United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-93/162 October 1993
&EPA Project Summary
Weatherability of Enhanced
Degradable Plastics
Anthony L. Andrady
The performance and the associated
variability of several selected enhanced
degradable plastic (EDP) materials was
assessed under a variety of different
exposure conditions. Several commer-
cially available materials, including both
photodegradable and biodeteriorable
plastics, were exposed to direct sun-
light, soil burial, and marine and fresh-
water exposure. Laboratory exposure
consisted of accelerated weathering by
Xenon Arc Weather- Ometer* and labo-
ratory-accelerated soil burial.
Results of this study showed the
elongation at break and the energy to
break to be the tests most sensitive to
weathering-induced changes.
This Project Summary was developed
by EPA's Risk Reduction Engineering
Laboratory, Cincinnati, OH, to announce
key findings of the research project
that is fully documented in a separate
report of the same title (see Project
Report ordering information at back).
Introduction
The use of plastics in packaging and
other consumer applications has led to a
growing fraction of post-consumer plastic
waste in the municipal solid waste stream.
The United States presently generates over
195 mil tons of municipal solid waste an-
nually; of this, about 8% by weight is plas-
tics.
Mention of trade names or commercial products does
not constitute endorsement or recommendation for
Recently, scientific data have been gath-
ered to suggest that plastic waste may be
hazardous to wildlife, especially marine life,
e.g., sea lions and fur seals have been
entangled in plastic debris and marine
turtles and birds have eaten plastic litter.
With EDPs, the intention is to accelerate
the breakdown of plastic material by chemi-
cally modifying the polymer, synthesizing
new environmentally degradable thermo-
plastics, and incorporating additives into
commodity plastic materials to achieve
faster breakdown.
The goals of this study were to:
• study the performance and the
associated variability of several EDP
materials under a variety of different
geographic exposure conditions,
including air, sea, and soil, as well as
laboratory exposure conditions,
• better understand the underlying factors
governing enhanced degradability in
EDP systems including the effect of
enhanced degradation on the water
vapor and gas permeability of selected
EDPs; also study activation spectra of
the enhanced photodegradable plastics
to identify the spectral regions most
effective in bringing about light-induced
degradation.
• study the major products formed
during enhanced degradation of EDP
materials and assess the toxicity of
such products, and
• study the effects on the quality of
recycled products when a small
fraction of partially degraded EDP
materials are included in a recycling
stream
Printed on Recycled Paper
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Procedure
A representative set of sample types
was selected from commercially available
materials by using several criteria such as
type of resin and potential use of the ma-
terial:
• ethylene/carbon monoxide (1%)
copolymer (6P) selected because of
its use as a beverage ring holder in
six-pack packaging,
• polystyrene blended with copolymer
(PS),
• low-density polyethylene containing
metal prooxidant compounds (PG) and
low density polyethylene/6% starch
blends with and without metal
prooxidant compounds (ADM) used in
agricultural mulch films.
• linear, low-density polyethylene/
polycaprolactone (20%) blends (PCL),
• poly (hydroxybutyrate valeirate) film
(BP) (limited testing).
The materials were tested in sheet or
film form. Materials of low-density polyeth-
ylene as close in formulation as possible
to the tested materials were used for con-
trol.
The different types of exposure included:
• outdoor exposure at five locations
• direct weathering
• soil burial
• floating and sediment exposure in marine
and in fresh-water environments
• field soil burial
• laboratory accelerated weathering
(Weather-Ometer)
• laboratory-accelerated burial in different
soils
In general, photodegradable samples
were exposed to direct weathering and to
marine and freshwater floating environ-
ments, and biodegradable samples were
exposed to marine sediment and soil burial.
Other testing included tests for tensile prop-
erties, yellowness index, tumbling friability,
gel permeation chromatography for mo-
lecular weight measurements, water vapor
transmission rate, thermogravimetry to rap-
idly determine starch content of polyethyl-
ene/starch blends, gas transport proper-
ties, and toxicity.
Basic methodologies proposed in the
Quality Assurance Project Plan were
closely followed.
Detailed findings of all tests are given in
the full report.
Results and Conclusions
The study of the possible toxicity of deg-
radation products of the EDPs was limited
to selecting a toxicity screening test and to
determining if the leachate showed marked
toxicity. Data from the modified standard
tests did not show toxicity at realistic lev-
els of leachate concentration.
A limited study was done of the effect of
including a small fraction of partially de-
graded EDP in the composition of a recy-
cling stream. The exposed degradable plas-
tics could not be tested before entering
the stream because the films were too
brittle and thin to be tested. When some
unexposed films were used, both the
strength and flexibility of the extruded film
were enhanced by low concentrations of
degradable material.
The rate of photodegradation of six-pack
ring material (6P) was not affected signifi-
cantly by temperature (65°C to 85°C), but
the degradation of both PG and ADM ma-
terials was temperature dependent at the
same temperatures.
A rapid thermogravimetric method to de-
termine starch content of a polyethylene/
starch blend material was developed and
found suitable to study partially degraded
films and to determine residual starch con-
tent in starch/polymer systems.
The activation spectra for loss in tensile
elongation at break (the most sensitive
tensile property to degradation) was stud-
ied for certain materials. The region of the
sunlight spectrum most likely to cause deg-
radation was found to be <340nm.
In studying the effect of enhanced deg-
radation on gas permeability in PG and 6P
materials, where the photodegradation oc-
curred at an accelerated rate, carbon diox-
ide transport rates changed markedly with
duration of exposure. In 250 hr of Weather-
Ometer exposure, 6P sample permeability
decreased 40% and PG sample perme-
ability increased about 275%. This is ex-
plained by increased crosslinking and gen-
eration of sol material in the PG material
during oxidation and/or crystallinity of the
6P material during oxidation.
Water vapor transmission rate was af-
fected by enhanced photooxidative degra-
dation. A 10-day weathered sample of ADM
increased its water vapor transmission rate
30%. The increased rate for PG samples
was measured as a function of time. Forty
days of laboratory exposure to aerobic soil
did not, however, change the water vapor
transmission rate of PCL film.
When enhanced photodegradable plas-
tics were exposed at outdoor locations:
• the tensile test parameters most
sensitive to weathering changes were
elongation at break and energy to
break;
• the rate of breakdown markedly
increased as indicated by loss in
extensibility, with the ratio between
enhanced degradable and control
materials being called the "enhancement
factor:'
• the geographic location influenced the
photodegradability, with different
degradation rates for different types
of EDPs at the different sites;
• a moderate correlation existed
between loss of extensibility and the
amount of light received;
• the yellowness index increased with
exposure; and
• nearly all materials degraded faster in
the Weather-Ometer studies but not
at the same rates.
When enhanced photodegradable plas-
tics were exposed to marine and fresh
water:
• the loss of extensibility was lower for
the floating samples than for the
terrestrial exposure (possibly because
of lower temperatures and shielding
from light by foulants), with the
breakdown of the marine control
samples being, in some instances,
barely measurable;
• in Miami, FL the degradation rates
and enhancement factors were faster
than they were in Seattle, WA;
• in Miami, the breakdown rate at sea
was 2-1/2 times that for land exposure
of enhanced degradable polystyrene
foam materials and, for the controls,
it was about the same;
• BP samples under sea sediment
degraded at a rate more than 30 times
that of the film exposed on land, and
the fresh-water sediment degradation
rate was about 85% of that at sea;
and
• after 21 wk of marine sediment and 8
wk of fresh-water sediment exposure,
PCL samples lost 50% of their
extensibility.
When the EDP materials designed for
biologically mediated breakdown were ex-
posed outdoors under aerobic soil burial
conditions, the time was too short to ob-
serve any significant disintegration of the
PCL and ADM materials, but under similar
conditions, BP samples degraded rapidly
and were embrittled by 29 days. When
these materials were exposed to labora-
tory-accelerated soil burial, there was no
marked deterioration during the 10 wk ob-
servation time.
Recommendations
Data are needed from additional land
and marine locations and from exposures
at different seasons of the year to com-
plete this documentation of photodegrad-
able plastics. Longer observation periods
are needed to establish limits of the per-
formance of biodegradable and
biodeteriorable films, especially the poly-
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ethylene/starch system. Further toxicity
studies are needed, as is a full-scale recy-
cling study that involves including small
amounts of degraded post-consumer EDPs
in a recycling stream.
The full report was submitted in fulfill-
ment of Contract No. 68-02-4544 by Re-
search Triangle Institute under the spon-
sorship of the U.S. Environmental Protec-
tion Agency.
•&U.S. GOVERNMENT PRINTING OFFICE: 1993 - 7SO-07I/8009S
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Anthony L. Andrady is with Research Triangle Institute, Research Triangle
Park, NC 27709.
Lynnann Hitchens is the EPA Project Officer (see below).
The complete report, entitled "Weatherability of Enhanced Degradable Plastics"
(Order No. PB93-229 789/AS; Cost: $44.50, subject to change) will be
available only from:
' National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
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EPA/600/SR-93/162
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