Composites of Acrylonitrile-Butadiene-Styrene Filled with Wood- Flour

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1 Composites of Acrylonitrile-Butdiene-Styrene Filled with Wood-Flour Composites of Acrylonitrile-Butdiene-Styrene Filled with Wood- Flour L.M. Mtun 1*, S. Cm 2, K.B. Yuhsz 1 nd Q.J. Armstrong 1 1 Deprtment of Forestry, Michign Stte University, Est Lnsing, Michign 48824, USA 2 École Supérieure du Bois, Atlnpôle B.P , Nntes 44306, Frnce Received: 21 August 2006 Accepted: 21 November 2006 SUMMARY This study exmined both the use of crylonitrile-butdiene-styrene (ABS) s plstic mtrix for wood-plstic composites (WPCs) nd the effect of impct modifiction on the mechnicl properties of ABS/wood-flour composites. Blends of ABS filled with wood flour (both pine nd mple) were processed into profile shpe using conicl twin-screw extruder nd the mechnicl properties of the resulting composites were chrcterised nd compred to WPCs mde with polyolefins (HDPE nd PP) nd rigid PVC mtrices. Generlly, WPCs mde with ABS mtrix outperformed their polyolefin counterprts in both flexurl strength nd modulus, wheres ABS-bsed composites hd inferior strength but greter modulus thn those mde with rigid PVC. The impct strength of ABS/wood-flour composites ws below tht of wood plstic composites mde with polyolefins. However, impct modifiction with crylonitrile-butdiene-styrene terpolymers hd some effect in toughening of the ABS/wood-flour composites. INTRODUCTION Interest in wood plstic composites (WPCs) is on the rise in the United Sttes becuse of new Environmentl Protection Agency (EPA) regultions on pressure-treted wood lumber. As of Dec. 30, 2003, the once common chromted copper rsente, or CCA, cn no longer be used to tret wood tht is used ner homes 1. EPA regultors re concerned tht rsenic in CCA, which slowly seeps from wood over time, my pose helth risks. Children, especilly, could be t risk becuse they spend more time outside thn dults do, nd more frequently put unwshed hnds into their mouths. Wood plstic composites comprise n emerging clss of mterils tht combine the desirble durbility of * Corresponding uthor mtun@msu.edu Rpr Technology, 2007 plstics with the cost effectiveness of wood s filler or reinforcing gent 2. Becuse WPCs re true hybrid mterils, they hve strength nd stiffness properties tht re somewhere between both mterils 2,3. They hve outstnding bolt, screw nd nil retention nd the bility to be drilled nd mchined similrly to wood. Generlly, WPCs re stiffer thn net plstics nd hve ttributes tht solid wood does not hve. If properly mnufctured, WPCs re more resistnt to moisture (wter bsorption nd thickness swelling) thn wood. In ddition, they resist ttck by insects nd fungi better thn other wood products 2,3. This improved performnce is due to the fct tht the plstic mtrix encpsultes the individul wood fibres; thus interfering with moisture uptke by the wood element. Moisture cn only be bsorbed into the exposed sections of the wood 4. WPCs cn be snded, stined, pinted nd finished just like nturl solid wood. Becuse of the bove-mentioned ttributes, WPC products re being selected by homebuilders over other mterils such s solid pressure-treted wood, concrete, cly, nd luminium, etc., in vriety of innovtive pplictions, such s decking, docks, lndscping timbers, fencing, plyground equipment, window nd door frmes, etc 2,3. WPCs re lso used s moulded pnel components for utomotive interiors. Combining thermoplstics with wood fibres hs become lucrtive industry in North Americ nd prticulrly the United Sttes 2,5. The ltest mrket study indicted tht the WPC mrket in the U.S. ws 320,000 tons (700 million pounds) in 2001 nd the volume is expected to more thn double by Experts believe tht the production of WPCs will continue to grow, prticulrly due to their cceptnce s Polymers & Polymer Composites, Vol. 15, No. 5,

2 L.M. Mtun, S. Cm, K.B. Yuhsz nd Q.J. Armstrong substitute for chromted copper rsente pressure-treted lumber 5. Currently, the mjority of these WPCs re mde using commodity plstics such s polyethylene (PE), polypropylene (PP), polystyrene (PS), nd polyvinylchloride (PVC). These thermoplstics re selected minly becuse they cn be processed t lower tempertures ( C) to prevent the degrdtion of cellulosic mterils 2. Another importnt thermoplstic with mjor mrket shre is crylonitrile butdiene styrene (ABS) copolymer. However, ABS hs not been extensively investigted s polymeric mtrix for WPCs. ABS copolymer is high-impct nd high-het deflection temperture grde of polystyrene. For exmple, typicl ABS formultion contins 15 to 35% crylonitrile (this imprts chemicl resistnce nd het stbility), 5-30% butdiene (controlling toughness nd impct strength), nd 40-60% styrene (rigidity nd processing ese) 6. Becuse the three monomers in the ABS system cn be tilored to the endproduct needed by vrying the rtios in which they re combined, ABS is thermoplstic tht hs performnce between those of commodity nd engineering thermoplstics (Tble 1). The wide spectrum of pplictions for ABS rnges from utomotive pplictions (18% of the totl mrket), smll nd lrge pplinces (22%, e.g., refrigertors) nd office business mchines nd telecommunictions (e.g., telephone hndsets, computers, etc.). By the yer 2007, experts predict tht refrigertor disposl will yield metric tonnes (126 million pounds) of polyurethne fom nd metric tonnes (203 million pounds) of other plstics (minly ABS nd HIPS) 7. The utomotive industry lso constitutes substntil resource for recycled engineering plstics. The proportion of plstics in the totl weight of cr ws pproximtely 10-13% in 1990; nd ws predicted to pproch 15-20% in The primry destintion of this wste hs been lndfills. However, environmentl concern nd reductions in vilble lndfill cpcity require tht lterntives be developed to utilise the mteril vlue of this post-consumer plstic. Any recycling process developed for plstics recovered from refrigertors or utomobiles discrded tody should not only ccommodte mterils used 15 to 20 yers go, but should lso be dptble for effective reclmtion of future mterils. A better technology of utilistion must first be developed to promote the use of this resource. Incinertion nd recycling re two other methods vilble to recover some of the vlue from post-consumer ABS. Since plstics re mde from fossil fuels they contin s much energy s petroleum or nturl gs, mking them idel fuel for wste-to-energy plnts. Therefore their incinertion becomes n lterntive method to recover useful chemicl energy needed to produce stem nd electricity. On the other hnd, recycling recovers the rw mteril tht cn then be used to mke new plstic products. However, cost is one of its min issues becuse virgin resins often cost less thn recycled plstics 9. Both incinertion nd recycling hve been extensively prctised in North Americ. Nevertheless, the use of ABS s mtrix for wood-plstic composites (WPCs) hs not been extensively exmined. Becuse ABS is thermoplstic tht hs performnce between commodity nd engineering thermoplstics, its use s mtrix in WPCs could led to composites with properties superior to those mde with common commodity plstics. Consequently, the objective of this study ws to evlute the fesibility of utilising ABS s plstic mtrix for wood-plstic composites. In prticulr, the processbility nd mechnicl properties of WPCs mde with ABS were compred to those of PE, PP, nd PVC counterprts. The effects of wood flour species (softwood versus hrdwood) nd impct modifiction on the mechnicl properties of ABS/ wood-flour composites were lso exmined. EXPERIMENTAL Mterils In this study, virgin ABS resin designted s MAGNUM AG700 Tble 1. Properties of vrious thermoplstics 6 Properties HDPE PP HIPS PVC ABS Density g/cm Melt temperture/softening temperture, o C ~110 Tensile strength, MP Tensile modulus, GP Elongtion to brek, % Notched Izod impct strength, J/m Het deflection temperture, o C t 455 kp HIPS stnds for high impct polystyrene 366 Polymers & Polymer Composites, Vol. 15, No. 5, 2007

3 Composites of Acrylonitrile-Butdiene-Styrene Filled with Wood-Flour from Dow Chemicl Compny ws used s the polymeric mtrix insted of recycled mteril. Its melt flow index (MFI) nd density were 3.9 g/10 min (ASTM D1238, 190 C nd 2.16 kgf) nd 1.04 g/cm 3, respectively. The mm (40 mesh) mple nd pine wood flours obtined from Americn Wood Fibres (Schofield, WI) were used s filler. The wood flours were oven-dried t 105 C for pproximtely 48 h before processing to remove moisture. The TR-251 lubricnt from Struktol Compny (Stow, OH) ws used to reduce friction between components nd equipment, which esed processing. This lubricnt is complex oleochemicl mixture contining mono- nd dimides nd metl sop. Two impct modifiers were used: poly(methylmethcryltecrylonitrile-butdiene-styrene) or Blendex-362 nd poly(crylonitrilebutdiene-styrene) or Blendex-338, both supplied by Crompton Corp. (Middlebury, CT). The physicl properties of these impct modifiers re summrised in Tble 2. All mterils were used s received from the mnufcturers. Rigid polyvinyl chloride (PVC with K vlue of 66 from Oxyvinyls, Pedricktown, NJ), flke type highdensity polyethylene (HDPE- Fortiflex TM B53-35H with melt flow index of 0.49 g/10 min nd density of g/cm 3 ) nd polypropylene (PP-Fortilene TM HB 9000 with MFI of 0.7g/10 min nd density of g/cm 3 ) supplied by B.P. Solvy (Houston, TX) were lso used s mtrices for comprison with ABSbsed composites. The melt flow rtes of HDPE nd PP were mesured ccording to ASTM D1238 (190 C nd 2.16 kgf). Compounding nd Extrusion of Composites A 10 litre high intensity mixer (Ppenmeier, Type TGAHK20) ws used for room temperture dryblending of either unfilled ABS or ABS mtrix filled with dried wood flour, lubricnt, nd impct modifiers. The formultions of the composites without impct modifier were mintined t 50% wood flour (mple or pine), 46% ABS, nd 4% lubricnt by totl weight of the composites. The mount of impct modifier used in the formultions ws fixed t 20% bsed on the totl weight of wood flour (Tble 3) since the ddition of up to 10% impct modifier did not significntly enhnce the impct strength of ABS/wood-flour composites 10. The compounded mterils were fed into 32 mm conicl counter-rotting twin-screw extruder (C.W. Brbender Instruments Inc.) with length to dimeter rtio of 13:1. This twinscrew extruder ws equipped with n unpressurised vent to llow residul moisture to escpe nd ws powered by 5.6 kilowtt (7.5 hp) Intelli-Torque Plsti-Corder Torque Rheometer. Tble 3 summrises the processing conditions for ech formultion in terms of heting temperture profile nd rottionl speed of the screws. Tble 2. Physicl properties of crylonitrile-butdiene-styrene terpolymer impct modifiers Properties Typicl vlues Blendex-338 Blendex-362 Density (g/cm 3 ) Bulk density (kg/m 3 ) Hrdness, Shore D Voltiles (%) Men prticle size (:m)) 180 (80 mesh) 900 Butdiene content (%) Dt obtined from Crompton s mterils sfety dt sheet Tble 3. Formultions for ABS/wood-flour composites nd their processing conditions Composites Twin Screw Extrusion Processing Conditions Types Formultions Temperture profile from hopper to die ( o C) Unfilled-ABS Pine-ABS Mple-ABS ABS : TR : 4 Pine : ABS : TR :46 : 4 (Formultion #1) Mple : ABS : TR :46 : 4 (Formultion #2) Screw speed (rpm) Pine-ABS-Blendex-362 (Formultion #1) % Blendex-362 Pine-ABS-Blendex-338 (Formultion #1) % Blendex-338 The impct modifi er content ws bsed on the totl mount of wood fl our in the composites Polymers & Polymer Composites, Vol. 15, No. 5,

4 L.M. Mtun, S. Cm, K.B. Yuhsz nd Q.J. Armstrong The rectngulr die creted smples with nominl width nd thickness of 2.54 cm (1 ) nd 0.95 cm (3/8 ), respectively. The smples were cooled using recirculted wter bth to mintin the smple size nd geometry fter exiting the die (prevent die swell). These smples were used for flexurl property testing. The smples used for notched Izod impct tests were mnufctured using different process. A 19.1-mm singlescrew extruder (Brbender, L/D rtio 30:1) driven by 5.6 kilowtt (7.5 hp) Intelli-Torque Plsti-Corder Torque Rheometer ws utilised to process the blended compounds listed in Tble 3. A single-stge mixing screw (3:1 compression rtio) with torpedo screw tip (35 degrees) ws used during processing. The temperture profile from hopper to horizontl rod die ws 190/180/160/150 C nd the rottionl speed of the screw ws set t 20 rpm, regrdless of the formultions. The rod extrudtes were compressionmoulded into pnels in hydrulic preheted press (Erie Mill Co. Erie, PA.) t 190 C nd 6.2 MP (900 psi) for 5 min. The mould ws then cooled to room temperture under pressure. From these pnels, rectngulr smples with dimensions of 12.7 mm x 63.5 mm were cut from the pnel sheets for impct testing (3 mm thick). Property Testing Three-point flexurl tests were crried out in wlk-in conditioning room t 23 C ± 2 C nd 65% ± 4% reltive humidity using n Instron 4206 testing mchine (with Series IX softwre). The crosshed rte ws 4.5 mm/min in conformnce with ASTM stndrd D At lest ten replictes were tested nd dt were collected on the modulus of rupture (MOR or flexurl strength) nd modulus of elsticity (MOE or stiffness). The modulus of rupture reflects the mximum lod-crrying cpcity of member in bending nd is proportionl to the mximum moment borne by the specimen. It is n ccepted criterion of strength, lthough it is not true stress becuse the formul by which it is computed is vlid only to the elstic limit 11. The notched Izod impct strength of the smples ws determined by using Tinius Olsen Izod impct tester (Model 92) in wlk-in conditioning room ccording to the procedure outlined in ASTM D The smples were notched with fly cutter (V-notch, 45 ngle) to the desired depth nd swn with rzor blde to produce shrp crck. The sttisticl verge of the mesurements of t lest 15 specimens ws tken to obtin relible verge nd stndrd devition. Sttisticl Anlysis A two-smple t test (single-fctor) nd Duncn s multiple rnge tests were employed to determine the sttisticl differences in mechnicl properties mong the formultions investigted t 95% significnce level. Bsed on Duncn s grouping, the mens with different letters in Tbles 4-6 denote significnce between formultions t the α = 0.05 level, while the mens with the sme letter indictes no difference between formultions. All nlyses were done using Design-Expert v.6 softwre from the Stt-Ese Corp. (Minnepolis, MN). RESULTS AND DISCUSSION Effect of Mtrix Types on the Properties of WPCs The bending properties nd notched Izod impct strength of ABS/woodflour composites with pine nd mple flours re summrised in Tbles 4 nd 5 respectively. To evlute the effects of wood flour species s well s polymer types on the mechnicl properties of the composites, dt for WPCs mde with HDPE, PP, nd rigid PVC re lso listed in these tbles for comprison with ABS-bsed composites mnufctured in this study. It should be mentioned tht HDPE, PP, nd PVC-bsed composites lso contined 50% wood flour (mesh size 40) but vrious processing conditions were used in their mnufcture, s described in our previous ppers Overll, the results listed in Tbles 3-5 clerly demonstrte tht ABS cn be processed with wood flour using existing mchinery nd processing conditions similr to those used to process commodity plstics. The resulting composites hd mechnicl properties tht compred fvourbly to those mde with other plstic mtrices. Generlly, wood plstic composites mde with ABS mtrix outperformed their polyolefin (HDPE nd PP) nd rigid PVC counterprts in stiffness (Tbles 4 nd 5), regrdless of wood species, due primrily to the higher stiffness of ABS mtrix (Tble 1). Different trends were observed for the strength. ABS-bsed composites hd lower flexurl strength thn those of PVC counterprts, regrdless of wood species. By contrst, the strength of ABS-bsed composites ws greter thn tht of polyolefinbsed composites when pine ws used s filler. Mple-PP composites ppered to hve greter flexurl strength thn mple-abs counterprts. However, the difference ws not sttisticlly significnt t the α = 0.03 level. Wood plstic composites mde with PP outperformed their HDPE counterprts in flexurl strength nd stiffness regrdless of wood species, due primrily to the higher stiffness of polypropylene. When compred to unfilled ABS mtrix (Tbles 4 nd 5), the ddition of wood flour to the mtrix did not ffect the flexurl strength of the composites, regrdless of wood species. Becuse of the greter stiffness of wood fibres compred to ABS, the flexurl modulus of the composites ws significntly improved with the ddition of wood 368 Polymers & Polymer Composites, Vol. 15, No. 5, 2007

5 Composites of Acrylonitrile-Butdiene-Styrene Filled with Wood-Flour Tble 4. Mechnicl properties of unfilled ABS nd wood flour (pine)-plstic composites mde with vrious polymer mtrices Unfilled ABS nd Properties composites with 50% pine flour MOR (MP) MOE (GP) Impct strength (J/m) Unfilled ABS A A A Pine-ABS A B B Pine-rigid PVC B C - Pine-PP C D C Pine-HDPE D E D The mens with different letters indicte signifi cnce between tretments t the α = 0.05 level, while the mens with the sme letter indictes no difference between tretments Tble 5. Mechnicl properties of unfilled ABS nd wood flour (mple)-plstic composites mde with vrious polymer mtrices Unfilled ABS nd Properties composites with 50% mple flour MOR (MP) MOE (GP) Impct strength (J/m) Unfilled ABS A A A Mple-ABS A B B Mple-rigid PVC B C - Mple-PP C D C Mple-HDPE D E D The mens with different letters indicte signifi cnce between tretments t the α = 0.05 level, while the mens with the sme letter indictes no difference between tretments Tble 6. Effect of impct modifier on the properties of ABS/wood-flour composites Composites with Properties 50% pine flour MOR (MP) MOE (GP) Impct strength (J/m) b Pine-ABS A A A 20% Blendex-362/ pine-abs flour to the mtrix, s expected from the rule of mixtures 15. The deleterious effect of the ddition of wood fibres to the plstic mtrix ws pprent, becuse ABS/woodflour composites exhibited much lower cpbility for bsorbing impct AB B B 20% Blendex-338/ pine-abs B C C The mens with different letters indicte signifi cnce between tretments t the α = 0.05 level, while the mens with the sme letter indictes no difference between tretments b The notched Izod impct strength of unfi lled ABS ws J/m energy thn the unfilled copolymer (Tbles 4 nd 5). The notched Izod impct strength of ABS/wood-flour composites ws below tht of wood plstic composites mde with polyolefin mtrices. For unknown resons, the ABS/pine-flour composites hd lower impct strength thn mple counterprt. As expected, we observed n opposite trend in Izod impct strength, where softer polyethylene-bsed WPCs hd stronger impct resistnce thn their polypropylene counterprts. As mentioned, the Izod impct strength of the ABS/wood-flour composites (14-27 J/m) ws fr inferior to tht of unfilled ABS (106 J/m). This difference is typicl trde-off of improving the stiffness of the mtrix by incorporting wood filler into the mtrix. It hs been reported in previous studies tht the ddition of wood fibres to plstic reduces the ductile behviour of the mtrix nd mkes the composites more brittle 15,16. As consequence, ductile deformtion of the mtrix is inhibited, nd n incresing proportion of the frcture energy will rise from fibre debonding nd frictionl pull-out losses s the fibre concentrtion increses in the mtrix. In ddition, ech fibre cts s discontinuity cpble of inititing crcks in the composite 17. Therefore, the introduction of impct modifiers into the composites is needed to toughen ABS/wood-flour composites. Impct Modifiction of ABS/ Wood-Flour Composites The toughening of ABS/wood-flour composites by introducing impct modifiers into the composites ws lso exmined. Two different crylonitrilebutdiene-styrene terpolymer impct modifiers (Blendex 338 nd Blendex 362) t 20% ddition level were evluted nd the results re summrised in Tble 6. The reduced Izod impct strength of ABS/pine-flour composites due to the incorportion of brittle wood flour ws enhnced by the introduction of impct modifiers into the composites. Impct modifiers function s n elstomeric dhesive between the mtrix prticles nd efficiently inhibit brittle crck propgtion in the composites 15. Although Blendex-362 with the lowest content of polybutdiene rubber ABS resin (62%) developed higher Izod Polymers & Polymer Composites, Vol. 15, No. 5,

6 L.M. Mtun, S. Cm, K.B. Yuhsz nd Q.J. Armstrong impct strength vlues reltive to Blendex-338 with 70% polybutdiene rubber ABS resin, our most recent results (to be published soon) show tht these two impct modifiers perform similrly when dded to ABS composites with 30% wood flour. Impct modifiction did not ffect the strength of ABS/wood-flour composites, irrespective of modifier type (Tble 6). By contrst, the stiffness of the composites ws ffected by impct modifiction. It is believed tht t 20% ddition level, the impct modifier begins to become the dominnt component of the blend, nd the compounds become softer nd flexible, lowering the modulus of the composites. CONCLUSIONS This study exmined both the use of ABS s plstic mtrix for wood plstic composites nd the effect of impct modifiction on the mechnicl properties of the ABS/wood-flour composites. From this reserch, it cn be concluded tht: ABS cn be processed with wood flour using existing mchinery under processing conditions similr to those used to process commodity plstics. Generlly, WPCs mde with ABS mtrix outperformed their polyolefin counterprts in both flexurl strength nd modulus. ABS-bsed composites hd inferior flexurl strength but greter flexurl modulus thn those mde with rigid PVC mtrix. Notched Izod impct strength of ABS/wood-flour composites ws generlly below tht of composites mde with HDPE nd PP mtrices. The ddition of wood flour to ABS mtrix significntly lowers the cpbility of the resulting composites for bsorbing impct energy. Impct modifiction hd some effect in toughening the composites for the types of modifiers nd ddition level used in this study. ABS/wood-flour composites pper to be promising wy to utilise recycled mteril nd reduce the mount of wste going into lndfills. ACKNOWLEDGMENTS This work ws supported by the USDA- CSREES Grnt-Advnced Technology Applictions to Estern Hrdwood Utilistion (Grnt No ). The uthors re grteful for the generous dontion of mterils provided by the mnufcturers listed in the Experimentl Section. REFERENCES 1. Anonymous, Arsenic-treted wood to be phsed out of residentil use, Chemicl nd Engineering News, Feb. 2002, 27 (2002). 2. Clemons C., For. Prod. J., 52(6), (2002) Mtun L.M. nd Heiden P.A., Wood Composites, in Encyclopedi of Polymer Science nd Technology, Jcqueline I. Kroschwitz, Editor, John Wiley & Sons, Inc., (2004) interscience.wiley.com/epst/rticles/ pst474/frme.html (published online- April 2004). 4. Dwson-Andoh B., Mtun L.M. nd Hrrison J., J. Vinyl Additive Technol., 10(4), (2004) Defosse M., Wood Composites re Expnding Among Sectors, Modern Plstics, (Jnury 2003). 6. Fried J.R., Polymer Science nd Technology, Prentice Hll PTR, Upper Sddle River, New Jersey, (1995). 7. Zolotor A.M., Composition, Properties nd Economic Study of Recycled Refrigertors, report prepred for the Americn Plstics Council (APC) posted t s_plsticsresource/doc.sp?trac KID=&CID=174&DID=381, site ccessed on Jnury 20, (2005). 8. Liu X., Boldizr A., Rigdhl M. nd Bertilsson H., J. Appl. Polym. Sci., 86, (2002) Rchtnpun P., Ph.D. Disserttion, Michign Stte University, Est Lnsing, Michign, USA, (2003). 10. Yuhsz K.B., Cm S. nd Mtun L.M., Acrylonitrile-Butdiene- Styrene (ABS) s Mtrix for Wood- Plsti Composites, pper presented t the 2 nd Europen Symposium on Wood Fibre Polymer Composites: Applictions nd Prospectives, Mrch 24-25, 2005, Cité Mondile- Bordeux-Frnce (2005). 11. Anonymous, Wood Hndbook: Wood s n Engineering Mteril, Forest Products Lbortory Generl Technicl Report (FPL-GTR-113), USDA Forest Service, (1999). 12. Pilrski J.M. nd Mtun L.M., J. Vinyl Additive Technol., 11(1), (2005) Pilrski J.M. nd Mtun L.M., J. Appl. Polym. Sci., 100(1), (2006) Kim J.W., Mtun L.M. nd McCullough D.G., Forest Prod. J., 55(11), (2005) Mtun L.M., Prk C.B. nd Bltinecz J.J., J. Vinyl Additive Technol., 3(4), (1997) Mengeloglu F., Mtun L.M. nd King J.A., J. Vinyl Additive Technol., 6(3), (2000) Piggott M.R., Lod Bering Fibre Composites, Chpter 7, Pergmon Press, Toronto (1980). 370 Polymers & Polymer Composites, Vol. 15, No. 5, 2007