Effect of Dispersed Phase Particle Dispersion on the Thermal Stability of Recycled Poly(ethylene terephthalate)/polypropylene Blend

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1 Effet of Dispersed Phse Prtile Dispersion on the Therml Stility of Reyled Poly(ethylene terephthlte)/polypropylene Blend Yew Wei Leong 1*, Hiroyuki Inoy 2, Supphorn Thumsorn 1 nd Hiroyuki Hmd 1 1 Deprtment of Advned Firo Siene, Kyoto Institute of Tehnology, Jpn 2 Ysud-Sngyo Co. Ltd., Kyoto, Jpn *Corresponding uthor e-mil ddress: leong@kit..jp ABSTRACT: Blending of reyled polyethylene terephthlte (RPET) from wste ottles with polypropylene (PP) ws performed in n ttempt to enhne the proessility of RPET. The ide of lending RPET with PP sprouted from the intention of reyling PET ottles together with their PP-sed ps. Therefore, preliminry lending of RPET with PP (RPET/PP) ws performed t vrious PP nd omptiilizer ontents. The inorportion of omptiilizers redued the PP prtile size nd improved the overll homogeneity of the lends. This effetively redued stress onentrtion points nd enhned the mehnil performne of the lends. More importntly, the inorportion of PP into RPET signifintly inresed the degrdtion temperture of the lends provided the dispersion of PP phse in RPET ws exellent. KEYWORDS: Reyling, Polymer Blends, Therml Stility, Comptiiliztion INTRODUCTION Puli wreness of environmentl nd energy prolems from plstis wstes hs posed hllenge to mny reserh groups to find wys to onvert plsti wste into useful mterils nd produt insted of ending up in lndfills. Polyethylene terephthlte (PET), whih is reognized to e one of the most verstile engineering plstis tht re minly used for produing textiles nd soft-drink ottles [1, 2], is lso one of the most disrded pkging mterils. In previous works, some efforts were devoted to investigte the possiilities in mnufturing produts suh s household equipments, struturl prts of vehiles, ontiners, ottles, omposite mterils, et. from reyled PET (RPET) through injetion, extrusion nd thermoforming proesses [3]. However, the mount of RPET usge is still very miniml ompred to the quntity of disrded PET (minly from soft drink ottles) euse of diffiulty in olleting nd seprting the PET ottle from the ps nd lels prior to reyling. Thus, it is neessry to estlish n effiient nd ost-effetive reovery method tht n onvert post-onsumer PET ottles (inluding the ps) into useful produts in pkging, ommodity nd engineering filed. To do this, we reognized the importne to lend RPET with PP sine most ps re mde from the ltter mteril. PET nd PP re inomptile due to differenes in hemil struture, wherey the former is known to e polr polymer while the ltter is non-polr. Therefore, their lends would exhiit two phse morphology wherey the dispersed phse tkes the

2 form of miro-spheres due to wek interfil intertion. Typilly, the strength nd stiffness of PET lends is proportionl to the PET ontent, ut owing to the phse seprtion, the lend exhiits very poor impt strength nd elongtion t rek. Previous works hve minly foused on the lending of polyolefins nd PET where PET ws the minor phse. As suh, the proessing tempertures were limited to etween 200 to 230 o C pprently to void therml degrdtion [4]. However, very few works hve onsidered produing lends with RPET s the mjor phse, muh less to proess these lends t tempertures ove 270 o C sine it is ssumed tht polyolefins would undergo therml degrdtion. Moreover, onsidering the verge PET ottle to p weight rtio is 90:10, it is importnt to develop tehniques for produing lends with RPET s the mjor phse in order to simulte tul reyling senrios. In the present work, lending of RPET with vrious ontents of PP nd omptiilizer ws performed in order to otin the optimum lend formultion with the est possile mehnil performne. In prtiulr, the effet of omptiiliztion on the morphologil hrteristis ws eluidted. Sine the typil proessing tempertures employed for PET nd PP re very different, the therml degrdtion hrteristis of the individul omponents nd the lends were lso evluted in order to onfirm the viility of lending RPET nd PP t high tempertures. Mterils EXPERIMENTAL The RPET ws otined in the form of flkes from rushed post-onsumer PET ottles ourtesy of Ysud Sngyo Co. Ltd. Sine the ps were seprted from the ottles nd hve ll een disrded efore the ottles were rushed, the soure of polypropylene (PP) from the ps were not ville. Therefore, insted of reyled PP, net PP J900GP (MI = 13, M w = 2.3x10 5 ) otined from Idemitsu Petrohemil Co., Ltd., Jpn, ws inorported into RPET. Styrene-ethylene-utdiene-styrene-sed terpolymer (SEBS) ws used s omptiilizer t lodings of etween 1 to 7 phr. Speimen ompositions re listed in Tle 1. Only RPET/PP lend ompositions of 95/5 nd 90/10 (fter referred to s 95/5 nd 90/10 lends) were hosen sed on the PET/PP ontent of drinking ottle with p (for 500 nd 1250 ml ottles). The RPET nd PP were dry-lended prior to ompounding in single srew extruder (SRV-P500, Nihon Yuki Co., Ltd.) set t rrel temperture etween o C nd srew rottion speed of 430 rpm. The extrudte ws pelletized nd molded into dumell speimens y using 50-ton injetion molding mhine (UM50, PO YUEN Mhinery Co. Ltd.). The mximum rrel temperture, mold temperture, nd injetion speed ws set t 285 o C, 30 o C nd 100 mm/s, respetively. Morphologil Oservtions Morphologil oservtions were performed on the e ross-setions of ryogenillyfrtured pellets y using snning eletron mirosope (SEM), JSM-5200 (JEOL Jpn Co. Ltd.). From the high mignifition SEM imges, the size (re) of the PP prtiles were mesured y using n imge nlysis softwre (Imge J). From these mesurements, the volume verge dimeter, d v, for t lest 200 dispersed phse prtiles in eh mteril omposition were lulted through the following eqution: d v = N i d i 4 / N i d i 3 (1)

3 where N i is numer of prtiles hving dimeter d i. Tensile frtured surfes of injetion molded smples were lso sujeted to mirosopi exmintion nd the prtile size distriution ws found to resemle tht of the pellets. Thermogrvimetry Anlysis (TGA) The therml degrdtion hrteristis of the individul omponents s well s the lends were evluted y using TA Instrument TGA2950 high-resolution modulted thermogrvimetri nlyzer. Aout 10 mg of RPET, PP, omptiilizer nd their lends in pellet form were heted from room temperture to 600 o C y employing highresolution temperture rmp feture to urtely pinpoint the onset degrdtion tempertures. All smples were nlyzed in dry ir. PP Prtile Size nd Distriution in RPET Effet of Comptiilizer Content RESULTS AND DISCUSSION Figure 1 depits the morphologil hrteristis of RPET/PP (95/5) lends upon the inorportion of omptiilizers t vrying onentrtions. Signifint hnges to the size nd distriution of the PP phse ould e oserved s the ontent of omptiilizer ws inresed from 1 to 7 phr. The smller dispersed phse prtile nd vity sizes ould hve mde the rk propgtion pth more omplited nd promoted rzing during tensile nd impt loding. The volume verge prtile dimeter, d v tht ws lulted from eqution (2) is plotted in Figure 2. In the un-omptiilized lend, rod distriution of lrge PP prtiles n e oserved in oth the skin nd ore regions due to the instility nd olesene of the PP phse during melt mixing. However, the numer of lrge prtiles ws fr more prominent in the ore region s ompred to the skin irrespetive of PP ontent in the lend. When only 1 phr of omptiilizer ws dded to the 95/5 lends, the PP prtile size distriution eme signifintly nrrower while the d v vlues experiened signifint redution of out 50% t the skin nd 22% t the ore. By inresing the omptiilizer ontent up to 7 phr, the prtile size distriution t the skin eme muh nrrower lthough the d v vlues remined similr. This is n indition tht the prtiles t the skin hve lredy ttined the smllest possile size with minimum d v vlue of out 0.65 m. Menwhile, the prtile size t the ore regions grdully deresed towrds similr minimum d v vlue t the skin with inresing omptiilizer ontent. Similr omptiiliztion effets hve lso een reported elsewhere for other polymer lend systems [5, 6]. Therml Stility of RPET, PP, Comptiilizer nd their Blends From thermogrvimetri nlysis (TGA) results, the onset degrdtion temperture (T onset ) of RPET pellets in ir ws reorded t 340 o C nd the rod derivtive peks indite grdul degrdtion of RPET, whih is minly due to hydrolysis. Therefore, RPET is not expeted to degrde t the designted proessing temperture of 285 o C during injetion molding s well s ompounding. However, the respetive T onset reorded for net PP nd omptiilizers were 257 o C nd 275 o C. The shrp derivtive peks following T onset for these omponents suggest tht oth mterils would degrde

4 t very high rte minly due to oxidtive retions. Hene, these omponents would e extremely unstle nd voltile if they were to e proessed individully t 285 o C. However, when these omponents were heted in nitrogen tmosphere, the T onset for ll omponents inresed signifintly. The most notle improvement in therml degrdtion resistne ws in PP where 140 o C inrement from T onset of 258 o C ould e oserved. Even the T onset of the omptiilizer ws inresed to 326 o C from 275 o C with the sene of oxygen. This is strong indition tht oth PP nd omptiilizer re extremely sensitive to oxidtive degrdtion ut they n nevertheless e proessed t high tempertures should their exposure to oxygen e limited. Interestingly, when TGA ws performed on RPET/PP/omptiilizer lends in ir, the T onset of PP nd omptiilizer were sent, s ould e oserved in Figure 3. Furthermore, the T onset of the lends reorded t ove 355 o C were even higher thn tht of monotoni RPET. It is lso interesting to note in Figure 4 tht higher PP ontent in the lend ould lso result in n inrese in T onset of the lends despite the pprent immisiility nd phse seprtion etween PP nd RPET. The pprent inrement in T onset of the lends is ttriuted to the exellent rrier properties of RPET, whih limited the exposure of PP nd omptiilizer to oxygen nd therefore preventing extensive degrdtion of these phses. The dispersed phses, on the other hnd, were le to enhne the overll therml degrdtion resistne of the lend provided they re homogeneously dispersed. The effet of PP prtile size (d v ) on the T onset ws eluidted nd presented in Figure 5. Sine the onset of degrdtion would most likely our from the surfe of the pellets, the d v vlues t the skin region of the pellets re presented. From the results, it ould e dedued tht smller PP prtile size t the skin region ws effetive in suppressing therml degrdtion of the lends. Therefore, it should e noted tht good therml stility of the lends n e hieved provided exellent homogeneity nd smll PP prtile size (preferly in the sumiron rnge) n e otined in the pellets. CONCLUSIONS In this investigtion, the PP minor phse prtile dispersion ws found to e vstly different t the skin nd ore regions of the pellets s well s injetion molded speimens. The PP prtile size nd homogeneity of the RPET/PP lends ould e modified y the use of omptiilizers nd this would profoundly influene the mehnil properties s well s therml stility of the lends. At n optimum omptiilizer ontent of 5 phr, the PP prtile size in the lends would e mostly in the sumiron rnge while exellent overll homogeneity ould e hieved. This level of prtile dispersion nd homogeneity ws the key towrds otining lends with exellent mehnil performne nd enhned therml resistne. This informtion will e very useful for the PET wste ottle reyling industry sine it provides the possiility of reyling the ottles even without first seprting the PP ps nd yet le to otin lends with enhned properties. REFERENCES 1. Y. Imi, S. Nishimur, E. Ae, H. Tteym, A. Aiko, A. Ymuihi, T. Aoym, H. Tguhi. Chem. Mter., 14 (2002), C.C. Lin. Mromol Symp., 135 (1998), S. Birh, J. Ymguhi, A. Demmler, K.Jost, Automot. Eng., 101 (1993), 109.

5 4. Z.-M. Li, M.-B. Yng, B.-H. Xie, J.-M Feng, nd R. Hung. Polym. Eng. Si., 43, 615 (2003). 5. P. Mrino, R. Lorenze, C. Dontell, & G. Andrzej. Mromol. Chem. Phys. 203(2002), J. M. Willis & B. D. Fvis, Polym. Eng. Si., 30(1990), Tle 1: Speimen designtion nd Izod impt strength of RPET/PP lends t vrious PP nd omptiilizer ontents d v Smple Composition RPET (wt%) PP (wt%) Comptiilizer (phr) 100/ / / / / /5/ /5/ /5/ /5/ /10/ /10/ /10/ /10/ d e Figure 1: SEM photogrphs showing PP dispersed phse size in 95/5 lends t vrious omptiilizer ontents: () 0 phr; () 1 phr; () 3 phr; (d) 5 phr; (e) 7 phr 95-5 skin 95-5 ore skin ore Comptiilizer Content (phr) Figure 2: Volume verge PP prtile dimeter (d v ) of 95/5 nd 90/10 lends t vrious omptiilizer ontents. Derivtive Weight (%/ o C),.u. T onset ( o C) T onset = 365 o C T onset = 363 o C T onset = 355 o C Temperture ( o C) Figure 3: Effet of omptiilizer ontent in 95/5 lends on the T onset during thermogrvimetri nlysis in ir. Comptiilizer ontent = () 0 phr; () 3 phr; () 5 phr Derivtive Weight (%/ o C),.u. T onset = 371 o C T onset = 365 o C T onset = 362 o C Temperture ( o C) Figure 4: Effet of omptiilizer ontent in 90/10 lends on the T onset during thermogrvimetri nlysis in ir. Comptiilizer ontent = () 0 phr; () 3 phr; () 5 phr /5 skin 90/10 skin dv Figure 5: Influene of PP prtile size (d v ) on T onset of oth 95/5 nd 90/10 lend pellets