Properties of wood plastic composites made of milled particleboard and polypropylene

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1 Eur. J. Wood Prod. (1) 73:87 9 DOI 1.17/s ORIGINAL Properties of wood plstic composites mde of milled prticlebord nd polypropylene Cezry Gozdecki Arnold Wilczyński Mrek Kociszewski Stnisłw Zjchowski Received: 1 October 13 / Published online: 11 October 1 Ó The Author(s) 1. This rticle is published with open ccess t Springerlink.com Abstrct Prticles derived from milling three-lyer prticlebords, with sizes from. to 3 mm, were used for mking composites with polypropylene by n injection moulding method. Mleted polypropylene ws used s coupling gent. The objective of this study ws to evlute the mechnicl nd physicl properties of the composites mde from prticlebord nd polypropylene with respect to the content of prticles derived from prticlebord nd coupling gent ddition. Properties of the composites did not differ significntly from those of composites with virgin industril wood prticles used for mnufcturing prticlebords. Moreover, these properties were comprble with the properties of typicl wood plstic composites with wood flour. Prticles derived from milling prticlebords hve proved to be n effective lterntive wood component of wood plstic composites. 1 Introduction Wood plstic composites (WPCs) hve been rpidly developed in recent yers due to their numerous dvntges. One is the possibility of using recycled mterils, both recycled polymers nd wood, for WPC mnufcturing. Mny studies hve shown tht the properties of WPCs mde from recycled polymers, especilly from polypropylene nd high-density polyethylene, re only slightly C. Gozdecki (&) A. Wilczyński M. Kociszewski Institute of Technology, Kzimierz Wielki University, Bydgoszcz, Polnd e-mil: gozdecki@ukw.edu.pl S. Zjchowski Fculty of Chemicl Technology nd Engineering, University of Technology nd Life Sciences, Bydgoszcz, Polnd inferior to those of WPCs mde from virgin polymers. Most WPC compnies in the United Sttes use recycled polymers (Winndy et l. ). The wood component of WPCs is very often mde from wste generted by wood industry. Wood flour which is commonly used in WPC s wood component is minly produced from swdust which is the primry wste product of swmills. Post-consumer wood pllets (Strk 1999) nd poles (Kmdem et l. ) proved to be good source of wood flour. The second common wood component in WPCs is recycled wood fibre including newspper fibre. The usefulness of fibres from old newsppers hs been confirmed by Sndi et l. (199), English et l. (1996), Ashori nd Nourbkhsh (9), Ashori (1), Ashori nd Sheshmni (1), Lopez et l. (1). Ashori nd Nourbkhsh (8) proved tht lignocellulosic fibres from old corrugted continers could be considered s potentil filler of WPCs. In some countries wood wste, like plstic nd pper wste, is mjor component of municipl solid wstes in lndfills. A lrge prt of the wood wste is post-consumer wood-bsed pnels. The volume of these pnels generted per yer is still growing. In Polnd, their nnul supply ws 9, tons in nd is estimted to rech 66, tons in 1 (Rtjczk et l. 3). The most common wood-bsed pnels re prticlebords. Only smll number of recycled prticlebords re used for mking new prticlebords; most of them re destined for lndfill or burned. One of the possibilities of recycling these bords is using them for mnufcturing WPCs. Kmdem et l. () studied the properties of WPCs mde from recycled ure formldehyde (UF) resin bonded prticlebord nd virgin or recycled high-density polyethylene. Prticlebords were milled to obtin prticlebord flour with prticle size from.1 mm (1 mesh) to.6 mm (3 mesh). Compression moulding ws used to mnufcture

2 88 Eur. J. Wood Prod. (1) 73:87 9 WPCs with : prticlebord flour-to-plstic weight rtio. For comprison WPCs from virgin pine wood flour were prepred. In generl, the mechnicl properties of WPCs with prticlebord flour were lmost the sme s those of WPCs with wood flour. The thickness swelling of WPCs contining prticlebord flour ws much smller. The properties of WPCs mde from recycled prticlebord with UF resin s binder were lso investigted by Chhrmhli et l. (8). They used the swdust from prticlebord swing nd the flour from prticlebord milling. The obtined prticles were smller thn.6 mm (3 mesh). The swdust nd flour prticles were mixed t rtio of : by weight. The WPCs were mde by compression moulding method using recycled high-density polyethylene nd 6:, 7:3 nd 8: prticlebord prticles-to-plstic weight rtio. The mechnicl properties of these WPCs were similr to, or in some cses better thn those of conventionl prticlebords. In previous studies on WPCs mde from recycled prticlebords (Kmdem et l. ; Chhrmhli et l. 8) only smll prticles, smller thn.6 mm, were used. These WPCs were mde by compression moulding method nd high-density polyethylene ws used s composite mtrix. WPCs cn lso be produced from lrge wood prticles, lrger thn.6 mm (3 mesh). These prticles contribute to better mechnicl properties of WPCs becuse they usully hve higher length-to-thickness rtio. This ws confirmed in the studies on WPCs with virgin industril wood prticles used for mnufcturing prticlebords (Bledzki nd Fruk 3; Gozdecki et l. 11, 1; Kociszewski et l. 1). In this study, the novel prticlebord-polypropylene composite mde by injection moulding method ws tested. Lrge prticles derived from prticlebords contining the UF resin were used to prepre this WPC. The objectives of the study were to evlute the mechnicl nd physicl properties of these WPCs s ffected by (1) prticlebord prticle content, () coupling gent ddition, nd to compre these properties, (3) with the properties of WPC mde from virgin industril wood prticles nd () with the properties of WPC mde from wood flour. Methods.1 Mterils The polypropylene (PP) used in this study ws homopolymer Moplen HP68T (Bsell Orlen Polyolefins, Polnd). Its density ws.9 g/cm 3, nd its melt flow index ws 3 g/1 min (3 C/.16 kg). Mleted polypropylene (MAPP) Fusbond P33 (DuPont) with density of.9 g/cm 3, melt flow index of 7 g/1 min (19 C/.16 kg), nd grft degree of 1. % ws used s coupling gent. Three kinds of wood prticles (WPs) were used s fillers: recycled wood prticles (RWPs), virgin wood prticles (VWPs) nd wood flour (WF). The RWPs were derived from three-lyer prticlebords with density of.7 g/cm 3, thickness of 18 mm, shelling rtio (the rtio of the thickness of the fce lyers to the thickness of the core lyer) of :6, bonded with UF resin using resin content of 1 % in the fce lyers nd 8 % in the core lyer. Pine wood ws rw mteril of the wood prticles of these prticlebords. The prticlebords were supplied by Kronospn Szczecinek, Polnd. The freshly produced industril prticlebords were used becuse their composition ws known. They were milled by lbortory hmmer-mill, nd then screened by n nlyticl sieve shker (LAB-11-/UP, EKO-LAB Polnd), using 3 nd. mm sieves. Prticles tht pssed through the 3 mm sieve nd remined on the. mm sieve were used s filler of WPCs. The VWPs were derived from industril pine wood prticles used for mnufcturing three-lyer prticlebords, from fine prticles for the fce lyers nd corse prticles for the core lyer. These prticles, which were supplied by Kronospn Szczecinek, Polnd, were the sme s those used for producing prticlebords described in the previous prgrph. The fine prticles were screened nd only those tht remined on the. mm sieve were used. Regrding the corse prticles, those tht pssed through the 3 mm sieve nd remined on the. mm sieve were used. In order to simulte similr content of fine nd corse prticles s tht in prticlebords, the mix consisting of % fine prticles nd 6 % corse prticles ws prepred s filler of WPCs. The WF from softwood, of type Lignocel Ò BK /9 ws supplied by J. Rettenmier & Söhne GmbH, Rosenberg, Germny. The frction nlysis of ech kind of WPs ws performed using three, 1 g oven dry smples. Ech smple ws plced on the top sieve (the. mm sieve for RWPs Tble 1 Frction nlysis per weight of the wood prticles used Screen hole size rnge (mm) WF (%) VWP (%) RWP (%) \

3 Eur. J. Wood Prod. (1) 73: Fig. 1 RWPs, b VWPs of the frction 1 mm, c WF nd VWPs, nd.7 mm sieve for WF) nd shken on n nlyticl shker for min. Portions of WP smples remining on ech screen were weighed with n ccurcy of.1 g nd expressed s the percentge of totl smple weight. The WP mss loss during sieve nlysis did not exceed. %. The verge results of the frction nlysis of three smples of ech kind of WPs re presented in Tble 1. The RWPs nd VWPs of the frction 1.. mm, nd the WF re shown in Fig. 1.. Wood prticle geometry The WPs, both the RWPs nd VWPs, were mesured to determine their geometry. The length, width nd thickness of rndomly selected RWPs nd VWPs for ech of the three frctions,. 1., 1.. nd. 3. mm were mesured using n opticl microscope with mesuring scle. The dimensions of rndomly selected WF prticles were lso mesured. The length-to-thickness nd width-to-thickness rtios of prticles were clculted for ech group of prticles..3 Processing All WPs nd WF were dried t 8 C in n ir-circultion oven for h prior to the mixing process in order to chieve moisture content of less thn 3 %. WPs, WF, PP nd MAPP were dispensed into the hopper using three DSH screw feeders (Hydrpress, Polnd) nd then mixed in one-step mixing process in the feed zone of AH-8 (METALCHEM, Polnd) injection moulding mchine. The temperture profile ws 1 nd 18 C in feed zone 1 nd zone, respectively. The injection pressure time nd hold pressure time were 3 nd 6 s, respectively. To minimise mechnicl degrdtion of WPs during moulding, the dimeter of the injection die ws enlrged to. mm nd the dimeter of the sprue bush to 8 mm. The cross section Tble WPC formultions (percent by weight) WPC code Type of wood prticles of the runner nd the gte ws nd 6 9 6mm, respectively. Three kinds of specimens for tensile tests ccording to EN ISO 7- (type 1A), for flexurl tests ccording to EN ISO 178, nd for impct strength tests ccording to EN ISO were mde. After processing, they were stored in controlled conditions ( % reltive humidity nd C) for weeks prior to testing. Six experimentl WPCs were prepred ccording to the formultions shown in Tble. Four WPCs with the RWPs were produced in order to determine the effect of the WP content nd the effect of MAPP. Two WPCs, with the VWPs nd the WF, were produced for comprison purposes.. Mechnicl testing Wood content PP content RWP--3 RWP 77 3 RWP--3 RWP 7 3 RWP-6-3 RWP RWP-- RWP 6 VWP-- VWP 6 WF-- WF 6 MAPP content Mechnicl properties of tested WPCs were evluted in reltion to tensile, flexurl, nd impct properties. Tensile nd flexurl tests were performed ccording to EN ISO 7- nd EN ISO 178, respectively, using n Instron 3367 mchine. The speed of the cross-hed ws mm/min. Unnotched Chrpy impct strength tests were conducted ccording to EN ISO Ten replictes were run for ech test. All tests were performed t room temperture ( C) nd t constnt reltive humidity ( %).

4 9 Eur. J. Wood Prod. (1) 73:87 9. Wter bsorption nd thickness swelling Wter bsorption nd thickness swelling of WPCs were determined using the sme specimens s those used in flexurl tests. Ten specimens of ech WPC formultion were dried in n oven for h t 1 C, nd the weight nd thickness of oven-dried specimens were mesured. The specimens were then immersed in distilled wter nd fter h their weight nd thickness were mesured. The sme procedure ws followed fter 8 dys. The vlues of wter bsorption were clculted ccording to the formul: Wter bsorption ð%þ ¼ W t W 1 ð1þ W where W t is the specimen weight fter given immersion time, W is the oven-dried weight. The vlues of thickness swelling were clculted with the following eqution: Thickness swelling ð%þ ¼ T t T 1 ðþ T where T t is the specimen thickness fter given immersion time, T is the oven-dried thickness..6 Sttisticl nlysis The obtined dt were sttisticlly nlyzed using the Sttistic version 1. The one-wy nlysis of vrince (ANOVA) ws conducted to determine the significnce of the effect of RWP content on WPC mechnicl properties. Tukey s nd Student s test were pplied to evlute the sttisticl significnce between men vlues of the properties of WPCs with different WPs nd of WPCs mde with nd without MAPP, respectively. 3 Results nd discussion 3.1 WP geometry Tble 1 presents the frction nlysis of RWPs, VWPs nd WF. The RWPs hd greter content of the frctions nd 1.. mm, wheres the VWPs hd firly uniform distribution of frctions. The min WF frctions were.1. nd.. mm. The dimensions of RWPs, VWPs nd WF s well s their length-to-thickness nd width-to-thickness rtios for severl frction groups re listed in Tble 3. The men vlues of RWP length rnged from.3 mm for the frction. 1. to.1 mm for the frction. 3. mm, while those of VWP length rnged from 3.9 mm for the frction. 1. to 16. mm for the frction. 3. mm. Thus, the RWP lengths were much smller, nd s result the length-to-thickness rtio of RWPs ws considerbly smller, on verge. times, thn tht of VWPs. The men vlue of length-to-thickness rtio of WF prticles (Tble 3) ws smller thn tht of RWPs. The VWPs were slender, wheres the RWPs nd WF prticles were thick. The men vlues of width-to-thickness rtio of RWPs nd WF prticles were smller thn those of VWPs. 3. Effect of RWP content Figures, 3 nd show the results for mechnicl nd physicl properties of WPCs mde from PP, RWPs nd MAPP, nd hving different content of RWPs. The results of the ANOVA nlysis showed tht ll properties depended significntly on RWP content (Tble ). The tensile nd flexurl moduli incresed grdully with incresing RWP content from to 6 % (Fig. ). The increse of the moduli ws considerble. These results were expected becuse the elstic modulus of wood, especilly in the grin direction, is higher thn tht of the polymer. The primry objective of wood s filler is to increse the stiffness of WPC. Similr results for the WPCs consisting of PP nd WF hve been reported by Bledzki et l. (), Strk nd Rowlnds (3) nd Tjvidi nd Ebrhimi (3) for the tensile modulus, nd Strk nd Rowlnds (3) nd Cheng et l. (9) for the flexurl modulus. The tensile nd flexurl strengths of WPCs decresed modertely when RWP content incresed (Fig. 3). A Tble 3 Dimensions, length-to-thickness nd width-to-thickness rtios of the WPs Wood prticles Frction Length (mm) Width (mm) Thickness (mm) Length-to-thickness Width-to-thickness VWP. \ F \ (1.).6 (.).3 (.1) 16.3 (.1). (.9) 1. \ F \. 1. (6.) 1. (.6).6 (.). (6.1).6 (1.). \ F \ (6.).1 (.9).9 (.).8 (6.).7 (1.1) RWP. \ F \ 1..3 (.9).7 (.3). (.).3 (.) 1. (.) 1. \ F \..9 (1.) 1.3 (.).9 (.6) 3. (1.) 1. (.3). \ F \ 3..1 (.). (.8) 1. (.7) 3.8 (1.7) 1. (.) WF F \.7.7 (.3). (.1).3 (.1) 3. (1.1) 1.3 (.) Men vlues from mesurements. Stndrd devition in prentheses

5 Eur. J. Wood Prod. (1) 73: Modulus (GP) Tensile Flexurl (.) (.3) (.) (.1) (.31) (.18) 6 RWP content (%) WA or TS (%) (.7) WA fter hours TS fter hours WA fter 8 dys TS fter 8 dys (.6) (.1) (.7) (.1) (.8) (.1) (.) (1.6) (.77) (.3) (.) 6 RWP content (%) Fig. Effect of RWP content on tensile nd flexurl moduli of WPCs with MAPP (stndrd devition in prentheses) Strength (MP or kj/m ) (3.6) (1.3) Tensile Flexurl Impct (3.7) (1.) (.9) (1.7) (1.1) (1.) (1.) 6 RWP content (%) Fig. 3 Effect of RWP content on tensile, flexurl nd impct strengths of WPCs with MAPP (stndrd devition in prentheses) possible reson for these decreses might be not quite strong interfcil dhesion between the hydrophilic RWPs nd hydrophobic PP mtrix, despite the presence of MAPP. As result, the RWPs were not ble to support stresses trnsferred from the mtrix. The slight decrese in the tensile strength with incresing WP content ws observed in other studies on WF-PP composites (Zini et l. 1996; Tjvidi nd Ebrhimi 3; Yng et l. 6). Cheng et l. (9) concluded tht the flexurl strength of WF-PP composite decresed slightly s WP content incresed. Bledzki et l. () found tht the content of soft WF did not ffect the tensile strength of WPC, nd Strk nd Rowlnds (3) reported tht the tensile nd flexurl strengths slightly incresed with incresing WF content. These vried effects of WP content on the strengths of WPCs my be explined by the fct tht these strengths depend on vrious fctors including the size of WPs, their length-to-thickness rtio nd wood species, processing Fig. Effect of RWP content on wter bsorption (WA) nd thickness swelling (TS) of WPCs with MAPP (stndrd devition in prentheses) methods nd prmeters, nd type nd mount of coupling gent used. The impct strength of WPCs decresed modertely, like the tensile nd flexurl strengths, with incresing RWP content from to 6 % (Fig. 3). The RWPs s stiff filler provided points of stress concentrtion. The higher the RWP content the more numerous these points nd the lower the impct strength. These results were in firly good greement with the dt reported by Zini et l. (1996); Bledzki et l. () nd Strk nd Rowlnds (3). The results for the physicl properties of WPCs re shown in Fig.. The wter bsorption incresed strongly when RWP content incresed. The vlues of wter bsorption for the WPC with 6 % RWPs were pproximtely.7 times nd 1.8 times greter thn those for the WPC with % RWPs, for the wter bsorption fter h nd 8 dys, respectively. The wter bsorption in the WPC is due to the wood component becuse the PP component does not bsorb ny moisture s hydrophobic mteril (Tjvidi nd Ebrhimi 3; Yng et l. 6; Ashori nd Nourbkhsh 8). The hydroxyl groups inside the cellulose nd hemicelluloses ttrct the wter molecules nd form hydrogen bonding. As result, the higher the wood content in the composite, the higher the wter bsorption. Moreover, due to the porous structure of wood fibres, the composite with higher wood content bsorbs more wter which penetrtes into the pores ccording to the principle of cpillry flow. A similr effect of wood content on WPC wter bsorption ws observed by Bledzki et l. () nd Tjvidi nd Ebrhimi (3) for WPCs with WF-PP fter h immersion, nd by Khlil et l. (6) for WPCs with swdust-pp fter -h nd -dy immersion.

6 9 Eur. J. Wood Prod. (1) 73:87 9 Tble One-wy ANOVA test on the effect of RWP content on WPC mechnicl nd physicl properties (p vlues) Vrible Tensile modulus Tensile strength Flexurl modulus Flexurl strength Impct strength Wter bsorption Thickness swelling h 8 dys h 8 dys RWP content \.1* \.* \.1*.113** \.7* \.1* \.1* \.1* \.1* * Denotes significnce t.1. ** Denotes significnce t. The thickness swelling of WPCs, similrly to the wter bsorption, incresed s RWP content incresed (Fig. ). The vlues of thickness swelling for the WPC with 6 % RWPs were pproximtely.8 times nd.6 times greter thn those for the WPC with % RWPs, for the swelling fter h nd 8 dys of immersion in wter, respectively. 3.3 Effect of MAPP The mechnicl properties of WPCs contining % RWPs mde with nd without MAPP re presented in Figs., 6, 7, 8 nd 9. The men vlues mrked with different cpitl letters for given property were significntly different t the % significnce level. The tensile properties of WPC with MAPP (Figs., 6) were modertely greter thn those of WPC without MAPP. The tensile modulus nd strength of WPC with MAPP were pproximtely 1 nd % higher, respectively. These increses in the tensile properties were due to better chemicl bonding between the RWPs nd PP mtrix in the presence of MAPP. A similr effect of MAPP on the tensile modulus of WPCs mde from PP nd WF hs been found by Strk (1999), Strk nd Rowlnds (3), Bledzki nd Fruk (3), Slemne nd Luyt (6) nd Ashori (1). Furthermore, Bledzki nd Fruk (3) found similr effect of MAPP on the tensile modulus of WPC mde from PP nd VWPs. However, the effect of MAPP on tensile strength presented in these studies ws stronger thn in the current study. The effect of MAPP on the WPC flexurl properties ws lmost the sme s on the tensile properties. The flexurl modulus nd strength of WPCs with MAPP were pproximtely 1 nd % higher, respectively, thn those of non-coupled WPCs (Figs. 7, 8). A similr effect of MAPP on the flexurl modulus of WPCs mde from PP nd WF hs been found by Cheng et l. (9). Bledzki nd Fruk (3) nd Strk nd Rowlnds (3) observed tht this effect ws not significnt. Regrding the effect of MAPP on the flexurl strength of WPCs from PP nd WF, Cheng et l. (9) concluded tht it ws slight, nd Bledzki nd Fruk (3) nd Strk nd Rowlnds (3) found tht it ws comprble to the result of this study here. The reson for the different results of these studies might be different sizes nd shpes of WPs used to prepre the WPCs. The Tensile modulus (GP) 3 1 A WF-- VWP-- RWP-- RWP--3 Fig. Tensile modulus of WPCs with % wood content. Mens with the sme letter re not sttisticlly different; smll letters effect of wood component kind, cpitl letters effect of MAPP Tensile strength (MP) b WF-- VWP-- RWP-- RWP--3 Fig. 6 Tensile strength of WPCs with % wood content. Mens with the sme letter re not sttisticlly different; smll letters effect of wood component kind, cpitl letters effect of MAPP effect of MAPP on the WPC impct strength ws insignificnt (Fig. 9). The wter bsorption nd thickness swelling of WPCs contining % RWPs did not depend significntly on the presence of MAPP (Figs. 1, 11). These results were not confirmed in other studies. Generlly, dding MAPP ba B B

7 Eur. J. Wood Prod. (1) 73: Flexurl modulus (GP) 3 1 A B Impct strength (kj/m ) 1 1 A A WF-- VWP-- RWP-- RWP--3 WF-- VWP-- RWP-- RWP--3 Fig. 7 Flexurl modulus of WPCs with % wood content. Mens with the sme letter re not sttisticlly different; smll letters effect of wood component kind, cpitl letters effect of MAPP Fig. 9 Impct strength of WPCs with % wood content. Mens with the sme letter re not sttisticlly different; smll letters effect of wood component kind, cpitl letters effect of MAPP 1 Flexurl strength (MP) WF-- VWP-- RWP-- RWP--3 reduced the wter bsorption (Bledzki nd Fruk 3; Njfi et l. 8; Schirp nd Stender (1). Probbly, the weker-thn-expected influences of MAPP on the tensile nd flexurl strengths, nd tht MAPP did not ffect the wter bsorption nd thickness swelling of WPCs with the RWPs my be ttributed to the presence of UF resin. Further studies re needed to clrify the role of UF resin contined in the RWPs on the WPC properties. 3. Comprison of the properties of WPCs mde from different WPs b Fig. 8 Flexurl strength of WPCs with % wood content. Mens with the sme letter re not sttisticlly different; smll letters effect of wood component kind, cpitl letters effect of MAPP The performnce of WPC without MAPP mde from RWPs ws compred with tht of WPC mde from VWPs ba B Wter bsorption (%) b b A WF-- VWP-- RWP-- RWP--3 Kind of composite Fig. 1 Wter bsorption of WPCs with % wood content fter 8 dys. Mens with the sme letter re not sttisticlly different; smll letters effect of wood component kind, cpitl letters effect of MAPP Thickness swelling (%) 3 1 A WF-- VWP-- RWP-- RWP--3 Kind of composite Fig. 11 Thickness swelling of WPCs with % wood content fter 8 dys. Mens with the sme letter re not sttisticlly different; smll letters effect of wood component kind, cpitl letters effect of MAPP A A

8 9 Eur. J. Wood Prod. (1) 73:87 9 (Figs., 6, 7, 8, 9, 1, 11). The men vlues mrked with the sme smll letter for given property were not significntly different t the % significnce level. There were no sttisticl differences between the properties of these WPCs. It ws expected tht the mechnicl properties of WPC with the VWPs would be better. The VWPs hd much higher length-to-thickness rtio thn the RWPs (Tble 3) nd it should result in improving the WPC mechnicl properties (Zini et l. 1996; Strk nd Rowlnds 3; Gozdecki et l. 1; Kociszewski et l. 1). Probbly, the fct tht the mechnicl properties of WPC with RWPs were not worse thn those of WPC with VWPs my be ttributed to the presence of UF resin in the RWPs. The properties of WPC without MAPP mde from RWPs were lso compred with those of WPC mde from WF (Figs., 6, 7, 8, 9, 1, 11). Among the mechnicl properties, the tensile nd flexurl moduli nd the impct strength of compred WPCs did not differ significntly, wheres the tensile nd flexurl strengths of the WPC with RWPs were greter, pproximtely by 1 %, thn those of the WPC with WF. This increse in the strengths my be ttributed to higher length-to-thickness rtio of RWPs nd the presence of UF resin in the RWPs. These results greed with Bledzki nd Fruk (3), who concluded tht the tensile nd flexurl moduli of the WPC with chips were lmost the sme, nd the tensile nd flexurl strengths of tht WPC were slightly greter in comprison with the WPC with soft WF. Gozdecki et l. (1) found tht ll mechnicl properties of the WPC with WPs of the size 1 mm were better thn those of the WPC with soft WF. The wter bsorption of the WPC with RWPs ws less, by pproximtely %, thn tht of the WPC with WF, wheres there ws no significnt difference between the thickness swelling of these WPCs. Conclusion The RWPs derived from milling three-lyer prticlebords ws found to be good wood mteril for mking composites with PP by n injection moulding method. These prticles hd sizes from. to 3 mm, nd were shorter nd hd considerbly smller length-to-thickness rtio thn the industril VWPs used for producing prticlebords. Nevertheless, neither the mechnicl nor physicl properties of WPC with RWPs differed sttisticlly from those of WPC with VWPs. Moreover, the properties of WPC with RWPs were comprble with the properties of typicl WPC mde from WF. Further studies re needed to clrify the role of UF resin contined in the WPCs with RWPs. Acknowledgments This work ws supported by grnt /8 from the Polish Ministry of Science nd Higher Eduction. The uthors would like to thnk Kronospn Szczecinek Sp. z o.o. for providing wood mteril for this study. 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