10A(-3.7587e-3x) RA2 = 0.897
PS Dup: y = 0.83593 * 10A(-3.6807e-3x) RA2 = 0.838
PSC: y = 1.0347 * 10A(-2.2277e-3x) RA2 = 0.804 .
PSC Dup: y = 1.1010 * 10*(-2.595&e-3x) RA2 = 0.854
Figure 4.1.8 (e) Semi-logarithmic plot of tumbling friability data versus duration of
exposure for polystyrene foam exposed outdoors - (Wittmann, AZ ).
4-95
-------
o
r«
a
c
Q
20 • 40 60
Exposure Time (days)
PS: y = 0.71872 •+- 3.8665e-2x RA2 = 0.844
PSC: y = 1.0811e-2 :+ 2.2063e-2x RA2 = 0.993
@ PS
O PSC
80
Figure 4.1.9 (a) GPC data for PS plotted as reciprocal degree of polymerizat
duration of exposure - (Outdoor - Chicago, IL).
ion vs.
o
rt
G
I
fl
I
oo
0
20 40 60
Exposure Time (days)
PS: y = 0.67541 + 2.5237e-2x RA2 = 0.730
PSC: y = 0.12389 + 1.4315e-2x RA2 = 0.703
© PS
O PSC
80
Figure 4.1.9 (b) GPC data for PS plotted as reciprocal degree of polymerization vs
duration of exposure - (Outdoor - Miami, FL).
4-96
-------
o
cf
o7
Q
0
10
20 30 ' 40 50
Exposure Time (days)
PS: y = 6.16602 + 6.2791e-2x RA2 = 0.975
PSC: y = 2.1521e-2 + 1.4294e-2x RA2 = 0.971
Figure 4.1.9 (c) GPC data for PS plotted as reciprocal degree of polymerization vs.
duration of exposure - (Marine floating - Miami, FL).
10 20
Exposure Time (days)
PS: y = 0.13528 + 4.3049e-2x RA2 = 0.899
PSC: y = - 1.8654e-4 + 1.2972e-2x RA2 = 0.979
Figure 4.1.9 (d) GPC data for PS plotted as reciprocal degree of polymerization vs.
duration of exposure - (Marine floating - Seattle, WA).
4-97
-------
v!*«
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6-PACK RINGS
MARINE FLOATING EXPOSURE AT
MIAMI, FL
35 DAYS: 6/1/90-7/6/90
Figure 4.1.10 (a) Marine-floating exposure of LDPE control and (ethylene-carbon monoxide)
copolymer in Miami, FL - (6P - 35 days).
g*. A
-f «^»
it' k t. >f ~f- * f V
v «t v^^ '* hi®
A -
6-PACK CONTROL •; ' ,
MARINE FLOATING EXPOSURE AT
' MIAMI, FL ' t !
35 DAYS: 6/1/90-7/6/90
Figure 4.1.10 (b) Marine-floating exposure of LDPE control and (ethylene-carbon monoxide)
copolymer in Miami, FL - (6PC - 35 days).
4-98
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6-PACK"RINGS'
'MARINE FLOATING EXPOSURE
AT SEATTLE, WA
59 DAYSr 6/19/90-8/17/90
Figure 4.1.11 (g) Marine floating exposure of LDPE control and (ethylene-carbon monoxide)
copolymer in Seattle, WA.- (6P - 59 days ).
4-103
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^^fc^^c^siiifcl^
..W-,';-.<;T ;...,-,»-' «rites§*-:'.v.: i-.-.
Figure 4.1.12 (a) Marine floating exposure of LDPE control and Plastigone (LDPE/MX)
material in Miami, FL - (PG - 39 days).
PG - PLASTIGONE „
MARINE FLOATING EXPOSUR^ AT
^lAMI, FL
42 DAYS: 6/1/90-7/13/90
Figure 4.1.12 (b) Marine floating exposure of LDPE control and Plastigone (LDPE/MX)
material in Miami, FL - (PG - 42 days).
4-104
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4-106
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^GAJiNG EXPOSURE AT
^::-- MIAMI, FL ''.
DAYS; 6/1/90-8/8/90'
Figure 4.1.12 (g) Marine floating exposure of LDPE control and Plastigone (LDPE/MX)
material in Miami, FL - (PG - 68 days).
4-107
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Figure 4.1.13 (g) Marine floating exposure of LDPE control and Plastigone (LDPE/MX)
material in Seattle, WA - (PG - 59 days ).
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4-114
-------
2000
Total Global
Exposure Time (days)
y = 41.102 + 14.456x RA2 = 0.996
Figure 4.1.16 (a) Total solar radiation (45° south) versus the duration of exposure - (Cedar
Knolls, NJ).
4-115
-------
® Total Global
O TUVR
0 20 40 60 80 100 120 140
Exposufe Time (days)
Total Global: y = - 8.1630 + 16.511x RA2 = 0.998
TUVR: y = 2.0811 + 0.62485x RA2 = 0.994
Figure 4.1.16 (b) Total solar radiation (45° south) versus the duration of exposure -
(Chicago, IL). :
4-116
-------
1400-
Exposure Time (days)
Total Global: y = - 19.254 + 14.498x RA2 = 0.999
TUVR: y = - 0.42290 + 0.70222x RA2 = 0.999
Figure 4.1.16 (c) Total solar radiation (45° south) versus the duration of exposure - (Miami
FL).
4-117
-------
2000
Total Global
80
Exposure Time (days)
y = 25.129 4- 18.273x RA2 = 0.993
Fi°ur 1 1 16 (d) Total solar radiation (45° south) versus the duration of exposure - (Seattle,
° ' ' WA).
4-118
-------
3000
2000-
w
o 1000
oo
Total Global
O TUVR
0
Exposure Time (days)
Total Global: y = - 18.727 + 21.855x RA2 = 0.998
TUVR: y = 0.49238 + 0.97707x RA2 = 0.999
Figure 4.1.16 (e) Total solar radiation (45° south) versus the duration of exposure.
(Wittmann, AZ).
4-119
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03
c*
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o
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o
0.14
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0.08-
0.06-
0.04-
0.02-
0.00
o
• PG
O PGC
15 20 25 30 35 40
Average Daily Temperature (°C)
PG: y = - 5.2742e-2 + 4.6752e-3x RA2 = 0.842
PGC: y = - 1.7802e-2 + 1.4136e-3x RA2 = 0.699
fr
0.14
0.12-
i 0.081
Q
® PG
O PGC
10 20 30
Average Daily Total Radiation (MJ/m2)
PG:y= - 1.6167e-2 + 4.6426e-3x RA2 = 0.708
PGC: y = - 1.2776e-2 + 1.8805e-3x RA2 = 0.345
Figure 4.1.17 (b) Degradation rate versus the average temperature and average solar radiation
at exposure site - (Plastigone [LDPE//MX] film).
4-121
-------
Average Daily Temperature (°C)
ADM I: y = - 0.21580 + 1.6146e-2x RA2 = 0.750
ADMH:y= - 0.13317 + 8.4269e-3x RA2 = 0.948
ADMC: y = - 1.6068e-2 + 1.1398e-3x RA2 = 0.721
« ADM I
A ADMH
O ADMC
c
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&
5e-3
4e-3-
3e-3-
2e-3-
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15 20 25 30
Average Daily Temperature (°C)
PS: y = 4.4024e-4 + 1.1778e-4x RA2 = 0.409
PSC: y = 1.1392e-3+4.9866e-5x RA2 = 0.120
© PS
O PSC
35
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"3
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o
» PS
O PSC
14 16 18 20 22 24
Average Daily Total Radiation (MJ/m2)
PS: y = 2.5149e-3 + 5.1942e-5x RA2 = 0.051
PSC: y = 2.1411e-3 + 8.7154e-6x RA2 = 0.002
Figure 4.1.17 (d) Degradation rate versus the average temperature and average solar radiation
at exposure site - (Expanded polystyrene foam [Polysar material]).
4-123
-------
1000
o
'i
bO
rt
o
g
O Cedar KnoUs, NJ
® Chicago, IL
O Miami, FL
B Seattle, WA
& Wittmann, AZ
800
Total Global Radiation (45°S) - MJ/sq m
y = 122.98 * 10A(-3.1555e-3x) RA2 = 0.711
Figure 4.1.18 (a) Semi-logarithmic plot of elongation at break versus the total radiation at
exposure site: composite data for all outdoor locations ([Ethylene-carbon
monoxide] copolymer).
4-124
-------
1000
a
a
o
§
O Cedar Knolls, NJ
© Chicago, EL
D Miami, FL
E Seattle, WA
& Wittmann, AZ
200 400 600 800 1000
Total Global Radiation (45°S) - MJ/sq m
y = 751.61 *
RA2 = 0.717
Figure 4.1.18 (b) Semi-logarithmic plot of elongation at break versus the total radiation at
exposure site: composite data for all outdoor locations (Plastigone
[LDPE/MX] film).
4-125
-------
100
PQ
o
W
a
10:
O Cedar Knolls, NJ
® Chicago, IL
D Miami, FL
m Seattle, WA
A Wittmann, AZ
0
100
200
300
Total Global Radiation (45°S) - MJ/sq m
y = 42.464 * 10A(-6.6797e-3x) RA2 = 0.693
Figure 4.1.18 (c) Semi-logarithmic plot of elongation at break versus the total radiation at
exposure site: composite data for all outdoor locations (ADM
[LDPE/starch/MX] film). .
4-126
-------
IP
•a
•a.
a
oo
O Cedar Knolls, NJ
® Chicago, IL
D Miami, FL
M Seattle, WA
A Wittmann, AZ
1000
2000
3000
Total Global Radiation (45°S) - MJ/sq m
y = 0.88510 * 10A(-1.7588e-4x) RA2 = 0.753
Figure 4.1.18 (d) Semi-logarithmic plot of elongation at break versus the total radiation at
exposure site: composite data for all outdoor locations (Expanded
polystyrene foam [Polysar material]).
4-127
-------
400
PQ
~ 300
G
.2
4—*
|° 200
o
55
4—1
I 100;
o
©
© ADM
O ADMC
0 20 40 60 ,80 100 120
Exposure Time (days)
140
1000
PQ
§
20
40 60 • 80 100
Exposure Time (days)
120
140
ADM: y = 98.041 * 10A'(-7.0416e-3x) RA2 = 0.880
ADMC: y = 213.17 * 10/H-3.4784e-3x) RA2 = 0.593
Figure 4.1.19 (a) Elongation at break versus duration of exposure for outdoor soil burial at
Research Triangle Park, NC - (ADM/ADMC materials).
4-128
-------
o>
a
o
o
W
PH
800
600
400
200
0
9
100
Exposure Time (days)
0
© PCL
O LLDPE
200
8
PQ
o
•3
I
1000
6
100
0 100
Exposure Time (days)
PCL: y = 543.62 * 10A(-9.1419e-4x) RA2 = 0.567
LLDPE: y = 571.45 * 10A(-1.3476e-3x) RA2 = 0.670
@ PCL
O LLDPE
200
Figure 4.1.19 (b) Elongation at break versus duration of exposure for outdoor soil burial at
Research Triangle Park, NC - (PCL/LLDPE materials).
4-129
-------
70
H 60"-
cs 50
o
I 4°
o
—
cd
o
o
I
30
20
10
©
10 ' 20
Exposure Time (days)
BP
30
100
PQ
rt
o
W
4«>
I
10
BP
0 10 i 20 30
i
Exposure Time (days)
y = 40.999 * 10A(-3;831 le-2x) RA2 = 0.933
Figure 4.1.19 (c) Elongation at break versus duration of exposure for outdoor soil burial at
Research Triangle Park, NC - (BP materials).
4-130
-------
-C
o
o
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BIOPOL
.SOIL BURIAL - RTI
BLOCK 1 - #67
48 DAYS: 3/27/90-5/14/90
Figure 4.1.20 (i) Outdoor soil burial of BP at Research Triangle Park, NC - (48 days).
4-135
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800,
600 P
cd
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n 6P-Literature Values
O 6PC-Literature Values
200 400 ! 600 . 800 1000
Exposure Time (hours)
© 6P
D 6P-Literature Values
O 6PC-Literature Values
1000
Figure 4.2.1 (a)
6P: y = 234.80 * 10A(-8.7401e-3x) R*2 = 0.852
6PC: y = 903.41 * 10A(-1.6727e-3x) R*2 = 0.958
Elongation at break versus the duration of exposure for Weather-Ometer®
exposure - (6P/6PC).
4-136
-------
800 f
T: 600
«s
rt
o
o
W
400
200
0
5
® PG
O PGC
100 200
Exposure Time (hours)
300
1000
PQ
100
200
300
PG: y = 927.44 * 10A(-6.3486e-3x) RA2 = 0.961
PGC: y = 598.72 * 10A(-9.3713e-4x) RA2 = 0.534
Figure 4.2.1 (b) Elongation at break versus the duration of exposure for Weather-Ometer®
exposure - (PG/PGC).
4-137
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O PSC
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© PS
O PSC
200
Exposure Time (hours)
PS: y = 1.2002 * 10A(-1.9955e-3x) RA2 = 0.964
PSC: y = 1.5985 * 10A(-1.1165e-3x) RA2 = 1.000
300
Figure 4.2.2 Change in mass (as measured by tumbling friability) versus the duration of
exposure for Weather-Ometer® exposure of photodegradable polystyrene
foam .
4-139
-------
1000 r
03
a
o
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100
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• 6P
<& PG
O ADM
60 70 80
Exposure Temperature (°C)
PG: y = 1105.6 * 10A(-1.2556e-2x) RA2 = 0.513
ADM: y = 2.8544e+6 * 10A(-5.9924e-2x) RA2 = 0.943
90
Figure 4.2.3 Elongation at break versus the exposure temperature for Weather-Ometer®
exposure (50 hours) for 6P> PG, and ADM samples.
4-140
-------
10
1'
.1
60
© PS
70
80
90
Exposure Temperature (°C)
Figure 4.2.4 Change in mass (as measured by tumbling friability) versus exposure
temperature for Weather-Ometer® exposure (50 hours) of photodegradable
polystyrene foam.
4-141
-------
-------
SECTION 5.0
OTHER EFFECTS OF WEATHERING
A convenient means of establishing the rates of disintegration is by monitoring the
changes in mechanical properties of a plastic film undergoing environmental exposure.
However, the mechanical properties of the material are not the only material properties
affected by the weathering process. Changes in color, density, molecular weight, solution
properties, transport properties, and electrical properties of the polymer can also change
with degradation.
This chapter summarizes experiments pursued to study changes in selected physical
properties of the disintegrating enhanced degradable plastic materials. Transport proper-
ties, thermal properties, and molecular weight changes, in particular, will be examined.
5.1 CHANGES IN MOLECULAR WEIGHT
The number average molecular weight (Mn), weight average molecular weight (Mw),
and molecular weight distribution of partially degraded polymers were obtained from gel
permeation chromatography (GPC) data. When chain scission is the predominant degrada-
tion mechanism, average molecular weight decreases with duration of exposure. However,
some crosslinking may also take place concurrently. Molecular weight distribution (or
polydispersity) is the ratio of weight average molecular weight to number average mole-
cular weight and would be expected generally to increase with increased extent of polymer
degradation. Mw is more sensitive to the presence of higher molecular weight species,
whereas Mn is influenced more by the presence of low molecular weight species.
5.1.1 Polystyrene Foam
Previous studies [George and Hodgeman, 1976; Rabek and Ranby, 1974] on the
mechanism of polystyrene degradation have shown it to occur due to photo-initiation by
impurities. This leads to the formation of oxidation products which in turn absorb solar
radiation and react to cause main-chain scission in the polymer, thereby reducing molecular
weight. The enhanced photodegradable polystyrene is a blend of regular polystyrene resin
with about 20% of a copolymer of styrene/vinyl ketone. This copolymer contains pendant
ketone groups which are efficient chromophores able to absorb UV radiation and initiate
degradation reactions.
Table 5.1.1 shows average values of molecular weight as determined by GPC for PS
and PSC samples for selected exposure sites. For outdoor exposure in both Miami, FL
5-1
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and Chicago, EL, the degradation (based on decrease in the number average molecular
weight) occurred more rapidly in the enhanced degradable material than in the control.
After only 14 days of exposure in both locations, Mn of the enhanced degradable
polystyrene had decreased by about 60%, while that of the control polystyrene had
decreased only by about 30%. After 57 days of exposure in Chicago, IL, Mn for PS sam-
ples had decreased by 75% and for PSC by 64%. The degradation reactions in turn gener-
ate new light-absorbing functional groups. The control material, PSC, might be expected
to eventually degrade to the same extent as the enhanced degradable material given a long
enough exposure duration.
Studies of degradation in expanded polystyrene foam (as opposed to films) are
complicated by the formation of a yellow, embrittled surface layer which absorbs UV
radiation and, upon build-up, effectively screens the underlying polymer. In comparing
polystyrene foam exposed on land and floating in sea water, Andrady and Pegram (1991)
have shown that the degradation rate is initially faster in air, but for longer exposure dura-
dons, degradation in sea water is faster and occurs to a greater extent. This observation
was attributed to gradual removal by the water of the outer protective yellow layer. For the
present work, GPC data for marine floating exposures at longer durations could not be
obtained due to excessive fouling, but the Miami, FL outdoor and marine floating exposure
results showed similar extents of degradation for the exposure durations which could be
directly compared.
Comparison of enhanced degradable polystyrene foam, PS material, to control mate-
rial, PSC, for marine floating exposure shows that for both locations (Miami, FL and
Seattle, WA), the enhanced degradable material showed much higher extents of degradation
for comparable exposure durations. For example, in Seattle, WA, Mn for PS had
decreased by 59% after 21 days, whereas Mn for PSC control samples had decreased only
by 29% for the same exposure duration. The observation is consistent with that for regular
polystyrene foam reported previously by Andrady and Pegram (1991).
Accelerated weathering (Weather-Ometerf) of the enhanced degradable material
resulted in a large reduction (65%) in the average molecular weight after only 50 hours of •
exposure. This corresponded to about 14 days iof outdoor exposure in Miami, FL or
Chicago, IL. The extent of degradation (as measured by reduction in the molecular weight
reduction) leveled off at about 80% after 150 hours of exposure. Longer expo: "re times
did not further reduce molecular weight significantly. This might be due to the 'elop-
ment of the yellow protective layer which, unlike the cases of outdoor and marine expo-
sures, is left undisturbed and remains intact.
5-4
-------
Figures 5.1. La through 5.1.1.1 show molecular weight distributions for the PS and
PSC samples obtained by GPC. The graphs show the fraction of each molecular weight
species (MO plotted against GPC retention volume. The width of each peak relates to the
molecular weight distribution, while the retention volume at the peak maximum is propor-
tional to the number average molecular weight. These graphs illustrate the more rapid loss
in molecular weight in the enhanced photodegradable polystyrene compared to the regular
polystyrene control. The peaks (particularly for the PS samples) also tend to broaden with
increased exposure duration, indicating higher values of molecular weight distribution at
greater extents of degradation.
5.1.2 Polvcaprolactone/Polyethylene Blend
Table 5.1.2 shows molecular weight values obtained from GPC on the extracted
polycaprolactone fraction of PCL samples exposed to outdoor soil burial at RTI and to
marine sediment conditions in Miami, FL. One month of exposure in both biotic environ-
ments had little or no .effect on the average moleculav weight at all, and only a slight
decrease was noted for the longer exposure times (up to 6 months). Evidently, much
longer exposure durations are required before the polycaprolactone begins to break down
on a molecular level. The slow breakdown of the polycaprolactone (reported to be
biodegradable) may be in part due to the fact that it is contained within the polyethylene
matrix, which restricts its exposure to the microorganisms and/or extra-cellular enzymes
which cause degradation. However, the test procedure employed does not take into
account the oligomeric species which could have leached out of the plastic blend during
exposure.
5.2 CHANGES IN TRANSPORT PROPERTIES
The transport properties of polymers to gases, vapors, and liquids are of great impor-
tance in applications such as packaging for food and other items, corrosion resistant coat-
ings, electrical application of plastics, materials for biomedical applications, etc. In the
packaging field, for example, the resistance of flexible films to moisture and oxygen is
essential for the preservation of packaged goods. Polymer degradation (biodegradation,
photodegradation, and thermal degradation) can potentially lead to changes in the perme-
ability of such plastic materials. In this section, water vapor transmission rates (WVTR) of
three kinds of plastic films, i.e., photodegradable plastic (PG), biodeteriorable plastic
blends (PCL), and photodegradable-biodeteriorable plastic (ADM), were measured for
samples exposed to several different environments, and the results were compared with that
of unexposed film. Additionally, the gas (carbon dioxide) permeabilities of two types
5-5
-------
Table 5.1.2. Gel Permeation Chromatography Results for Polycaprolactone Fraction of
PCL/LLDPE Blend.
Location
Unexposed
RTI
Miami
Exposure
Exposure Type Duration
(days)
o :
Outdoor Soil Burial 28
56 ;
84
140 ,
168
Marine Sediment 29
43 ;
Mn
(x 10'4)
3.7
3.6
3.3
3.0
3.4
3.1
3.6
2.9
Mw
(x 10"4)
5.6
5.4
5.3
5.0
5.2
5.0,
5.5
5.0
M\v/Mri
1.53
1.49
1.60
1.65
1.54
1.59
1.54
1.71
n = number average molecular weight
= weight average molecular weight
MH = molecular weight distribution
5-6
-------
of photodegradable films (PG and 6P) exposed to Weather-Ometer® conditions were mea-
sured using a gravimetric technique. The relationships between the permeabilities and
exposure time for different samples were determined.
5.2.1 Water Vapor Transmission Rate (WVTR)
Figure 5.2.1 shows the typical permeation results for PG samples which were
exposed under outdoor conditions at Miami, FL for various durations. For both unex-
posed and exposed film samples, the amounts of water vapor which permeated through the
films were proportional to the permeation time (correlation coefficient > 0.97), and the
longer the exposure, the larger the amount of water permeated. The intercept of the linear
portion of the curve, the so-called "lag time", T, allows the calculation of the diffusion
coefficient D of the film, as follows:
where /is the film thickness. As the weight increase was not continuously recorded in the
present experiments, lag time could not be accurately determined and are not reported here.
The slope of the weight gain versus time curves, on the other hand, gave the water vapc
transmission rate (WVTR). The plots of the WVTR as a function of exposure time are
shown in Figure 5.2.2 where the WVTR of the PG films increased linearly with the expo-
sure time. In outdoor weathering of PG material, the polymer (polyethylene) undergoes
light-initiated thermo-oxidative degradation in a free-radical reaction, leading to scission of
polymer chains. The shorter average chain length of degraded molecules may "plasticize" .
the film and render it more permeable to water vapor. Small molecules such as water and
CO2 tend to diffuse relatively easily through a plasticized polymer matrix. The linear rela-
tionship between WVTR and the time of weathering of the film, shown in Figure 5.2.2,
suggests the meal-catalyzed chain scission process (which generates the oligomeric sol
fraction of polyethylenes responsible for plasticization) to increase with duration of expo-
sure. Table 5.2. 1 summarizes WVTR data for PG.
Figure 5.2.3 and Table 5.2.2 show the WVTR data for a PCL film (blends of LLDPE
and polycaprolactone) exposed in an aerobic soil slurry for 40 days in comparison with that
of unexposed PCL. As can be seen in the figure, the WVTR of the exposed and unex-
posed film are about the same. This suggests that attempted biodegradation of the PCL
sample by aerobic exposure was not successful in this short time-scale of exposure to an
extent to alter the experimental WVTR values. This is consistent with the other data (GPC,
mechanical strength) reported these blends.
5-7
-------
Table 5.2.1. Water Vapor Transmission Test Data (LDPE/MX Samples).
Duration of
Exposure*
(days)
0
4
7
11
Water Vapor Transmission Average of W/A
Time
(day)
0
3
3
3
3
6
6
6
6
8
8
8
8
10
10
10
10
0
3
3
6
6
9
9
0
1
1
3
3
5
5
8
8
0
3
3
6
6
9
9
•yy**
(g)
0
0.088
0.093
0.090
0.085
0.185
0.192
0.176
0.180
0.269
0.279
0.267
0.267
0.346
0.358
0.358
0.360
0
0.164
0.132
0.322
0.298
0.471
0.440
0 1
0.048
0.048
0.132
0.138
0.233
0.239
0.382
0.398
0 i
0.209
0.203
0.377
0.381
0.576
0.533
W/A
(mg/cm2)
0.00
4.54
4.79
4.64
4.38
9.54
9.90
9.07
9.28
13.87
14.38
13.76
13.76
17.84
18.45
18.45
. 18.56
0.00
8.45
6.80
16.60
15.36
24.28
22.68
0
2.47
2.47
6.80
7.11
12.01
12.32
19.69
20.52
0.00
10.77
10.46
19.43
19.64
29.69
27.47
(mg/cm2)
0.00
4.59
9.45
13.94
18.32
0.00
7.63
15.98
23.48
0.00
2.47
6.96
12.16
20.10
0.00
10.62
19.54
28.58
- continued -
5-8
-------
Table 5.2.1. (continued).
Duration of
Exposure*
(days)
15
19
22
25
Water Vagor Transmission
Time
(day)
0
3
3
6
6
9
9
0
1
3
5
8
0
3
3
3
6
6
6
9.5
9.5
9.5
0
3
3
3
6
6
6
9.5
9.5
9.5
w**
(g)
0
0.187
0.209
0.350
0.393
0.593
0.541
0
0.073
0.218
0.369
0.582
0
0.040
0.036
0.037
0.074
0.064
0.077
0.119
0.104
0.124
0
0.042
0.050
0.043
0.083
0.095
0.085
0.128
0.138
0.133
W/A
(mg/cm2)
0
9.64
10.77
18.04
20.26
30.57
27.89
0
3.76
11.24
19.02
30.00
0.00 '
12.12
10.91
11.21
22.42
19.39
23.33
36.06
31.52
37.58
0
12.73
15.15
13.03
25.15
28.79
25.76
38.79
41.82
40.30
Average of W/A
(mg/cm2)
0.00
10.21
19.15
29.23
0.00
0.00
11.41
21.72
35.05
0.00
13.64
26.57
40.30
* Exposure:Outdoor exposure at Miami
** W = mass of water uptake
Permeation Area: A = 19.4 cm2 for 0 to 20 days exposure
Permeation Area: A = 3.3 cm2 for 22 and 25 days exposure.
5-9
-------
Table 5.2.2. Water Vapor Transmission Test Data (LLDPE/PCL Blend Samples).
Unexposed Samples '
Time
(day)
0
3
3
3
3
w**
(g)
0
0.197
0.181
0.151
0.177
W/A
(mg/cm2)
0
10.15
9.33
7.78
9.12
Average of
W/A
(mg/cm2)
0.00
9.10 !
Samples Exposed Under Aerobic Conditions*
Time
(day)
0
3
3
3
3
5
5
5
5
W
(8)
0
0.169
0.177
0.160
0.175
0.295
0.298
0.293
0.305
W/A
(mg/cm2)
0.00
8.71
9.12
8.25 '
9.02
15.21
15.36
15.10
15.72
Average of
W/A
(mg/cm2)
0.00
8.78
15.35
7
7
7
7
10.5
10.5
10.5
10.5
0.417
0.420
0.368
0.416
0.660
0.652
0.558
0.608
21.49
21.65
18.97
21.44
20.89
9
9
9
9
0.512
0.522
0.495
0.536
26.39
26.91
25.52
27.63
26.61
34.02
33.61
28.76
31.34
31.93
*
**
Exposure was in a solution of mineral salts innoculated with garden soil
W = mass of water uptake
Permeation Area: A = 19.4 cm2
5-10
-------
Effects of the degradation of ADM samples (LDPE/starch/MX) on the WVTR are
shown in Figure 5.2.4. The samples of ADM films were exposed outdoors for 10 days at
Miami, FL (Table 5.2.3) and also immersed in enzyme (cc-amylase) solutions for 40 days
(Table 5.2.4). The WVTR of the outdoor-weathered film was apparently larger compared
to the unexposed film because the chain scission (resulting from photooxidation) during
weathering tends to make the film more permeable. The WVTR measurements of the film
exposed in the enzyme solution, however, showed no difference in rate between the
.exposed firm and unexposed one. In order to avoid the effect of thermal degradation of the
ADM sample in the solution at 37°C, ADM films compounded solely for biodeteriorability
only (no pro~oxidant metal compound additive) were used for the enzyme exposure exper-
iment. According to thermogravimetric analysis (TGA) of the enzyme-exposed ADM, less
than 10 percent of the starch content of the film was hydrolyzed by the enzyme after the
exposure. Such a small decrease in the starch content may not significantly increase the
WVTR of the sample. In conclusion, the photodegradation (or photooxidation) of the
polyethylene films (PG and ADM) increased their WVTR in proportion to the exposure
time. The biodeterioration of both PCL and ADM samples in the present study was too
limited to make the change in the WVTR in the time scale of exposure used.
5.2.2 Gas Permeability
In order to investigate the effect of photodegradation of PG and 6P samples on gas
permeability, measurements of CC>2 permeability were carried out with plastic films
exposed for various durations in a Weather-Ometer®. Several techniques are available for
the experimental determination of the diffusion coefficient (D), solubility (S), and the per-
meability (P) of a film to a gas or a vapor. These can be classified into four groups, i.e.
(i) constant volume method, (ii) gravimetric method, (iii) volume loss method, and (iv)
continuous flow method. The technique used in the present study was a gravimetric
method where the gain in mass of a gas dissolving in a polymer was continuously mea-
sured as a function of time, using an electric microbalance.
Figures 5.2.5 and 5.2.6 show the time-dependent mass gain due to CC>2 absorbed in
PG films and 6P films, respectively. In both figures, the results for the exposed (and
therefore, weathered) samples with different exposure times of up to 250 hours are shown.
All curves show a rapid increase in the amount of gas absorbed during the initial period and
limiting values at steady state. The amount of COi absorbed in PG film at any given time
increased with the duration of Weather-Ometer® exposure (or the extent of photodegrada-
tion), while that in 6P material decreased. To obtain the diffusion coefficient D and the
permeability P, the data from the sorption experiments are usually plotted as the relative
5-11
-------
Table 5.2.3. Water Vapor Transmission Test Data (ADM Samples).
Unexposed Samples
Time
(day)
0
2
2
4
4
7
7
10
10
W*
(g)
0
0.169
0.165
0.323
0.322
0.560
0.554
0.869
0.799
W/A
(mg/cm2)
0
8.71
8.51
16.65
16.60
28.87
28.56
44.79
41.19
Average of
W/A
(mg_/cm2)
0.00
8.61
9.10
16.62
28.71
42.99
Samples Exoosed Ten Days (Outdoor)
Time
: (day)
i
; 0
4
4
; 6
6
'. 8
8
W
(g)
0
0.069
0.083
0.106
0.128
0.150
0.174
W/A
(mg/cm2)
0.00
20.91
25.15
32.12
38.79
45.45
52.73
Average of
W/A
(mg/cm2)
0.00
23.03
35.45
49.09
* W = mass of water uptake
Permeation Area: A = 19.4 cm2 for unexposure
Permeation Area: A = 3.3 cm2 for Outdoor Exposure
5-12
-------
Table 5.2.4. Water Vapor Transmission Test Data (LDPE/Starch/MX Samples).
Unexposed Samples'
Time
(day)
0
2
2
2
2
4
4
4
4
7
7
7
' 7
9
9
9
9
11
11
W
(g)
0
0.175
0.173
0.173
0.169
0.345
0.346
0.338
0.356
0.583
0.577
0.615
0.609
0.765 .
0.759
0.790
0.776
0.947
0.932
W/A
0
9.02
8.92
8.92
8.71
17.78
17.84
17.42
18.35
30.05
29.74
31.70
31.39
39.43
39.12
40.72
40.00
48,81
48.04
Average of ~.
w£ Jme
0.00 0
8.89
3
3
3
3
17.85
6
6
6
6
30.72
9
39.82 9
9
9
48.43
13
13
13
13
Samples Exposed to Enzyme*
W
(g)
0
0.169
0.191
0.226
0.185
0.398
0.402
0.475
0.404
0.622
0.652
0.716
0.661
0.925
0.997
1.150
0.956
W/A Average of
W/A
0.00 0.00
8.71
9.85 9.94
11.65
9.54
20.52
20.72 21.64
24.48
20.82
32.06
33.61 34.16
36.91
34.07
47.68
• 51.39 51.91
59.28
49.28
* a- Amylase
Permeation Area: A = 19.4 cm2
5-13
-------
mass gain, Mt/Meq, versus square root of time.; The typical plots for both PG and 6P
samples are shown in Figures 5.2.7 and 5.2.8, respectively. Here Mt and Meq are the
cumulative amount of CO2 in the polymer at time t and at equilibrium respectively. All
curves in the films were linear in the initial stage with a correlation coefficient >0.93. From
the slope (k) of the initial linear portion, the diffusion coefficient D can be calculated as
follows: i
D=-^(k02 : (5-2)
The permeability P is obtained by
P = D»S ! (5-3)
where S is the solubility which can be determined from the equilibrium mass gain, Meq (as
described in the Section 2.5.7). The values of D, S, and P for CO2 sorption to PG and 6P
samples at various exposure times are listed in Table 5.2.5. In Figures 5.2.9 and 5.2.10,
the permeabilities for both films are plotted as aifunction of the duration of Weather-
Ometer® exposure. As seen in the figures, the relationships between the permeabilities and
duration of exposure showed quite different trends for the two samples, although both
films are made up of similar materials, i.e. low density polyethylene. The permeability for
PG film increased linearly with the duration of exposure which is consistent with the result
of the linear relationship between the WVTR and the outdoor exposure time as shown in
Figure 5.2.2. The data for the (ethylene-carbon monoxide) copolymer (6P) samples, how-
ever, showed decreasing curvature with a sharp'decline in permeability during the first 50
hours of osure.
Inci >e in permeability in the PG films made of LDPE/MX can be explained in terms
of plasticization by the sol fraction generated during oxidation. Generation of sol
molecules during catalyzed autoxidation of polyethylene is well established. Early decrease
in tensile modulus on exposure(see Table 5.2.6) is also consistent with the generation of
sol molecules. At longer durations of exposure, however, the modulus increases, indicat-
ing crosslinking of the matrix. Apparently the plasticizing effect of the sol fraction more
than offsets any reduction in diffusion brought about by the crosslinking, yielding a net
increase in permeability and water vapor transport rate (WVTR) with duration of exposure.
Table 5,2.6 compares transport parameters and tensile moduli for PG and 6P.
In the case of (ethylene-carbon monoxide) copolymer (6P), ph 'odegradation is pre-
dominantly a Norrish n type reaction which does not result in free-iv .cal formation.
However, the terminal unsaturation and methyl ketones resulting from the Norrish n pro-
cess are readily autoxidizable. These would promote free radical processes within the
matrix. These secondary oxidation reactions m^y involve radical-radical interactions
5-14
-------
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5-15
-------
Table 5.2.6. Comparison of Transport Parameters and Tensile Modulus of Photodegradable
Films Weathered in Weather-Ometer®.
Type
Plastigone
PG
(0.034 mm)
HiCone
6P
(0.42 mm)
Exposure
Time
(hr)
0
50
100
150
200
250
0
50
100
200
250
Diffusion
Coefficient
(xlO'8 cm2/s)
1.68
1.83
2.48
2.32
2.79
2.93
47.0,
33.1
32.0
30.6
30.1
Solubility
(xlO-3)
i 4.53
; 4.83
5.64
; 6.40
1 6.47
7.18
: 2.16
2.12
2.07
2.08
2.05
Permeability
[xlO-10cc/
(cm.s.cmHg)]
0.761
0.884
1.399
1.485
1.805
2.104
10.2
7.02
6.62
6.36
6.17
Modulus
(kg/mm2)
15.1
12.6
16.0
20.8
23.1
26.6
16.8
30.3
36.5
37.2
37.4
5-1.6
-------
leading to crosslinking. Such crosslinking is extensive and has been reported to render a
fraction as high as 30 percent of polymer insoluble [Cornell et al, 1984]. The tensile
modulus of (6P) films exposed in a Weather-Ometer® does show an increase consistent
with crosslinking. Such increased moduli cannot be explained solely in terms of the
Nonish II process. However, the free-radical processes in the 6P material do not lead to
plasticization via sol formation. The permeability therefore decreases with the duration of
exposure, as the effect of crosslinking and consequent decrease in diffusivity override the
effects of any minor amounts of sol generated.
It is not unreasonable to expect crosslinking in both processes but sol formation in the
case of PG material only. PG is a metal pro-oxidant catalyzed polyethylene (LDPE) system
where the chain scission reaction is accelerated relative to that in regular LDPE. Multiple
scission events on the same macromolecular chain are more likely to occur in such a cat-
alyzed system. In the 6P material, the free-radical process is a secondary phenomenon,
occurring at a slow rate. In a thick sample (/- 0.42 mm), the oxidation is likely to be
diffusion-controlled with the radicals undergoing combination leading to crosslinking.
Multiple scissions on the same macromolecular chain leading to sol formation are likely to
be very limited.
5.3 DEVELOPMENT OF METHODOLOGY TO DETERMINE CHANGES IN
STARCH CONTENT IN LDPE/STARCH BLENDS
5.3.1 TGA of Unweathered Samples
To determine the starch content of ADM (LDPE/starch) samples, thermogravimetric
analysis (TGA) was used. Upon heating the ADM film samples to 450°C at a heating rate
of 10°C/min. in He, a rapid step decrease in weight was seen in the temperature range of
270°C to 350°C, followed by a second large decline in weight at temperatures above 380°C,
Figure 5.3.1 shows a typical TGA tracing for unexposed ADM film containing 6% starch.
The initial weight loss is apparently due to pyrolysis of starch within the LDPE matrix,
while LDPE itself pyrolyzes from about 380°C. A TGA tracing for regular LDPE film is
shown in Figure 5.3.2. For LDPE/starch films, weight loss at the lower temperature range
should^be proportional to starch content. Percent weight losses in the temperature range of
250 to 350°C are listed in Table 5.3.1 for unexposed ADM(2) samples containing various
weight percents of starch. The starch contents listed in column 2 of the table are the values
provided by the manufacturer. A good linear relationship between the weight loss (TGA)
and the known starch content of the film was obtained with a correlation coefficient of 0.98
as shown in Figure 5.3.3.
5-17
-------
Table 5.3.1 TGA Data for ADM (LDPE/Starch), LDPE Mixes, and ADM(2) Films
with Different Starch Contents.
Type Weiaht Fraction* Percent Decrease in
weignt fraction
ADM Film Samples
ADM(2)
ADM/LDPE Mixes
ADM(l)
0
0.02
0.04
0.06
6.08
0.10
0.12
0
6.197
0.333
6.501
0.675
0.803
1.00
0.35
1.92
2.17
5.40
6.46
7.66
8.75
0.44
1.73
2.72
3.79
4.73
5.59
6.84
For ADM(l) series, weight fractions are accurately known and indicate
the amount of ADM material containing 6% starch blended with LDPE.
For ADM(2) series, weight fractions of starch are approximate and were
provided by manufacturer.
For ADM(l) series, At = 194-350°C.
For ADM(2) series, At = 250-350°C
5-18
-------
To further validate the method, a second series of samples was prepared by mixing
ADM film samples* containing 6% starch with regular LDPE film of the same thickness.
The LDPE compound used was the same used in ADM (LDPE/MX). The minced shreds
of film samples were placed in the same sample pan and subjected to TGA analysis. In
Figure 5.3.4 the percent weight losses in the temperature range 194 to 350°C are plotted
against the weight fraction of ADM in the mixture of the ADM and LDPE. The data are
listed in Table 5.3.1. As expected, the weight loss obtained by TGA increased linearly
(correlation -1.0) with the weight fraction of ADM (or the fraction of starch in mixture). It
is apparent from Figures 5.3.3 and 5.3.4 that TGA can form the basis of an accurate test
method to rapidly determine the starch content in LDPE.
5.3.2 Effect of Biodeterioration of ADM Samples on TGA
(a) Outdoor Soil Burial
TGA measurements were carrried out on ADM(l) films exposed outdoors in a soil
environment, and the results were compared with those for unexposed samples. Table
5.3.2 shows the percent weight decrease in the temperature range 250 to 350°C, WD, for
the samples exposed to different durations. The WD values for 6'to 12 weeks exposure
were smaller than WD for unexposed samples, as might be expected. However, the values
for samples with 16 and 20 weeks exposure were larger compared to the control. Assum-
ing the weight decrease, WD, is totally due to pyrolysis of the starch, percent of residual
starch content after exposure (presumably due to biodegradation of starch) is expressed as
the following:
% residual starch = WD of exposed ADM - WD of unexposed LDPE
WD of unexposed ADM - WD of unexposed LDPE
content after exposure
The calculated values of WD are shown in Table 5.3.2.
The average value of weight loss obtained for unexposed LDPE samples was 0.35%
(Figure 5.3.2), possibly due to losses in low molecular weight additives. The starch con-
tents of ADM samples after exposure for 6 to 12 weeks outdoors were almost constant and
were generally about 10 percent lower than that of the unexposed sample. This suggests
that the 10 percent of starch in LDPE/starch blends can be consumed in relatively short
exposure times, but little change in starch content occurs thereafter, even for fairly long
exposure times. Surprisingly, the determined starch contents for 16 and 20 weeks expo-
sure were observed to be larger than that for unexposed samples of ADM films. This was
probably due to limitations of this technique in determining starch content of extensively
deteriorated samples. Heavily deteriorated films often contain fungi and other organisms
5-19
-------
Table 5.3.2. Effect of Environmental Exposure on Starch Content of ADM Film Samples.
Exposure
1 . Outdoor soil burial
2. Laboratory soil
burial at 37°C
3. a-amylaseat37°C
4. Soil innoculum at
37°C in mineral salt
medium
Duration
(week)
0
6
10
12
16
20
0
16
0
16
0
16
0
6
0
6
Initial Starch
Content
(%):
~6 ;
~ 2
>
~6 i
-12
~6 ;
~6
% Weight Change
at250°-350°C
5.20
4.59
4.98
4.58
5.85
6.19
1.92
1.73
5.40
5.03
8.75
7.69
5.61
5.20
5.61
4.96
% of Residual
Starch Content
87
95
87
>100
>.100
-
88
_
93
_
87
.
92
-
88
Note: :
(a) No shredding, cutting, or grinding was used to increase the surface area of film samples
exposed to microbes
(b) Total weight change was assumed to be due to complete pyrolysis of starch
(c) % residual = % wt. decrease of exposed ADM - % wt. decrease of LDPE [ADMC] .-_
Starch content % wt. decrease of unexposed ADM - % wt. decrease of LDPE [ADMC]
after exposure
5-20
-------
growing within the plastic matrix. These, especially the cellulosic material, would prob-
ably pyrolyze at about the same temperature as starch and therefore interfere with the deter-
mination of weight loss. A second possibility was interference due to photothermal oxida-
tion of the polyethylene due to exposure. In a metal compound catalyzed system, oxidation
can yield low molecular weight oligomers and reaction products. Volatilization of these
compounds also interferes with the determination.
Figure 5.3.5 is a TGA tracing for an ADM sample exposed 20 weeks outdoors
showing weight losses at temperatures as low as 180°C. Accurate determination of weight
loss by TGA requires a tracing which is essentially flat at lower temperatures.
(b) Effect of Starch Content on WD
ADM(2) film samples specially prepared by the manufacturer with various starch
contents (2, 6, and 12%) were exposed in the laboratory (accelerated soil under aerobic
conditions) for up to 114 days. The percent weight decrease and the percent change in
starch content for these exposed and unexposed ADM(2) samples are listed in Table 5.3.2.
As can be seen from the table, the higher the percentage of starch contained in the sample,
the larger is the percent residual starch as obtained by TGA of unexposed material. This
high degree of correlation obtained suggests the technique to be a sensitive one. The per-
cent change in starch content after exposure, however, was generally independent of initial
starch content of the sample and was about 10 percent lower for all three starch contents.
(c) Tests on Other Samples
Both enzymatic and aerobic exposures were attempted to enhance the biological dete-
rioration of ADM(3) film samples. An amount of enzyme (a-amylase) derived from
Bacillus sp. (type Xl-B having an activity of 575 units/mg protein) sufficient to hydrolyze
the starch in the sample was placed in contact with the sample film in buffer solution (pH
6.9) at 37°C for 46 days. Enzyme solution was replaced twice during this period of expo-
sure.
Samples were also placed in a soil environment with added urea and phosphate under
aerobic conditions at 37°C in the dark. As shown in Table 5.3.2, only a 10% decrease in
starch content after exposure was again observed for both types of samples.
From trie above results, it appears that in soil burial exposure of a film sample of
ADM, the starch content of the sample decreases by about 10% within a relatively short
exposure time (< 6 weeks), but this decrease in starch content does not continue for longer
exposure times. In the presence of light or heat (such as in composting), additional chemi-
cal mechanisms are available for disintegration of material, and the rate of starch loss might
be higher.
5-21
-------
During exposure, only those starch particles near the surface of the film are likely to
be decomposed rapidly by means of enzyme action. Assuming the starch particles to be
uniform and to be distributed homogeneously throughout the whole LDPE matrix, the
starch decomposed would then be that which exists in 5% of the total film thickness,
approximately 3 |im from each side of the film. The thickness of this thin layer at the sur-
face corresponds approximately to the average particle size of the starches blended in
LDPE, suggesting that the layer of starch granules exposed or contacted to the surface
would be readily decomposed in aerobic soil-burial exposure.
5-22
-------
REFERENCES
Andrady, A. L. and J. E. Pegram, Weathering of Polystyrene Foam on Exposure in Air
and in Seawater, J. Appl. Polymer Sci, 42, 0000-00 (1991).
Cornell, J. H. , A. M. Kaplan, and M. R. Rogers, Biodegradability of Photooxidized
Polyallcylenes, J. Appl. Polym. Sci.,_29, 2581-2597 (1984).
George, G. A. and D.K.C. Hodgeman, Photooxidation of Polystyrene - The Role of
Impurities as Prodegradants, J. Polymer Sci.: Symposium No. 55, 195-200 (1976).
Rabek, Jan F. and Bengt Ranby, Studies on the Photooxidation Mechanism of Polymers.
L Photolysis and Photooxidation of Polystyrene, J. Polymer Sci.: Polymer
Chemistry Edition, 12, 273-294 (1974).
5-23
-------
6.0-
4.0-
35
40 45
Volume (mL)
O Unexposed
• 14 Days
G 29 Days
• 64 Days
Figure 5.1.1 (a) Molecular weight distribution (as measured by GPC) of exposed
polystyrene foam - (PS - Outdoor - Chicago, IL).
40 ; 45
Volume (mL)
O Unexposed
• 14 Days
D 29 Days
• 57 Days
Figure 5.1.1 (b) Molecular weight distribution (as measured by GPC) of exposed
polystyrene foam - (PSC - Outdoor - Chicago, IL).
5-24
-------
6.0-
35
40 45
Volume (mL)
O Unexposed
© 2 Weeks
D 6 Weeks
H 10 Weeks
50
Figure 5.1.1 (c) Molecular weight distribution (as measured by GPC) of exposed
polystyrene foam - (PS - Outdoor - Miami, FL).
35
40 45
Volume (mL)
O Unexposed
• 2 Weeks
D 4 Weeks
B 6-Weeks
Figure 5.1.1 (d) Molecular weight distribution (as measured by GPC) of exposed
polystyrene foam - (PSC - Outdoor - Miami, FL).
5-25
-------
40 , 45
Volume (mL)
50
O Unexposed
• 7 Days
O 29 Days
• 35 Days
Figure 5.1.1 (e) Molecular weight distribution (as measured by GPC) of exposed
polystyrene foam - (PS - Marine floating - Miami, FL).
40 ; 45
Volume (mL)
O Unexposed
® 43 Days
58 Days
Figure 5.1.1 (0 Molecular weight distribution (as measured by GPC) of exposed
polystyrene foam - (PSC - Marine floating - Miami, FL).
5^26
-------
6.0-
4.0-
Unexposed
14 Days
21 Days
28 Days
40 45
Volume (mL)
Figure 5.1.1 (g) Molecular weight distribution (as measured by GPC) of exposed
polystyrene foam - (PS - Marine floating - Seattle, WA).
IX!
40 45
Volume (mL)
O Unexposed
• 14 Days
Q 21 Days
B 28 Days
Figure 5.1.1 (h) Molecular weight distribution (as measured by GPC) of exposed
polystyrene foam - (PSC - Marine floating - Seattle, WA).
5-27
-------
6.0-
O Unexposed
« 50 Hours
D 150 Hours
• 250 Hours
Volume (mL)
Figure 5.1.1 (i) Molecular weight distribution (as measured by GPC) of exposed
polystyrene foam - (PS - Weather-Ometer®).
5-28
-------
I
1
0 2 4 68 10 12
Permeation Time (days)
Figure 5.2.1 Water vapor transmission data for LDPE/MX samples weathered in Miami,
FL.
5-29
-------
a
o
cr
0.20
0.18
0.16
0.14
0.12
0.10
0.08
0.06
0
y = 8.4501e-2 + 3.5412e-3x RA2 = 0.943
10
20
30
Exposure Time (days)
Figure 5.2.2 Change in WVTR with weathering time for PG (LDPE/MX) samples.
5-30
-------
O Unexposed
Aerobic Exposed
Permeation Time (days)
Figure 5.2.3 Water vapor transmission data for PCL (LLDPE/PCL blend) unaged film
and a film exposed to an aerobic biotic environment (40 days).
5-31
-------
Permeation Time (days)
O ADM(l) Unexposed
® 10 Days Weathered
D ADM(3) Unexposed
H ADM(3) Enzyme
Figure 5 2.4 Water vapor transmission data for unexposed and weathered ADM
° ' (LDPE/starch/MX) films. ;
5-32
-------
'toO
£
-o
,0
s-l
o
^
o
U
fj
o
a
U.1Z
0.10
0.08
0.06
0.04
0.02
OAA I
i i . ~T nr- r- . ,
A A A & A A A
*
Ae$iid^~
A
. AE _ Q D a n a
A gj Q "
A ^ Q
au
&i D « ® ® • © •
g o o o o o
• *A 0° © §
MSQ ©
' ° ©
^^^ ©
"J 8
.1%
%
?r, i 1 - i i i , i
O Unexposed
© 50hr Exposed
Q lOOhr
• 150hr
A 200hr
* 250hr
.UU fe ~~ — — — ™ F— — n. , .— j
0 100 200 300 400 500
Time (sec)
Figure 5.2.5 Gas (CO2) sorption curves for weathered PG (LDPE/MX) films exposed in
Weather-Ometer®-
5-33
-------
0.06
1
1
i-i
8 0.04
x>
CO
O
O
o
£ 0.02
(••i
£3
5
a
0.00
(
r- r >- -r ^ — — | < — — r •
anOOeO"
S 8 * asr EBT °R Q 1 D ^
02®^BS H* *
0® 1 A
o*S *
°e&
^A
•P :
oH*
^A
"fe
g^,
f
. , i i | ' • I i »
O Unexposed
® 50hr Exposed
a lOOhr
B 200hr
A 250hr
3 1000 2000 : 3000 4000 5000
Time (sec)
Figure 5.2.6 Gas (CO2) sorption curves for weathered 6P (ethylene-carbon monoxide)
copolymer films exposed in a Weather-Ometer®.
5-34
-------
1.2
1.0
0.8
0.6
0.4
0.2
0.0
© © ©
• 0
e o
c
e o
e
o
0
j—__4_
10
15
20
O Unexposed
© 250bir Exposed
25
Figure 5.2.7 Difference in short-time gradient in sorption curves for aged and unaged PG
samples.
5-35
-------
1.2
1.0 -
0.8
0.6
0.4
0.2
0.0
o ©
o •
•
o •
«
0
20
40
g ^5 @©@O®
O Unexposed
• 250hr Exposed
60
80
Figure 5.2.8 Difference in short-time gradient in sorption curves for aged and uriaged 6P
samples.
5^36
-------
200
300
Exposure Time (hours)
Figure 5.2.9 Effect of Weather-Oraeter® exposure upon the CO2 permeability for PG
material.
5-37
-------
11
-T
4)
O, 9
o
>-»
4—*
;=}
I
0
100
200
300
Exposure Time (hours)
Figure 5.2.10
Effect of Weather-Ometer® exposure upon the CO2 permeability for 6P
material.
5-38
-------
moo
ADM/BI07
8.4137«g RATE, lO.COdeg/min
O
•—i
UJ
3:
75.00
SJ.Q0
FROM« 250. 64
TO) 350. 51
J. »T % CHANGEi 5,34
-4. - . _, ____ ____
• SJ.M 100. DO i«Li» "iSabo
F!L£t OSAVE. TG
3KLOO
EMPERATURE CO
B3.5SX
TG
Figure 5.34 A TGA tracing of LDPE/starch/MX film containing -6% starch.
5-39
-------
10X00
FROM! 250.34
TDi 350. 38
WT X CHANGEi . 35
X
CD
£60.00 +
3=
20.00
LDPE/CSCO%)
WTi .7.6928 mg RATEi 10.00 deg/mln
-L
100.03%
50.00
9C.OO
170.00
210,00
zsaoo
"aaoo"
333.00
370.00
410.00
UNEXPOSED
FILEiADMOX. TC
TEMPERATURE CO
TG
' Figure 5.3.2 A TGA tracing of an LDPE control film.
5-40
-------
Heating Rate: 10°C/min
Percent Weight of Starch in ADM
Figure 5.3.3 Percent weight loss versus known starch content of ADM
(LDPE/starch/MX) films in TGA experiments .
5-41
-------
CO
O
H-l
o
0
0.0
Heating Rate: 10°C/min
0.2
0.4'
0.6
0.8
1.0
Weight Fraction, [ADM/(ADM+ADMC)j
Figure 5.3.4
Percent weight loss versus weight fraction of ADM (LDPE/starch/MX) film
in mixtures of ADM and control LDP.
5-42
-------
100.00
75-°°
50.00
ADM/S-RTI/20WK<2>
FROMi 250. 04
TOi 349.93
WT Z CHANGEi 8. 19
60.00
FILE, OSAYE. TG
9. 1052 mg RATEi 10. 00 deg/min
220.00 260, 00 300.00
TEMPERATURE
TG
Figure 5.3.5 A TGA tracing of an ADM (LDPE/starch/MX) film exposed outdoors for 20
- weeks showing variability in 140°C-260°C range.
5-43
-------
-------
SECTION 6.0
PRELIMINARY TOXICITY STUDIES
The toxicity of the degradation products generated from enhanced degradable plastics
has always been a popular concern. For the most part, however, the products formed
would qualitatively be little different from those formed during the photodegradation of the
base plastic material. Both metal-catalyzed and uncatalyzed photooxidation of polyethylene
will essentially result in similar products.
However, the rate of generation of these products is much higher in the case of
enhanced degradable plastic materials. Since the rate of leaching (or diffusing out) of these
from the plastic matrix will consequently be faster, higher local concentrations of products
are likely to occur in the micro-environment about the degrading plastic film. As the toxi-
• city is determined by the concentration to which the organism is exposed, both the identity
and the kinetics of generation of the products of degradation needs to be addressed. The
main issue is then to determine if any of the compounds accumulate at a rate high enough to
allow the build up of unacceptably high local concentrations.
The comprehensive toxicity studies needed to'address these concerns were outside the
scope of this study. Such an exercise should ideally involve a study of rates of generation
of compounds, soil microbial toxicity assessments as well as standardized toxicity studies
(such as the EPA-accepted acute and chronic tests). It was, however, felt that some
exploratory testing was needed to establish the toxicity of extracts from partially degraded
photodegradable plastics to form the basis for a detailed study in the future.
Three factors determine the outcome of the toxicity studies:
(a) Test organisms used.
(b) Extent of degradation of the .test plastic material prior to extraction.
(c) Protocol for preparation of test solution ("effluent").
The use of a standard test organism was considered advantageous for the purpose of
this exploratory experiment. EPA has a large database of information on tests carried out
on two species [USEPA, 1989], Ceriodaphnea dubia (water flea) and Pimiphales promelas
(fathead minnow). These indicator organisms are well suited for a test of this nature
because of their importance in the food chain and also because of their cosmopolitan distri-
bution. A second consideration is the extent to which the plastic material is degraded prior
to testing. An undegraded enhanced-degradable plastic film is not likely to be associated
with any toxicity, there being little or no organic materials which are water extractable.
Manufacturers of the enhanced photodegradable plastics have sufficient test data to support
6-1
-------
such a claim. Once exposed outdoors, the plastic material wiH contain extractives, the
amount of which will depend on the duration and location of exposure. In the case of
accelerated laboratory exposure, it will depend upon the spectral qualities of the source in
the equipment as well as the duration of exposiiire. The other key issue is the extraction
procedure to be used to prepare the "effluent" on which the tests are to be carried out. This
is a critical consideration, as even relatively innocuous organic compounds in sufficiently
high concentrations may show biological and tpxicological effects. Florida protocol for
toxicity testing, for instance, proposed the use of one percent by weight (undegraded) of
the plastic in water and a 24 hr 20 - 25°C extraction procedure, to prepare the extract.
Testing was then carried out on a diluted extract equivalent to a concentration of 1 g plastic
in 2400 g of water. The methods under development at the ASTM (subcommittee D20.96)
suggest the use of 2-4 g of degraded plastic material in 1-2 liters of water and extraction
under similar conditions. The latter concentrations were based on considerations of levels
of rainfall to be expected and the incidence of degraded litter under field conditions and are
"worst case" concentrations. Testing in the presence of plastic fragments is acceptable, and
complete filtration is not necessary in the case of this latter approach.
The intent of the testing carried out in this study was not to provide independent unbi-
ased test data on commercially available enhanced degradable plastic materials. Results
should not therefore be construed as being "acceptable" or otherwise under any specific set
of requirements. The aim was more to obtain exploratory data to determine the concentra-
tio" of extractives which may show biological effects for the two species in question. As
sut , the prc nt work used the following basic experimental cond* ns.
(a) Tt,, organisms: Ceriodaphnea dubia (water flea) and Pimiphales promelas
(fathead minnow)
(b) Test method: A modified standard ;test method (given in Chapter 2).
(c) Duration of outdoor exposure: 15 days in Miami, FL under summer conditions.
190 MJ/sq.m total radiation.
(d) Extraction: 20 g (weight after degradation) per liter in distilled water. 24
hours. 20-25°C with moderate stirring. Plastic film cut into 1 cm squares for
extraction. Polystyrene foam ground in blender with water prior to extraction.
(e) Test solutions : A series of solutions ranging from 3-100 percent of the above
stock "effluent" solution. Figure 6.1 illustrates the concentrations in g/1 for
some of these solutions. ,
All testing was done by a subcontractor specializing in toxicity measurement and bio-
logical monitoring studies.
-------
CONCENTRATIONS OF EXTRACTS USED IN TOXICITY TESTS
QMS/LITER
15
10
05
100 percent concentration
20g/l
60 percent concentration
12g/l
3 percent concentration
0.6 g/I
^ ASTM (proposed concentration)
"*"" Florida rule concentration
Figure 6.1 Concentrations of test solutions used in toxicity experiments.
6-3
-------
6.. (ETHYLENE-CARBON MONOXIDE) COPOLYMER
Table 6.1.1 shows the data from chronic toxicity tests using Ceriodaphnea species.
While die data is of a preliminary nature, it suggests the extractives, even at the unrealisti-
cally high concentrations tested, to be without observable toxicity in this test procedure.
All data passes the Chi Square test for normality. The detailed test data was statistically
analyzed both for the control [6PC] and the test plastic [6P]. Fishers Exact test yielded
NOEC values of 100 percent for survival and 60 percent for reproduction. LOEC value for
reproduction calculated using Dunnett's test was 100 percent. NOEC is the concentration
at which no effect is observed, and LOEC is the concentration at which the least effect is
observed.
Table 6.1.2 shows acute toxicity test data using Pimiphales promelas species. Again
the test data show high levels of survival except at the very high concentrations. The
LC(50%) value is 91 percent for the enhanced degradable material and 100 percent for the
control polymer. Since these concentrations are higher than those commonly employed, it
is not surprising that the manufacturers claim the copolymer to pass the various state and
EPA toxicity tests.
Special attention was paid to this particular enhanced degradable material in view of
its use in six-pack rings. While the testing reported is not expected to be a pass/fail type
test employed to qualify this plastic material, the test results are encouraging, and virtually
no toxicity might be expected under field conditions. The conclusion applies to two species
only and unfortunately cannot be necessarily extended to soil microorganisms and marine
planktons. Further work Involving a wider cross-section of organisms is needed for a
complete assessment.
6 2 POLYSTYRENE BLENDED WITH (STYRENE - VINYL KETONE)
COPOLYMER [PS]
The available resources did not allow the testing of a control sample of polystyrene
foam for this study. Only a single set of test data is therefore available. In the case of
polystyrene foam the possibility of the embrittled, yellow surface layer abrading off the
foam during exposure complicates the interpretation of data. A significant removal of this
layer, particularly rich in water-soluble degradation products, will result in the underesti-
mation of any toxicity. With the 15 day exposures used, it is unlikely that significant
amounts of the surface layer were lost during exposure and sample collection.
6-4
-------
Table 6.1.1 Chronic Toxicity Test Data Summary for (ethylene-carbon monoxide) Copolymer
Material (6P and 6PC). Test Organism: Ceriodaphnea dubia.
Concentration1 Dissolved2
(%) oxygen
(mg)
0 7.1-7.4
3 7.0-7.6
10
30 7.0-7.7
60
100 7.0-8.5
Control
Survival3
(%)
100/100
100/100
100/100
100/90
100/100
100/100
Polymer
Offspring
(Number) -
247
273
288
293
331
139
Enhanced Degradable
Polymer
Survival3
(%)
100/100
100/100
100/100
100/100
100/100
100/90
Offspring
(Number)
245
276
338
385
394
lit
1 100 Percent concentration equals 20 gms degraded polymer/liter
2 Range of pH values from start and end measurements for control and test samples.
3 Survival at 48 hours/7 days are reported.
NOTE:
Test solution renewal: 2 times
Replicates of 1 organism per concentration: 10
Organism age at start of test: 16-24 hours
Test duration: 7 days
6-5
-------
Table 6.1.2 Acute Toxicity Test Data Summary for (ethylene-carbon monoxide) Copolymer
Material (6P and 6PC). Test Organism: Pimephales proinelas.
Concentration1 Dissolved
(%) oxygen
(mg)
0 8.1-8.4
3
10
30 8.1-8.4
60
00 8.0-9.4
Control Polymer
Percent Survival
i
100
100
100
100
100
165
Enhanced Degradable
Polymer
Percent Survival
100
100
100 .
100
100
35
1 100 Percent concentration equals 20 gms degraded polymer/liter
NOTE:
Number of organisms per concentration: 20
Replicates per concentration: 2 ;
Organism age at start of test: 8 days
Test duration: 96 hours •
6-6
-------
Table 6.2.1 shows the data from chronic toxicity tests using Ceriodaphnea species.
Biological effects begin to be noticed only at the 60 percent concentration. All detailed test
data was tested for homogeneity (Bartiett's test) and for normality (Chi Square test).
Fishers Exact test yielded NOEC values of 60 percent for survival and 30 percent for
reproduction. LOEC value for reproduction calculated using Dunnett's test was 60 percent.
Due to non-availability of test data for control samples, it is not clear if the biological effects
at veiy high concentrations are solely associated with enhanced degradable polymer or are
generally common to all polystyrene.
Table 6.2.2 shows acute toxicity test data using Pimiphales promelas species. The
data shows some toxicity to this species at very high concentrations. LC 50% value based
on the data is about 25 percent, with 95% confidence limits of 18.7 to 32.5 percent.
It should be appreciated that the concentration of test solution (the 100 percent solu-
tion) was very high, nearly 25-50 times that used in the various test protocols discussed in
Section 6.0. The 3 percent concentration is close to the concentrations generally employed
in pass/fail type tests proposed by state authorities and the ASTM. This material does not
show any significant toxicity at these lower concentrations typical of what might be
expected under field exposure conditions. The comments on the need for more complete
testing given in section 6.1 apply to this material as well.
6.3 LDPE/STARCH/MX MATERIAL [ADM FILMS]
In this instance as well, resource limitations did not allow the inclusion of a control
sample in the experiment. The manufacturer (Archer Daniels Midland Company) provided
resources to test a control sample to allow more complete interpretation of data. The
extract from the ADM material stored in a refrigerator for a few days before testing
developed growth (possibly fungal) which was filtered out before testing. As the effect of
this growth on the test result cannot be determined, the data presented must be regarded as
preliminary.
Table 6.3.1 shows the data from chronic toxicity tests using Ceriodaphnea species for
the ADM material. Biological effects become apparent at the 30 percent level of concentra-
tion. However, Fishers Exact test shows NOEC for survival and for reproductive effects
at 3 percent level of concentration. This concentration is-close to that used in the pass/fail
tests. Therefore, the enhanced degradable ADM material might be expected to be accept-
able under the state and ASTM type toxicity test requirements.
Table 6.3.2 shows acute toxicity test data using Pimiphales promelas species. The
data shows no measurable toxicity to this species and the LC (50%) concentration is greater
than 100 percent. Interestingly, the control plastic material with no starch/MX does show
6-7
-------
Table 6.2.1 Chronic Toxicity Test Data Summary for Polystyrene [(styrene-vinyl
ketone) copolymer blends] Copolymer Material (PS).
Test Organism: Ceriodaphnea diibia.
Concentration1 Dissolved2
(%) , oxygen
(mg)
0
3
10
30
60
100
7.5-7.6
7.6-7.6
-
7.5-7.8
-
7.5-8.4
i Enhanced Degradable
Polymer
Survival3
i (%)
; 100/100
: 100/100
100/100
1 100/100
; 90/80
: 0/0
Offspring
(Number)
263
291
231
237
117
-
1 100 Percent concentration equals 20 gms degraded polymer/liter
2 Range of pH values from start and end measurements for control and test samples.
3 Survival at 48 hours/7 days are reported.
NOTE:
Test solution renewal: 2 times
Replicates of 1 organism per concentration: 10
Organism age at start of test: 16-24 hours .
Test duration: 7 days
6-8
-------
Table 6.2.2 Acute Toxicity Test Data Summary for (polystyrene/(styrene-vinyl ketone)
blends) Copolymer Material (PS). Test Organism: Pimephalespromelas.
Concentration1
(%)
0
3
10
30
60
100
Dissolved
oxygen
7.6-8.0
•-
-
7.4-8.2
•
6.2-6.7
Enhanced Degradable
Polymer
Percent Survival
90
95
85
70
10
0
1 100 Percent concentration equals 20 gms degraded polymer/liter
NOTE:
Number of organisms per concentration: 20
Replicates per concentration: 2
Organism age at start of test: 8 days
Test duration: 96 hours
6-9
-------
Table 6.3.1 Chronic Toxicity Test Data Summary for LDPE/starch/MX (ADM film) Material
(ADM). Test Organism: Ceriodaphnea dubia.
Concentration1 Dissolved2
(%) oxygen
(mg)
0 7.7-8.0
3 7.7-8.1
10
30 7.8-8.1
Control Polymer EnHanCpe^gadable
Survival3 Offspring Survival3
(%) ; (Number) (%)
100/90
100/50
80/0
; 0
Offspring
(Number)
222
119
112
0
1 100 Percent concentration equals 20 gms degraded polymer/liter
2 Range of pH values from start and end measurements for control and test samples.
3 Survival at 48 hours/7 days are reported.
NOTE:
t
Test solution renewal: 2 times
Replicates of 1 organism per concentration: ,10
Organism age at start of test: 16-24 hours
Test duration: 7 days
6-10
-------
Table 6.3.2 Acute Toxicity Test Data Summary for LDPE/Starch/MX (ADM) Material.
Test Organism: Pimephalespromelas.
Concentration1
(%)
0
3
10
30
60
100
Dissolved Control Polymer
°(mg)n Percent Survival
7.9-7.9
-
-
7.8-7.9
-
7.6-8.4
Enhanced Degradable
Polymer
Percent Survival
100
100
100
100
100
100
1 100 Percent concentration equals 20 gms degraded polymer/liter
NOTE:
Number of organisms per concentration: 20
Replicates per concentration: 2
Organism age at start of test: 8 days
Test duration: 96 hours
6-11
-------
toxicity at 100 percent concentration. This reflects the experimental variability that might be
associated with a test of this nature. There is no reason to expect the control sample to gen-
erate an extract more toxic than the test sample; However, since different populations or
organisms were used in the two tests, some degree of variability was unavoidable.
6.4 CONCLUSIONS I
An assessment of the impact of using enhanced-degradable plastics as a solid-waste
management strategy must take into account the possible toxicity of degradation products.
While the nature of the breakdown products is iikely to be the same with enhanced-
degradable polymers as well as regular polymers, the former allows these products to be
accumulated faster in the environment
A comprehensive approach to studying toxicity of leachate from degrading polymers
to soil biota demands a broad study. In addition to standard test species, a wide selection
of soil microbes, marine microorganisms, phytoplanktons, algae, and at least the key mem-
bers of the primary food chain should be included in such a study.
The study reported in this chapter was not undertaken to generate such information
because such a task would be outside the scope of this effort The goal in this project was
to conduct selected standard toxicity screening tests and to determine if the leachate
showed marked toxicity. The data from the two tests did not show any toxicity at realistic
levels of leachate concentrations.
REFERENCE
USEPA 1989. "Short term methods for estimating chronic toxicity of effluents and receiv-
ing waters to freshwater organisms. EPA/600/4-89/001 Method #1002.0
6-12
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SECTION 7.0
PRELIMINARY RECYCLING STUDY
7.1 SAMPLE COMPOSITION
The compositions of films for the preliminary recycling study were identified in
Table 2.7.2. The enhanced degradable plastics selected for the preliminary study were the
enhanced photodegradable types: 6P and PS materials contain main-chain functional groups
which absorb solar radiation to cause direct hond scission; PG and ADM contain metal
complexes which use light to catalyze then 3xidative reactions. All these materials
demonstrated (see Section 4.1.3) significant changes in physical properties after relatively
short dt ons of outdoor weathering. Exposure durations of approximately 5, 10, and 15
days in Miami, FL were chosen for the recycling study. During this interval, degradation
appeared to be the most time-dependent, e.g., a plot of the physical property used to
measure degradation versus exposure time showed the greatest change in slope for this ttoe
interval for all samples except PS. The levels arbitrarily selected for percent of exposed
degradable material in the extruded films were 5,10, and 20%.
7.2 TENSILE PROPERTIES OF RECYCLED MATERIALS
The polyethylene-based extruded films containing exposed degradable plastics were
tested on an Instron Model 1122 according to the procedure described in section 2.5.1,
using a gauge length of 5.0 cm and a crosshead speed of 500 mm/min. The polystyrene
films were too brittle and thin to be tested. Future, more detailed recycling studies will
require an alternate method such as gel permeation chromatography for testing the proper-
ties of polystyrene films.
Only unexposed films were tested for this preliminary study; this data can be used to
study the effects of introducing small amounts of degradable plastic into the recycling
stream and the resulting quality of the extruded plastic. Further studies will be needed to
study the effects of the presence of enhanced degradable material on the weatherability of
the recycled plastic.
Table 7.2.1 shows the tensile properties of the extnided films identified in Table
2.7.2. Inclusion of low levels of 6P and PG material with the virgin resin did not seem to
have any detrimental effects on the properties of the extruded film; in fact, both strength
and flexibility were enhanced by low concentrations of the degradable material, probably
due to a plasticizing effect. For a given duration of exposure of the degradable m 'erial,
7-1
-------
7-2
-------
7-3
-------
however, both strength and elongation tended to decrease as the percent of degradable
material increased from 5 to 20%. ;
Extrusion of films containing ADM material was complicated by the presence of
starch. The presence of unexposed ADM in virgin LDPE did not adversely affect the
tensile properties of the extruded film, but with the extrusion conditions used for this pre-
liminary study, the presence of ADM exposed for as little as 5 days resulted in films which
were striated and very uneven in thickness. Additional studies are needed to optimize the
extrusion parameters for films containing pre-exposed (partially degraded/deteriorated)
ADM material.
It must be pointed out that the base resin used for this experiment was a medium-
density polyethylene. The polyethylene-based enhanced degradable plastics used in the
study were low-density polyethylenes.. The blending of polyethylenes of different densities
may also lead to variations in physical and mechanical properties. Of particular interest is
the effect of including partially degraded enhanced-degradable polymers in a recycling
stream on the weatherability of the recycled material. This aspect of the problem, however,
was beyond the scope of the present investigation.
7-4
-------
i,ACTION 8.0
CONCLUSIONS' AND RECOMMENDATIONS
The main conclusions, based on the findings given in thi- -al Report, are sum-
marized below along with recommendations base "•. the find! . ,
NOTE:
6P: Ethylene-carbon monoxide (~ 1 %) copolymer used in six-pack ring applica-
tions.
PG: Metal compound/low-density pol; 'lylene used in mulch and packaging
applications
ADM: Low densi",, polyethylene/6% starch/metal compound system. Used in mulch
and packaging applications.
PS: Expanded, extruded polystyrene containing carbonyl groups to render it
enhanced-photodegradable. Used in packaging applications.
8.1 . INCLUSIONS
(a) General Findings
1. Studies on me activation spectra for loss in tensile elongation at break of the
enhanced photodegradable polyethylene materials studied (6P, PG) show the region
of the sunlight spectrum most likely to cause the degradation to be < 340 nm.
Window glass (float glass) does transmit some of these wavelengths; the performance
of enhanced photodegradable plastics behind window glass must therefore be exper-
imental!^ established and not assumed.
2. A rapid thermogravimetric method suitable for reliable determination of starch content
in polyethylene/starch blends was developed in the study. This method was found to
be suited to study partially degraded films during early stages of degradation as well
and will result in considerable savings in time and effort in determining residual
starch contents in starch/polymer systems.
3. Data on the temperature d . -andence of the light-induced degradation in enhanced
photodegradable plastic products films are not readily available in the literature.
Studies carried out in the present research effort show that (a) the rate of photodegra-
dation of six-pack ring material (ethylene-carbon monoxide copolymer containing
-1% CO) is not affected significantly by temperature (65°C - 85°C); (b) both PG and
ADM systems show temperature dependence of degradation in the same temperature
range, with the latter being more sensitive to temperature.
8-1
-------
4. Gas permeability of pla&t, films, an important cl acteristic to be considered in pack-
aging applications, changes on photodegradation. In PG and 6P materials, where the
photodegradation occurred at an accelerated rate, carbon dioxide transport rates were
found to change markedly with duration o,f exposure.
In 6P samples, permeability decreased with extent of photodegradation by 40 percent
in 250 hours of Weather-Ometer® exposure. This decrease was due mainly to
decreasing diffusion coefficient.
In PG samples, the permeability increased by about 275 percent during the same
exposure, with increases in both the diffusion coefficient and the solubility contri-
buting to the increase. The finding is explained in terms of merged crosslinking as
well as generation of sol material in the case of PG material dur g oxidation. The 6P
material apparently undergoes crosslinking and/or crystallinity ing oxidation.
5. Water vapor transmission rate (WVTR) of films was also affected by enhanced
photooxidative degradation. A 10 day weathered sample of the ADM material, for
instance, showed a 30 percent increase in!WVTR. In the case of PG samples, the
increase in WVTR was measured as a function of the exposure time. With PCL
films, however, 40 days of aerobic soil exposure in the lab did not result in any
measurable change in the WVTR. j
(b) Outdoor Exposure
6. Variations of several different tensile test properties with the duration of exposure for
two enhanced photodegradable plastics at two exposure locations were studied to
determine the tensile test property most sensitive to weathering-related changes.
The results showed the elongation at break (or extensibility) and the ener^, £0 break
to be the test parameters most sensitive to, weathering-induced changes. The former
is more convenient to measure and was adopted for monitoring disintegration for the
purpose of this study.
7. Four types of enhanced photodegradable plastics studied showed marked increases in
the rate of breakdown compared to control materials, as indicated by loss in extensi-
bility (or tumbling friability data in the case of polystyrene) on exposure to outdoor
conditions. The increase could be conveniently quantified using the ratio of empiri-
cal rate constants for enhanced degradable and control materials, and this ratio is
called "enhancement factor" in this study.
Average values of enhancement factors obtained for the different samples were as
follows:
8-2
-------
PG (0.03 mm film) = 4
ADM (0.05 mm) film = 15
6P (0.42 mm film) = 7
PS (1.96 mm foam sheet) = 1-2
These numbers are average values and should not be compared to each other due to
different thicknesses of films used. They do, however, indicate the degree of
enhancement associated with film thicknesses typically used in applications such as
six-pack rings and mulch films. Note that the factor for polystyrene foam was based
on tumbling friability measurements. Films exposed outdoors generally embrittled
during the period of observation.
8. The effectiveness of the photodegradable plastic materials, as indicated by the value
obtained for enhancement factor, depended on the geographic location of exposure.
This was anticipated on account of different levels of sunlight and ambient tempera-
tures at each location. A knowledge of location-dependent variability is of interest in
formulating guidelines for standardizing and for legislative purposes.
9. In the case of enhanced photodegradable plastics, where light -xpected to be the
predominant factor responsible for degradation, good correlation between loss in
extensibility and the amount of light received by the sample is expected. However,
the data for three types of photodegradable plastics showed only moderate levels of
correlation with light levels. Other factors such as temperature possibly influence the
rates of breakdowns of these plastic materials.
10. The order of exposure sites ranked in terms of degradation rate varied for the different
types of enhanced degradable plastics, although the Wittmann, AZ location was gen-
erally tht ^.ifshest. This lack of agreement suggests that while light might be the pri-
mary factor determining the rate, other factors such as temperature and even rainfall
might be significant
11. Photodegradable polystyrene foam degradation was predominantly a surface phe-
nomenon with surface yellowing and development of an embrittled layer with the
duration of exposure. Yellowness Index of samples increased with duration of expo-
sure.
The average enhancement factor of 1.5 obtained on the basis of tumbling fri-
ability measurements was verified using Gel Permeation Chromatography studies of
changes in number average molecular weight The average rest', from the latter
experiment for Miami, FL and Seattle, WA locations was 1.8, a value which agreed
well with that based on the mechanical property measurement
8-3
-------
12. In Weather-Ometer® studies, not surprisingly, nearly all enhanced photodegradable
plastics tested showed faster rates of degradation. However, the acceleration factor
(how much faster the degradation proceeded as compared to outdoor exposure) was
not the same for each material. PS foam material showed the highest acceleration of
12-20 times the outdoor rate depending on the location being compared. ADM, PG,
and 6P samples showed accelerations of only 1-5. Comparisons of the accelerated
rate of degradation with that obtained in Wittmann, AZ generally yielded the smallest
factors. ;
(c) Marine/Fresh Water Exposure :
13. The foe pes of enhanced photodegradable plastics underwent enhanced breakdown
when exposed outdoors while floating in coastal marine environments (Florida and .
Washington) and in a freshwater lake (Virginia).
The rate of degradation in samples exposed floating at sea as indicated by loss in
extensibility (or based on tumbling friability data for PS samples), was lower than
that obtained for terrestrial exposure at the same location for both enhanced degrad-
able and the control plastic samples. i
This is possibly due to lower temperatures attained by floating samples as opposed to
those exposed on land and also due to shielding of light by foulants.
14. While the rate of photodegradation of plastic films was slower under marine floating
exposure compared to that on land, the breakdown of the control samples was
retarded to a much greater extent than thatlof the enhanced degradable materials. In
some instances the changes in extensibility in the control sample were b£ measur-
able in the same time scale of exposure which resulted in marked loss in. .sensibility
of enhanced degradable film samples.
As a result, the enhancement factors for marine floating exposure of the enhanced
photodegradable films are likely to be much higher than those obtained for exposure
on land at the same location. Accurate values of enhancement factors, however, are
not available for the marine exposures. '
15. In general, the Miami, FL location yielded faster degradation rates as well as faster
enhancement factors than Seattle, WA for the photodegradable materials tested. In
the case of PG san' s, however, the rates were about the -ime for both locations
and samples embr . during the period of observation.
Freshwater expos5- also resulted in enhancement of de iationbuttV -teswere
generally lower tlkui those obtained for either of the mariuo test location^. Only a
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minimal number of. freshwater (lake) exposures were carried out, and the data was
not sufficient to obtain reliable enhancement factors.
16. Enhanced degradable polystyrene foam materials exposed in Miami, FL, exhibited
much faster degradation rates (as measured by GPC) for marine exposures than for
outdoor exposure. The rate of breakdown at sea was found to be 2.5 times that for
land exposure, a reverse of the trend obtained.with other types of enhanced degrad-
able samples. Degradation rates for the control polystyrene material were about the
same for marine and outdoor exposure in Miami, FL.
17. Marine sediment exposures were carried out for those enhanced degradable plastics
where the breakdown was biologically mediated. The BP samples readily biode-
graded under sediment at a rate more than 30 times that obtained when the film was
exposed to sunlight under land conditions. BP films also degraded in a freshwater
lake sediment environment, but the rate was only about 85 percent of that at sea. All
samples were embrittled within 2-4 weeks of exposure.
18. PCL samples designed to biodeteriorate in biotic environments were also subjected to
marine sediment and freshwater lake sediment conditions. The project schedule did
not allow exposure durations in excess, of 21 weeks under these conditions. During
this period under marine sediment exposure, the material lost about 50 percent of its
extensibility; the time scale of observation was not sufficient to fully document the
disintegration process, which was expected to take a longer time under these expo-
sure conditions. Analysis of the polycaprolactone fraction of the blend showed an 18
percent decrease in the number average molecular weight during a six week period of
exposure.
Freshwater lake sediment exposure was carried out for a period of 8 weeks and also
resulted in a 50 percent decrease in extensibility. However, the rate of disintegration
in freshwater was 4-6 times faster than in marine sediment.
Initial exposure in the biotic environment apparently does lead to significant chain
scission in the biodegradable component of the blend, but more extensive degradation
is required before changes in extensibility become apparent
(d) Soil Exposure
19. Enhanced degradable plastic materials designed for biologically mediated breakdown
were exposed under outdoor aerobic soil burial conditions. The project schedule did
not allow exposure durations in excess of 29 weeks under these conditions. The
maximum duration of exposure was too short to observe the disintegration of the
PCL and ADM materials to a significant extent. The extensibilities at the end of 28
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weeks were 406% for PCL films (initial extensibility 717%) and 9% for ADM films
(initial extensibility 90%). In the case of PCL samples, about a 15 percent decrease
in number average molecular weight (GPQ was obtained during this period of expo-
sure. ;
20. Under exposure conditions similar to those discussed above, the BP films rapidly
degraded to give an extensibility of 4% (initial extensibility 61%) at the end of 29
days of exposure. These films seem to biodegrade rapidly under both soil and marine
exposure conditions. BP samples were embrittled by 29 days.
21. In addition to outdoor soil burial exposure, laboratory-accelerated soil burial studies
were carried out The duration of observation, up to 10 weeks, was insufficient to
show any marked deterioration of the PCL and ADM films under these conditions;
longer exposures were not possible because of the project schedule.
The scatter associated with the data was high in comparison to data from outdoor
exposure. It was not clear if the elongation at break was, in fact, a sensitive measure
for study of composite samples such as polyethylene/starch materials.
(e) Other ;
22. Preliminary toxicity studies were carried out using water extracts of partially pho-
todegraded materials.
23. A preliminary blending study was carried out to identify the optimum blend composi-
tions for studying the recyclability of enhanced degradable plastics. The data allowed
the identification of a ratio of virgin/recycled plastics that might be used in a future
recycling study. Establishing the levels of partially degraded post-consumer degrad-
able plastics that might be added to a recycling stream without adversely affecting the
quality of recycled materials is important.
8.2 RECOMMENDATIONS FOR FURTHER RESEARCH
1. The findings relating to rates of breakdown of photodegradable plastics, enhancement
factors, and geographic variability, are based on five exposure locations. Additional
data for alternate locations and exposures carried out in different seasons of the year
will help to complete the documentation of the performance of photodegradable plas-
tics.
2. The above considerations are even more important for the case of marine exposure,
where only two exposure sites were used.: While the data show the photodegradable
plastics, and some biodegradable plastics, to perform adequately under these condi-
tions, a study involving more exposure sites is needed before the observations can be
unequivocally accepted.
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3. A major limitation of this study was the relatively short duration of exposure used,
which did not allow the performance of the biodegradable and biodeteriorable films to
be properly studied. Specifically, the polyethylene/starch system needs to be studied
to establish the limits of its performance. Research on enhanced biodegradable plas-
tics to supplement this research effort is strongly recommended.
4. Further toxicity studies should be carried out to establish the full en ••;"onmental
impacts of the faster production of breakdown products in the case t enhanced
degradable plastics.
5. A full-scale recycling study is needed to unambiguously establish if the inclusion of
small amounts of degraded post-consumer enhanced degradable plastics in a recycling
stream has any impact on the quality of recy- i product. The research should at least
investigate 2-3 types each of enhanced photodegradable and biodegradable materials.
6. New generation starch/PE film.
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