E AP Project Summary

United States

Environmental Protection

Agency

Composites from Recycled

Wood and Plastics

John A. Youngquist, George E. Myers, James H. Muehl, Andrzej M. Krzysik,

and Craig M. Clemons

Risk Reduction

Engineering Laboratory

Cincinnati, OH 45268

Research and Development

The ultimate goal of our research was

to develop technology to convert recycled wood fiber and plastics into durable products that are recyclable and

otherwise environmentally friendly. Two

processing technologies were used to

prepare wood–plastic composites: airlaying 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 composites; (2) optimizing laboratory methods 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 program 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 useful in a wide variety of commercial applications. 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 composites made from these waste ingredients 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 composites, waste materials were wastepaper,

polyethylene from milk bottles, and

polypropylene from automobile battery

cases or ketchup bottles. Waste magazines 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 generally parallel to those of the plastics;

thus, different balances in composite

properties are possible from using

waste plastic. Outreach activities included the organization and presentation of two international conferences

on wood fiber–plastic composites, presentations at many conferences, publication of several papers, and several

spin-off cooperative studies with industry. One major study with industry demonstrated 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).

EPA/600/SR-95/003 March 1995
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Studies on Air-Laid Composites

Air-laid (AL) web composites provide

options for balancing performance properties and costs, depending upon the application under consideration. However, poor

attraction and low interfacial bonding between the hydrophilic wood and hydrophobic polyolefin limit the reinforcement

imparted to the plastic matrix by the wood

component. We compared the mechanical and dimensional stability properties of

flat panel composites made from virgin

and postconsumer waste wood and plastics 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. HDPE systems

• HF and virgin high-density polyethylene (VHDPE)

• HF and recycled HDPE (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 airlaid composites by testing the mechanical

properties of second-generation panels

made from AL Series 2 panels. Two formulations were tested. Each formulation

consisted of 30% RHDPE, 5% VPET, and

5% E-10 tackifier. In addition, one formulation had 60% DF and no refiberized

first-generation panels; the other formulation 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 uniform machine- and cross-machine direction webs could be produced routinely; (b)

converting raw materials into forms suitable for use in this equipment; (c) producing 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 analysis. 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 airforming 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 pressurized single-disk refiner from 100% pulpgrade 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 10-7 kg/m), 38 mm long, and

crimped, and had a softening temperature

greater than 215°C. The recycled polyester 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 cryogenically ground to a (-)35 mesh size. The

melt flow index of the recycled HDPE 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 HDPE.

Previous work showed that a tackifier was

needed to retain the granule HDPE 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 studies.

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 preliminary 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 maintain target thickness.

The recyclability part of the study required 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 panels made for AL Series 1 (PET systems),

AL Series 2 (HDPE systems), and

recyclability.

Results of Tests on PET

Systems (AL Series 1)

In general, the mechanical, water resistance, and dimensional stability properties

of panels made from recycled materials

were equivalent to similar properties obtained 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 formulation had the highest bending MOR value

(50.6 MPa), although no statistically significant differences were observed for MOR

values for either wood fiber or PET variations. 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 significantly higher than those of boards containing 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 formulation. However, when RPET or VPET

fibers were used with DF fibers, no significant 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 formulations, respectively, although these differences were not statistically significant.

Impact energy of specimens from the

HF and DF formulations showed a consistent trend. Impact strength was respectively 20% and 10% higher for HF and DF

formulations containing VPET fibers compared to formulations containing RPET fibers.

Physical and Dimensional Stability

Properties

Thickness swell values were significantly

different for HF/RPET and DF/VPET specimens (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

65% and 90% RH, the HF/RPET and DF/

RPET formulations had slightly higher values and were statistically different from

the HF/VPET and DF/VPET formulations.

Results of Tests on HDPE

Systems (AL Series 2)

Panels containing virgin and recycled

wood fiber/polyethylene had equivalent

mechanical and physical properties. Therefore, as in AL Series 1, the recycled materials 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 differences were observed for MOR values for

either wood fiber or HDPE 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 HDPE did

not significantly influence tensile strength

values. The HF/VHDPE panels had the

highest tensile MOE (2.81 GPa); incorporation of RHDPE lowered tensile MOE by

21% (2.23 GPa), a significant change. Tensile 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 formulation (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 lowest in the HF/RHDPE panels (43%).

The formulation had a consistent influence on water absorption (Table 1). Incorporating RHDPE with either type of wood

fiber produced a statistically significant increase in this property (average 13% increase). The HF/VHDPE and DF/VHDPE

formulations showed the lowest water absorption values.

Table 1. Results of Water Soak and Linear Expansion Tests for AL Seriesa

24-hr water soak Linear expansion (%)

Compositeb Thickness Water 30% RH 65% RH 90% RH

swell absorption

(%) (%)

AL Series 1

HF-80% 25.2 (9) 43.4 (20) 0.19 (10) 0.42 (4) 0.61 (6)

VPET-10%

PR-10%

HF-80% 22.3 (9) 41.3 (25) 0.21 (13) 0.44 (8) 0.70 (7)

RPET-10%

PR-10%

DF-80% 29.8 (14) 48.2 (25) 0.20 (11) 0.43 (6) 0.64 (7)

VPET-10%

PR-10%

DF-80% 26.9 (8) 44.1 (16) 0.20 (12) 0.45 (6) 0.71 (6)

RPET-10%

PR-10%

AL Series 2

HF-60% 43.8 (14) 54.9 (17) 0.15 (9) 0.39 (5) 0.68 (7)

VHDPE-30%

VPET-5%

E10 wax-5%

HF-60% 42.7 (21) 61.8 (19) 0.17 (12) 0.42 (12) 0.69 (12)

RHDPE-30%

VPET-5%

E10 wax-5%

DF-60% 45.2 (13) 58.7 (13) 0.17 (5) 0.40 (7) 0.64 (9)

VHDPE-30%

VPET-5%

E10 wax-5%

DF-60% 52.8 (15) 65.8 (16) 0.16 (7) 0.44 (6) 0.74 (6)

RHDPE-30%

VPET-5%

E10 wax-5%

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.
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Linear expansion values for all formulations at 30% RH ranged from 0.15 to

0.17% (Table 1). At 65% and 90% RH,

the HF/RHDPE and DF/RHDPE formulations had slightly higher values.

Results of Tests on

Recyclability

In general, the mechanical, water resistance, and dimensional stability properties

of second-generation panels made from

recycled materials were essentially equivalent to or better than properties obtained

from first-generation panels. Therefore, the

second-generation composites, or possibly higher generation composites, can be

produced using recycled materials without

the consequence of reduced property values.

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 values 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 tensile strength of second-generation panels

was 19% higher than that of first-generation 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 material from first-generation panels.

Impact energy values of specimens

made from first-generation panels and second-generation panels were nearly equal

and not statistically different.

Physical and Dimensional Stability

Properties

In the 24-hr water-soak tests, first-generation panels showed 53% thickness swell

(Table 2). Incorporating first-generation

panel fibers into second-generation panels improved this property by 21%. Similar trends were observed for water

absorption values (Table 2). Water absorption of second-generation panels was

18% lower than that of first-generation

specimens. These differences were statistically significant. The results suggest

that the additional HDPE from refiberized

first-generation panels further encapsulated 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 significant (Table 2). The incorporation of recycled panels into second-generation

panels significantly decreased linear expansion at both 65% and 90% RH.

The positive influence of incorporating

20% first-generation panels into the second-generation panels may be the result

of several factors. The incorporation of

20% refiberized first-generation panels reduced 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 HDPE, 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 reducing 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

uniformity in both the machine- and

cross-machine directions.

• Recycled and granulated HDPE 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 highdensity 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 firstgeneration 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 plastic. These blends can then be formed into

products using conventional plastics processing 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 meltblending 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 produced 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 meltblended composites, experimental operations generally proceed through the

Table 2. Results of Water Soak and Linear Expansion Tests on Recyclability Specimensa

24-hr water soak Linear expansion (%)

Composite Thickness Water 30% RH 65% RH 90% RH

swell absorption

(%) (%)

First-generation panelsb 52.8 (15) 65.8 (16) 0.16 (7) 0.44 (6) 0.74 (6)

Second-generation 42.0 (12) 54.3 (12) 0.15 (11) 0.37 (9) 0.52 (11)

panelsc

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. c DF-40%, recycled panel-20%, RHDPE-30%, VPET-5%, and E10 wax-5%
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following sequence of steps: (a) conversion of raw materials into forms suitable

for preparing dry mixtures quantitatively

and feeding those mixtures into the meltblending apparatus, (b) quantitative dry

mixing, (c) melt-blending by either an extruder 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 variables on mechanical and physical behavior 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 performance. Cellulosic fibers, plastics, and coupling agents are described in Table 3.

Plastics

Plastics act as the matrix in the composite. In this program, a baseline matrix

plastic, virgin polypropylene (VPP) homopolymer, was compared to three waste

plastics: polypropylene from auto battery

cases (BPP), recycled ketchup bottle

polypropylene (KPP), and recycled highdensity 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 availability.

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 polypropylene in extruded sheets for automobile

interior panels. We included relatively expensive (several times the price of WF)

pure cellulose fibers (BW40) as another

baseline filler for comparing against recycled fibers—waste newspaper (ONP)

and old magazines (OMG).

Both plastics and additives can be

readily used in traditional plastics processing machinery. However, wood or paper

fibers present difficulties during the meltblending 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 dispersed into individual particles in the plastic using a simple laboratory single-screw

extruder. Although difficult to disperse with

an extruder, a usable blend of BW40 cellulose 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 Descriptiona Source

Plastic

Virgin polypropylene VPP Fortilene 9101, 1602, 1902; Solvay Polymers, Inc., Deer Park, TX

nominal MFI 3, 12, 30.

Recycled polypropylene BPP Cleaned chips; nominal MFI 10 Gopher Smelting and Refining Co.,

from auto battery cases Eagon, MN

Recycled polypropylene KPP Cleaned chips; nominal MFI 3 Wheaton Plastic Recycling Co.,

from ketchup bottles Milleville, NJ

Recycled polypropylene HDPE–MB Cleaned chips; nominal MFI 0.7 Recycle Worlds, Madison, WI

from milk bottles

Cellulosic filler

Wood flour WF Western pine; -40+80 mesh American Woodfiber Co., Schofield, WI

Cellulose BW40 Pure cellulose fiber; mean length 60 μm James River Corp., Hackensack, NJ

Waste newspaper ONP Over-production issue Milwaukee Journal/Sentinel Inc.,

Milwaukee, WI

Waste magazine OMG Representative sample of Madison Recycling Center, Madison, WI

Madison waste stream

Coupling agent

Epolene E43 powder E43S Powdered maleated polypropylene; Eastman Chemical Co., Kingsport, TN

M = 4,200

Epolene E43 emulsion E43E Emulsified potassium salt Eastman Chemical Co.

Epolene G3002 powder G3002 Powdered maleated polypropylene; Eastman Chemical Co.

M = 11,000

a 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-blending 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 bonding (act as a “coupling agent”) between

filler and matrix. In this program, we restricted 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 matrix.

Mechanical and Physical

Properties

Materials were compounded in either a

38-mm single-screw extruder or a 1-L Kmixer. Extrusion parameters were temperature 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 specimens 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

23oC. Specimens and test methods followed ASTM D256, D638, D747, and

D790. Apparent melt viscosities and shear

rates were calculated from measured volumetric throughput rates and pressure drops

across the die during steady-state extrusion in a single-screw extruder at 190oC.

Selected properties from the various

studies are summarized in Table 4. This

table shows the larger effects of some

more-sensitive variables. Because the conditions of each study varied somewhat,

care must be taken when comparing data.

General trends rather than actual values

will be emphasized in the following discussion.

Reinforcement Effects

Addition of 30%–40% of any of the

wood/paper reinforcing fillers to the plastics 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 reinforced thermoplastics in general. Table 5

summarizes property changes with addition of 40% ONP to several virgin and

recycled polypropylenes.

Most major changes in composite performance occurred at filler contents below

30%. For example, aside from an approximate 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 interfered with bonding, resulting in decreased 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 viscosTable 4. Selected Mechanical Property Data from Various Studies

Plastic Filler Couplinga Tensile Tensile Izod impact energy

agent modulus strength Notched Unnotched

(GPa ) (MPa ) (J/m) (J/m)

PPV None None — 31.5 23.8 650

40% ONP E43 4.89 47.1 20.8 109

40% BW40 E43 4.80 48.2 24.7 114

40% WF E43 3.72 34.1 18.7 72

HDPE–MB 40% ONP E43 3.80 37.6 28.6 73

40% BW40 E43 3.79 36.6 30.8 68

40% WF E43 2.61 27.8 36.4 81

PPV 40% ONP None 4.97 34.0 20.8 113

40% ONP E43 4.90 47.4 19.8 144

40% ONP G3002 4.56 52.3 20.4 190

KPP None None 1.62 36.5 62.0 >800

40% ONP G3002 4.03 52.3 30.6 167

40% OMG G3002 3.55 38.9 34.2 138

BPP None None 1.32 24.5 165.0 >800

40% ONP G3002 3.98 42.5 34.3 150

40% OMG G3002 3.44 31.8 41.8 125

a Coupling agent was added at a level of 3%–5% of fiber weight depending on the study.
7

ity of the higher performance fibrous composites.

The polypropylene composites were

stronger and stiffer than the HDPE–MB

composites but had lower notched impact

energy values. The unfilled plastic composites showed the same trend, i.e., composite 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 affect composite properties, addition of reinforcement can affect the mechanisms

by which the plastic achieves its performance.

Analysis of the results of both the filler

and plastic effects can lead to some interesting conclusions. For example, the mechanical 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 associated with the high viscosity of the recycled system can be overcome.

Coupling Agent Effects

Coupling agents may be incorporated

into composites in different ways to concentrate the material at the interface where

it is active. In our studies, adding solid

coupling agent (E43) to the melt or applying 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 counteracted by the much lower chemical reactivity of the potassium salt with the

cellulose compared with the reactivity of

the anhydride with cellulose. Perhaps the

E43 functions more to enhance dispersion of the cellulosic fillers than to bond

the cellulose to the polymer.

The higher molecular weight maleated

polypropylene, G3002, had a very beneficial effect on composite strength, energy

absorption, and unnotched impact behavior. Initial moduli were approximately the

same but ultimate strength and area under the curves (a measure of toughness)

were much greater for systems with coupling agent (especially G3002). The fact

that unnotched rather than notched impact 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 affected by removal of failure loci than was

notched impact energy because the notch

itself constitutes a failure locus. The apparently greater interaction of G3002 with

polypropylene relative to E43 may be attributable to the higher molecular weight

of G3002.

Processing Effects

Little preference was shown for compounding in a K-mixer or a single-screw

extruder with WF or cellulose fiber. However, those fillers are relatively easily dispersed, and the ONP could not be

melt-blended with a single screw. Moreover, the small interaction terms between

Table 5. Change in Property after Addition of

40% ONP to Plastic

Filled/Unfilled

Property KPP BPP VPP

Tensile

Modulus 2.49 3.00 —

Strength 1.49 1.66 1.66

Energy 0.65 0.73 —

Elongation 0.47 0.46 —

Flexural

Modulus 2.29 3.01 2.94

Strength 1.52 1.91 2.00

Impact

Notched 0.49 0.21 0.86

Unnotched <0.21 <0.19 0.29

filler and compounder in the statistical

analysis also indicated some differences

in dispersibility between WF and cellulose

fiber.

We investigated the effects of re-extrusion 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 reductions 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 overall 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 highintensity 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

Apparent viscosity (poise)

10000

7000

4000

2000

1000

10 20 50 100 200 500 1000

Apparent shear rate (1/S)

42% ONP

37% ONP

32% ONP

42% WF

Unfilled PP

Figure 1. Apparent melt viscosity of composite blends.
8

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 cooperative 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 Resources (DNR) and by in-kind contributions from the eight cooperating

companies. Laboratory experiments demonstrated that old newspapers could be

dispersed as fibers into thermoplastics by

melt-blending, resulting in substantial improvements 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 compounding 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 investigating the use of waste LDPE “contaminated” 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 coordinated by the FPL. Major hurdles in this

program are the residual moisture in the

raw material from the hydropulping process and product applications.

Waste Jute–Polyester Panels as

Reinforcing Filler

In response to interest expressed by a

U.S. company in the possibility of recycling panels produced by impregnating jute

fibers with thermosetting polyester, we

granulated the panels and investigated the

ability to use the resultant mixture as reinforcing filler in melt-blended composites

with a polypropylene matrix. Overall, this

waste material produced composite mechanical properties approximately equivalent to those of similar composites

containing wood flour as the reinforcement.

Waste Kenaf Core as Reinforcing

Filler

This program resulted from a request

by the Agrecol Corporation (Madison, WI

to determine whether kenaf core material

could be useful as a reinforcing filler in

plastic composites. We granulated the

core material and successfully meltblended the -40 mesh fraction with polypropylene. The composite properties were

approximately equivalent to those of similar 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 thermoplastic composites. Although such solid

waste is available in large quantity, it contains wood with cured thermoset adhesives that might cause problems in

melt-processed composites because the

adhesives do not melt at processing temperatures. We granulated the plywood and

successfully melt-blended the -40 mesh

fraction with polypropylene. The composite properties were approximately equivalent 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
9

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 meltblending fiber and plastics on

a commercial scale at costs

acceptable to melt fabricators

(extruders, injection molders,

etc.)
10

John A. Youngquist, George E. Myers, James H. Muehl, Andrzej M. Krzysik,

and Craig M. Clemons are with USDA Forest Service, Madison, WI 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 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, OH 45268

BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35

United States

Environmental Protection Agency

Center for Environmental Research Information

Cincinnati, OH 45268

Official Business

Penalty for Private Use

$300

EPA/600/SR-95/003