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

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    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

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      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.)

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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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