EXPERIMENTAL STUDY OF EXTRUSION AND SURFACE TREATMENT OF ORGANO CLAY WITH PET NANOCOMPOSITES

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1 EXPERIMENTAL STUDY OF EXTRUSION AND SURFACE TREATMENT OF ORGANO CLAY WITH PET NANOCOMPOSITES Krnik Trverdi, Somchoke Sontikew Wolfson Centre for Mterils Processing School of Engineering nd Design Brunel University, United Kingdom Astrct The use of orgnocly in polymers is expected to increse nnully y out 5 percent. This pper descries melt lending techniques using PET nnocomposites contining commercilly ville orgnoclys with different percentge of surfctnt cotings. This pper will lso evlute the morphology nd mechnicl properties of the composites using rnge of techniques like, scnning electron microscopy, melt rheology nd therml nlysis. Comprisons will e mde etween properties of morphous nd semi crystlline films in terms of surfctnt used nd mteril properties. It will e demonstrted tht the quntity of surfctnt used with the orgnoclys cn significntly ffect dispersion nd properties of composites produced. Introduction Since Toyot successfully developed Nylon 6/orgnocly nnocomposite in 1986 [1], there hve een mny reports in the field of the orgnocly nnocomposites with different polymer systems, such s, nylon 11 nd 12, nylon-66, polypropylene, polystyrene, polyethylene, Poly(vinyl chloride) nd other polymeric mterils. It is over decde tht the PET/orgnocly nnocomposites hve een studied long with its morphology, its use in pckging s gs rrier, therml nd mechnicl properties hve lso een extensively investigted [2,3]. Generlly, the PET/orgnocly nnocomposites hve een prepred y three different methods: in situ polymeriztion [4], melt lending [5], nd solvent lending [6]. An importnt trget hs een to exfolite the cly uniformly throughout the polymer mtrix into individul lyers of cly, nd hoping tht the mixing techniques used will fully exfolite cly in PET nnocomposites nd in the process it might gretly improved mechnicl, therml nd gs rrier properties. Recently, Urko et l. [7] investigted the mount of surfctnt necessry to use on the nnostructure y dispersing two commercil orgnoclys, Cloisite 15A (15A) nd Cloisite 20A (20A), in the PET. Both orgnoclys hve the sme surfctnt i.e. dimethyl, dehydrogented tllow, quternry mmonium (2M2HT) ut the content of surfctnt in 20A ws less. The surfctnt hs two long lkyl groups (dehydrogented tllow), which possily reduces interction etween cly nd the polymer chins. XRD results of this study show tht the PET chins interclte more esily into the cly lyers of 20A thn tht of 15A due to the decrese in numer of non polr groups, resulting in n increse of interction etween the mtrix nd the cly. The commercil orgnoclys, Cloisite 10A (10A) nd Nnofil-2 (N2) re lso coted with the sme surfctnt, dimethyl, enzyl, hydrogented tllow, quternry mmonium (2MBHT), ut the percentge of surfctnt in N2 is less thn in 10A. While the surfctnt of 15A nd 20A hs two long lky tils, the surfctnt of 10A nd N2 hs one long lkyl til (hydrogented tllow). And with one long lky til in the surfctnt, the polymer molecules more esily enter the cly gllery. The interlyer distnce etween cly lyers of 10A is lrger thn tht of N2, 1.92 nm for the former nd 1.8 nm for the ltter, nd susequently 10A could e more dispersed in PET thn N2. However, 10A is proly more degrded thn N2 t high processing temperture due to higher content of modifier, cusing reduction of dispersion of cly in the PET mtrix. The reduction of modifier concentrtion in N2 possily increses the PET/cly interfce nd reduces degrdtion, resulting in the improvement of cly dispersion nd tensile properties. This work ims to disperse 10A nd N2 in PET in order to study the effect of using different concentrtions of modifier on the morphology, rheology, nd tensile properties, including the effects of vrying melt temperture in the rnge of C. Experimentl procedure The PET with n intrinsic viscosity of dl/g ws kindly supplied y Wellmn Interntionl Ltd., Irelnd. Two different orgnoclys were used, Nnofil-2 kindly supplied y Süd-Chemie, Germny nd Cloisite 10A from Southern Cly Products, USA. Both clys were coted with quternry mmonium, dimethyl, enzyl, hydrogented tllow (2MBHT), with different concentrtion. N2 with CEC of 75meq/100g with the interlyer distnce of 1.8 nm, while 10A with CEC of 125 meq/100g with the interlyer distnce of 1.92 nm. The orgnoclys nd PET were dried t 80 C nd t 140 C respectively in n oven for 24 hours. PET ws lended with 2.5 wt% of orgnocly in co-rotting intermeshing 40mm

2 dimeter twin screw extruder nd the modulr screws were ssemled with semi severe screw profile nd devolotlistion zone three qurters down strem, with rrel tempertures of 240, 245, 250, 255, 260, 265 C, from the hopper to the die. The extruder ws operted t screw speed of 350 rpm. The PET compound ws extruded through 6 mm die nd pelletized. Tensile specimens were otined y compression moulding. The PET grnules were heted to desired melting temperture nd kept t this temperture for 2 minutes. After tht, the melt ws pressed for 3 minutes to get uniform thickness of out 0.15 mm. Amorphous smples were otined y rpidly quenching the molten films. And to ttin semicrystlline films, the molten films were cooled to desired crystlliztion temperture with cooling rte of 40 C/min nd mintined t this temperture for 10 minutes. The dispersion of the lyered silicte in PET ws oserved using scnning electron microscope (SEM), ZEISS s SUPRA 35VP. Surfces were etched under vcuum in oxygen plsm for 8 minutes t 50 wtts. The plsm etched smples were coted with gold efore SEM. This tretment removed smll mount of top surfce lyers of the polymer smple. Susequently the 3-D dispersion of cly prticles in the PET nnocomposite ws clerly reveled. Rheology properties were exmined y using n ARES rheometer with 25 mm prllel plte geometry. Dynmic frequency sweep tests were performed in the frequency rnge of 0.1 to 500 rd/s with strin mplitude of 8% nd t 270 C under nitrogen. Thermo grvimetric nlysis (TGA) results were performed under nitrogen flow of 50 ml/min y using TA Instrument (TA500) to exmine the therml stility of the orgnoclys. All smples were heted up to 800 C t heting rte of 20 C/min. Extent of crystllinity in the smples ws determined y using differentil scnning clorimetry, TA instrument DSC Q1000. Smples were encpsulted in luminium pns nd plced in DSC cell nd heted to 300 C t rmp rte of 10 C/min under nitrogen tmosphere. The percentge crystllinity (X c ) for PET nd PET nnocomposites were clculted from the following eqution: H m H c X c ( wt%) = H 0 where H m of 136 J/g is the het of fusion of 100% crystlline PET [8]. Dog-one shped smples for tensile testing were cut from the compression moulded films. The dimensions m of the specimens were, guge length 25 mm, width 4 mm nd thickness 0.15 mm. The cross hed speed of the tensile tester ws set t 5 cm/min. The tests were crried out in n ir conditioned room set t 23 C nd reltive humidity of 43%. Results nd discussion In this study the morphology of the nnocomposites were oserved t the frcture nd lso non frcture flt surfces of the composite using SEM technique in order to identify the dispersion of the nnocomposites including phse seprtion with intercltion nd/or exfolition. SEM microgrphs of sectioned films of the PET nnocomposites contining 2.5 wt% 10A (PET-25-10A-HS) re shown in figure 1. The nnocly prticles re clerly oserved from the treted surfces. The low mgnifiction imge in figure 1 revels tht the nnocly prticles re finely nd rndomly dispersed in the mtrix. At higher mgnifiction in figure 1 the edges of cly prticles emerge from the mtrix. Although the numers of the lyers in ny cly stcks cnnot e counted, the thickness of the cly stcks re in nnoscle, less thn 100 nm. Figure 2 shows the morphology of the flt non frctured surfces of the nnocomposites s in figure 1 nd it revels the surfce res of clys rther thn the cly edges. With low mgnifiction imge, figure 2, the smll nd lrge prticles of cly re dispersed throughout the mtrix nd in figure 2 with higher mgnifiction, some of the cly stcks re completely roken down into smll stcks. However, these dispersed prticles do not connect together to form single re or network ecuse the numer of prticles re not high enough to develop networks of nnocly. The comintion of frcture nd flt surfce imges indictes tht PET-25-10A-HS exhiits mixture of interclted nd prtilly exfolited structure without the formtion of the network structure of nnocly prticles. The morphology of the PET nnocomposites contining 2.5 wt% N2 (PET-25-N2-HS) in figures 3 nd 4 ws oserved on the cross section nd flt surfce y using SEM respectively. From the SEM imges of the flt surfces, PET-25-N2-HS displyed lrger nd greter numer of ggregtes of cly thn PET-25-10A-HS. These results indicte tht it ws possile to disperse Cloisite 10A in the PET mtrix more thn Nnofil 2 ecuse the former hs higher hydrophoicity, resulting from high content of the modifier. TGA results of 10A nd N2 in figure 5 exhiit similr ptterns ecuse oth orgnoclys re MMT cly modified with identicl modifiers ut modifier concentrtion with N2 is lower thn tht used with 10A nd therefore N2 hs more finl residue of cly thn 10A. Neither of the orgnoclys seem to e very suitle for producing high qulity PET nnocomposites ecuse the onset decomposition temperture of 10A nd N2 (200 C) is

3 lower thn PET melt processing which is in the rnge of 255 to 280 C. However, weight loss of N2 t 260 C is 10% while tht of 10A is 15% nd therefore the therml stility of N2 is much etter thn tht of 10A. Rheology of PET/orgnocly nnocomposites ws studied using liner viscoelstic mesurements in oscilltory sher mode to exmine the structure of the composites. Figure 6 illustrtes the storge modulus (G ) of virgin PET (VPET), extruded PET (ExPET) nd nnocomposite smples. In generl, the high dispersion of the cly provides lrge res of cly lyers strongly intercting with the polymer chins, resulting in the increse of G especilly t low frequencies [9]. PET-25-10A-HS exhiits higher G thn PET-25-N2-HS in the low frequency rnge. This result shows tht the dispersion of 10A is etter thn tht of N2. It mens tht 10A is more comptile with PET thn N2 ecuse higher concentrton of surfctnt ws used. The tensile properties in the morphous stte of VPET, ExPET nd PET nnocomposites contining two different orgnoclys were studied nd the results of tensile modulus nd tensile strength re presented in figures 7 nd 7. In order to study the effect of processing temperture on mechnicl properties, the film specimens were prepred y compression moulding t two different melt tempertures of 255 C nd 280 C nd then rpidly quenched to otin the morphous films. The result indicte tht melt temperture does not ffect tensile modulus nd strength of the unfilled nd filled PET with morphous structure. Compred with VPET, the modulus is incresed y 18% for PET-25-10A-HS nd y 13% for PET-25-N2-HS. In figure 7, the filled PET with 10A shows higher tensile strength thn the filled polymer with N2 lthough oth nnocomposites exhiit decrese in strength in reltion to the virgin PET. But y comprison with the extruded PET, oth nnocomposites enhnce tensile strength. The improvement in tensile modulus confirms the SEM results tht the degree of dispersion for the 10A is greter thn N2 in the PET mtrix. In this work the effect of melt temperture on mechnicl properties of semicrystlline PET nd PET nnocomposites were lso studied. Figure 8 shows tensile modulus nd strength t different melt tempertures of 255, 260, 270 nd 280 C. The tensile modulus of ll smples, in figure 8, is not ffected y the melt temperture. The tensile moduli re enhnced y 24% for the semicrystlline PET-25-10A-HS nd 21% for the semicrystlline PET-25- N2-HS reltive to VPET. In contrst, the tensile strength of oth semicrystlline nnocomposites decreses with incresing melt temperture compred with VPET s well s ExPET. Interestingly, the tensile strength of the semicrystlline nnocomposites sed on N2 exhiits significntly higher tensile strength thn tht of the smples with 10A, especilly t the processing temperture of C. This is ecuse of the degrdtion of the modifier in the orgnoclys t tempertures higher thn 200 C, resulting in roken PET chins. According to the TGA result, N2 is more stle thn 10A t PET processing temperture. For this reson the tensile strength of semicrystlline PET with 10A ws poorer thn tht of PET with N2 for ll melt temperture. Conclusions It ws found tht the mount of surfctnt in the orgnocly significntly ffects nnocly dispersion nd consequently the tensile properties. Increse of surfctnt content from 75 meq/100g for N2 nd 125 meq/100g for 10A leds to greter degree of cly dispersion nd higher tensile modulus, in greement with the melt rheology results. For the morphous films, the tensile modulus nd strength incresed with the increse of surfctnt ut the results were not ffected y chnging the processing temperture. But for semicrystlline films, the tensile strength decresed when the processing temperture ws incresed mostly due to degrdtion of the surfctnt, especilly with the smples contining higher percentge of surfctnt. Acknowledgements The uthors would like to cknowledge The Thi Government, EU FlexiFunBr Frmework 6 Progrmme for funding this work. References 1. O. A., nd U. A., Mter. Sci. Eng. C 3, 109 (1995) 2. Y. Ke, C. Long, nd Z. Qi, J. Appl. Polym. Sci., 71, 1139 (1999) 3. J. C. Mtys, nd S. R. Turner. In Polymer-Cly Nnocomposites; T.J. Pinnvi, G. W. B., Ed.; Wiley: New York, S. H. Kim, nd S. C. Kim, J. Appl. Polym. Sci., 103, 1262 (2007) 5. C. H. Dvis, L. J. Mthis, J. W. Gilmn, D. A. Schirldi, J. R. Shields, P. Trulove, T. E. Sutto, nd H. C. Delong, J. Polym. Sci. Prt B: Polym. Phys., 40, 2661 (2002) 6. C. F. Ou, M. T. Ho, nd J. R. Lin, J. Appl. Polym. Sci., 91, 140 (2004) 7. U. Gurmendi, J. I. Eguizl, nd J. Nzl, Mcromol. Mter. Eng, 292, 169 (2007) 8. H. W. Strkwether, P. Zoller, nd G. A. Jones, J. Polym. Sci. Polym. Phys., 21, 295 (1983) 9. R. Krishnmoorti, nd K. Yurekli, Current Opinion in Colloid & Interfce Science, 6, 464 (2001) Key Words Recycling, PET, extrusion, nnocomposites, polymer modifictions

4 Figure 1 SEM imges of cross-section of PET-25-10A-HS t () low nd () high mgnifiction Figure 2 SEM imges of surfces of PET-25-10A-HS t () low nd () high mgnifiction Figure 3 SEM imges of cross-section of PET-25-N2-HS t () low nd () high mgnifiction Figure 4 SEM imges of surfces of PET-25-N2-HS t () low nd () high mgnifiction

5 Figure 5 TGA results of 10A nd N2 Figure 6 G of VPET, ExPET nd composites Tensile Modulus (GP) Melt Temperture ( C) Tensile Strength (MP) Melt Temperture ( C) Figure 7 () Tensile modulus () Tensile strength for morphous films of VPET, ExPET nd PET nnocomposites VPET ExPET PET-25-N2_HS PET-25-10A-HS Tensile Modulus (GP) Tensile Strength (MP) Melt Temperture ( C) Melt Temperture( C) Figure 8 () Tensile modulus, () Tensile strength for semicrystlline PET nd PET nnocomposite films (After compression moulding, crystllistion controlled t 200 C for 10 minutes)