Articles Indian Journal of Chemical Technology Vol. 1 0, January 2003, pp Steady state rheology of PP!PET blends

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1 Indian Journal of Chemical Technology Vol., January 23, pp Steady state rheology of PP!PT blends T Kitano', Ajay Naikb, S A R Hashmib, S R Vashishthab & Navin Chandb* "National Institute of Materials & Chemical Research (AlST), Higashi, Tsukuba, Ibaraki, Japan b Regional Research Laboratory (CSIR), Habibganj Naka, Hoshangabad Road, Bhopal , India Received 5 July 2 ; revised received March 22; accepted April 22 The objective of this study is to report the results of steady state viscoelastic properties in molten state investigated experimentally for PPIPT blends. They were prepared by the elastic extrusion method. The present paper discusses the influence of different types of PP, blending composition and effect of compatibilizer on steady state viscoelastic properties of PPIPT in molten state. Polymer blends are generally made by extrusion or by two roll mixing method. Apart from these two methods, the blends are also developed by melt blending on an elastic extruder. It is also important to analyze the flow/deformation behaviour of blend systems under a particular extrusion process, and to investigate the flow mechanisms and change of internal structure of these systems.2. PT (Polyethylene terephthalate) IS a semi crystalline polymer and is used for various applications but it is sensitive to notch and stress concentration, which restricts its wide applications. The shrinkage of PT makes its moulding very difficult. On the other hand, PP (Polypropylene) can be easily processed on all types of processing machines. The mechanical properties of the PT filled thermoplastic composites have been investigated by many researchers3.4. However, rheological properties of these materials have not been paid sufficient attention. Rheological studies have been reported mainly on the redmud filled and short organic fibre filled systems5 I. Lindsay et. al. 3 and Traugott et al. 4 investigated the use of compatibilizer for blends of P and PT. They concluded that adding up to 2% by weight SBS (Styreneethylenebutadienestyrene) copolymer to a / (P/PT) blend in an extruder at 3 C caused some reduction in modulus and yield strength but a dramatic increase in ductility was reported, which increased from 3% elongation to more than 2%. The impact strength was also improved. In this study a new PP/PT blend is prepared by combining *For correspondence (mail: navinchand@rrlbpl.org; Fax: , 495) different types of PP's with PT with and without compatibilizer. Rheological data such as shear rate, shear stress, viscosity and first normal stress difference for these new type of blends have been measured and analysed. xperimental Procedure Materials The materials used in this study were several blend systems consistmg of different types of polyproplylene and a polyethylene terephthalate (PT) melts. Polypropylene (Chisso Polypro Co Ltd, Japan) was used as a matrix material. Table lists the properties of polymer and coupling agents and names of their suppliers used in this study. Blends preparation PT concentrations used in this study were 5,, 2, 3 and wt% in the blend. Weighed amounts of PT were fed into the elastic extruder simultaneously with PP. The blend prepared by this apparatus was used as a base material for compression moulding. Material was kept in a steel mould, pressed in a hot press for 3 minutes under 5 Mpa pressure at 26 C temperature. Then this material along with mould was transferred to water circulating cold press to cool the materials to room temperature under same pressure. Test specimens for steady state rheological properties measurements were cut from the sheets obtained from above press. Measurements A cone and plate rheometer (RM 4, Nihon Rheology Kiki Co Ltd, Japan) was used for the measurement of steady state viscoelastic properties of

2 Indian. Chern. Techno!., January 23 Table ISource and specialty of materials used for making PPIPT blends Sample Name State Source PP (A 5 2) Unmodified, high viscosity Chisso Polypro Co Ltd, Japan PP (K 7) Unmodified, low viscosity Chisso Polypro Ltd, Japan PP (XKP 77W) Modified Chisso Polypro Co Ltd, Japan PT (MA 2 ) Virgin Untika Co Ltd, Japan MAH (compatib(lizer) Modified Commercial the samples. The specimens used were made from tqe compressionmoulded sheets cut into discs of 272 mm diameter. The gap between cone and plate was fixed at 3 mm. Under such gap condition, a test specimen was slightly compressed under molten state. The shear rate varied from 2 to S I and the cone angle of 4 was kept constant. The measurements were carried out for all the samples at 265 C. Cone radius was 2.5 mm. From the Torque T, normal shear stress crl 2 was calculated by using the equation:... ( ) and the viscosity was calculated by using the following equation:... (2) The first normal stress difference (N I) was calculated by the following relation:... (3) where, cr 2, T, R, y, N I and F were normal shear stress, torque, radius of cone, shear rate, first normal stress difference and force respectively. Results and Discussion Flow curves, shear stress (r) versus shear rate (y) for PP (A 2)/PT and their blend at various blending ratio are shown in Fig.. The flow curve of PP shows maximum shear stress while PT shows minimum. Flow curves of the blend samples lie in between PP and PT. Blend samples containing low concentration of PT are in the vicinity of PP. Separation between the flow curves for the blend samples increases at higher shear rates. These variations up to shere rate I s I are consistent with the following power law: 2 r = Ky n where, K and n are related to the intercept and slope of the flow curves. Values of the pseudoplasticity index (n) are shown in Table 2 and are.5 for PP and.9 for PT. Addition of PT initially does not affect the value of n up to 5 wt% PT and then decreases with an increase of PT content up to a value of.62 at wt% PT content. The significantly different pseudoplasticity index for blends having different blend composition shows a significant role of PT in the pseudoplasticity of the blend. Melt viscosity () as a function of shear rate is plotted in Fig. on the loglog scale for PP, PT and PP/PT blend. The polymers and blends show insignificant variation in melt viscosity with shear rate at low shear rates and a sharp decrease of melt viscosity with increasing shear rate above 3 S I. Figure 2 shows the plot of melt viscosity as a function of blend composition. On initial addition of less viscous component from 52 wt% PT to the PP, melt viscosity remains constant. Thereafter, it decreases rapidly on adding 2 to wt% PT. Figure 3 shows plots of shear stress versus shear rate on double logarithmic scale for low viscosity PP (K 7), PT and their blends at temperature 265 C. These curves are linear over the entire range of data. These linear curves are consistent with the power low. The values of n indicate that all these polymers and blends are pseudoplastic in nature. Variation of blend composition changes the slope of the flow curve effectively in Table 2 and Fig. 3. This may be due to the fact that viscosity of PP used in this case is different as compared to PP (A 5 2). Figure 3 also compares the shear viscosities of PP, PT and mechanically blended PP/PT blends at 265 C on double logarithmic scale. The polymer blends have lower viscosities than PP and higher than PT polymer at all studied shear rates. This is similar to the previous blend systems.

3 Kitano et at. : Steady state rheology of PPIPT blends Table 2 Compositions of the blends and their n values Sample Name PP (A 2) A PP (K 7) PP (XKP 77W) B PT MAH (% of PP) Density (glee) value C D F 7 3. t o G.99 H J K L M N 9 P Q.5.3 R S T U V W X Y Z AA..5 rei.. / / co.. Ui iii + VJ VJ III (f) 95/5 /+' lic 9/ +'/+' /2... 7/3 + /. Shear Rate (y). 5" Fig. I Shear stress and melt viscosity versus shear rates plots for PP (A I 2)IPT blend at 265 C 29

4 Indian J. Chern. Techno!., January 23 <ti.. :: CJl :: '(ij II> y (5.) B tr S. 5 e l /2 7/3 fi / / Blend C,mposition of PP{A :)/PT blend Fig. 2Varialion of melt viscosity with blend composition at 265 C for PP (A 2)IPT binary blend at various shear rates. <ti.. CJl : '(ij u CJl y (S'l) B l tr S e 9. 5 / 955 9/ /2 7/3 i / / Blend Composition of PP{A :)/PT blend Fig. 3Shear stress and melt viscosity versus shear rates plots for PP (K 7)IPT blend at 265 C 3

5 Kitano et at.: Steady state rheology of PPIPT blends ni en a. B / e / + 9/.!r /2 ""* 7/3... / 'iii en <II a.!::. en en U5 n; Q).s::: CJ) Shear Rate (y), S Fig. 4Shear stress as a function of shear rate for PP (XKP 77W)IPT binary blend at 265 C On comparing Figs and 3, it was observed that values of shear stress and viscosity of various PPIPT blends and PP are at higher side in Fig., which is due to the presence of higher viscosity component PP (A SO I 2) in the blend. The slope of the shear stress versus rate curves, however, shows a different behaviour. The low viscosity polypropylene based PP/PT blend show higher sensitivity to the shear rate as compared to higher viscosity PP based blends. Low viscosity PP behaves nearly similar to Newtonian fluid and higher viscosity PP based blends show non Newtonian behaviour. Flow curves in terms of shear stress and shear rate are presented in Fig. 4 for modified PP (XKP 77 W)/PT binary blend at various blending ratio. Data on modified PP and PT polymers are also included in this figure to illustrate the behaviour of the blend as well as its two component systems. Flow curves for binary blend at various compositions are quite in the vicinity of curves of matrix PP. Viscosity data of the modified PP (XKP 77W)/PT binary blend are presented in Fig. S as the variation of melt viscosity with shear rate and blend composition. At any given shear rate melt viscosity is highest at wt% PT content (i.e. unblended PP), and decreases with increase of PT content. PP (A SOI2) was modified by using a compatibilizer, maleic anhydride (. wt% of PP) and was then blended with PT. The compatibilizer used here was fed directly with the polymers in the elastic extruder at 26SoC and 4 rpm. The shear stressshear rate and melt viscosityshear rate behaviour of modified and unmodified PP (A SOI 2)IPT blends are compared in Figs S, 6, and '7 respectively. Shear stress and viscosity of the compatibilized PPIPT blends increased in comparison with uncompatibilized PPIPT blends with increasing shear rate up to l Os' for all the studied systems. In case of (SOISO)/PP/PT blend, opposite was observed which seems due to the higher concentration of molten PT having nearly onehundredth part of viscosity of PP (A 2). Such difference in viscosity makes the system heterogeneous and dominance of viscosity of PT is observed instead of PP. The compatibilizer maleic anhydride is nearly ineffective in such circumstances. Similar plots of PP (K 7S)/PT systems are shown in Figs and 9. The first normal stress difference for PP (A SO I 2)/PT binary blend system as a functions of shear rate is presented ' in Fig.. This figure also compares the effect of compatibilizer on the system. The first normal stress difference N/ increased with increasing shear rates for all the studied system. it 3

6 Indian. Chern. Techno!., January 23 ro Q. II> 'iii II>. PP/PT... /... 95/5 )I 2 ' 9/ 7/3 r /. Shear Rate (y), 5. Fig. 5Melt viscosity as a function of shear rate for PP (XKP 77W)/PT binary blend at 265 C, Q. Ul U5 n; III en & 95/ /5/ 6 9/ /2 + 9/ ij /2/... 7/3 7/3/ / + / +. Shear Rate (y), 5" Fig. 6Shear stress as a function of shear rate for PP (A 2)/PTIMAH ternary system at 265 C 32

7 Kitano et at. : Steady state rheology of PPIPT blends. <Ii Q. Vl Z'iii Vl G. / ' 955/ :.t( 9 / Shear Rate 2 + 7/3 7/3 / e / (r). 5. Fig. 7Melt viscosity as a function of shear rate for PP (A 2)IPTIMAH ternary system at 265 C. Cll Q. Vl Vl (J) lii Q) (J)... 9/ A /3 + / 9/ tr 2/ e 73 + // Shear Rate (y). 5. Fig. Shear stress as a function of shear rate for PP (K 7)IPTIMAH ternary system at 265 C 33

8 Indian J. Chem. Techno\.. January 23. Ul iii Q. iii Ul 5 9/ a 9 "' /2 "' 7/3 6 /2/ + 7/3/ ' / l:r // +._4 Shear Rate (y). 5. Fig. 9Melt viscosity as a function of shear rate for PP (K 7)/PT/MAH ternary system at 265 C PP(A2)IPTIMAH Ir 95/5 + 7/3 95/5/ + 9/ fl 9/ / e c + 73 i5 g (J) ti /2 + /2/ z u:.. +r f. Shear Rate (y). 5. Fig. Fi rst normal stress differenceshear rate plots for PP (A 5 l 2 )/PTIMAH blend system at 265 C 34

9 Kitano et af.: Steady state rheology of PPIPT blends G) c e i5 PP(K7)/PTIMAH + 9/ fit fit e & /2 US Iii 7/3 z /. u: + 9/ / _ /2/ 6 7/3/ + //. Shear Rate (y), Sl Fig. I IFirst normal stress differenceshear rate plots for PP (K 7)IPTIMAH blend system at 265 C G) u <:!! ;S :g PP(XKP 77W)IPT/MAH iii e z il u:: 95/ & /2 7/3 /. Shear Rate (y), Sl Fig. 2First normal stress differenceshear rate plots for PP (XKP 77W)IPT blend system at 265 C 35

10 Indian J. Chern. Technol., January 23 (5" )., y a !r 6. 5 c l!! & 9. 5 li 2. 5 & l!! ii) z i.l. +t++t i / Composition of PP(A 2)JPT blend 9/ 95/5 Blend 7/3 2 Fig. 3Variation of first normal stress difference with blend composition at 265 C for PP (A I 2)/PT binary blend at various shear rates decreased with increasing PT content in PP. I n general, compatibilizer increased the N, for all the systems. Similar plots for PP (K 7S)/PT and PP (XKP 77W)/PT systems are shown in Figs S, and 2. Figure 3 shows the effect of blending ratio of N, for blends of PP ( A SO I 2) and PT at 26SoC with shear rate as parameter. I t is seen that PP/PTISOISO blend shows a minimum value i n N,. Value of NJ for pure PP is higher as compared to blend of PP/PT which reduces at PP/PTI (9SIOS). The value of NJ remains almost constant up to 2% of PT i n PP. Thereafter, it reduces sharply with the increased content of PT in PP, which shows the i ncreased effect of PT in the systems. Nomenclature PP (A 5 2) Polypropylene (Unmodified and high viscosity) PP (K 7) Polypropylene (Unmodified and low viscosity) PP (XKP, 77W) Polypropylene (Modified) PT (MA 2 ) Polyethylene terephthalate (Virgin) MAH Maleic anhydrite (Compatibilizer) cr 2 Normal shear stress (Pa) or Shear stress (Pa) T Torque (N) R Radius of cone (mm) y Shear rate First normal stress difference (Pu) Conclusion I) H igh viscosity and low viscosity polypropylene were blended separately with polyester (polyethylene terephthalate) and their flow behaviour at 26SoC were determi ned. The low viscosity PP based PP/PT blend shows higher sensitivity to shear rate as compared to high viscosity PP based blend. 2 ) Addition o f compatabilizer t o the blends increase shear viscosity. 3) First normal stress difference decreases with the increase of PT content and it i ncreases with shear rate. 36 (S I) Force (N) Viscosity (Pu.s) Pseudoplasticity index References Czarnecki L & White J L, J Appl PO/YIII. 25 ( 9RO) 2 7. Ausias G. Agassant J F. Vincent M. Lafleur P G. Lavloie P A & Carrear P J, J Rheo/, 36 ( 992) 525. Lindsay C R, Paul D R & Barlow J W, J Appl PO/YIII Sci. 26 ( 9 ). Traugott T D, Barlow J W & Paul D R. J App/ PO/VIII Sci. 2X ( 93) Greene J P & Wikes J, J PoLYIII Sci. 35 ( 995) 67.

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