Effects of polymeric matrix on accelerated UV weathering properties of wood-plastic composites

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1 Holzforshung, Vol. 66, pp , 212 Copyright y Wltr Gruytr Brlin Boston. DOI.1515/hf Effts of polymri mtrix on lrt UV wthring proprtis of woo-plsti omposits Chi-Hung L, K-Chng Hung, Yong-Long Chn, Tung-Lin Wu, Yi-Chi Chin n Jyh-Horng Wu * Dprtmnt of Forstry, Ntionl Chung Hsing Univrsity, Tihung 42, Tiwn * Corrsponing uthor. Dprtmnt of Forstry, Ntionl Chung Hsing Univrsity, # 25, Kuo-Kung R., Tihung 42, Tiwn Phon: Fx: E-mil: ri@nhu.u.tw Astrt Th purpos of this work is to ompr th wthring proprtis of iffrnt typs of woo-plsti omposits (WPCs) s on high-nsity polythyln (HDPE), ryl highnsity polythyln (rhdpe-i n rhdpe-ii), low-nsity polythyln (LDPE), polypropyln (PP), ryl polypropyln (rpp), polystyrn (PS), n ryl polystyrn (rps). Th moulus of ruptur (MOR) n moulus of lstiity (MOE) of ll WPCs rs with inrsing xposur tim of wthring. Of ths, th rhdpe-ii-s omposit xhiit th highst MOR n MOE rtntion rtios ftr 2 h of lrt ultrviolt (UV) wthring, whil th PS-s WPC h th lowst vlus. In ition, th ronyl inx iffrn (CID) of vrious WPCs inrs signifintly s funtion of xposur tim. Among thm, th PS-s WPCs xhiit th most svr grtion u to photo-oxition on th surf, whil th grtion of PE-s WPCs ws th milst. Ths rsults r onsistnt with th hng in th surf rking n flxurl proprtis of th omposits. Th PS-s WPCs lso xhiit highr moistur iffusion offiints. Th mhnil hvior of WPCs ftr wthring is influn y omintion of ftors, suh s surf oxition, morphology hngs, n moistur sorption. Kywors: mhnil hvior; moistur iffusion offiint; photo-oxition; polymri mtrix; wthring; wooplsti omposit (WPC). Introution Rnwl n low-ost nturl firs hv gin populrity s rinformnt mtrils in plsti omposits st known s woo-plsti omposits (WPCs) ovr th pst. This pproh hs mny vntgs, suh s low-nsity, low quipmnt rsivnss, high stiffnss n strngth, low mintnn rquirmnts, n goo iogrility (Blzki t l ). WPCs long to th most ynmi stors of th plsti inustry (Rothlin 27 ). Th glol WPC mrkt hs xprin ouligit growth in North Amri n Europ (Ashori 28 ; Li n Wu 2 ), n th volum of WPCs is prit to inrs from 129, tons in 28 to 427, tons in 214 (Lmpinn 2 ). Som WPCs for rsintil pplitions r ing rpily introu to th mrktpl, suh s for king, winow frming, siing, n roof tils. WPCs r still topi of tiv worlwi rsrh s monstrt y th rnt rviw of Kumr t l. (211). Th nlysis of th plsti n woo moity in WPCs (L t l. 2 ; Wint t l. 211 ) n th sltion of th propr omptiilizr (Kumr t l. 211 ) r frquntly in fous. Howvr, th min onrn is on th urility of WPCs, whih is gnrlly poor. Fing, hlking, n strngth wkning us y nvironmntl xposur r mjor prolms for thir outoor pplition (Strk n Mtun 24 ; Kiguhi t l. 27 ). Thrmoplstis, suh s high- n low-nsity polythyln (HDPE n LDPE), polypropyln (PP), n polystyrn (PS) r th st-known WPC prouts (Nir t l. 21 ; Hrpr n Wolott 24 ; Bngtsson t l. 25 ). In our prvious ppr, th physiomhnil proprtis of ths WPCs wr trmin (L t l. 2 ). Only limit informtion is vill on th wthrility n photogrtion of polyolfins (LDPE, HDPE, n PP) n thir omposits (Li 2 ; Tijni 2 ; Slén t l. 24 ; Strk n Mtun 24 ; Strk 26 ; Kiguhi t l. 27 ; Fiyi t l. 28 ; Prk t l. 28 ; Ahikry t l. 2 ; Rort t l. 211 ). Thr r no prior rports ompring th iffrnt wthring hviors of WPCs. Alrt ultrviolt (UV) wthring is powrful tst for qulity ontrol n mtril rtifition (Fiyi n MDonl 2 ; Shni t l. 212 ). Thrfor, th im of th prsnt work is to monstrt th fft of th polymri mtrix on th wthring proprtis of WPCs osrv ftr QUV lrt wthring tst. To th st of our knowlg, this is th first omprtiv stuy onrning th wthring hrtristis of WPCs with iffrnt typs of polymri mtris. Mtrils n mthos Prprtion of woo prtils Trm orintlis (L.) Blum, fst-growing woo spis, ws smpl from th xprimntl forst of th Ntionl Chung Hsing Univrsity in Nn-Tou County. Woo prtils wr prpr y Brought to you y Ntionl Chung-Hsing Authntit Downlo Dt 12/3/12 :2 AM

2 982 C.-H. L t l. hmmr-milling n siving; prtils twn 24 n 32 msh wr invstigt. Plstis Commril virgin plstis: (1) HDPE [Unithn LH91; mlt flow inx (MFI):.95 g/ min; nsity:.95 g m -3 ]; (2) LDPE (Pxothn NA248; MFI: 46. g/ min; nsity:.92 g m -3 ); (3) PP (Gloln PT; MFI: 1.6 g/ min; nsity:.9 g m -3 ); (4) PS (Polyrx PG-8; MFI: 4. g/ min; nsity: 1.5 g m -3 ). Sour: ths mtrils wr purhs from USI Co. (Kohsing, Tiwn), LCY Chmil Inustry Co. (Kohsing, Tiwn), n Chi- Mi Co. (Tinn, Tiwn). Ryl plstis: (5) Ryl highnsity polythyln (rhdpe-i) (MFI:.22 g/ min; nsity:.95 g m -3 ); (6) rhdpe-ii (MFI:.35 g/ min; nsity:.92 g m -3 ); (7) ryl polypropyln (rpp) (MFI: 3.7 g/ min; nsity:.91 g m -3 ); (8) ryl polystyrn (rps) (MFI: 8.71 g/ min; nsity: 1.5 g m -3 ). Sour: ths ryl mtrils wr kinly suppli y Orit Polymrs Co., Lt (Tihung, Tiwn). All plsti pllts wr groun in n ttrition mill to ru thir prtil siz to < 2 msh for omposit prossing. Composit prossing Mnufturing WPCs: th flt-pltn prssing pross ws ppli, oring to our prvious pprs (Hung n Wu 2 ; L t l. 2 ). Th wight rtio of ovn-ri woo prtils (moistur ontnt, MC < 3 % ) to plsti powr ws 6/4 (wt % ). Th xpt nsity of th WPCs ws.85 ±.5 g m -3. Th WPC smpls h imnsions of 3 mm 2 mm with 4 mm thiknss. All WPCs wr prou in two-stp prssing pross s follows: (1) hot prssing t 17 2 C (17 C for LDPE; 18 C for HDPE, rh- DPE-I, rhdpe-ii, PS, n rps; 2 C for PP n rpp) for 4 min; n (2) finishing y ol prssing until th tmprtur of th WPCs rs to 25 C (pprox. 5 min). Mhnil nlysis Th flxurl proprtis [moulus of ruptur (MOR) n moulus of lstiity (MOE)] of th omposits wr trmin oring to ASTM D79-7. MOR n MOE t wr otin y th thr-point stti ning tst with loing sp of 1.7 mm min -1 n spn of 64 mm (spimn siz: 8 mm 16 mm 4 mm). Th smpls wr onition t 23 C n 5 % rltiv humiity (RH) for wk for tsting. Th rtntion rtios of MOR n MOE of th WPCs ftr lrt UV wthring wr trmin s follows: MOR (or MOE) rtntion rtio ( % ) = MORt (or MOE t )/MOR (or MOE ), whr th msurmnts with th inx n t r for th WPC t for n ftr lrt UV wthring for tim t, rsptivly. Hyrothrml hvior Th moistur sorption hvior of WPCs ws stui y xposing th smpls to humi nvironmnt, oring to th mtho of Don t l. (27). Dry smpls with imnsions of 8 mm 8 mm 4 mm wr pl in sitor with sturt K 2 SO 4 solution t 2 C (97 % RH). Th wight of th spimns ws msur t iffrnt tim intrvls until quilirium ws rh. Th iffusion onstnt ( D ) ws trmin from th following qutions: D = D A /(1 + h /l + h /w ), whr D A, h, l, n w r th pprnt iffusion onstnt, th plt thiknss, th lngth, n th with, rsptivly. Th vlu of D A ws trmin s follows: D A = π [ h 2 /16(% M st ) 2 ] [(% M 2 -% M 1 )/( t2 - t )] 2 1, whr % M 1 n %M 2 r th prnt wight gin of th plt t tims t 1 n t 2, rsptivly, n % M st is th prnt wight gin t sturtion. Alrt UV wthring Instrumnt for th lrt UV wthring: QUV lrt wthring tstr (Q-Pnl Co., OH, USA) quipp with fluorsnt UVA-34 lmps (Q-L Co., OH, USA), in orn with th ASTM G stnr. Conitions: 8 h UV irrition tim ws follow y 4 h wtr onnstion (8/4 yl) t lk pnl tmprtur of 5 ± 3 C. ATR-FTIR sptrl msurmnts Instrumnt: Sptrum FTIR sptromtr (Prkin Elmr, Bukinghmshir, UK) quipp with utrt triglyin sulft (DTGS) ttor n MIRl ATR ssory (Pik Thnologis, Wisonsin, USA). Th sptr wr ollt y o-ing 32 sns t rsolution of 4 m -1 in th rng from 65 to 4 m -1. Fiv sptr wr quir t r.t. for h smpl, yiling 25 sptr for h omposit. Th ronyl inx (CI) ws lult: (CI) = ( I 1732 /I p ), whr I p rprsnts th spifi pk intnsity of th plsti (HDPE, LDPE, PP: 2916 m -1 ; PS: 696 m -1 ) (Strk t l. 24 ; L t l. 2 ). Th ronyl inx iffrn (CID) ws lso lult: CID = CI w -CI, whr CI n CI w r th ronyl inis of th omposit for n ftr UV wthring, rsptivly. DSC n thrml nlysis Instrumnt: DSC-7 (Prkin Elmr, Bukinghmshir, UK). Th smpls (. 1 mg) wr npsult in luminum pns n ht from 5 C to 25 C t hting rt of C min -1 unr N 2 flow (2 ml min -1 ). Th rystllinity of th plsti ( X ) ws trmin oring to Zou t l. (28) n lult s: X = Δ H m /ϕ Δ H m, whr Δ H m is th xprimntl ht of fusion trmin from th DSC msurmnt, Δ H m is th ssum ht of fusion of th fully rystllin plsti (HDPE n LDPE: 293 J g -1 ; PP: 148 J g -1 ), n ϕ is th wight frtion of plsti in th omposits. Msurmnt of surf olor Instrumnt: Minolt CM-36 (Tokyo, Jpn) quipp with D 65 light sour with tst-winow imtr of 8 mm. Th X, Y, n Z tristimulus vlus of ll spimns wr otin irtly from th olorimtr. Bs on ths t, th L * (vlu on th whit/lk xis), * (vlu on th r/grn xis), * (vlu on th lu/yllow xis), n Δ E * (th olor iffrn, Δ E * = [(Δ L *)2 + ( Δ *)2 + (Δ *) 2 ]1/2 ) olor prmtrs wr lult, s stlish y th Commission Intrntionl l Elirg (CIE) in 1976 (Wu t l. 25 ). Snning ltron mirosopy SEM instrumnt: Hithi TM- (Tokyo, Jpn) with n lrting voltg of 15 kv. All spimns wr viw prpniulr to th surf. Anlysis of vrin All rsults r xprss s th mn ± SD. Th signifin of iffrn ws lult y Shff s tst, n P-vlus <.5 wr onsir to signifint. Brought to you y Ntionl Chung-Hsing Authntit Downlo Dt 12/3/12 :2 AM

3 Alrt UV wthring proprtis of vrious WPCs 983 Rsults n isussion Color hngs Th CIE L*** olor spifitions r prsnt in Figur 1. Figur 1 shows tht th Δ E * vlus of ll WPCs gnrlly inrs with inrsing xposur tim. Among th ight typs of WPCs, th WPC PP xhiit th most svr olor hngs. Th vlu of Δ E * hng signifintly, inrsing linrly to 14.4 in th first 75 h n thn lvling off. In ontrst, th WPC rhdpe-ii hs th st olor stility; th vlu of Δ E * ws < 3.5 (Δ E * < 3 inits olor iffrn tht is not ttl y th humn y) ftr lrt UV wthring for 2 h. Th fft of wthring on Δ L * is prsnt in Figur 1. Expt for th WPC PS n WPC rps, wthring lrly rsult in lightning, n th trn of Δ L * is similr to tht of Δ E *. Rltiv to virgin plstis, most ryl plstis xhiit lss olor hng. Proly, th itivs or impuritis in ryl plstis hv signifint prottiv fft ginst photo isolortion. On th othr hn, s visil in Figur 1, th Δ * vlu of ll omposits ppr to inrs with inrsing xposur tim, through h. Howvr, ftr h of xposur, xpt for th PS n rps omposits, th Δ * vlu grully rs s funtion of tim. Th Δ * vlu isply th sm trn for ll of th lns, n th WPC PS n WPC rps xhiit th most svr * hngs. Aftr lrt UV wthring for 2 h, th Δ * vlus of oth WPCs rh pproximtly (Figur 1). Aoringly, th photo-snsitiv romti groups in th si hin of som polymrs (i.., PS n rps) l to surf yllowing upon UV xposur. Surf hrtristis Th surf hrtristis of WPCs lso hng signifintly ftr wthring. Mny uthors osrv rks on th surf of WPCs uring nturl or lrt wthring (Li 2 ; Sl é n t l. 24 ; Strk n Mtun 24 ; Kiguhi t l. 27 ; Chohnhikul t l. 212 ). SEM mirogrphs in Figur 2 of WPCHDPE ftr lrt UV wthring for,,, n 2 h rvl orsning of th initilly smooth surfs. Th fft ws visil ftr h, n th orsning ws follow y mtrix rks n intrfil fts upon xtn wthring tim to 2 h. Similr trns wr lso osrv for othr omposits (Figur 3 ). Th HDPE-, rhdpe-i-, n rhdpe-ii-s WPCs suffr lss rk formtion ftr 2 h of xposur. In othr wors, th wthrility of th WPCs m with virgin or ryl HDPE is ttr thn tht of othr WPCs. Furthrmor, th intrfil fts twn th woo prtils n th polymri mtrix ppr to mor svr for oth WPC PS n WPC rps thn for othr plstis. Flxurl proprtis Th flxurl proprtis of vrious WPCs vri s funtion of wthring tim. As list in Tl 1, th flxurl MOR n MOE of ll omposits gnrlly rs with inrsing wthring tim. Aftr 2 h, th MOR rtntion rtios of th WPCs r rhdpe-ii (85 % ) > LDPE (78 % ) > rhdpe-i (77 % ) > HDPE (7 % ) = PP (7 % ) > rpp (69 % ) > PS (51 % ) > rps (43 % ). Of ths, th polythyln-s WPCs, prtiulrly th rhdpe-ii omposit, rtin th grtst strngth ovr Color hng (ΔE*) HDPE rhdpe-i rhdpe-ii LDPE PP rpp PS rps ΔL* vlu 2-2 Δ* vlu 5-5 Δ* vlu Alrt wthring (h) Alrt wthring (h) Figur 1 Chngs in olor prmtrs of vrious WPCs s funtion of lrt UV wthring tim ( n = 5). Brought to you y Ntionl Chung-Hsing Authntit Downlo Dt 12/3/12 :2 AM

984 C.-H. L t l. Control h 2 μm h 2 μm 2 h 2 μm 2 μm Figur 2 SEM mirogrphs of HDPE-s WPC ftr lrt UV wthring for (ontrol),,, n 2 h, rsptivly. th wthring prio, whil th polystyrn-s WPCs rtin th lst.

ftr 2 h. Corrsponing to th olor hng rsults n SEM, oth th PS n rps omposits show th grtst ttnution of flxurl proprtis uring th wthring pross.

(27) rport tht improving th intrfil hsion twn th woo firs n th mtrix l to lowr vlus of th quilirium wtr ontnt n th iffusion offiint.

Th PS- n rps-s omposits hv signifintly highr moistur iffusion offiints thn th othr omposits. Aoringly, poor intrfil hsion is nothr mjor rson for th rution of flxurl proprtis osrv in WPC PS n WPC rps.

4 984 C.-H. L t l. Control h 2 μm h 2 μm 2 h 2 μm 2 μm Figur 2 SEM mirogrphs of HDPE-s WPC ftr lrt UV wthring for (ontrol),,, n 2 h, rsptivly. th wthring prio, whil th polystyrn-s WPCs rtin th lst. Similr to th trn osrv for th flxurl strngth, th MOE rtntion rtios of ll WPCs wr rhdpe-ii (63 % ) > rhdpe-i (55 % ) > LDPE (52 % ) = HDPE (52 % ) > PP (5 % ) > rpp (46 % ) > PS (42 % ) > rps (33 % ) ftr 2 h. Corrsponing to th olor hng rsults n SEM, oth th PS n rps omposits show th grtst ttnution of flxurl proprtis uring th wthring pross. In gnrl, th mhnil proprtis of th WPCs wr not only influn y th ntur of th woo n plsti mtrils ut lso y th intrfil hsion of th omposits. Don t l. (27) rport tht improving th intrfil hsion twn th woo firs n th mtrix l to lowr vlus of th quilirium wtr ontnt n th iffusion offiint. Tl 1 shows tht th moistur iffusion offiints of th ight WPCs r PS > rps > rhdpe-ii > rhdpe-i = PP > rpp > HDPE > LDPE. Th PS- n rps-s omposits hv signifintly highr moistur iffusion offiints thn th othr omposits. Aoringly, poor intrfil hsion is nothr mjor rson for th rution of flxurl proprtis osrv in WPC PS n WPC rps. Th mjority of flxurl MOR n MOE hngs ourr uring th first h (Tl 1). Ths rsults r similr to thos in th rport y Strk t l. (24), who invstigt th loss in MOR n MOE for 5 % woo flour-rinfor HDPE omposits ftr wthring. Mtrix rystllinity Cross-linking n hin sission n our in polyolfins uring wthring, whih r ling to pprnt iffrns in th rystllinity of smpls. In this stuy, th mtrix rystllinity of vrious WPCs ws lult from th mlting nothrms otin from DSC. Aoringly, th ht of fusion of fully rystllin polymrs ws sought for. Th polystyrn in fous is n morphous polymr. Morovr, th rystllinity of th PS n rps in th omposits nnot vlut us of th lk of mlting nthlpy t for % rystllin PS. Tking Δ H m = 293 J g -1 n 148 J g -1 for PE (Khumlo t l. 2 ) n PP (Bg n Pikring 28 ), rsptivly, th mtrix rystllinitis of th six WPCs with known Δ H m vlus wr trmin s funtion of wthring tim (Tl 2 ). Th rystllinity of th vrious mtris signifintly inrs uring th first h of xposur. A pltu ws rh uring furthr wthring to 2 h, xpt for th rhdpe-i n rpp omposits. Th litrtur rports similr rsults (Ki t l. 21 ). Zou t l. (28) lim tht th inrs in rystllinity oul usful s n initor for polymr hin sission uring photo-oxitiv grtion. Aoring to this intrprttion, it n stt tht th rystllinity inrmnts osrv in th prsnt invstigtion r u to hin sission in th morphous phs of th polymr. Th rsulting shortr moluls my hv suffiint hin moility to filitt sonry rystlliztion, whih ls to rk initition (Figur 2) (Jrin n Lofgrn 1994 ). Howvr, s hin sission ws proing, th ti moluls m fft, n th rystllinity ws rs. Tl 2 shows tht th rystllinity of th rhdpe-i n rpp mtris rs signifintly twn n 2 h of wthring. Brought to you y Ntionl Chung-Hsing Authntit Downlo Dt 12/3/12 :2 AM

Alrt UV wthring proprtis of vrious WPCs 985 HDPE rhdpe-i 2 μm 2 μm rhdpe-ii LDPE 2 μm 2 μm PP rpp

Tl 1 Th moistur iffusion offiint ( D ) n rtntion rtios in trms of MOR n MOE of vrious WPCs ftr lrt

WPC D -6 (mm 2 s -1 ) MOR (MP) MOR rtntion rtio (%) MOE MOE rtntion rtio (%) (GP) h 5 h h 2 h h 5

29 ±.9 B 2.4 ± 1.8 CD 9 ± 2 91 ± 4 91 ± 3 77 ± 2 1.6 ±.2 C 98 ± 4 69 ± 7 72 ± 11 55 ± 5 rhdpe-ii 1.

14 C. ±.3 E 9 ± 2 87 ± 4 87 ± 6 78 ± 6 1. ±.1 D 76 ± 7 53 ± 4 63 ± 8 52 ± 6 PP 1.29 ±.16 B 24.

2 A 9 9 ± 6 8 ± 5 73 ± 6 69 ± 8 2.3 ±.1 AB 81 ± 11 55 ± 4 47 ± 6 46 ± 4 PS 2.7 ±.8 A 2.9 ± 2.

8 D 9 7 ± 8 64 ± 4 48 ± 7 43 ± 6 2.2 ±.2 AB 82 ± 3 45 ± 3 39 ± 7 33 ± 7 Vlus r th mn ± SD ( n = 5).

5 Alrt UV wthring proprtis of vrious WPCs 985 HDPE rhdpe-i 2 μm 2 μm rhdpe-ii LDPE 2 μm 2 μm PP rpp 2 μm 2 μm PS rps 2 μm 2 μm Figur 3 SEM mirogrphs of vrious WPCs ftr lrt UV wthring for 2 h. Tl 1 Th moistur iffusion offiint ( D ) n rtntion rtios in trms of MOR n MOE of vrious WPCs ftr lrt UV wthring for iffrnt trtmnt tims. WPC D -6 (mm 2 s -1 ) MOR (MP) MOR rtntion rtio (%) MOE MOE rtntion rtio (%) (GP) h 5 h h 2 h h 5 h h 2 h HDPE 1.8 ±.24 B 22.5 ± 1. ABC 98 ± 1 84 ± 3 82 ± 4 7 ± ±.1 C 89 ± 2 63 ± 6 65 ± 7 52 ± 4 rhdpe-i 1.29 ±.9 B 2.4 ± 1.8 CD 9 ± 2 91 ± 4 91 ± 3 77 ± ±.2 C 98 ± 4 69 ± 7 72 ± ± 5 rhdpe-ii 1.35 ±.13 B 2.8 ±.5 BCD 2 ± 5 94 ± 4 88 ± 4 85 ± ±.1 C 84 ± 8 68 ± 3 7 ± ± 7 LDPE.56 ±.14 C. ±.3 E 9 ± 2 87 ± 4 87 ± 6 78 ± 6 1. ±.1 D 76 ± 7 53 ± 4 63 ± 8 52 ± 6 PP 1.29 ±.16 B 24.4 ± 1.5 AB 9 2 ± 3 84 ± 3 79 ± 3 7 ± 4 2. ±.1 B 82 ± 4 56 ± 4 55 ± 4 5 ± 5 rpp 1.23 ±.2 B 24.8 ± 1.2 A 9 9 ± 6 8 ± 5 73 ± 6 69 ± ±.1 AB 81 ± ± 4 47 ± 6 46 ± 4 PS 2.7 ±.8 A 2.9 ± 2.2 BCD 2 ± 3 63 ± 3 59 ± 8 51 ± 2.4 ±.1 A 8 ± 5 49 ± 8 46 ± 7 42 ± 9 rps 1.95 ±.2 A 18.7 ± 1.8 D 9 7 ± 8 64 ± 4 48 ± 7 43 ± ±.2 AB 82 ± 3 45 ± 3 39 ± 7 33 ± 7 Vlus r th mn ± SD ( n = 5). Diffrnt pitl n lowrs suprsript lttrs init signifint iffrns (P <.5) within olumn n row, rsptivly. Brought to you y Ntionl Chung-Hsing Authntit Downlo Dt 12/3/12 :2 AM

6 986 C.-H. L t l. Tl 2 Th mtrix rystllinity of vrious WPCs ftr lrt UV wthring for iffrnt tims. formtion n rs in flxurl proprtis u to th poor intrfil hsion n strss trnsfr. WPC typ Crystllinity ( % ) h h h 2 h Conlusions HDPE 2.5 ± ± ± ±.5 rhdpe-i 22.7 ± ± ± ± 6.1 rhdpe-ii 26.5 ± ± ± ±.5 LDPE 11.6 ± ± ± ± 1.3 PP 18.4 ± ± ± ± 6. rpp 18.5 ± ± ± ± 4.9 Vlus r th mn ± SD (n = 3). Diffrnt suprsript lttrs within row init signifint iffrn t P <.5. ATR-FTIR nlysis Th photostility of polyolfins is strongly pnnt on th gr of oxition uring wthring (Tijni 2 ; Strk n Mtun 24 ). During UV irrition, hin sission n inu y photogrtion vi Norrish I n II rtions, s init y n inrs in th onntrtion of ronyl n vinyl groups. Figur 4 shows th ronyl inx iffrn (CID) of vrious WPCs for n 2 h irrition tim. Th CID vlu of ll WPCs inrs with inrsing xposur tim, n thr r no signifint iffrns twn th virgin n ryl WPCs upon wthring. Othrs lso foun similr inrsing CID trn (Fiyi t l. 28 ; Niy t l. 28 ). Of ll WPCs in this stuy, th polystyrn-s WPCs xhiit th highst CID vlu, whil th polythyln-s WPCs h th lowst. Th polystyrn omposits r lss photostl thn th polyolfin omposits. Ths t r lso onsistnt with th hng in th omposit morphology (Figur 3) n flxurl proprtis (Tl 1). In summry, if UV wthring ls to high CID vlus, this is sign for svr photogrtion (hin sission prosss). An inrs in rystllinity inits th grtion of th morphous moity of th polymr. This pross is ttn y mirork CID (%) HDPE h 2 h rhdpe-i rhdpe-ii LDPE PP rpp PS rps Figur 4 CID of vrious WPCs ftr lrt UV wthring for n 2 h. Vlus r th mn ± SD (n = 5). Brs with iffrnt lttrs init signifint iffrns t P <.5. Th physiomhnil n UV wthring proprtis of WPCs r grtly influn y th typ of plsti utiliz. Of ll WPCs in this stuy, th rhdpe-ii-s omposit xhiit th highst MOR n MOE rtntion rtios ftr 2 h of lrt UV wthring, whil th PS-s WPC h th lowst rtios. In ition, th olor hng of th rhdpe-ii-s omposit ws th lowst. Aoringly, th rhdpe-ii-s omposit hs ttr wthring proprtis thn th othrs. Th PS- n rps-s omposits hv highr moistur iffusion offiint, whih ls to grtr moistur pntrtion n grtion of th intrf twn th woo n th plsti mtrix. This lowrs th wthring rsistn. Th wthring proprtis of th ryl omposits r suprior to thos of virgin ons. Aknowlgmnts This work ws finnilly support y rsrh grnt from th Forstry Buru of th Counil of Agriultur (AS FB-1) n in prt y th Ntionl Sin Counil (NSC B-5-19). Rfrns Ahikry, K.B., Png, S., Stigr, M.P. (2) Effts of th lrt frz-thw yling on physil n mhnil proprtis of woo flour-ryl thrmoplsti omposits. Polym. Compos. 31: Ashori, A. (28) Woo-plsti omposits s promising grnomposits for utomotiv inustris! Biorsour. Thnol. 99: Bg, M.D.H., Pikring, K.L. (28) Rprossing of woo fir rinfor polypropyln omposits. Prt I: Effts on physil n mhnil proprtis. Composits A 39:91 1. Bngtsson, M., Gtnholm, P., Oksmn, K. (25) Th fft of rosslinking on th proprtis of polythyln/woo flour omposits. Compos. Si. Thnol. 65: Blzki, A.K., Rihmn, S., Gssn, J. (1998) Thrmoplstis rinfor with woo fillrs: litrtur rviw. Polym.-Plst. Thnol. Eng. 37: Chohnhikul, K., Jyrmn, K., Rosrpitk, V., Somtsompop, N. (212) Influn of lignin ontnt on photogrtion in woo/hdpe omposits unr UV wthring. BioRsours 7: Don, T.T.L., Broowsky, H., M ä r, E. (27) Jut fir/polypropyln omposits II. Thrml, hyrothrml n ynmi mhnil hviour. Compos. Si. Thnol. 67: Fiyi, J.S., MDonl, A.G. (2) Physil morphology n quntittiv hrtriztion of hmil hngs of wthr PVC/ pin omposits. J. Polym. Environ. 18: Fiyi, J.S., MDonl, A.G., Wolott, M.P., Griffiths, P.R. (28) Woo plsti omposits wthring: visul pprn n hmil hngs. Polym. Dgr. Stil. 93: Brought to you y Ntionl Chung-Hsing Authntit Downlo Dt 12/3/12 :2 AM

7 Alrt UV wthring proprtis of vrious WPCs 987 Hrpr, D., Wolott, M. (24) Intrtion twn oupling gnt n lurints in woo-polypropyln omposits. Composits A 35: Hung, K.-C., Wu, J.-H. (2) Mhnil n intrfil proprtis of plsti omposit pnls m from strifi moo prtils. J. Woo Si. 56: Jrin, S.A., Lofgrn, E.A. (1994) Photooxitiv ffts on proprtis n strutur of high-nsity polythyln. J. Appl. Polym. Si. 53: Ki, M., Soun, T., Cimmino, S. (21) Crystllinity msurmnts of unstiliz n HALS-stiliz LDPE films xpos to nturl wthring y FT-IR, DSC n WAXS nlyss. Int. J. Polym. Anl. Chrt. 6: Khumlo, V.M., Krgr-Kosis, J., Thomnn, R. (2) Polythyln/ synthti ohmit lumin nnoomposits: strutur, thrml n rhologil proprtis. Exprss Polym. Ltt. 4: Kiguhi, M., Ktok, Y., Mtsung, H., Ymmoto, K., Evns, P.D. (27) Surf triortion of woo-flour polypropyln omposits y wthring trils. J. Woo Si. 53: Kumr, V., Tygi, L., Sinh, S. (211) Woo flour-rinfor plsti omposits: rviw. Rv. Chm. Eng. 27: Lmpinn, J. (2) Trns in ioplstis n ioomposits. In: Dvlopmnts in Avn Bioomposits. Es. Hrlin, A., Vikmn, M. VTT Thnil Rsrh Cntr of Finln, Finln. pp L, C.-H., Wu, T.-L., Chn, Y.-L., Wu, J.-H. (2) Chrtristis n isrimintion of fiv typs of woo-plsti omposits y FTIR sptrosopy omin with prinipl omponnt nlysis. Holzforshung 64: Li, Y., Wu, Q. (2) Woo plsti omposits s on mirofirillr lns of high nsity polythyln/poly(thyln trphthlt). Biorsour. Thnol. 1: Li, R. (2) Environmntl grtion of woo-hdpe omposit. Polym. Dgr. Stil. 7: Nir, K.C.M., Thoms, S., Groninkx, G. (21) Thrml n ynmi mhnil nlysis of polystyrn omposits rinfor with short sisl firs. Compos. Si. Thnol. 61: Niy, D., Fnton, E., Morlt-Thris, S., Vil, L., Tijni, A., Grtt, J.L. (28) Durility of woo polymr omposits: Prt 1. Influn of woo on th photohmil proprtis. Compos. Si. Thnol. 68: Prk, J.-M., Kim, P.-G., Jng, J.-H., Wng, Z., Hwng, B.-S., DVris, K.C. (28) Intrfil vlution n urility of moifi jut firs/polypropyln (PP) omposits using miromhnil tst n ousti mission. Composits B 39: Rort, M., Cousin, P., Fm, A., Bnmokrn, B. (211) Efft of th ition of moifi mi on mhnil n urility proprtis of FRP omposit mtrils for ivil nginring. Polym. Compos. 32: Rothlin, O. (27) Prossing woo-plsti omposits pls nw mns on frs. Plst. Ait. Compos. 9: Slén, R., Nyström, B., Långström, R. (24) UV ging of poly (propyln)/woo-fir omposits. Polym. Compos. 25: Shni, A., vn Rnn, A., Minkn, M. (212) Using xtrtiv-fr woo s rinformnt in woo-lldpe omposits. J. Rinf. Plst. Compos. 31: Strk, N.M. (26) Efft of wthring yl n mnufturing mtho on prformn of woo flour n high-nsity polythyln omposits. J. Appl. Polym. Si. : Strk, N.M., Mtun, L.M. (24) Surf hmistry n mhnil proprty hngs of woo-flour/high-nsity-polythyln omposits ftr lrt wthring. J. Appl. Polym. Si. 94: Strk, N.M., Mtun, L.M., Clmons, C.M. (24) Efft of prossing mtho on surf n wthring hrtristis of wooflour/hdpe omposits. J. Appl. Polym. Si. 93:21 3. Tijni, A. (2) Comprison of formtion of oxition prouts uring photo-oxition of linr low-nsity polythyln unr iffrnt nturl n lrt wthring onitions. Polym. Dgr. Stil. 68: Wint, M., Mir, D., Lhnn, R. (211) Quntifition of polypropyln (PP) in woo plsti omposits (WPCs) y nlytil pyrolysis (Py) n iffrntil snning lorimtry (DSC). Holzforshung 65: Wu, J.-H., Chung, M.-J., Chng, S.-T. (25) Grn olor prottion of moo ulms using on-stp lkli prtrtmnt-fr pross. J. Woo Si. 51: Zou, P., Xiong, H., Tng, S. (28) Nturl wthring of rp strw flour (RSF)/HDPE n nno-sio 2 /RSF/HDPE omposits. Crohyr. Polym. 73: Riv Otor 4, 211. Apt My 8, 212. Prviously pulish onlin Jun 1, 212. Brought to you y Ntionl Chung-Hsing Authntit Downlo Dt 12/3/12 :2 AM

(2) If we multiplied a row of B by λ, then the value is also multiplied by λ(here lambda could be 0). namely

(2) If we multiplied a row of B by λ, then the value is also multiplied by λ(here lambda could be 0). namely . DETERMINANT.. Dtrminnt. Introution:I you think row vtor o mtrix s oorint o vtors in sp, thn th gomtri mning o th rnk o th mtrix is th imnsion o th prlllppi spnn y thm. But w r not only r out th imnsion,