Mechanical and thermal properties of extruded soy protein sheets

Transcription

1 Polymr 42 (2001) Mhnil n thrml proprtis of xtru soy protin shts J. Zhng, P. Mungr, J. Jn* Dprtmnt of Foo Sin n Humn Nutrition & Cntr for Crops Utiliztion Rsrh, Iow Stt Univrsity, Ams, IA 50011, USA Riv 17 Mrh 2000; riv in rvis form 11 August 2000; pt 15 August 2000 Astrt Soy protin plsti shts wr m y xtrusion. Th ffts of wtr, glyrol, mthyl gluosi, ZnSO 4, pihlorohyrin, n glutri ilhy on th mhnil proprtis of soy protin plsti shts wr stui. Th thrml trnsition tmprturs n ynmi mhnil proprtis of soy protin plstis wr lso invstigt. Dpning on th moistur n glyrol ontnts, soy protin plsti shts isply proprtis from rigi to soft. Th glss trnsition tmprturs of th shts vri from. 7 to50 C with moistur ontnts rnging from 26 to 2.8% n 30 prts of glyrol. Th soy protin plsti shts wr usully in thir glssy stts t room tmprtur unlss thy ontin high moistur. Th -trnsitions of soy protin plsti shts rng from 33 to 72 C pning on th moistur. Aftr ing sumrg in wtr for 20 h, th soy protin shts sor up to 180% wtr. With th prsn of two prts of ZnSO 4, wtr sorption of th soy protin shts rs y 30%. Soy protin shts sor or lost moistur pning on th rltiv humiity of th nvironmnt Elsvir Sin Lt. All rights rsrv. Kywors: Soy protin plstis; Extrusion; Mhnil proprtis 1. Introution Ptrolum-s plstis omint toy s plstis mrkt us of thir high strngth, lightwight, low ost, sy prossiility, n goo wtr rrir proprtis. Howvr, most of th synthti polymrs r not iogrl. Synthti iogrl polymrs, suh s poly(lti i), polyprolton, n poly(hyroxy utyrt) hv high proution osts. With th inrsing onrns of nvironmntl pollution us y non-iogrl ptrolum-s plstis, inrsing fforts hv n m to utiliz th polymri mtrils riv from griulturl prouts. Th Unit Stts is on of th mjor prours of soyns in th worl. Soyns, $17.5 illion mrkt in th Unit Stts, r minly us for niml fs. Soyns ontin pproximtly 42% protin, 20% oil, 33% rohyrts, n 5% sh on ry sis [1]. In ition to its us s foo ingrint, non-foo pplitions of soy protin s polymri mtrils hv ttrt inrsing ttntion in rnt yrs. Th min ttrtiv fturs of soy Journl Ppr No. J of th Iow Agriultur n Hom Eonomis Exprimnt Sttion, Ams, Iow, Projt No. 3258, n support y Hth At n Stt of Iow Funs. * Corrsponing uthor. Tl.: ; fx: E-mil rss: jjn@istt.u (J. Jn). protin-s plstis r tht thy r iogrl, nvironmntlly frinly, n from n unnt rnwl rsour. Us of soy protin s plsti mtril n tr k to th 1930s. Brothr n Mkinny stui th formlhy-hrn soy plstis n thir ompouning with th phnoli rsin [2,3]. Th formlhy-trt soy plstis ompoun with phnoli rsin wr rport to isply vry low wtr sorption. In our lortory, w stui th ffts of ph [4], moistur ontnt [4], prossing onitions [4], ross-linking gnts [5], n llulos [5] (s fillr) on mhnil n physil proprtis of omprssion-mol soy plstis, n th morphology n iogrtion of soy protins plstis [6,7]. Effts of polyhyri lohols s plstiizrs on mhnil proprtis of soy protin-s plstis hv lso n stui n rport [8]. Otig n Ams stui th omposit of soy protin with polyphospht, n thir rsults show nhn strngth, stiffnss n improv wtr rsistn [9]. It is wll known tht wtr plstiizs protins n is ritil for prossing. Morls n Kokini stui th glss trnsition (T g ) of soy protin s funtion of moistur ontnt [10]. Thy rport tht th T g of onglyinin (7S) frtion rng from 114 to 67 C with moistur ontnt twn 0 n 35%, whrs tht of th glyinin (11S) frtion rng from 160 to 17 C with moistur ontnt twn 0 n 40%. Klihvsky t l. stui th glss /01/$ - s front mttr 2000 Elsvir Sin Lt. All rights rsrv. PII: S (00)

2 2570 J. Zhng t l. / Polymr 42 (2001) Tl 1 Efft of glyrol onntrtion on mhnil proprtis of soy protin shts (Formultion: SPI 610 (100 prts), H 2 O (80 prts). Smpls wr quilirt for 48 h prior to tst) Glyrol (prts) s y (MP) s (MP) P.E.Y. (%) P.E.B. (%) Strngth (MP) E (MP) Toughnss (MP) ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 1.3 s y is th strss t yil point. s is th strss t rk point. P.E.Y. is th prntg longtion t yil point. P.E.B. is th prntg longtion t rk point. E is Young s moulus. trnsition tmprtur of glutn n foun tht it ws littl fft y trioln, orn oil, n glyrol monostrt [11]. In this stuy, w invstigt xtrusion of soy plsti shts n th plstiizing ffts of wtr, glyrol, n mthyl gluosi on mhnil n ynmi mhnil proprtis of soy protin plstis. W lso invstigt th rosslinking ffts of soy protin y Zn 2, trnsition mtl ion, n othr ross-linking rgnts. 2. Exprimntl 2.1. Mtrils Soy protin isolt (SPI, Supro 760 n 610) ws purhs from Protin Thnologis Intrntionl, St. Louis, MO, n us s riv. It ontin pproximtly 92% protin (ry sis), lss thn 1% rohyrt, 4.7% moistur, n 4.0% sh. Glyrol n slts wr rgnt gr qulity n wr otin from Fishr (Fishr Sintifi, Pittsurgh, PA). Epihlorohyrin n glutri ilhy wr purhs from Alrih (Alrih Chmil Compny, Milwuk, WI). Mthyl gluosi ws gift from Grin Prossing Corportion (Mustin, IA) Compouning SPI, wtr, glyrol, n othr itivs wr thoroughly mix in high-sp mixr (Hnshl Mixrs Amrin, In., Houston, TX). Th gnrl formultion of th soy protin shts ws SPI (100 prts), H 2 O (60 90 prts), glyrol (20 50 prts), n othr itivs. Th mixtur ws quilirt ovrnight in sl plsti g for ompouning. Th ompouning xtrusion ws prform with twin-srw o-rotting xtrur (Listritz Miro 18, Amrin Listritz Corp., Sommrvill, NJ) quipp with n uto fr. Th imtr of th srw ws 18 mm, n th lngth to imtr rtio L=D ws 30. Th srw sp ws 150 rpm. Th rrl of th xtrur h fiv hting zons. Th prossing tmprturs vri from 60 to 115 C pning on th formultion. Th xtrut ws plltiz, n th moistur ontnt ws trmin Sht xtrusion Soy protin shts wr xtru from ov pllts using singl-srw xtrur (C.W. Brnr Instrumnts, In., Hknsk, NJ) quipp with 6-inh flt-sht i. Th rrl tmprtur vri from 120 to 160 C, n th i tmprtur ws 100 to 120 C, pning on th formultion. Th srw sp ws rpm. Th sht ws rwn with Brnr tk-off unit. Th thiknss of th shts rng from 0.35 to 1.5 mm Mhnil proprtis Th shts wr ut into strips of 19 mm 100 mm n ri t 50 C for 24 h. Thy wr quilirt t 50% rltiv humiity (RH) for 48 h right for tsting n kpt in sl plsti gs till tsts. Mhnil proprtis wr msur using n Instron Univrsl Tst Mhin (Mol 4502, Cnton, MA) following th ASTM D mtho. Th rossh sp ws 100 mm/min, n fiv rplits wr tst for h smpl Thrml nlysis Spimns with iffrnt moistur ontnts wr prpr from th sm th of sht smpls y quilirting thm in sprt hmrs of iffrnt RH for 1 wk. Sturt slt solutions of LiCl, MgCl 2, Mg(NO 3 ) 2, NCl, n KNO 3, giving RH of 11, 32, 50, 75 n 93%, rsptivly, wr us for this stuy. RH of 0% ws hiv y pling P 2 O 5 in sitor. Moistur ontnts of th quilirt sht smpls wr nlyz using Prkin Elmr thrmogrvimtri nlyzr TGA-7 (Norwlk, CT). A smpl ( 10 mg) ws snn from 30 C t20 C/min, n wight loss low 150 C ws tkn s th moistur ontnt. Dynmi mhnil proprtis wr msur on Prkin Elmr DMA-7 using prlll plt msuring systm. Th sht smpls wr shp into isk of out 7 mm in imtr n 1.3 mm in thiknss. Th tmprtur sn ws from 100 to 130 C t2 C/min, n th frquny of th ynmi for ws 1 Hz. Th stti n ynmi fors wr st t 300 n 330 yn,

3 J. Zhng t l. / Polymr 42 (2001) Tl 2 Efft of mthyl gluosi on mhnil proprtis of soy protin shts (formultion: SPI 760 (100 prts), H2O (80 prts)) Mthyl gluosi (prts) Glyrol (prts) ZnSO4 (prts) s y (MP) s (MP) P.E.Y. (%) P.E.B. (%) Strngth (MP) E (MP) Toughnss (MP) ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 3.8 s y is th strss t yil point. s is th strss t rk point. P.E.Y. is th prntg longtion t yil point. P.E.B. is th prntg longtion t rk point. E is Young s moulus. rsptivly. Th pk vlus of tn urvs wr ror s trnsition tmprturs. Eh smpl ws nlyz t lst in uplit. Diffrntil snning lorimtry ws prform on Prkin Elmr DSC-7, with tmprtur snning from 55 to 160 C t20 C/min Wtr sorption To msur th wtr-solul ontnt in th soy protin sht, wtr sorption tst ws onut following th ASTM D with minor moifition. Th smpls ri t 50 C for 24 h wr pl in istill wtr t room tmprtur. Aftr th sht ws rmov from wtr, th ontinr ws pl in n ovn t 50 C for 24 h to vport th wtr. Th rsiuls wr th wtrsolul ontnts. Th wight gin of th sht plus th wight of th wtr-solul rsiuls ws ount s th totl sor wtr. Thr rplits of nlysis wr on for h smpl. 3. Rsults n isussion 3.1. Mhnil proprtis Effts of plstiizrs Glyrol. Plstiizing ffts of glyrol t vrious onntrtions on mhnil proprtis of soy protin plsti shts r shown in Tl 1. Th xtrusion prossing of soy protin shts ontining 10 prts of glyrol or lss ws vry iffiult, n th rsulting shts m vry rittl ftr losing moistur. Shts m with 10 prts of glyrol show th highst tnsil strngth n Young s moulus, ut th prntg longtion t rk ws only 3%. Shts m with 20 prts of glyrol show high toughnss, strngth, Young s moulus, n prntg longtion t yil point. Th lrgst hngs in strngth, Young s moulus, n longtion t rk wr isply twn 20 n 30 prts of glyrol. A furthr inrs in glyrol onntrtion ov 30 prts rsult in lrg rss in yil strss n yil longtion, ut show fw hngs in othr mhnil proprtis. Elongtion t rk inrs ontinuously with th inrs of glyrol ontnt. Soy protin onsists of polr n non-polr si hins. Thr r strong intr- n intr-molulr intrtions, suh s hyrogn oning, ipol ipol, hrg hrg, n hyrophoi intrtions. Th strong hrg n polr intrtions twn si hins of soy protin moluls rstrit sgmnt rottion n molulr moility, whih l to inrss in moulus, stiffnss, yil point, n tnsil strngth. Th hrg n polr intrtions twn protin moluls lso rsult in th rittlnss of soy protin plstis. As plstiizr, glyrol rus th intrtion twn protin moluls n inrss th flxiility, xtnsiility n prossiility of soy protin plstis. Th

4 2572 J. Zhng t l. / Polymr 42 (2001) Tl 3 Efft of moistur ontnt on mhnil proprtis of soy protin shts (formultion: SPI 610 (100 prts), wtr (80 prts), glyrol (30 prts)) %RH Moistur (%) s y (MP) s (MP) P.E.Y. (%) P.E.B. (%) Strngth (MP) E f (MP) Toughnss (MP) ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 0.2 f Smpls wr quilirt for 1 wk t iffrnt wtr tivitis. s y is th strss t yil point. s is th strss t rk point. P.E.Y. is th prntg longtion t yil point. P.E.B. is th prntg longtion t rk point. E is Young s moulus. T g of soy protin rs with th inrs of glyrol onntrtion. High glyrol onntrtion lso hlp to rtin moistur in th shts, whih furthr rs th T g. Th rmnnt moistur ontnts wr foun to inrs from 3.9% for th sht with 20 prts of glyrol to 9.6% for th sht with 50 prts of glyrol. Th moulus of soy protin shts ws grtly hng y justing th glyrol lvl; thrfor, soy protin shts rnging from rigi to smirigi wr otin. For th shts ontining 10 n 20 prts of glyrol, th high Young s mouli init tht soy protin shts hv lik rigi plstis, n th yil strss of shts ontining 10 prts of glyrol ws los to tht of glssy polymrs [12]. Whn th glyrol ontnt inrs to 30 prts, oth Young s moulus n yil strss of soy protin shts rs signifintly, initing th soy plstis wr grtly softn n m smi-rigi. Th rsti rs in yil strss with th inrs of glyrol to 40 n 50 prts oul ttriut to htrognous systms with high glyrol ontnts Mthyl gluosi. Bus th T g of simpl sugr is sustntilly highr thn tht of glyrol, using sugrs s plstiizrs n prou soy plstis with highr T g n rigiity. For xmpl, th T g of gluos n suros r 38 n 78 C, rsptivly, ompr with tht of glyrol t 93 C [13]. In this stuy, mthyl gluosi ws us s plstiizr to prtilly rpl glyrol, n rigi shts wr prou. Th rsults r shown in Tl 2. Whn glyrol ws prtilly rpl with 10 prts of mthyl gluosi, tnsil strngth n toughnss inrs up to 24.4 n 33.3%, rsptivly. Howvr, glyrol ws still nssry in orr to mintin goo prossiility Moistur ontnt. In ition to its ruil rol in th gltion of soy protin n prossing of soy protin rsins, th moistur ontnt in prouts grtly fft th proprtis of soy protin plstis s shown in Tl 3. With th inrs in moistur ontnt, oth tnsil strngth n moulus of th sht spimns rs rpily, whrs th longtion grtly inrs. At 2.8% moistur ontnt (quilirt t 0% RH, TGA t), th soy protin sht h th highst tnsil strngth n Young s moulus, ut ws vry rittl. Th high mouli t low moistur (2.8 n 3.2%) init tht th soy protin shts hv lik rigi plstis. Th longtion grtly inrs with th inrs in moistur ontnt, whrs mhnil strngth n moulus ontinuously rs. Th toughnss of th soy protin sht pss through mximum t 3.2 n 4.2% moistur (quilirt t 11 n 32% RH, rsptivly). At 26% moistur lvl (quilirt t 93% RH), th sht lost most of its tnsil strngth n rigiity. Compring th t in Tls 1 n 3, th rsults init tht moistur fft th mhnil proprtis mor fftivly thn glyrol. Th rsults lso init tht soy protin-s shts wr vry snsitiv to th RH of th surrouning nvironmnt. With moistur ontnt vrying from 2.8 to 26%, th mhnil proprtis of soy protin shts hng from thos of rigi to smi rigi to soft plstis. Rsults of thrml nlysis of ths shts r shown in Figs. 1 n Effts of ross-linking gnts To improv th rigiity of th shts, ZnSO 4 ws us to introu hlting ross-links, n pihlorohyrin n glutri ilhy wr us for ovlnt ross-links twn soy protin moluls. Both pihlorohyrin n glutri ilhy n form ovlnt ons with mino n hyroxyl groups of soy protin. Rsults of ross-linking ffts r shown in Tls 4 6. Th Young s moulus of th soy protin plsti sht ws signifintly inrs (29 51%) with th ition of ZnSO 4, whrs th strngth, prntg longtion, n strss t yil wr not signifintly hng xpt whn 2% of ZnSO 4 ws (Tl 4). In ition to forming ioni ons with funtionl groups (suh s glutmi n sprti is), Zn 2 n form hlting omplxs with oxygn, nitrogn, n sulfur

5 J. Zhng t l. / Polymr 42 (2001) Fig. 1. DSC thrmogrms of soy protin shts t iffrnt moistur ontnts. Th shts ontin 30 prts of glyrol pr 100 prts of soy protin. Hting rt ˆ 20 C/min. Th ontrol ws m y omprssion-moling n ontin 0.5% moistur without glyrol. ontining groups of soy protin [14,15]. Ths intrtions stiffn th soy protin moluls, n onsquntly, l to inrss in Young s moulus. Rsults show tht ross-linking using pihlorohyrin n glutri ilhy ws mor fftiv in inrsing th rigiity (highr Young s moulus) of soy protin plsti shts thn using ZnSO 4 (Tl 4 6). Howvr, th prossiility m vry poor whn soy protin ontin 0.4% pihlorohyrin or glutri ilhy. Th rsin with 1.5% ZnSO 4 still rtin goo prossiility, initing tht th ross-linking y Zn 2 ws lil [14] t n lvt tmprtur Thrml n ynmi mhnil proprtis DSC nlysis Fig. 1 shows th DSC thrmogrms of soy protin shts with iffrnt moistur ontnts. Th soy protin sht smpls us in this stuy wr th sm s thos in Tl 3. Bus glyrol (30 prts) ws inlu in th sht formultion to filitt xtrusion prossing n to improv mhnil proprtis of th prouts, th soy protin sht ws plstiiz with or without itionl moistur. With th inrs in moistur ontnt, th glss trnsition tmprtur (T g ) of th protin sht hng to

6 2574 J. Zhng t l. / Polymr 42 (2001) Fig. 2. Vrition of tn () n E 0 () of soy protin shts with tmprtur t iffrnt moistur ontnts. Th shts ontin 30 prts of glyrol pr 100 prts of ry soy protin. Th tmprtur sn ws from 100 to 130 C t2 C/min, n th frquny of th ynmi for ws 1 Hz. signifintly lowr tmprturs, rflting th plstiizing fft of wtr. Unlik th intt soy protin tht hs th hrtristi of two glss trnsitions for 11S n 7S frtions [10], th DSC of soy protin shts show singl T g, initing omplt nturtion of soy protin uring th sht prossing. A soy protin plsti smpl m y omprssion-moling, ontining 0.5% moistur n no glyrol, ws us s n unplstiiz ontrol in this stuy. Th ontrol soy protin plsti show shrp glss trnsition, with T g t. 145 C. This rsult gr with tht (150 C) rport y Su t l using DMA nlysis [7]. With glyrol n wtr, th plstiiz protin shts show rs T g. Th T g rs ontinuously with n inrs in moistur ontnt. Whn th moistur ontnt

7 J. Zhng t l. / Polymr 42 (2001) Tl 4 Efft of zin sulft on mhnil proprtis of soy protin shts (formultion: SPI 760 (100 prts), wtr (80 prts), glyrol (30 prts)) ZnSO 4 (prts) s y (MP) s (MP) P.E.Y. (%) P.E.B. (%) Strngth (MP) E (MP) Toughnss (MP) ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 3.9 s y is th strss t yil point. s is th strss t rk point. P.E.Y. is th prntg longtion t yil point. P.E.B. is th prntg longtion t rk point. E is Young s moulus. ws low, vn with 30 prts of glyrol, th T g of soy protin sht ws ov room tmprtur. This rsult in rltivly high yil strsss n mouli for thos smpls t room tmprtur (Tl 3). DSC thrmogrm of soy protin shts ontining 26% moistur show pk t out 18 C (onst tmprtur) (Fig. 1), initing th xistn of rystllizl (or frzl) wtr (mix with glyrol in this s), n th T g of soy protin shts (. 7 C) ws msk y this pk. This rsult gr with tht rport y Ponomriov n oworkrs [16,17] who stui th funtion of wtr in hyrophili polymr wtr systm, suh s poly(vinyl lohol) n polyrylmi. Thy onlu tht whn th wtr ontnt ws ov th ritil onntrtion ( ) whr it gn to rystlliz upon ooling, th T g i not rs oring to th Fox qution ut rmin onstnt n mrg with th rystlliztion or i mlting pk. Th vry low Young s moulus of th soy protin sht ontining 26% moistur lso init tht this sht ws in rury stt t room tmprtur (Tl 3). In this stuy, th soy protin shts show T g vlus vrying from. 50 to 7 C with 30 prts of glyrol n moistur rnging from 2.8 to 26% Dmping sptr Fig. 2 shows th DMA sptr of soy protin shts with 30 prts of glyrol n iffrnt moistur ontnts. Th trnsitions tht ourr in th low tmprtur rng wr ttriut to -trnsitions. Bus ths trnsitions vri sustntilly with moistur ontnt n thrml xpnsion, thy wr likly motions of th hyrt soy protin si groups, whih pn on moistur ontnt [18] n/or th rnkshft motion of th min hins. Ths shts show th tmprtur of -trnsition vrying from 72 to 33 C with moistur rnging from 26.0 to 2.8% (Fig. 2). Th -trnsition fll into ro rng pning on th moistur ontnt. For th sht with 26% moistur, th tn urv show mjor pk t. 15 C, whih orrspon with th mlting of th frzl wtr (mix with glyrol) rvl y DSC. Th -trnsition tmprturs of th smpls wr muh highr thn th T g vlus trmin y using th mipoint of th hng in ht pity msur y DSC (Fig. 1). This ws ttriut to th ontinuous loss of moistur s th tmprtur inrs uring DMA snning. To onfirm this osrvtion, sht smpls with 26% moistur wr snn from 115 C to 40, 60, 80 n 100 C n th wight losss t h of ov tmprturs wr foun to 8.8, 9.4, 15.5 n 22.7%, rsptivly. Aitionlly, oth th - n -trnsitions wr shift to highr tmprturs in susqunt rsns (t not shown). Although th slow vporiztion of Tl 5 Efft of pihlorohyin s ross-linking gnt on mhnil proprtis of soy protin shts (formultion: SPI 760 (100 prts), wtr (80 prts), glyrol (30 prts)) ECH (prts) s y (MP) s (MP) P.E.Y. (%) P.E.B. f (%) Strngth (MP) E g (MP) Toughnss (MP) Wtr sorption %, 2 h ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 9 f ECH ˆ pihlorohyrin. s y is th strss t yil point. s is th strss t rk point. P.E.Y. is th prntg longtion t yil point. P.E.B. is th prntg longtion t rk point. E is Young s moulus.

8 2576 J. Zhng t l. / Polymr 42 (2001) Tl 6 Efft of glutri ilhy s ross-linking gnt on mhnil proprtis of soy protin shts (formultion: SPI 760 (100 prts), wtr (80 prts), glyrol (30 prts)) Glutri ilhy (prts) s y (MP) s (MP) P.E.Y. (%) P.E.B. (%) Strngth (MP) E (MP) Toughnss (MP) Wtr sorption %, 2 h ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ 3 s y is th strss t yil point. s is th strss t rk point. P.E.Y. is th prntg longtion t yil point. P.E.B. is th prntg longtion t rk point. E is Young s moulus. glyrol n othr voltil omponnts in soy protin oul lso ontriut to th totl wight loss, th mjor wight loss ws ttriut to wtr. A similr osrvtion ws rport for glss trnsition of glutn y Klihvsky t l. [13]. In thir stuy, th uthors stui th phnomn of moistur loss uring th DMA sn n foun tht loss of 1% in th wtr ontnt uring snning rsult in 5 C upwr shift in th tn pk tmprtur. In our stuy, th -trnsition tmprturs of shts ontining 7.7 n 2.8% moistur wr ov 100 C n wr quit los to h othr. Two xplntions oul ount for this phnomnon. First, us smpls wr snn in n ovn in DMA inst of sl pns (in DSC), th loss of moistur uring th sn rsult in hngs of -trnsitions to highr tmprturs. Son, thr ws glyrol (30 prts) in th soy protin formultion, n th plstiizing fft of glyrol m th fft of moistur t low ontnts lss signifint. On th sis of th ov osrvtions, th T g vlus otin y DSC wr mor urt n rlil for soy protin plstis ontining moistur. Th T g vlus from th tn pks, on th othr hn, tn to sustntilly highr Dynmi moulus Similr to wht ws rport y Coro n Kokini for glutnin [19], th rop in storg moulus (E 0 ) of soy plsti shts t T g ws not tstrophi s in th s of synthti polymrs (usully mor thn 3 orrs of mgnitu). Th E 0 vlus of smpls with low moistur ontnt (2.8 n 7.7% H 2 O) show th lst tmprtur pnn in th whol tmprtur rng (Fig. 2). On th othr hn, th E 0 vlus of smpls ontining high moistur (26 n 13.9% H 2 O) grtly rs with th inrs in tmprtur. Furthrmor, E 0 of th shts ontining 2.8 n 7.7% moistur grully rs with th inrs in tmprtur, rhing minimum t. 5 n 16 C, rsptivly. E 0 thn show n ovious rovry (sn s ump in th urv) with furthr inrs in tmprtur, spilly for th sht with 7.7% moistur. This hvior ws similr to tht of rttil tnons n plstiiz ollgn mmrns rport y Chin n Chng [20]. Aoring to thos uthors, th minimum E 0 ws ttriut to th vitrifition of wtr oun to th protin. Aftr vitrifition, th rovry of mhnil strngth ws ovious for shts tht ontin rltivly low moistur, ut not for th shts with xss moistur. Th rovry of mhnil strngth ws ttriut to th inrs intrtions twn protin moluls rsulting from th loss of wtr. For smpls with xss moistur ontnt, howvr, th mhnil strngth ws signifintly ru us of th plstiizing fft of moistur tht rmin in th smpls. In th su-mint tmprtur, th E 0 of soy protin shts inrs with th inrs in moistur ontnt. This oul ttriut to th ntiplstiiztion fft t th vry low tmprtur [7]. At this low tmprtur, th wtr glyrol mixtur rystllizs [21]. Thrfor, th plstiizrs, wtr n glyrol, stiffn th soy protin plstis inst of softning thm. A similr phnomnon ws rport for nylon 6 n poly(l-luin-o-glutmi i) [22] Wtr sorption Fig. 3 shows th wtr sorption of soy protin shts ftr iffrnt immrsion tims. Th wtr sorption of th soy protin sht ftr 20 h immrsion ws up to. 180%, n most of th wtr uptk ourr in th first fw hours. With th prsn of two prts of ZnSO 4, th wtr sorption of soy protin shts ws signifintly ru (. 30%). Thr ws no lr rltionship twn wtr sorption n th onntrtion of ross-linking rgnts (pihlorohyrin n glutri ilhy) prsnt in th soy protin shts, s shown in Tls 5 n 6. This oul ttriut to th ft tht ross-linking i not hng th hyrophili ntur of soy protin. In ition, t suh low onntrtions of ross-linking gnts, grs of rosslinking wr not suffiint to ru th swlling n wtr uptk uring immrsion. Thus, it ws monstrt tht ovlnt ross-linking rtions wr not fftiv in ruing wtr sorption of soy protin plstis.

9 J. Zhng t l. / Polymr 42 (2001) Fig. 3. Wtr sorption of soy protin shts s funtion of tim. W: Shts ontin 30 prts of glyrol pr 100 prts of soy protin; X: shts ontin 30 prts of glyrol n two prts of ZnSO 4 pr 100 prts of soy protin. 4. Conlusions Th soy protin sht ws usully in its glssy stt n show rltivly high strngth n moulus unlss it ontin high moistur n glyrol s plstiizrs. Mthyl gluosi oul us to prtilly rpl glyrol for mking rigi shts. Zin sulft, pihlorohyrin, n glutri ilhy ll inrs rigiity n othr mhnil proprtis of th soy protin shts through ross-linking, ut thy lso l to poor prossiility t high onntrtions. Th ynmi mhnil hvior of soy protin plstis ws omplit us of th loss of wtr uring DMA snning t iffrnt tmprturs. Thus, glss trnsition tmprturs of soy protin shts with iffrnt moistur ontnts trmin y using DSC wr mor rlil thn tht otin y using DMA. At vry low tmprturs ( 50 C), wtr n glyrol show n ntiplstiiztion fft. Crosslinking of soy protin shts y using ovlnt rosslinking rgnts i not ru th wtr sorption of th plstis. Aknowlgmnts Th uthors grtfully knowlg finnil support from th Iow Soyn Promotion Bor. Rfrns [1] Wlsy D, Kolr C, Rihrt S. Inform 1998;9:250. [2] Brothr GH, Mkinny LL. In Eng Chm 1939;30:84. [3] Brothr GH, Mkinny LL. In Eng Chm 1940;32:1002. [4] Ptu I, Chn C, Jn J. In Eng Chm Rs 1994;33:1821. [5] Ptu I, Chn C, Jn J. J Environ Polym Dgr 1994;2:211. [6] Spn K, Alln AL, Wng S, Jn J. In: Ottnrit R, Hung S, Prk K, itors. Hyrogls n iogrl polymrs for iopplitions. Wshington, DC: ACS, p [7] Su H, Wng S, Jn J. Polymr 1996;38:5035. [8] Wng S, Su H, Jn J. J Mromol Si-Chm A 1996;33(5):557. [9] Otig J, Ams D. J Environ Polym Dgr 1997;5:199. [10] Morls A, Kokini JL. Biothnol Prog 1997;13:624. [11] Klihvsky M, Jroszkiwz E, Blnshr J, Int J. Biol Mromol 1992;14:267. [12] Millr E. Proprtis moifition in nginring plstis. Enginr

10 2578 J. Zhng t l. / Polymr 42 (2001) mtrils hnook, vol. 2. Mtl Prk, OH: ASM Intrntionl, p [13] Klihvsky M, Jroszkiwz E, Blnshr J, Int J. Biol Mromol 1992;14:257. [14] Ktz AK, Gluskr J, B S, Bok C. J Am Chm So 1996;118:5752. [15] Brg J, Shi Y. Sin 1996;271:1081. [16] Ponomriov T, Mlnihnko Y, Alouy PA, Rult J. Polymr 1997;38:3561. [17] Rult J, Grff R, Ping ZH, Nguyn QT, Nl J. Polymr 1995;36:1655. [18] Bshk G, Hrtwig G, Zhrnik F. Polymr 1999;40:3433. [19] Coro AM, Kokini JL. J Rhol 1991;35:257. [20] Chin JCW, Chng EP. Biopolymrs 1972;11:2015. [21] Grn JL, Fn J, Angll CA. J Phys Chm 1994;98: [22] Hiltnr A, Anrson JM, Br E. J Mromol Si-Phys B 1973;8(3 4):431.