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United StatesEnvironmental Protection

Agency

Risk ReductionEngineering LaboratoryCincinnati, OH 45268

Research and Development EPA/600/SR95/003 March 1995

Project Summary

Composites from RecycledWood and Plastics

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

and Craig M. Clemons

The ultimate goal of our research wasto develop technology to convert re-cycled wood fiber and plastics into du-rable products that are recyclable andotherwise environmentally friendly. Twoprocessing technologies were used toprepare wood-plastic composites: air-laying and melt-blending. Research wasconducted in (1) developing laboratorymethods for converting waste wood,wastepaper, and waste plastics intoforms suitable for processing into com-posites; (2) optimizing laboratory meth-ods for making composite panels fromthe waste materials; (3) establishing adatabase on the effects of formulationand bonding agent on physical andmechanical properties of composites;(4) establishing the extent to which thecomposites can be recycled withoutunacceptable loss in properties; and(5) reaching out to industry to provideeducation, to develop applications, andto extend the database. Overall, the pro-gram demonstrated that both air-laidand melt-blended composites can bemade from a variety of waste wood,wastepaper, and waste plastics. Thecomposites exhibit a broad range ofproperties that should make them use-

ful in a wide variety of commercial ap-plications. For air-laid composites, thewaste materials were demolition woodwaste and waste plastics from milkbottles (polyethylene) and beveragebottles (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 thevirgin ingredients. In addition, air-laidcomposites containing 20% regroundpanels possessed some properties thatwere superior to those of the originalcomposites. For melt-blended compos-ites, waste materials were wastepaper,polyethylene from milk bottles, andpolypropylene from automobile batterycases or ketchup bottles. Waste maga-zines were slightly inferior to wastenewspapers as a reinforcing filler; theproperties of composites made fromwaste newspaper were better thanthose of composites made from woodflour, which is currently used in somecommercial composites. Properties ofwood-plastic composites were gener-ally parallel to those of the plastics;thus, different balances in compositeproperties are possible from usingwaste plastic. Outreach activities in-cluded the organization and presenta-tion of two international conferenceson wood fiber-plastic composites, pre-sentations at many conferences, publi-cation of several papers, and severalspin-off cooperative studies with indus-try. One major study with industry dem-onstrated the commercial feasibility of

making melt-blended composites fromold newspapers and polypropylene.

This Project Summary was developed

by EPAs Risk Reduct io n Engineering

Laboratory, Cincinnati, OH, to announcekey f indings of the research project

that is ful ly docum ented in a separate

report of the same t i t le (see Project

Report ordering inform at ion at back).

Printed on Recycled Paper

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Studies on Air-Laid CompositesAir-laid (AL) web composites provide

options for balancing performance proper-ties and costs, depending upon the appli-cation under consideration. However, poorattraction and low interfacial bonding be-tween the hydrophilic wood and hydro-phobic polyolefin limit the reinforcement

imparted to the plastic matrix by the woodcomponent. We compared the mechani-cal and dimensional stability properties offlat panel composites made from virginand postconsumer waste wood and plas-tics in two series of tests:

AL Series 1. PET systemsl Virgin hemlock wood fiber (HF), virgin

polyester fiber (VPET), phenolic resinl HF, recycled PET (RPET), phenolic

resinl Demolition waste wood fiber (DF),

VPET, phenolic resinl DF, RPET, phenolic resin

AL Series 2. HDPE systemsl HF and virgin high-density poly-

ethylene (VHDPE)l HF and recycled HDPE (RHDPE)l DF and VHDPEl DF and RHDPE

Proportions of components were basedon 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 panelsmade from AL Series 2 panels. Two for-mulations were tested. Each formulationconsisted of 30% RHDPE, 5% VPET, and5% E-10 tackifier. In addition, one formu-lation had 60% DF and no refiberizedfirst-generation panels; the other formula-tion had 40% DF and 20% refiberizedfirst-generation panels.

Methods and MaterialsExperiments consisted of the following

sequence of steps: (a) modifying the FPLair-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 andstacking the webs to produce mats of agiven weight; (e) consolidating the mats ina platen press to produce test panels; (f)

cutting test specimens from panels; and(g) testing properties.

For both test series, each data set wastested for normality at the 95% confidencelevel using Shapiro-Wilk statistical analy-sis. An analysis of variance was performedand the means were compared at the95% confidence level using Tukeys

method of multiple comparisons.The raw materials studied in the air-forming portion of this research programfell into three general classes: cellulosicfibers, plastics, and additives.

Cellulosic FibersTwo basic types of wood fiber were

used in the AL series of tests. The firstwas virgin western hemlock wood fiber(HF), which was produced in a pressur-ized single-disk refiner from 100% pulp-grade chips. The second was demolitionwood fiber (DF), which was derived fromwaste wood from buildings that had beentorn down in the Boston, MA, area.

PlasticsThe virgin polyester (VPET) was 5.5

denier (6.1 x 10-7

kg/m), 38 mm long, andcrimped, and had a softening temperaturegreater than 215C. The recycled polyes-ter fiber, which was spun from recycledsoft drink containers, was 6.00 denier, 51mm long, and crimped. For all the air-laidexperiments, VPET served as a matrix tohold the fibers together within the mat.

The virgin high-density polyethylene(VHDPE) was a blow-molding polymernormally used as a feedstock for plasticmilk bottles. The flakes were cryogeni-

cally ground to a (-)35 mesh size. Themelt flow index of the recycled HDPE was0.7.

AdditivesLiquid phenolic resin was used as the

binder for the AL Series 1 panels; it had asolids content of 51% to 53% and a pH of9.5 to 10.0 at 25C. The resin was sprayedon the wood fiber at 25C at a level of10% solids by weight as it rotated in adrum-type blender.

For the AL Series 2 boards, the woodfiber was blended with granulated HDPE.Previous work showed that a tackifier was

needed to retain the granule HDPE in theweb during the web formation process.Preliminary testing had also indicated thatthe tackifier, a wax emulsion of oxidizedlow molecular weight polyethylene (E-l 0),did not have an adverse effect on theproperties of the resultant test panels. The

tackifier was applied to the wood fibers ina rotating drum blender with an air spraygun in a manner similar to the applicationof phenolic resin in the AL Series 1 studies.

Equipment Modifications andAdditions

A 305-mm-w id e, la bo ra to ry -sca leRando-Webber forming machine was usedto make nonwoven mats for the air-laidcomposites. The equipment was modifiedto minimize the density gradient acrossthe web, a problem encountered in preliminary experiments.

Panel FabricationNonwoven webs were weighed, sorted

and stacked on the basis of weight andspecific gravity. A steam-heated platenpress was used to press the panels to athickness of 3.2 mm and a specific gravityof 1.0. A cooling cycle was used to maintain target thickness.

The recyclability part of the study required that we determine the feasibility orecycling panels made for AL Series 2which contained DF and RHDPE. Wefound that we needed to recycle the boardsthrough the pressurized refiner to be ableto produce the desired fiber length andbundles.

Tests on Mechanical and PhysicalProperties

We evaluated the performance of panels made for AL Series 1 (PET systems)

AL Se ri es 2 (H DPE sy stems) , an drecyclability.

Results of Tests on PETSystems (AL Series 1)

In general, the mechanical, water resistance, and dimensional stability propertiesof panels made from recycled materialswere equivalent to similar properties obtained from panels containing all virgin ovirgin/recycled materials. Therefore, therecycled ingredients tested in AL Series 1could replace virgin materials with minoconsequences.

Mechanical PropertiesPanels made with the HF/VPET formu

lation had the highest bending MOR value(50.6 MPa), although no statistically significant differences were observed for MORvalues for either wood fiber or PET variations. The modulus of elasticity (MOEvalues followed a different pattern. In boththe 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 forthis property was 16% for both groups.

For the HFNPET formulation, tensile

tent trend. Impact strength was respec-tively 20% and 10% higher for HF and DFformulations containing VPET fibers com-pared to formulations containing RPET fi-bers.

strength was 33.0 MPa; tensile strengthdecreased 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 totensile strength, the incorporation of RPETfibers increased tensile modulus (MOE)by 6% and 7% for HF and DF formula-tions, respectively, although these differ-ences were not statistically significant.

Physical and Dimensional StabilityProperties

Thickness swell values were significantlydifferent for HF/RPET and DFNPET speci-mens (Table 1). The HF/RPET specimenshad the lowest thickness swell value(22.3%), and the DFNPET specimens thehighest value (29.8%). Water absorptionvalues were not significantly different.

Impact energy of specimens from the Linear expansion values at 30% RHHF and DF formulations showed a consis- were statistically equivalent (Table 1). At

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

24-hr water soak Linear expansion 1%)

Cornpositeb Thicknessswell

(%)

Waferabsorption

(%)

30% RH 65% RH 90% RH

AL Series 1HF-80%VPET-10%PR-10%

HF-80%RPET-10%PR-70%

DF-80%VPET-70%PR-10%

DF-80%

RPET-70%PR-10%

AL Series 2HF-60%VHDPE-30%VPET-5%E10 wax-5%

HF-60%RHDPE-30%VPET-5%E10 wax-5%

DF-60%VHDPE-30%VPET-5%E10 wax-5%

DF-60%RHDPE-30%VPET-5%E10 wax-5%

25.2 (9)

22.3 (9)

29.8 (14)

26.9 (8)

43.8 (14)

42.7 (21)

45.2 (13)

52.8 (15)

43.4 (20)

41.3 (25)

48.2 (25)

44.1 (16)

54.9 (17)

61.8(19)

58.7(13)

65.8(16)

0.19 (10)

0.21 (13)

0.20 (11)

0.20 (12)

075 (9)

0.17 (12)

0.17 (5)

0.16 (7)

0.42 (4)

0.44 (8)

0.43 (6)

0.45 (6)

0.39 (5)

0.42 (12)

0.40 (7)

0.44 (6)

0.61 (6)

0.70 (7)

0.64 (7)

0.71 (6)

0.68 (7)

0.69 (12)

0.64 (9)

0.74 (6)

aValues in parentheses are coefficients of variation (%).

bDF is demolition wood fiber; E10, epolene-maleated polyethylene; HF. hemlock fiber; VPET,virgin polyester fiber; RPET, recycled polyester; RHDPE, recycled high-density polyethylene; andVHDPE, virgin high-density polyethylene.

65% and 90% RH, the HF/RPET and DFIRPET formulations had slightly higher val-ues and were statistically different fromthe HFNPET and DF/VPET formulations.

Results of Tests on HDPESys terns (AL Series 2)

Panels containing virgin and recycled

wood fiber/polyethylene had equivalentmechanical and physical properties. There-fore, as in AL Series 1, the recycled mate-rials used in AL Series 2 could replacevirgin materials with minor consequences.

Mechanical PropertiesThe DFNHDPE panels had the highest

bending MOR value at 19.1 MPa, followedby 18.7 MPa for the HF/RHDPE panels.Generally no statistically significant differ-ences were observed for MOR values foreither wood fiber or HDPE variations. Incontrast, the HF/RHDPE panels had thehighest bending MOE value (2.13 GPa)

and the DFNHDPE panels the lowestMOE value (1.75 GPa); however, theseresults were not statistically significant.

For tensile strength, the highest value(12.4 MPa) was observed for the DF/VHDPE formulation; tensile strength of theDF/RHDPE panels was 7% lower (11.5MPa). For both wood fiber variations, theuse of either virgin or recycled HDPE didnot significantly influence tensile strengthvalues. The HFNHDPE panels had thehighest tensile MOE (2.81 GPa); incorpo-ration of RHDPE lowered tensile MOE by21% (2.23 GPa), a significant change. Ten-sile MOE values of DF formulations wereabout equal, averaging 2.11 GPa.

Type of wood fiber and formulation didnot significantly affect impact energy.


Thickness swelling of DF specimenswas an average of 22% higher than thatof HF specimens; the highest value (53%)was observed for the DF/RHDPE formula-tion (Table 1). Particularly notable is thefact that RHDPE had a significant effecton only the DF formulation and not the HFformulation. Thickness swelling was Iow-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 woodfiber produced a statistically significant in-crease in this property (average 13% in-crease). The HF/VHDPE and DFNHDPEformulations 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 to0.17% (Table 1). At 65% and 90% RH,the HF/RHDPE and DF/RHDPE formula-tions had slightly higher values.

Results of Tests on

Recyclabi l i tyIn general, the mechanical, water resis-

tance, and dimensional stability propertiesof second-generation panels made fromrecycled materials were essentially equiva-lent to or better than properties obtainedfrom first-generation panels. Therefore, thesecond-generation composites, or possi-bly higher generation composites, can beproduced using recycled materials withoutthe consequence of reduced property val-ues.

Mechanical PropertiesThe 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 higherthan that of second-generation panels(2.01 vs. 1.77 GPa). These differenceswere not statistically significant. The ten-sile strength of second-generation panelswas 19% higher than that of first-genera-tion panels. Similar results were obtainedfor tensile modulus. The higher propertiesof the second-generation panels indicatethat wood fiber/RHDPE composites canbenefit 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 equaland not statistically different.


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

(Table 2). Incorporating first-generationpanel fibers into second-generation pan-els improved this property by 21%. Simi-lar trends were observed for waterabsorption values (Table 2). Water ab-sorption of second-generation panels was18% lower than that of first-generationspecimens. These differences were sta-

tistically significant. The results suggestthat the additional HDPE from refiberizedfirst-generation panels further encapsu-lated the wood fibers, thus limiting wateruptake by the wood fibers.

Linear expansion values were similarfor both formulations at 30% RH, althoughthe differences were statistically signifi-cant (Table 2). The incorporation of re-cycled panels into second-generationpanels significantly decreased linear ex-pansion at both 65% and 90% RH.

The positive influence of incorporating20% first-generation panels into the sec-ond-generation panels may be the result

of several factors. The incorporation of20% refiberized first-generation panels re-duced the percentage of wood fiber (DF)from 60% to 40%. The actual amount oftotal wood fiber was reduced from 60% to52%, and the total amount of RHDPE wasincreased from 30% to 36%. Likewise, thepercentage of PET and E-10 each wasincreased by 1%. The increase of thesecomponents, particularly the HDPE, andthe decrease of the wood fiber may be adirect cause of some improvements inproperty values. More wood fiber was ableto be encapsulated by plastic, thereby re-ducing exposure of the wood to moisture.

ConclusionsThe Rando-Webber air-formingequipment can be adapted to handleboth long and short synthetic andnatural fibers as well as powder.Nonwoven air-laid webs can beproduced tha t have exce l len t

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

24-hr water soak Linear expansion (%)

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

swell absorption(%) (%)

First-generation panelb

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)pan el

c

aValues in parentheses are coefficients of variation (%).

bDF-60%, RHDPE-30%, VPET-5%, E10 wax-5%. DF is demolition wood fiber; RHDPE, recycledhigh-density polyethylene; VPET, virgin polyester fiber; and E10, epolene-maleated polyethylene.

cDF-40%, recycledpanel-20%. RHDPE-30%, VPET-5%. and E10 wax-5%

uniformity in both the machine- andcross-machine directions.

l Recycled and granulated HDPE canbe used in the FPL air-formingequipment to produce an air-laid webthat can be subsequently made intoflat panels or shaped sections.

l Pressure refining techniques can

convert post-consumer demolitionwood or construction waste into fiberbundles that can be processed verysuccessfully in the FPL air-formingequipment and subsequently pressedinto flat panels or shaped sections.

l Panels made with recycled materialscompare favorably to those made ofvirgin materials. Mechanical andphysical properties of panels madewith recycled polyester fiber or high-density polyethylene and demolitionwaste wood are similar to those ofpanels made with virgin materials.

l Second-generation composites, or

possibly higher generationcomposites, can be produced usingrecycled materials without theconsequence of reduced propertyvalues. Mechanical and physicalproperties of second-generationpanels made from recycled materialswere essentially equivalent to or betterthan properties obtained from first-generation panels.

Studies on Melt-BlendedComposites

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 intoproducts using conventional plastics pro-cessing techniques such as extrusion andinjection molding. The plastic acts as ameans to convey the wood/paper duringprocessing and the wood/paper fiber bearsthe load in the final composite, offering aneffective balance between processabilityand strength of end product. With melt-blending techniques, wood fiber providesseveral advantages as reinforcement inthermoplastic composites. These includeeconomy on a cost per unit volume basis,desirable aspect ratios, flexibility (henceless fiber breakage), and low abrasivenessto equipment. Composites can be pro-duced containing up to 50 weight percentwood fiber and are low cost,thermoformable, and relatively insensitiveto moisture.

Methods and MaterialsIn 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 suitablefor preparing dry mixtures quantitativelyand feeding those mixtures into the melt-blending apparatus, (b) quantitative drymixing, (c) melt-blending by either an ex-truder or a K-mixer, (d) injection moldingof test specimens, and (e) measurementof properties.

Five major studies were undertaken toinvestigate the effects of a number of vari-ables on mechanical and physical behav-ior of wood-fiber-reinforced thermoplastics.The studies were statistically designed andanalyzed and all comparisons were madeat a 95% confidence level. However, forthe sake of brevity, the results will. bepresented as a whole, centering on thelarger effects of the variables because oftheir greater impact on composite perfor-mance. Cellulosic fibers, plastics, and cou-pling agents are described in Table 3.

Table 3. Materials Used in Melt-Blending Studies

PlasticsPlastics act as the matrix in the com-

posite. In this program, a baseline matrixplastic, virgin polypropylene (VPP) ho-mopolymer, was compared to three wasteplastics: polypropylene from auto batterycases (BPP), recycled ketchup bottlepolypropylene (KPP), and recycled high-density polyethylene from blow-moldedmilk bottles (HDPE-MB). These plasticswere chosen on the basis of low meltingtemperature (necessary for use with wood/paper fiber), cost, performance, and avail-ability.

Cellulosic FibersCelluloses act as the reinforcing filler in

the composite. We used wood flour (WF)as the primary baseline filler because it iscurrently used commercially with polypro-pylene in extruded sheets for automobileinterior panels. We included relatively ex-

Material Abbreviation Descriptiona

pensive (several times the price of WF)pure cellulose fibers (BW40) as anotherbaseline filler for comparing against recycled fibers-waste newspaper (ONP)and old magazines (OMG).

Both plastics and additives can bereadily used in traditional plastics process-ing machinery. However, wood or paperfibers present difficulties during the melt-blending step. Cellulosic filler must be in aform that can be completely dispersedinto the molten plastic by the shear forcesexerted during melt-blending. Wood flourwas readily disaggregated and fully dis-persed into individual particles in the plas-tic using a simple laboratory single-screwextruder. Although difficult to disperse withan extruder, a usable blend of BW40 cel-lulose fibers was also obtained in thisway. Wastepaper fibers were much moredifficult to handle because of their lowbulk density. For melt-blending in a high

Source

Plastic

Virgin polypropylene VPP

Recycled polypropylenefrom auto battery cases

Recycled polypropylenefrom ketchup bottles

Recycled polypropylenefrom milk bottles

Cellulosic filler

Wood flour

Cellulose

Waste newspaper

BPP

KPP

HOPE-MB

WF

BW40

ONP

Waste magazine OMG

Coupling agent

Epolene E43 powder E43S

Epolene E43 emulsion E43E

Epolene G3002 powder G3002

Fortilene 9101, 1602, 1902;nominal MFI 3, 12, 30.

Cleaned chips; nominal MFI 70

Cleaned chips; nominal MFI 3

Cleaned chips; nominal MFI 0.7

Western pine; -40+80 mesh

Pure cellulose fiber; mean length 60 m

Over-production issue

Representative sample ofMadison waste stream

Powdered mateated 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.,Mitteville, NJ

Recycle Worlds, Madison, WI

American Woodfiber Co., Schofield, WI

James River Corp., Hackensack, NJ

Milwaukee Journal/Sentinel Inc.,Milwaukee, WI

Madison Recycling Center, Madison, WI

Eastman Chemical Co., Kingsport, TN

Eastman Chemical Co.

Eastman Chemical Co.

aMFI is melt flow index. M is molecular weight.

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intensity K-mixer, the paper was milled orground into approximately 4 to 8-mm flakesusing a small granulator. For melt-blend-ing in an extruder, the paper was firstreduced to fibers by a small modifiedhammermill.

Coupling Agents

Additives aid the dispersion of filler intothe matrix plastic and/or enhance the bond-ing (act as a coupling agent) betweenfiller and matrix. In this program, we re-stricted ourselves to Eastman Epolenes(E43, G3002)-maleated polypropylenewaxes in which the small degree ofmaleation provides polar groups capableof bonding to the cellulose while thepolypropylene segments, in theory, offercompatibility with the polypropylene ma-trix.

Mechanical and PhysicalProperties

Materials were compounded in either a38-mm single-screw extruder or a 1-L K-mixer. Extrusion parameters were tem-perature profile 170C to 190C screwspeed 15 rpm, and residence time l-2min. The K-mixer parameters were 4500to 5500 rpm and discharge temperature171C to 200C. In all studies, test speci-mens were prepared by injection molding.

At least five specimens of each blendwere tested for each mechanical property.After molding, the specimens were stored

over dessicant for at least 3 days beforetesting.

Mechanical properties were measuredon the dry specimens at approximately23C. Specimens and test methods fol-lowed ASTM D256, D638, D747, andD790. Apparent melt viscosities and shearrates were calculated from measured volu-

metric throughput rates and pressure dropsacross the die during steady-state extru-sion in a single-screw extruder at 190C.

Selected properties from the variousstudies are summarized in Table 4. Thistable shows the larger effects of somemore-sensitive variables. Because the con-ditions of each study varied somewhat,care must be taken when comparing data.General trends rather than actual valueswill be emphasized in the following dis-cussion.

Reinforcement EffectsAddit ion of 30%-40% of any of the

wood/paper reinforcing fillers to the plas-tics resulted in a composite with highermodulus and strength but lower impactenergy and percentage of elongation andenergy to maximum load. These effectsare not surprising and are typical of rein-forced thermoplastics in general. Table 5summarizes property changes with addi-tion of 40% ONP to several virgin andrecycled polypropylenes.

Most major changes in composite per-formance occurred at filler contents below

Table 4. Selected Mechanical Property Data from Various Studies

Plastic

PPV

HDPE-MB

PPV

KPP

BPP

Filler

None

40% ONP40% BW4040% WF40% ONP

40% BW4040% WF40% ONP40% ONP40% ONPNone

40% ONP40% OMGNone

40% ONP40% OMG

Coupling,agent

None

E43E43E43E43E43E43None

E43G3002None

G3002G3002None

G3002G3002

Tensile Tensile

modulus strength

(GPa) (MPa)

- - 31.5

4.89 47.14.80 48.2

3.72 34.13.80 37.6

3.79 36.6

2.61 27.84.97 34.0

4.90 47.4

4.56 52.31.62 36.5

4.03 52.3

3.55 38.91.32 24.5

3.98 42.5

3.44 31.8

Izod impact energyNotched Unnotched

(J/ml (J/m)

23.8 65020.8 10924.7 114

18.7 7228.6 7330.8 68

36.4 81

20.8 11319.8 14420.4 190

62.0 >80030.6 16734.2 138

165.0 >80034.3 15041.8 125

30%. For example, aside from an approxi-mate 10% increase in modulus, no majorchanges in mechanical performance werefound over the rather narrow range of32% to 42% ONP in VPP.

Typically, the more fibrous fillers (ONPand BW40) resulted in composites withsuperior mechanical properties but were

more difficult to process when comparedto WF. However, the presence of claysand other impurities in the OMG made thematerial more difficult to disperse and in-terfered with bonding, resulting in de-creased mechanical performance whencompared with other fibrous fillers.

Figure 1 demonstrates some effectson viscosity at low shear rates. Viscositymeasurements showed dramatic increaseswhen WF was replaced with ONP and asfiber content was increased. This increasein viscosity demonstrated the effects ofboth aspect ratio and filler contents oncomposite melt behavior. Even at a fiber

loading of 32% ONP, PPV composite meltswere significantly more viscous than a 42%WF-filled PPV.

Matrix EffectsChanging the melt flow index (MFI) of

VPP had a significant effect on viscositybut little effect on mechanical performanceover the range studied (330 g/10 min).This result suggests that MFI could beused to compensate for increased viscos-

aCoupling agent was added at a level of 3%~5% of fiber weight depending on the study.

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Table 5. Change in Property after Addition of40% ONP to Plastic

Filled/Unfilled

Property KPP BPP VPP

Tensile

ModulusStrength

EnergyElongation

Flexural

2.49 3.00 -1.49 1.66 1.660.65 0.73 -

0.47 0.46 -

ModulusStrength

impact

2.29 3.01 2.941.52 1.97 2.00

Notched 0.49 0.21 0.86Unnotched >0.21 >0.19 0.29

ity of the higher performance fibrous com-posites.

The polypropylene composites werestronger and stiffer than the HDPE-MBcomposites but had lower notched impactenergy values. The unfilled plastic com-posites showed the same trend, i.e., com-posite properties qualitatively followedthose of the matrix polymers. Similar trendswere also seen for composites made withBPP and KPP. For example, the use ofBPP (a block copolymer with highernotched impact strength) instead of VPPresulted in composites with higher notchedimpact strength, although the difference inthis property was not nearly as great asthat in the unfilled polymers. In other

words, although choice of plastic can af-fect composite properties, addition of re-inforcement can affect the mechanismsby which the plastic achieves its perfor-mance.

Analysis of the results of both the fillerand 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 goodas those of the current commercial WF/polypropylene system. This may offersome practical utility if problems associ-ated with the high viscosity of the re-cycled system can be overcome.

Coupling Agent EffectsCoupling agents may be incorporated

into composites in different ways to con-centrate the material at the interface whereit is active. In our studies, adding solidcoupling agent (E43) to the melt or apply-ing emulsified E43 directly to the fiber hadlittle effect on mechanical performance of

1 0 0 0 0

7 0 0 0

4 0 0 0

2 0 0 0

42% ONP37% ONP32% ONP42% WFUnfilled PP

Figure 1. Apparent melt viscosity of composite b/ends.

composites. Concentrating the emulsifiedadditive 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 thecellulose compared with the reactivity ofthe anhydride with cellulose. Perhaps theE43 functions more to enhance disper-sion of the cellulosic fillers than to bondthe cellulose to the polymer.

The higher molecular weight maleatedpolypropylene, G3002, had a very benefi-cial effect on composite strength, energyabsorption, and unnotched impact behav-ior. Initial moduli were approximately thesame 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 factthat unnotched rather than notched im-pact energy was increased indicates thatG3002 probably enhances dispersion ofthe fibers and reduces aggregates thatwould act as failure loci. For example,unnotched impact energy was more af-fected by removal of failure loci than wasnotched impact energy because the notchitself constitutes a failure locus. The ap-parently greater interaction of G3002 withpolypropylene relative to E43 may be at-tributable to the higher molecular weightof G3002.

Processing EffectsLittle preference was shown for com-

pounding in a K-mixer or a single-screwextruder with WF or cellulose fiber. How-ever, those fillers are relatively easily dis-persed, and the ONP could not bemelt-blended with a single screw. More-over, the small interaction terms between

filler and compounder in the statisticalanalysis also indicated some differences

in dispersibility between WF and cellulosefiber.

We investigated the effects of re-extru-sion on the mechanical and rheologicalperformance of three different compositeblends. For almost all mechanical andrheological properties, very little changeoccurred as the material was recycled overfive cycles. The length and therefore theaspect ratio of the ONP fiber decreased,but these decreases were apparently notgreat enough to result in any large reduc-tions in composite performance. The WFwas reduced in both thickness and length,as smaller bundles of wood fibers were

sheared off the larger particles. Thesechanges in dimension resulted in no over-all change in aspect ratio nor, ultimately,in composite performance.

Conclusionsl Melt-blended composites cannot be

prepared with wastepapers asreinforcing filler using a conventionallaboratory single-screw extruder.However, these composites can beprepared with a laboratory high-intensity K-mixer, an industrial-scaleK-mixer, or a twin-screw extruder thatemploys a properly designed feederfor the fiber.

. Old newspaper (ONP) as reinforcingfiller provides better properties thanwood flour, which is currently used asfiller in commercial composites. Oldmagazines (OMG) can also be usedas a filler, but they are less easilydispersed into the matrix plastic andresult in somewhat lower properties

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than those of composites containingONP.

l With the same filler, substitutingrecycled milk bottle polyethylene forVPP leads to lower strength, stiffness,and unnotched impact energy, buthigher notched impact energy.

l Use of recycled high density

polyethylene from milk bottles andrecycled polypropylene from batterycases as a matrix in composites withONP results in improved impactperformance when compared with thatof composites made from VPP andONP.

lAddition of the coupling agent EpoleneG3002 at 3 weight percent of fillerresults in very useful increases incomposite properties, probably as aresult of improved fiber dispersion.

l Select composite systems showedl i t t le or no loss in mechanicalproperties when repeatedly

reprocessed (m-extruded and injectionmolded).

Commercial ImplementationThe research program led to many co-

operative studies with industry andacademia, all with the ultimate goal ofcommercializing composites made withwaste materials.

Commercial Feasibility of WasteNewspaper-ThermoplasticComposites

The program was partially funded bythe Forest Products Laboratory (FPL) and

the Wisconsin Department of Natural Re-sources (DNR) and by in-kind contribu-t i ons f rom the e igh t coopera t ingcompanies. Laboratory experiments dem-onstrated that old newspapers could bedispersed as fibers into thermoplastics bymelt-blending, resulting in substantial im-provements in some properties comparedwith the unfilled plastic or plastic filledwith wood flour. Major conclusions are asfollows:

l Old newspaper/polypropylene (ONP/PP) composites can be compoundedon a commercial scale using eitherthe K-mixer with ONP flakes as feedor using a twin-screw extruder withONP fibers fed separately from theplastic.

l An ONP/PP sheet containing 42weight percent ONP can be preparedby extrusion on a commercial scale.This sheet meets existing

specifications for automobile panelsand can be thermoformed into avariety of shapes.

l Given p roper des ign o f me l tprocessing equipment, a wide varietyof other commercial products couldbe manufactured from ONP/PPcomposites with similar ONP content.

l Firm estimates of production costsfor ONP/PP composite products mustawait:a. additional examination of com-

pounding methods to defineoptimum balance of dispersionability, throughput rate, and cost;and

b. improvement in methods todeliver wastepaper in a form anda t a cos t accep tab le to acompounder or a manufacturerof plastic products.

Waste LDPE Program

A consortium of companies is investi-gating the use of waste LDPE contami-nated b y r e s i d u a l f i b e r f r o m ahydropulping operation that scavengeswood fiber from coated paper stock. Theprogram involves raw material processors,compounders, plastics processors, andresearch institutions and is being coordi-nated by the FPL. Major hurdles in thisprogram are the residual moisture in theraw material from the hydropulping pro-cess and product applications.

Waste Jute-Polyester Panels asReinforcing Filler

In response to interest expressed by aU.S. company in the possibility of recy-cling panels produced by impregnating jutefibers with thermosetting polyester, wegranulated the panels and investigated theability to use the resultant mixture as rein-forcing filler in melt-blended compositeswith a polypropylene matrix. Overall, thiswaste material produced composite me-chanical properties approximately equiva-lent to those of similar compositescontaining wood flour as the reinforcement.

Waste Kenaf Core as ReinforcingFiller

This program resulted from a requestby the Agrecol Corporation (Madison, WIto determine whether kenaf core materialcould be useful as a reinforcing filler inplastic composites. We granulated thecore material and successfully melt-blended the -40 mesh fraction with polypro-

pylene. The composite properties wereapproximately equivalent to those of simi-lar composites containing wood flour.Therefore, where kenaf core is readilyavailable at low cost, it could very likelysubstitute for wood flour as a reinforcingfiller.

Wastewood Composite asReinforcing FillerThe University of Tennessee Extension

requested an evaluation of waste woodcomposite as a reinforcing filler in thermo-plastic composites. Although such solidwaste is available in large quantity, it con-tains wood with cured thermoset adhe-sives that might cause problems inmelt-processed composites because theadhesives do not melt at processing tem-peratures. We granulated the plywood andsuccessfully melt-blended the -40 meshfraction with polypropylene. The compos-ite properties were approximately equiva-

lent to those of similar compositescontaining wood flour. This waste materialcould therefore substitute for wood flouras a reinforcing filler in melt-processedcomposites.

Recommendations

ResearchAdditional research is needed on both

air-laid and melt-blended composites madefrom recycled wood fiber and plastics toimprove properties and processing andincrease potential applications as follows:

1.

2.

3.

4.

5.

6.

Evaluate the potential for makingcomposite materials with othermajor components of the wastestream, including low-densitypolyethylene, polystyrene, andmixed waste plastics.Verify the recyclability of compositesmade with reground first-generationingredients.Improve melt-blending processes toachieve better fiber dispersion withminimal fiber breakage.Improve bonding between woodfiber and plastic matrix to enhancephysical and mechanical properties.Improve impact energy and creep

resistance (decreased deflectionunder long-term load), currently thel im i t i ng p roper t ies o f thesecomposite systems.Determine the resistance of thesecomposite systems to relativelyextreme environments and develop

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means to enhance resistance tomoisture, biodegradation, and fire.

Commercialization1. Continue extensive outreach to

industry to acquaint companies withthese types of composite systems,to develop applications, and to

cooperate in product development.

2. To obtain commercial acceptanceof mel t -b lended composi tescontaining wastepaper fiber;

a. improve methods for converting wastepaper atcosts acceptable to industrialusers, or at least the currentcost of wood flour (about

$0.22/kg);

b. improve methods for melt-blending fiber and plastics ona commercial scale at costsacceptable 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. 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 avail-able only from:

National Technical Information Service5285 Port Royal RoadSpringfield, VA 22161Telephone: 703-487-4650

The EPA Project Officer can be contacted at:Risk Reduction Engineering LaboratoryU.S. Environmental Protection AgencyCincinnati, OH 45268

United StatesEnvironmental Protection AgencyCenter for Environmental Research InformationCincinnati, OH 45268

Official BusinessPenalty for Private Use$300

EPA/600/SR-951003

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