United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/SR-95/003
March 1995
^ EPA Project Summary
Composites from Recycled
Wood and Plastics
John A. Youngquist, George E. Myers, James H. Muehl, Andrzej M. Krzysik,
and Craig M. demons
The ultimate goal of our research was
to develop technology to convert re-
cycled wood fiber and plastics into du-
rable products that are recyclable and
otherwise environmentally friendly. Two
processing technologies were used to
prepare wood-plastic composites: air-
laying and melt-blending. Research was
conducted in (1) developing laboratory
methods for converting waste wood,
wastepaper, and waste plastics into
forms suitable for processing into com-
posites; (2) optimizing laboratory meth-
ods for making composite panels from
the waste materials; (3) establishing a
database on the effects of formulation
and bonding agent on physical and
mechanical properties of composites;
(4) establishing the extent to which the
composites can be recycled without
unacceptable loss in properties; and
(5) reaching out to industry to provide
education, to develop applications, and
to extend the database. Overall, the pro-
gram demonstrated that both air-laid
and melt-blended composites can be
made from a variety of waste wood,
wastepaper, and waste plastics. The
composites exhibit a broad range of
properties that should make them use-
ful in a wide variety of commercial ap-
plications. For air-laid composites, the
waste materials were demolition wood
waste and waste plastics from milk
bottles (polyethylene) and beverage
bottles (polyethylene terephthalate).
Results showed that air-laid compos-
ites made from these waste ingredi-
ents possessed properties very similar
to those of composites made from the
virgin ingredients. In addition, air-laid
composites containing 20% reground
panels possessed some properties that
were superior to those of the original
composites. For melt-blended compos-
ites, waste materials were wastepaper,
polyethylene from milk bottles, and
polypropylene from automobile battery
cases or ketchup bottles. Waste maga-
zines were slightly inferior to waste
newspapers as a reinforcing filler; the
properties of composites made from
waste newspaper were better than
those of composites made from wood
flour, which is currently used in some
commercial composites. Properties of
wood-plastic composites were gener-
ally parallel to those of the plastics;
thus, different balances in composite
properties are possible from using
waste plastic. Outreach activities in-
cluded the organization and presenta-
tion of two international conferences
on wood fiber-plastic composites, pre-
sentations at many conferences, publi-
cation of several papers, and several
spin-off cooperative studies with indus-
try. One major study with industry dem-
onstrated the commercial feasibility of
making melt-blended composites from
old newspapers and polypropylene.
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).
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Studies on Air-Laid Composites
Air-laid (AL) web composites provide
options for balancing performance proper-
ties and costs, depending upon the appli-
cation under consideration. However, poor
attraction and low interfacial bonding be-
tween the hydrophilic wood and hydro-
phobic polyolefin limit the reinforcement
imparted to the plastic matrix by the wood
component. We compared the mechani-
cal and dimensional stability properties of
flat panel composites made from virgin
and postconsumer waste wood and plas-
tics in two series of tests:
AL Series 1. PET systems
• Virgin hemlock wood fiber (HF), virgin
polyester fiber (VPET), phenolic resin
• HF, recycled PET (RPET), phenolic
resin
• Demolition waste wood fiber (DF),
VPET, phenolic resin
• DF, RPET, phenolic resin
AL Series 2. HOPE systems
• HF and virgin high-density poly-
ethylene (VHDPE)
• HF and recycled HOPE (RHDPE)
• DF and VHDPE
• DF and RHDPE
Proportions of components were based
on ovendry fiber weight. For AL Series 1,
the proportions were 80% wood fiber/10%
PET/10% phenolic resin. For AL Series 2,
the proportions were 60% wood fiber/30%
HDPE/5% PET/5% tackifier (E-10).
We also studied the recyclability of air-
laid composites by testing the mechanical
properties of second-generation panels
made from AL Series 2 panels. Two for-
mulations were tested. Each formulation
consisted of 30% RHDPE, 5% VPET, and
5% E-10 tackifier. In addition, one formu-
lation had 60% DF and no refiberized
first-generation panels; the other formula-
tion had 40% DF and 20% refiberized
first-generation panels.
Methods and Materials
Experiments consisted of the following
sequence of steps: (a) modifying the FPL
air-forming equipment to ensure that uni-
form machine- and cross-machine direc-
tion webs could be produced routinely; (b)
converting raw materials into forms suit-
able for use in this equipment; (c) produc-
ing air-formed webs; (d) selecting and
stacking the webs to produce mats of a
given weight; (e) consolidating the mats in
a platen press to produce test panels; (f)
cutting test specimens from panels; and
(g) testing properties.
For both test series, each data set was
tested for normality at the 95% confidence
level using Shapiro-Wilk statistical analy-
sis. An analysis of variance was performed
and the means were compared at the
95% confidence level using Tukey's
method of multiple comparisons.
The raw materials studied in the air-
forming portion of this research program
fell into three general classes: cellulosic
fibers, plastics, and additives.
Cellulosic Fibers
Two basic types of wood fiber were
used in the AL series of tests. The first
was virgin western hemlock wood fiber
(HF), which was produced in a pressur-
ized single-disk refiner from 100% pulp-
grade chips. The second was demolition
wood fiber (DF), which was derived from
waste wood from buildings that had been
torn down in the Boston, MA, area.
Plastics
The virgin polyester (VPET) was 5.5
denier (6.1 x 10~7kg/m), 38 mm long, and
crimped, and had a softening temperature
greater than 215°C. The recycled polyes-
ter fiber, which was spun from recycled
soft drink containers, was 6.00 denier, 51
mm long, and crimped. For all the air-laid
experiments, VPET served as a matrix to
hold the fibers together within the mat.
The virgin high-density polyethylene
(VHDPE) was a blow-molding polymer
normally used as a feedstock for plastic
milk bottles. The flakes were cryogeni-
cally ground to a (-)35 mesh size. The
melt flow index of the recycled HOPE was
0.7.
Additives
Liquid phenolic resin was used as the
binder for the AL Series 1 panels; it had a
solids content of 51% to 53% and a pH of
9.5 to 10.0 at 25°C. The resin was sprayed
on the wood fiber at 25°C at a level of
10% solids by weight as it rotated in a
drum-type blender.
For the AL Series 2 boards, the wood
fiber was blended with granulated HOPE.
Previous work showed that a tackifier was
needed to retain the granule HOPE in the
web during the web formation process.
Preliminary testing had also indicated that
the tackifier, a wax emulsion of oxidized
low molecular weight polyethylene (E-10),
did not have an adverse effect on the
properties of the resultant test panels. The
tackifier was applied to the wood fibers in
a rotating drum blender with an air spray
gun in a manner similar to the application
of phenolic resin in the AL Series 1 stud-
ies.
Equipment Modifications and
Additions
A 305-mm-wide, laboratory-scale
Rando-Webber forming machine was used
to make nonwoven mats for the air-laid
composites. The equipment was modified
to minimize the density gradient across
the web, a problem encountered in pre-
liminary experiments.
Panel Fabrication
Nonwoven webs were weighed, sorted,
and stacked on the basis of weight and
specific gravity. A steam-heated platen
press was used to press the panels to a
thickness of 3.2 mm and a specific gravity
of 1.0. A cooling cycle was used to main-
tain target thickness.
The recyclability part of the study re-
quired that we determine the feasibility of
recycling panels made for AL Series 2,
which contained DF and RHDPE. We
found that we needed to recycle the boards
through the pressurized refiner to be able
to produce the desired fiber length and
bundles.
Tests on Mechanical and Physical
Properties
We evaluated the performance of pan-
els made for AL Series 1 (PET systems),
AL Series 2 (HOPE systems), and
recyclability.
Results of Tests on PET
Systems (AL Series 1)
In general, the mechanical, water resis-
tance, and dimensional stability properties
of panels made from recycled materials
were equivalent to similar properties ob-
tained from panels containing all virgin or
virgin/recycled materials. Therefore, the
recycled ingredients tested in AL Series 1
could replace virgin materials with minor
consequences.
Mechanical Properties
Panels made with the HF/VPET formu-
lation had the highest bending MOR value
(50.6 MPa), although no statistically sig-
nificant differences were observed for MOR
values for either wood fiber or PET varia-
tions. The modulus of elasticity (MOE)
values followed a different pattern. In both
the HF and DF groups, the MOE values
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of boards containing RPET were signifi-
cantly higher than those of boards con-
taining VPET; total average increase for
this property was 16% for both groups.
For the HF/VPET formulation, tensile
strength was 33.0 MPa; tensile strength
decreased by 14% for the HF/RPET for-
mulation. However, when RPET or VPET
fibers were used with DF fibers, no signifi-
cant differences were noted. In contrast to
tensile strength, the incorporation of RPET
fibers increased tensile modulus (MOE)
by 6% and 7% for HF and DF formula-
tions, respectively, although these differ-
ences were not statistically significant.
Impact energy of specimens from the
HF and DF formulations showed a consis-
tent trend. Impact strength was respec-
tively 20% and 10% higher for HF and DF
formulations containing VPET fibers com-
pared to formulations containing RPET fi-
bers.
Physical and Dimensional Stability
Properties
Thickness swell values were significantly
different for HF/RPET and DF/VPET speci-
mens (Table 1). The HF/RPET specimens
had the lowest thickness swell value
(22.3%), and the DF/VPET specimens the
highest value (29.8%). Water absorption
values were not significantly different.
Linear expansion values at 30% RH
were statistically equivalent (Table 1). At
Table 1. Results of Water Soak and Linear Expansion Tests forAL Series3
24-hr water soak
Composite*1 Thickness
swell
(%)
AL Series 1
HF-80% 25.2 (9)
VPET-10%
PR-10%
HF-80% 22.3 (9)
RPET-10%
PR-10%
DF-80% 29.8 (14)
VPET-10%
PR-10%
DF-80% 26.9 (8)
RPET-10%
PR-10%
AL Series 2
HF-60% 43.8 (14)
VHDPE-30%
VPET-5%
E10wax-5%
HF-60% 42.7(21)
RHDPE-30%
VPET-5%
E10wax-5%
DF-60% 45.2 (13)
VHDPE-30%
VPET-5%
E10wax-5%
DF-60% 52.8 (15)
RHDPE-30%
VPET-5%
E10wax-5%
Water
absorption
(%)
43.4 (20)
41.3(25)
48.2 (25)
44.1 (16)
54.9(17)
61.8(19)
58.7(13)
65.8(16)
Linear expansion (%)
30% RH 65% RH 90% RH
0.19(10) 0.42 (4) 0.61 (6)
0.21 (13) 0.44 (8) 0.70 (7)
0.20(11) 0.43 (6) 0.64 (7)
0.20(12) 0.45 (6) 0.71 (6)
0.15 (9) 0.39 (5) 0.68 (7)
0. 1 7 (12) 0.42 (12) 0.69 (12)
0.17 (5) 0.40 (7) 0.64 (9)
0.16 (7) 0.44 (6) 0.74 (6)
a Values in parentheses are coefficients of variation (%).
b DF is demolition wood fiber; E10, epolene-maleated polyethylene; HF, hemlock fiber; VPET,
virgin polyester fiber; RPET, recycled polyester; RHDPE, recycled high-density polyethylene; and
VHDPE, virgin high-density polyethylene.
65% and 90% RH, the HF/RPET and DF/
RPET formulations had slightly higher val-
ues and were statistically different from
the HF/VPET and DF/VPET formulations.
Results of Tests on HOPE
Systems (AL Series 2)
Panels containing virgin and recycled
wood fiber/polyethylene had equivalent
mechanical and physical properties. There-
fore, as in AL Series 1, the recycled mate-
rials used in AL Series 2 could replace
virgin materials with minor consequences.
Mechanical Properties
The DF/VHDPE panels had the highest
bending MOR value at 19.1 MPa, followed
by 18.7 MPa for the HF/RHDPE panels.
Generally no statistically significant differ-
ences were observed for MOR values for
either wood fiber or HOPE variations. In
contrast, the HF/RHDPE panels had the
highest bending MOE value (2.13 GPa)
and the DF/VHDPE panels the lowest
MOE value (1.75 GPa); however, these
results were not statistically significant.
For tensile strength, the highest value
(12.4 MPa) was observed for the DF/
VHDPE formulation; tensile strength of the
DF/RHDPE panels was 7% lower (11.5
MPa). For both wood fiber variations, the
use of either virgin or recycled HOPE did
not significantly influence tensile strength
values. The HF/VHDPE panels had the
highest tensile MOE (2.81 GPa); incorpo-
ration of RHDPE lowered tensile MOE by
21% (2.23 GPa), a significant change. Ten-
sile MOE values of DF formulations were
about equal, averaging 2.11 GPa.
Type of wood fiber and formulation did
not significantly affect impact energy.
Physical and Dimensional Stability
Properties
Thickness swelling of DF specimens
was an average of 22% higher than that
of HF specimens; the highest value (53%)
was observed for the DF/RHDPE formula-
tion (Table 1). Particularly notable is the
fact that RHDPE had a significant effect
on only the DF formulation and not the HF
formulation. Thickness swelling was low-
est in the HF/RHDPE panels (43%).
The formulation had a consistent influ-
ence on water absorption (Table 1). Incor-
porating RHDPE with either type of wood
fiber produced a statistically significant in-
crease in this property (average 13% in-
crease). The HF/VHDPE and DF/VHDPE
formulations showed the lowest water ab-
sorption values.
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Linear expansion values for all formula-
tions at 30% RH ranged from 0.15 to
0.17% (Table 1). At 65% and 90% RH,
the HF/RHDPE and DF/RHDPE formula-
tions had slightly higher values.
Results of Tests on
Recyclability
In general, the mechanical, water resis-
tance, and dimensional stability properties
of second-generation panels made from
recycled materials were essentially equiva-
lent to or better than properties obtained
from first-generation panels. Therefore, the
second-generation composites, or possi-
bly higher generation composites, can be
produced using recycled materials without
the consequence of reduced property val-
ues.
Mechanical Properties
The MOR of second-generation panels
was higher than that of first-generation
panels (19.6 MPa compared to 17.4 MPa).
On the other hand, the bending MOE val-
ues of first-generation panels were higher
than that of second-generation panels
(2.01 vs. 1.77 GPa). These differences
were not statistically significant. The ten-
sile strength of second-generation panels
was 19% higher than that of first-genera-
tion panels. Similar results were obtained
for tensile modulus. The higher properties
of the second-generation panels indicate
that wood fiber/RHDPE composites can
benefit by the addition of refiberized ma-
terial from first-generation panels.
Impact energy values of specimens
made from first-generation panels and sec-
ond-generation panels were nearly equal
and not statistically different.
Physical and Dimensional Stability
Properties
In the 24-hr water-soak tests, first-gen-
eration panels showed 53% thickness swell
(Table 2). Incorporating first-generation
panel fibers into second-generation pan-
els improved this property by 21%. Simi-
lar trends were observed for water
absorption values (Table 2). Water ab-
sorption of second-generation panels was
18% lower than that of first-generation
specimens. These differences were sta-
tistically significant. The results suggest
that the additional HOPE from refiberized
first-generation panels further encapsu-
lated the wood fibers, thus limiting water
uptake by the wood fibers.
Linear expansion values were similar
for both formulations at 30% RH, although
the differences were statistically signifi-
cant (Table 2). The incorporation of re-
cycled panels into second-generation
panels significantly decreased linear ex-
pansion at both 65% and 90% RH.
The positive influence of incorporating
20% first-generation panels into the sec-
ond-generation panels may be the result
of several factors. The incorporation of
20% refiberized first-generation panels re-
duced the percentage of wood fiber (DF)
from 60% to 40%. The actual amount of
total wood fiber was reduced from 60% to
52%, and the total amount of RHDPE was
increased from 30% to 36%. Likewise, the
percentage of PET and E-10 each was
increased by 1%. The increase of these
components, particularly the HOPE, and
the decrease of the wood fiber may be a
direct cause of some improvements in
property values. More wood fiber was able
to be encapsulated by plastic, thereby re-
ducing exposure of the wood to moisture.
Conclusions
• The Rando-Webber air-forming
equipment can be adapted to handle
both long and short synthetic and
natural fibers as well as powder.
Nonwoven air-laid webs can be
produced that have excellent
Table 2. Results of Water Soak and Linear Expansion Tests on Recyclability Specimens3
24-hr water soak
Composite
First-generation panels'1
Second-generation
panels0
Thickness
swell
(%)
52.8 (15)
42.0 (12)
Water
absorption
(%)
65.8(16)
54.3 (12)
Linear expansion (%)
30% RH
0.16 (7)
0. 15 (1 1)
65% RH
0.44 (6)
0.37 (9)
90% RH
0.74 (6)
0.52(11)
a Values in parentheses are coefficients of variation (%).
b DF-60%, RHDPE-30%, VPET-5%, E10 wax-5%. DF is demolition wood fiber; RHDPE, recycled
high-density polyethylene; VPET, virgin polyester fiber; and E10, epolene-maleated polyethylene.
0 DF-40%, recycled panel-20%, RHDPE-30%, VPET-5%, and E10 wax-5%
uniformity in both the machine- and
cross-machine directions.
• Recycled and granulated HOPE can
be used in the FPL air-forming
equipment to produce an air-laid web
that can be subsequently made into
flat panels or shaped sections.
• Pressure refining techniques can
convert post-consumer demolition
wood or construction waste into fiber
bundles that can be processed very
successfully in the FPL air-forming
equipment and subsequently pressed
into flat panels or shaped sections.
• Panels made with recycled materials
compare favorably to those made of
virgin materials. Mechanical and
physical properties of panels made
with recycled polyester fiber or high-
density polyethylene and demolition
waste wood are similar to those of
panels made with virgin materials.
• Second-generation composites, or
possibly higher generation
composites, can be produced using
recycled materials without the
consequence of reduced property
values. Mechanical and physical
properties of second-generation
panels made from recycled materials
were essentially equivalent to or better
than properties obtained from first-
generation panels.
Studies on Melt-Blended
Composites
Melt-blending is an inherently low cost,
high production-rate process in which wood
and/or paper are mixed with molten plas-
tic. These blends can then be formed into
products using conventional plastics pro-
cessing techniques such as extrusion and
injection molding. The plastic acts as a
means to convey the wood/paper during
processing and the wood/paper fiber bears
the load in the final composite, offering an
effective balance between processability
and strength of end product. With melt-
blending techniques, wood fiber provides
several advantages as reinforcement in
thermoplastic composites. These include
economy on a cost per unit volume basis,
desirable aspect ratios, flexibility (hence
less fiber breakage), and low abrasiveness
to equipment. Composites can be pro-
duced containing up to 50 weight percent
wood fiber and are low cost,
thermoformable, and relatively insensitive
to moisture.
Methods and Materials
In laboratory investigations of melt-
blended composites, experimental opera-
tions generally proceed through the
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following sequence of steps: (a) conver-
sion of raw materials into forms suitable
for preparing dry mixtures quantitatively
and feeding those mixtures into the melt-
blending apparatus, (b) quantitative dry
mixing, (c) melt-blending by either an ex-
truder or a K-mixer, (d) injection molding
of test specimens, and (e) measurement
of properties.
Five major studies were undertaken to
investigate the effects of a number of vari-
ables on mechanical and physical behav-
ior of wood-fiber-reinforced thermoplastics.
The studies were statistically designed and
analyzed and all comparisons were made
at a 95% confidence level. However, for
the sake of brevity, the results will be
presented as a whole, centering on the
larger effects of the variables because of
their greater impact on composite perfor-
mance. Cellulosic fibers, plastics, and cou-
pling agents are described in Table 3.
Plastics
Plastics act as the matrix in the com-
posite. In this program, a baseline matrix
plastic, virgin polypropylene (VPP) ho-
mopolymer, was compared to three waste
plastics: polypropylene from auto battery
cases (BPP), recycled ketchup bottle
polypropylene (KPP), and recycled high-
density polyethylene from blow-molded
milk bottles (HDPE-MB). These plastics
were chosen on the basis of low melting
temperature (necessary for use with wood/
paper fiber), cost, performance, and avail-
ability.
Cellulosic Fibers
Celluloses act as the reinforcing filler in
the composite. We used wood flour (WF)
as the primary baseline filler because it is
currently used commercially with polypro-
pylene in extruded sheets for automobile
interior panels. We included relatively ex-
pensive (several times the price of WF)
pure cellulose fibers (BW40) as another
baseline filler for comparing against re-
cycled fibers—waste newspaper (ONP)
and old magazines (OMG).
Both plastics and additives can be
readily used in traditional plastics process-
ing machinery. However, wood or paper
fibers present difficulties during the melt-
blending step. Cellulosic filler must be in a
form that can be completely dispersed
into the molten plastic by the shear forces
exerted during melt-blending. Wood flour
was readily disaggregated and fully dis-
persed into individual particles in the plas-
tic using a simple laboratory single-screw
extruder. Although difficult to disperse with
an extruder, a usable blend of BW40 cel-
lulose fibers was also obtained in this
way. Wastepaper fibers were much more
difficult to handle because of their low
bulk density. For melt-blending in a high
Table 3. Materials Used in Melt-Blending Studies
Material
Abbreviation
Description3
Source
Plastic
Virgin polypropylene VPP
Recycled polypropylene BPP
from auto battery cases
Recycled polypropylene KPP
from ketchup bottles
Recycled polypropylene HDPE-MB
from milk bottles
Cellulosic filler
Wood flour WF
Cellulose 61/1/40
Waste newspaper ONP
Waste magazine OMG
Coupling agent
Epolene E43 powder E43S
Epolene E43 emulsion E43E
Epolene G3002 powder G3002
Fortilene 9101, 1602, 1902;
nominal MFI3, 12, 30.
Cleaned chips; nominal MF110
Cleaned chips; nominal MFI 3
Cleaned chips; nominal MFI 0.7
Western pine; -40+80 mesh
Pure cellulose fiber; mean length 60 \im
Over-production issue
Representative sample of
Madison waste stream
Powdered maleated polypropylene;
M = 4,200
Emulsified potassium salt
Powdered maleated polypropylene;
M= 11,000
Solvay Polymers, Inc., Deer Park, TX
Gopher Smelting and Refining Co.,
Eagon, MN
Wheaton Plastic Recycling Co.,
Milleville, NJ
Recycle Worlds, Madison, I/I//
American Woodfiber Co., Schofield, I/I//
James River Corp., Hackensack, NJ
Milwaukee Journal/Sentinel Inc.,
Milwaukee, Wl
Madison Recycling Center, Madison, Wl
Eastman Chemical Co., Kingsport, TN
Eastman Chemical Co.
Eastman Chemical Co.
MFI is melt flow index. M is molecular weight.
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intensity K-mixer, the paper was milled or
ground into approximately 4 to 8-mm flakes
using a small granulator. For melt-blend-
ing in an extruder, the paper was first
reduced to fibers by a small modified
hammermill.
Coupling Agents
Additives aid the dispersion of filler into
the matrix plastic and/or enhance the bond-
ing (act as a "coupling agent") between
filler and matrix. In this program, we re-
stricted ourselves to Eastman Epolenes
(E43, G3002)—maleated polypropylene
"waxes" in which the small degree of
maleation provides polar groups capable
of bonding to the cellulose while the
polypropylene segments, in theory, offer
compatibility with the polypropylene ma-
trix.
Mechanical and Physical
Properties
Materials were compounded in either a
38-mm single-screw extruder or a 1-L K-
mixer. Extrusion parameters were tem-
perature profile 170°C to 190°C, screw
speed 15 rpm, and residence time 1-2
min. The K-mixer parameters were 4500
to 5500 rpm and discharge temperature
171°C to 200°C. In all studies, test speci-
mens were prepared by injection molding.
At least five specimens of each blend
were tested for each mechanical property.
After molding, the specimens were stored
over dessicant for at least 3 days before
testing.
Mechanical properties were measured
on the dry specimens at approximately
23°C. Specimens and test methods fol-
lowed ASTM D256, D638, D747, and
D790. Apparent melt viscosities and shear
rates were calculated from measured volu-
metric throughput rates and pressure drops
across the die during steady-state extru-
sion in a single-screw extruder at 190°C.
Selected properties from the various
studies are summarized in Table 4. This
table shows the larger effects of some
more-sensitive variables. Because the con-
ditions of each study varied somewhat,
care must be taken when comparing data.
General trends rather than actual values
will be emphasized in the following dis-
cussion.
Reinforcement Effects
Addition of 30%-40% of any of the
wood/paper reinforcing fillers to the plas-
tics resulted in a composite with higher
modulus and strength but lower impact
energy and percentage of elongation and
energy to maximum load. These effects
are not surprising and are typical of rein-
forced thermoplastics in general. Table 5
summarizes property changes with addi-
tion of 40% ONP to several virgin and
recycled polypropylenes.
Most major changes in composite per-
formance occurred at filler contents below
30%. For example, aside from an approxi-
mate 10% increase in modulus, no major
changes in mechanical performance were
found over the rather narrow range of
32% to 42% ONP in VPP.
Typically, the more fibrous fillers (ONP
and BW40) resulted in composites with
superior mechanical properties but were
more difficult to process when compared
to WF. However, the presence of clays
and other impurities in the OMG made the
material more difficult to disperse and in-
terfered with bonding, resulting in de-
creased mechanical performance when
compared with other fibrous fillers.
Figure 1 demonstrates some effects
on viscosity at low shear rates. Viscosity
measurements showed dramatic increases
when WF was replaced with ONP and as
fiber content was increased. This increase
in viscosity demonstrated the effects of
both aspect ratio and filler contents on
composite melt behavior. Even at a fiber
loading of 32% ONP, PPV composite melts
were significantly more viscous than a 42%
WF-filled PPV.
Matrix Effects
Changing the melt flow index (MFI) of
VPP had a significant effect on viscosity
but little effect on mechanical performance
over the range studied (3-30 g/10 min).
This result suggests that MFI could be
used to compensate for increased viscos-
Table 4. Selected Mechanical Property Data from Various Studies
Plastic
PPV
HDPE-MB
PPV
KPP
BPP
Filler
None
40% ONP
40% BW40
40% WF
40% ONP
40% BW40
40% WF
40% ONP
40% ONP
40% ONP
None
40% ONP
40% OMG
None
40% ONP
40% OMG
Co u pi ing g
agent
None
E43
E43
E43
E43
E43
E43
None
E43
G3002
None
G3002
G3002
None
G3002
G3002
Tensile
modulus
(GP.)
4.89
4.80
3.72
3.80
3.79
2.61
4.97
4.90
4.56
1.62
4.03
3.55
1.32
3.98
3.44
Tensile
strength
(MPJ
31.5
47.1
48.2
34.1
37.6
36.6
27.8
34.0
47.4
52.3
36.5
52.3
38.9
24.5
42.5
31.8
Izod impact energy
Notched Unnotched
(J/m) (J/m)
23.8
20.8
24.7
18.7
28.6
30.8
36.4
20.8
19.8
20.4
62.0
30.6
34.2
165.0
34.3
41.8
650
109
114
72
73
68
81
113
144
190
>800
167
138
>800
150
125
Coupling agent was added at a level of3%-5% of fiber weight depending on the study.
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Table 5. Change in Property after Addition of
40% ONP to Plastic
Filled/Unfilled
Property
Tensile
Modulus
Strength
Energy
Elongation
Flexural
Modulus
Strength
Impact
Notched
Unnotched
KPP
2.49
1.49
0.65
0.47
2.29
1.52
0.49
<0.21
BPP
3.00
1.66
0.73
0.46
3.01
1.91
0.21
<0.19
VPP
—
7.66
2.94
2.00
0.86
0.29
.to
o
Q.
in
8
.to
I
10000 -
7000 -
4000
2000
1000 4
10
42% ONP
37% ONP
32% ONP
42% WF
Unfilled PP
20
50 100 200 500
Apparent shear rate (1/S)
woo
Figure 1. Apparent melt viscosity of composite blends.
ity of the higher performance fibrous com-
posites.
The polypropylene composites were
stronger and stiffer than the HDPE-MB
composites but had lower notched impact
energy values. The unfilled plastic com-
posites showed the same trend, i.e., com-
posite properties qualitatively followed
those of the matrix polymers. Similar trends
were also seen for composites made with
BPP and KPP. For example, the use of
BPP (a block copolymer with higher
notched impact strength) instead of VPP
resulted in composites with higher notched
impact strength, although the difference in
this property was not nearly as great as
that in the unfilled polymers. In other
words, although choice of plastic can af-
fect composite properties, addition of re-
inforcement can affect the mechanisms
by which the plastic achieves its perfor-
mance.
Analysis of the results of both the filler
and plastic effects can lead to some inter-
esting conclusions. For example, the me-
chanical properties of a recycled ONP/
HDPE-MB system were at least as good
as those of the current commercial WF/
polypropylene system. This may offer
some practical utility if problems associ-
ated with the high viscosity of the re-
cycled system can be overcome.
Coupling Agent Effects
Coupling agents may be incorporated
into composites in different ways to con-
centrate the material at the interface where
it is active. In our studies, adding solid
coupling agent (E43) to the melt or apply-
ing emulsified E43 directly to the fiber had
little effect on mechanical performance of
composites. Concentrating the emulsified
additive at the fiber/matrix interface by
precoating the fibers was apparently coun-
teracted by the much lower chemical re-
activity of the potassium salt with the
cellulose compared with the reactivity of
the anhydride with cellulose. Perhaps the
E43 functions more to enhance disper-
sion of the cellulosic fillers than to bond
the cellulose to the polymer.
The higher molecular weight maleated
polypropylene, G3002, had a very benefi-
cial effect on composite strength, energy
absorption, and unnotched impact behav-
ior. Initial moduli were approximately the
same but ultimate strength and area un-
der the curves (a measure of toughness)
were much greater for systems with cou-
pling agent (especially G3002). The fact
that unnotched rather than notched im-
pact energy was increased indicates that
G3002 probably enhances dispersion of
the fibers and reduces aggregates that
would act as failure loci. For example,
unnotched impact energy was more af-
fected by removal of failure loci than was
notched impact energy because the notch
itself constitutes a failure locus. The ap-
parently greater interaction of G3002 with
polypropylene relative to E43 may be at-
tributable to the higher molecular weight
of G3002.
Processing Effects
Little preference was shown for com-
pounding in a K-mixer or a single-screw
extruder with WF or cellulose fiber. How-
ever, those fillers are relatively easily dis-
persed, and the ONP could not be
melt-blended with a single screw. More-
over, the small interaction terms between
filler and compounder in the statistical
analysis also indicated some differences
in dispersibility between WF and cellulose
fiber.
We investigated the effects of re-extru-
sion on the mechanical and rheological
performance of three different composite
blends. For almost all mechanical and
rheological properties, very little change
occurred as the material was recycled over
five cycles. The length and therefore the
aspect ratio of the ONP fiber decreased,
but these decreases were apparently not
great enough to result in any large reduc-
tions in composite performance. The WF
was reduced in both thickness and length,
as smaller bundles of wood fibers were
sheared off the larger particles. These
changes in dimension resulted in no over-
all change in aspect ratio nor, ultimately,
in composite performance.
Conclusions
• Melt-blended composites cannot be
prepared with wastepapers as
reinforcing filler using a conventional
laboratory single-screw extruder.
However, these composites can be
prepared with a laboratory high-
intensity K-mixer, an industrial-scale
K-mixer, or a twin-screw extruder that
employs a properly designed feeder
for the fiber.
• Old newspaper (ONP) as reinforcing
filler provides better properties than
wood flour, which is currently used as
filler in commercial composites. Old
magazines (OMG) can also be used
as a filler, but they are less easily
dispersed into the matrix plastic and
result in somewhat lower properties
-------
than those of composites containing
ONP.
• With the same filler, substituting
recycled milk bottle polyethylene for
VPP leads to lower strength, stiffness,
and unnotched impact energy, but
higher notched impact energy.
• Use of recycled high density
polyethylene from milk bottles and
recycled polypropylene from battery
cases as a matrix in composites with
ONP results in improved impact
performance when compared with that
of composites made from VPP and
ONP.
• Addition of the coupling agent Epolene
G3002 at 3 weight percent of filler
results in very useful increases in
composite properties, probably as a
result of improved fiber dispersion.
• Select composite systems showed
little or no loss in mechanical
properties when repeatedly
reprocessed (re-extruded and injection
molded).
Commercial Implementation
The research program led to many co-
operative studies with industry and
academia, all with the ultimate goal of
commercializing composites made with
waste materials.
Commercial Feasibility of Waste
Newspaper-Thermoplastic
Composites
The program was partially funded by
the Forest Products Laboratory (FPL) and
the Wisconsin Department of Natural Re-
sources (DNR) and by in-kind contribu-
tions from the eight cooperating
companies. Laboratory experiments dem-
onstrated that old newspapers could be
dispersed as fibers into thermoplastics by
melt-blending, resulting in substantial im-
provements in some properties compared
with the unfilled plastic or plastic filled
with wood flour. Major conclusions are as
follows:
• Old newspaper/polypropylene (ONP/
PP) composites can be compounded
on a commercial scale using either
the K-mixer with ONP flakes as feed
or using a twin-screw extruder with
ONP fibers fed separately from the
plastic.
• An ONP/PP sheet containing 42
weight percent ONP can be prepared
by extrusion on a commercial scale.
This sheet meets existing
specifications for automobile panels
and can be thermoformed into a
variety of shapes.
• Given proper design of melt
processing equipment, a wide variety
of other commercial products could
be manufactured from ONP/PP
composites with similar ONP content.
• Firm estimates of production costs
for ONP/PP composite products must
await:
a. additional examination of com-
pounding methods to define
optimum balance of dispersion
ability, throughput rate, and cost;
and
b. improvement in methods to
deliver wastepaper in a form and
at a cost acceptable to a
compounder or a manufacturer
of plastic products.
Waste LDPE Program
A consortium of companies is investi-
gating the use of waste LDPE "contami-
nated" by residual fiber from a
hydropulping operation that scavenges
wood fiber from coated paper stock. The
program involves raw material processors,
compounders, plastics processors, and
research institutions and is being coordi-
nated by the FPL. Major hurdles in this
program are the residual moisture in the
raw material from the hydropulping pro-
cess and product applications.
Waste Jute-Polyester Panels as
Reinforcing Filler
In response to interest expressed by a
U.S. company in the possibility of recy-
cling panels produced by impregnating jute
fibers with thermosetting polyester, we
granulated the panels and investigated the
ability to use the resultant mixture as rein-
forcing filler in melt-blended composites
with a polypropylene matrix. Overall, this
waste material produced composite me-
chanical properties approximately equiva-
lent to those of similar composites
containing wood flour as the reinforce-
ment.
Waste Kenaf Core as Reinforcing
Filler
This program resulted from a request
by the Agrecol Corporation (Madison, Wl
to determine whether kenaf core material
could be useful as a reinforcing filler in
plastic composites. We granulated the
core material and successfully melt-
blended the -40 mesh fraction with polypro-
pylene. The composite properties were
approximately equivalent to those of simi-
lar composites containing wood flour.
Therefore, where kenaf core is readily
available at low cost, it could very likely
substitute for wood flour as a reinforcing
filler.
Wastewood Composite as
Reinforcing Filler
The University of Tennessee Extension
requested an evaluation of waste wood
composite as a reinforcing filler in thermo-
plastic composites. Although such solid
waste is available in large quantity, it con-
tains wood with cured thermoset adhe-
sives that might cause problems in
melt-processed composites because the
adhesives do not melt at processing tem-
peratures. We granulated the plywood and
successfully melt-blended the -40 mesh
fraction with polypropylene. The compos-
ite properties were approximately equiva-
lent to those of similar composites
containing wood flour. This waste material
could therefore substitute for wood flour
as a reinforcing filler in melt-processed
composites.
Recommendations
Research
Additional research is needed on both
air-laid and melt-blended composites made
from recycled wood fiber and plastics to
improve properties and processing and
increase potential applications as follows:
1. Evaluate the potential for making
composite materials with other
major components of the waste
stream, including low-density
polyethylene, polystyrene, and
mixed waste plastics.
2. Verify the recyclability of composites
made with reground first-generation
ingredients.
3. Improve melt-blending processes to
achieve better fiber dispersion with
minimal fiber breakage.
4. Improve bonding between wood
fiber and plastic matrix to enhance
physical and mechanical properties.
5. Improve impact energy and creep
resistance (decreased deflection
under long-term load), currently the
limiting properties of these
composite systems.
6. Determine the resistance of these
composite systems to relatively
extreme environments and develop
-------
means to enhance resistance to
moisture, biodegradation, and fire.
Commercialization
1. Continue extensive outreach to
industry to acquaint companies with
these types of composite systems,
to develop applications, and to
cooperate in product development.
2. To obtain commercial acceptance
of melt-blended composites
containing wastepaper fiber;
a. improve methods for
converting wastepaper at
costs acceptable to industrial
users, or at least the current
cost of wood flour (about
$0.22/kg);
b. improve methods for melt-
blending fiber and plastics on
a commercial scale at costs
acceptable to melt fabricators
(extruders, injection molders,
etc.)
-------
John A. Youngquist, George E. Myers, James H. Muehl, Andrzej M. Krzysik,
and Craig M. demons are with USDA Forest Service, Madison, Wl 53705-
2398
Lisa Brown is the EPA Project Officer (see below).
The complete report, entitled "Composites from Recycled Wood and Plastics,'
(Order No. PB95-160008; Cost: $27.00, subject to change) will be avail-
able 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, OH 45268
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-95/003
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