Stud ies on M echan ical Properties of Full-Biodegradable Starch-PVA-Polyester F ilm s

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1 CH EM. R ES. CH IN ESE U. 2003, 19 (1), Stud ies on M echan ical Properties of Full-Biodegradable Starch-PVA-Polyester F ilm s RAN X iang2hai 1, D EN G Peng2yang 1, DON G L i2song 1 3, GAO Ge 2, ZHAO Chun 2 and L IU Feng2qi 1. Chang chun Institu te of A pp lied Chem istry, Ch inese A cad em y of S ciences, Chang chun , P. R. Ch ina; 2. Colleg e of Chem istry, J ilin U n iversity, Chang chun , P. R. Ch ina R eceived June 14, 2002 A k ind of full2biodegradable film m aterial is discussed in th is article. T he film m aterial is compo sed of starch, PVA, degradable po lyesters (PHB, PHB 2V, PCL ) w ith built p lasticizer, a cro ss2link ing reinfo rcing agent and a w et strengthening agenṫ It contains a h igh percentage of starch, co sts cheap and is excellent in w eather fastness, tem perature resistance and w aterp roof and it could be com p letely biodegraded. T he p resent paper deals m ainly w ith a new technical route using a new type of electrom agnetic dynam ic blow mo lding ex2 truder and som e effects on m echanical p roperties of the system. Ke yw o rds Starch, PVA, D egradable po lyester, Full2biodegradable, M echanical p roperties A rtic le ID (2003) In troduction A s w e have been look ing fo r the m ethods deal2 ing w ith the w h ite po llu tion of PE and o ther p lastic m aterials [1 ], the first attemp t has been m ade to in2 troduce starch o r ester group in to a PE film to ac2 celerate the b io logical degradation p rocess o r to m ake u se of the ligh t ox idation. A t first, the p las2 tic m aterials w ere decompo sed in to o rgan ic acid o r ester, and carbon diox ide and w ater at lasṫ D u ring that p rocess, som e b io logical m aterials, such as PEgstarch [2 ], starchgpo ly ( ethylene acrylic acid ) (EEA ) gpe, cam e ou ṫ How ever, w e have found that on ly starch cou ld be decompo sed by m icroo r2 gan ism. In stead of PEgstarch b io logical decompo s2 ab le film s, a series of o rgan ic acid and ester film m aterials has been developed, such as B iopo l, w h ich is a copo lym er of hydroxyl bu tyrate and hy2 droxyl pen tano ic acid, po ly ( lactic acid ) ( PLA ), po lycap ro lactone ( PCL ), po lycarbonate ( PC ) and po lyesters by po lyconden sa t ion react ion from aliphatic b inary acid and diatom ic alcoho l. T ho se types of film m aterials are really b io logical, bu t they are no t su itab le fo r being m ade in to general p ackage film and field film m a teria ls due to their expen sive co st [2 8 ]. [9 Am erican F. H. O tey et a l. ] have developed a new typ e of film m ade of PVA 2sta rch2pv C, w h ich con tain s 60% starch and 15% PVA. T he function of PV C is to increase w aterp roof ab ility by coating PV C on to PVA 2starch film. T h is film al2 mo st has no w et strength in the case of no t coating PV C on to PVA 2sta rch film, bu t the covering of PV C on to the film is unfavo rab le fo r degradation p rocesṡ In N ovamon t Company, Italy, starch and de2 natu red PVA have been u sed to m ake a b io logical degradation film called "M eter2b i" w h ich is fu lly degradab le and has a reasonab le p rice. It is one of the th ree k inds of the mo st famou s p lastics fu lly b i2 o logically degradab le. T he o ther tw o are B ritish IC I B iopo l and Am erican N ovon. But the app lica2 tion of M eter2b i is heavily lim ited due to its defects in w ea ther2 fa stness, tem p era tu re resistance and w aterp roof. Fo r examp le, it can no t be u sed w hen the temperatu re is beyond 0 50 and relative hu2 m idity is beyond 30% 80%. T he p resen t w o rk is differen t from the above research in experim en tal fram e and techn ical rou te. O u r aim is to develop a k ind of film s w h ich con tain s a h igh starch con ten t, co sts cheap and is excellen t in w ea ther2fa stness, tem p era tu re resistance and w aterp roof and it cou ld be fu ll2b iodegraded to tally and qu ick ly. T he film m aterial is compo sed of starch, PVA, degradab le po lyesters (PHB, PHB 2 V, PCL ) w ith a bu ilt p lasticizer, a cro ss2link ing reinfo rcing agen t and a w et st reng then ing agen ṫ T he w o rk also p resen ts a new key techn ical rou te by m ean s of w h ich the raw m aterials are p rocessed v ia b lending fo r modification, pelleting and b low mo lding by a new type of electrom agnetic dynam ic 3 To w hom co rrespondence should be addressed.

2 1 08 CH EM. R ES. CH IN ESE U. V o l. 19 ex truder [10 ]. Starch is an inducer fo r b io logical degradation. Starch2based b io logical po lym ers are thu s natu rally recycled by a b io logical p rocesṡ To adju st its con2 ten t can con tro l the tim e and the rate of degrada2 tion. Becau se the strength of pure starch is no t h igh enough fo r general app lication, PVA, a b io2 logically degradab le po lym er, u sefu l fo r so il condi2 tioner, good at film strengthen ing, m u st be b lend2 ed to increase the strength. T he w et strength and the w a terp roof of sta rch2pva a re inferio r, so the in troduction of PHB, PHB 2V, PCL w ou ld increase the w aterp roof p roperty, especially w hen tempera2 tu re is h igh. T he bu ilt2in p lasticizer system of gly2 co l2glycerine2po ly (ester2o ls) has th ree function s, that is, ( 1 ) p lasticizing and lub ricating, ( 2 ) strengthen ing w eatherab ility, especially at a low temperatu re, ( 3) increasing the compatib ility of sta rch2pva w ith deg radab le po lyesters. In the m ean tim e, the in troduction of a cro ss2link ing rein2 fo rcing agen t and a w et strengthen ing agen t w ou ld greatly increase the ten sile strength and the w et strength of the film, up to 24 M pa, h igher than that of M eter2b i. T he w aterp roof, the temperatu re resistance and the w ea therab ility of sta rch2pva film s have been greatly imp roved. T he op tim al techno logical condition s have been confirm ed by ad2 ju sting the p rescrip tion and u sing an electrom ag2 netic dynam ic ex truder [11 13 ]. T he film m aterial can almo st cover the app lication field of the PE film. Exper im en ts 1 M a ter ia ls Co rn sta rch w a s supp lied by Changchun D acheng Co rn Ch inese2fo reign Jo in t V en tu re L td. and Changchun H uang long Food stuff Indu st ry L td.. PVA : PVA w as ob tained from Beijing O rgan ic Chem ica l Facto ry w ith a po lym eriza t ion degree 1700 and degradation degree 99%. W et strengthen ing agen t (A PE ) w as hom e2 m ade. T he coup ling agen t of o rgan ic titanate w as ob ta ined from N an jing N o. 1 Shuguang Chem ica l Facto ry. T ribu tyl pho sphate w as purchased from Bei2 jing Chem ical Facto ry. D egradab le po lyesters (PHB, PHB 2V, PCL ), the bu ilt p la st icizer, the cro ss2link ing reinfo rcing agen t and the w et strengthen ing agen t, glyco l2 glycerine2po ly (ester2o ls), bo rax, bo ric acid, alu2 m in ium po tassium su lfate, basic alum in ium ox ide, sodium silicate w ere purchased from m arkeṫ 2 Exper im en ta l In strum en ts A h igh2speed m ixer (GH 210D Y, Beijing P lastic M ach ine) w as u sed to m ix the raw m aterials. T hen the raw m aterials w ere pelletized w ith a g 20 mm, g 35 mm sing le screw ex t ruder, m ade in Ger2 m any. A t last tho se pellets w en t th rough a set of b low mo lding m ach ine (a new type electrom agnetic dynam ic ex truder SJDD 2260 m ade by H uanan Co l2 lege of Science and T echno logy). 3 M ea surem en t Appara tus T he m echan ical p roperties w ere m easu red w ith an electron ic ten sile testing m ach ine (A GH 25KN, Japan SH IM AD ZU ) at a speed of 100 mm gm in. 4 Technology Route and Technolog ica l Param e- ters PVA, starch and degradab le po lyesters (PHB, PHB 2V, PCL ) w ere added to a h igh sp eed m ixer first, to w h ich the cro ss2link ing reinfo rcing agen t and the w et strengthen ing agen t w ere added. A t la st the bu ilt p la st icizer and the defoam ing agen t w ere added to the system un til it w as m ixed un i2 fo rm ly. T he techno logical param eters are listed in T ab le 1. Table 1 Technology parameters A pparatus Single screw extruder g g g Ram head D ie Electrom agnetic dynam ic extruder Results and D iscuss ion 1 The Effect of PVAgstarch M a ss Ra tio on The F ilm M echan ica l Properties F ig. 1 show s the effect of PVA gstarch m ass ratio on the ten sile strength. T he change of PVA g starch ratio obviou sly has influence on the film ten2 sile strength. W hen the con ten t of PVA is low, the ten sile st reng th increa ses g radua lly w ith the in2 crea se of PVA con ten ṫ A s PVA con ten t equa ls 40%, the ten sile strength reaches the m ax im um va lue, and then the ten sile st reng th beg in s to de2 crease w ith the fu rther increase of PVA con ten ṫ F ig. 2 show s the dependence of elongation at b reak on PVA gstarch m ass ratio. W ith the increase of PVA gstarch m ass ratio, the film elongation at b reak increa ses step by step from the beg inn ing, and reaches the m ax im um value w hen PVA gstarch m ass ratio is 0. 4, and then decreases. Com b in ing the resu lts of F ig. 1 and F ig. 2, it cou ld be conclud2

3 N o. 1 RAN X iang2hai et al. 109 F ig. 1 Inf luence of PVAgstarch mass retio on the ten sile strength of the blend. F ig. 2 Inf luence of PVAgstarch mass ratio on the elongation at break of the blend. ed that the m echan ical p roperties of the film are ex2 cellen t w hen PVA gstarch m ass ratio equals The Inf luence of the D egradable Polyester on the M echan ica l Properties of The F ilm F ig. 3 and F ig. 4 show the change of the film m echan ical p roperties w ith the change of po lyesterg starch m ass ratio. In the experim en t PVA gstarch m ass ratio w as fixed and o ther componen ts kep t con stan ṫ T he resu lt s show tha t the film ten sile st reng th reaches the m ax im um va lue w hen the po lyestergsta rch m a ss ra t io is and tha t of elongation at b reak is The Inf luence of the Built Pla stic izer Con ten t on the F ilm M echan ica l Properties F ig. 5 show s the effect of the bu ilt p lasticizer con ten t on the ten sile st reng th. W ith the increa se of the bu ilt p lasticizer, the film ten sile strength in2 crea ses very qu ick ly a t first, then the increa sing trend is smoo th, and reaches the m ax im um w hen the m ass ratio of the bu ilt p lasticizerg( PVA + starch) is It goes dow n after thaṫ T he ex2 perim en tal resu lt of elongation at b reak (F ig. 6) is differen t from that of the ten sile strength, that is, the elongation at b reak goes up in the w ho le p roce2 du re. T he addition of the bu ilt p lasticizer to the PVA gstarch system is under the condition s of h igh temperatu re, h igh p ressu re and h igh shear. So the bu ilt p lasticizer can penetrate in to PVA gstarch, b reak dow n the inner hydrogen bond, decrease the acting fo rce among starch mo lecu les, and m ake starch mo lecu le chain s slide easily. F ig. 3 Inf luence of degradable polyestergstarch on the ten sile strength of the blend. F ig. 5 Inf luence of the built plastic izer con ten t on the ten sile strength of the blend. F ig. 4 Inf luence of degradable polyestergstarch on the elongation at break of the blend. F ig. 6 Inf luence of the built plastic izer con ten t on the elongation at break of the blend.

4 1 10 CH EM. R ES. CH IN ESE U. V o l Inf luence of the Cross- link ing Agen t on M e- chan ica l Properties F ig. 7 show s the effect of the cro ss2link ing agen t on the m echan ica l p rop ert ies of the film. W hen the m ass ratio of the cro ss2link ing agen t to sta rch is low er than 0105, the ten sile st reng th of the film decreases gradually to a m in im um. T hen it increases con tinuou sly w hen the ratio of the cro ss2 link ing agen t to starch increases. F ig18 show s the effect of the m ass ratio of the cro ss2link ing agen t to starch on the elongation at b reak. W hen the ratio is 0. 08, the elongation at b reak reaches a peak val2 ue. the condition s of h igh temperatu re, h igh p ressu re and h igh shea r. T he react ion w ou ld m ake the movem en t of starch mo lecu les difficu lt and the val2 ue of elonga t ion a t b reak up to the m ax im um. T hen the va lue of elonga t ion a t b reak decrea ses. T he change of ten sile strength is differen ṫ W hen the reaction of ester bond fo rm ation dom inates, the ten sile strength goes up con tinuou sly. 5 The Effect of the W et Strength Agen t on the M echan ica l Properties T he effect of the w et strength agen t (A PE) on the ten sile strength is no t rem arkab le ( F ig19 ). W ith the increase of A PE, the ten sile strength goes up, and then goes dow n. T he peak value appears w hen the A PEgstarch m ass ratio is It is the op tim al amoun t of A PE. W ith the increase of A PE, elonga t ion a t b reak increa ses slow ly up to the m ax im um (F ig110), and then goes dow n. T he op tim al ratio is w hen the elongation at b reak is taken in to accoun ṫ F ig. 7 Inf luence of the cross- link ing agen tgstarch mass ratio on the ten sile strength of the blend. F ig. 9 Inf luence of the wet strength agen tgstarch mass ratio on the ten sile strength of the blend. F ig. 8 Inf luence of the cross- link ing agen tgstrach mass ratio on the elongation at bresk of the blend. T he addition of bo rax has a rem arkab le effect on the film m echan ical p roperties. T he reason is that bo ron atom in bo rax is easy to fo rm comp lexes w ith m any com pound s. U nder the cond it ion s of h igh temperatu re, h igh p ressu re and h igh shear, bo rax reacts w ith w ater to fo rm bo ric acid. Bo th the bo ron atom in bo ric acid and its th ree hydroxyl group s take part in the comp licated chem ical reac2 tion. Bo ric acid mo lecu les m ay penetrate in to starch mo lecu les, b reak dow n the in teractive fo rce of starch mo lecu les, increase elongation at b reak, and decrea se the ten sile st reng th. W ith the in2 crease of bo ric acid, its th ree hydroxyl group s react w ith starch mo lecu les to fo rm ester bonds under F ig. 10 Inf luence of wet strength agen tgstarch on the elongation at break of the blend F rom F igṡ 9 and 10, w e know that under the condition s of h igh temperatu re, h igh p ressu re and h igh shear in the ex truder, the addition of w et strength agen t A PE increases the in ter2mo lecu lar fo rce betw een starch and PVA. W ith the increase of w et strength agen t A PE, a net structu re fo rm s step by step, show ing tha t the ten sile st reng th

5 N o. 1 RAN X iang2hai et al. 111 goes up a t firsṫ W hen the net st ructu re increa ses to a certa in va lue, the flex ib ility of the film de2 creases and defo rm ab ility of the film becom es infe2 rio r, show ing that the cu rve reaches a peak value then goes dow n. T he elongation at b reak has the sam e trend. 6 B iolog ica l D egradability of the F ilm T he b iodeg radab ility of the film w a s deter2 m ined by m ean s of A STM and the Q uan titative Petri D ish and bu rial trials m ethod M icrobiolog ica l D eteriora tion E xp erim en t W e selected the carbon less ino rgan ic salt and agar cu ltu re m edium compo sed of 017 g K 2H PO 4, 017 g KH 2PO 4, 019 g N H 4NO 3, 017 g M gso 4 7H 2O, g ZnSO 4 7H 2O, g M nso 4 H 2O, 110 g N ac l, 15 g agar, 1000 ml distilled w a2 ter. T he ph of that agar cu ltu re m edium w as 7. T he m ixed bacteria such as bacillu s, sub tilis, etc. w ere cho sen as the experim en t bacteria. A certain num ber of samp les w ere dried and w eighed, and w ere p laced on to the ino rgan ic salt2agar cu ltu re m edium. By coating the bacteria liqu id on the sam 2 p les su rface and covering the w atch glass, they w ere p laced in to the cu ltu re box (35, 70% hu2 m idity). T hen the tw o samp les w ere taken ou t ev2 ery o ther ten days and w ere dried fo r several tim eṡ T he last step w as to w eigh the samp les and calcu2 la te the w eigh t lo ss ra te. T he resu lt is listed in T ab le 2. Table 2 The sample we ight loss rate statistics of differen t starch con ten ts(% ) Starch content (% ) Culture days W e can reach a conclu sion from the data in T ab le 2, tha t is, if the con ten t of sta rch is the sam e, the w eigh t lo ss rate increases w ith p ro long2 ing the degradation tim e. If the tim e is equal, fo l2 low ing the increa se of the sta rch con ten t, the w eigh t lo ss rate is increased. T he resu lt reveals an acceleration effect of starch on the degradation B u ria l T ria ls Sta rch2pva 2po lyester film s and po lyethylene film s w ere bu ried in the sand tho se dep th w as 20 cm. T he samp les w ere taken ou t in special tim e and the change of differen t p roperties w as tested. A fter tw o mon th s, the elongation at b reak of the starch2pva 2po lyester film has decreased almo st to 0%. It revealed that the m aterial had b rittled obvi2 ou sly. But the elongation at b reak of the PE film w as on ly reduced by 27%. In addition, w e compared the degradation rate betw een the sta rch2pva 2po lyester film and the PE film (T ab le 3). Table 3 The degradation rate statistics(% ) Samp le Burial days PE film Starch2PVA po lyester film It is eviden t that the degradation rate of the sta rch2pva 2po lyester film is h igher than tha t of the PE film. In o ther w o rds, the b io logical degra2 dation p roperty of the starch2pva 2po lyester film is very good. T he fo llow ing fo rm u la is u sed to calcu2 late the b io logical degradation rate. R = (A s - A r) ga s 100% w here R is the b io logical degradation rate; A s is the samp le s area; A r is the rem ain area. In o rder to m ake the p roduct to be p ractical, w e took som e m easu res to slow dow n the degrada2 tion rate. A t p resen t, the degradation rate cou ld be 3, 6 and 12 mon th s by m ean s of con tro lling the fo r2 m u la. Re fe re nce s [ 1 ] Snelly F rancis., J. P lastics Comp ound ing, 1989, (11), 20 [ 2 ] Yu J iu2gao, W ang X iao2dong, Chem. J. A cta P olym erica S inica, 2001, 2 (1), 99 [ 3 ] M oo re G. F., Saunders X. M., A d vances in B iod eg rad able P olym ers, 1997, 9, 2 [ 4 ] L unt J., P olym. D eg rad. S tab., 1998, 59, 145 [ 5 ] Xu X iao2yang, L in Yong2lin, Chem. J. Chem. Ind. Gongzhou., 2001, 29 (1), 101 [ 6 ] L u J iang, Xu J ing2w en, Chem. J. P lastic T echnology, 2000, 6, 47 [ 7 ] A lbertsson A. C., Karlsson S., Chem. J. M acrom olecu lar S cience2p u re A pp l. Chem., 1996, A 33, 208 [ 8 ] Q u W eiyang, Yu J iw en., Chem. J. P lastic Ind ustry, 1998, 26 (4), 106 [ 9 ] T ang Saizheng, P lastic, 1993, 7, 12 [ 10 ] Q u J inp ing, 3rd International Conf erence on M anuf actu ring T echnology, Hong Kong, 1995 [ 11 ] Ph. D ubo is J. M acrom olecu les, 1991, 24 [ 12 ] Feng yan2hong, Q u J in2p ing, Ren Hong2lie, et al., J. Ch ina P lastics, 2000, 14 (11), 1 [ 13 ] Am buj D. Sagar, Edw ard W. M errill, Chem. J. P olym er, 1995, 36 (9), 1883