PET Blends

The motivations for the preparation of blends based on thermoplastic polyesters (as PET) and other polymers are (32)  

Polycarbonate (PC) and polyesters blends are phase separated and are obtained without ester exchange reaction. So, the crystallinity of polyester is maintained. These blends combine the characteristics of both polymers. Catalysts could be added to promote ester exchange reaction and yielding to the disappearance of the PET crystallinity. 

PC/polyester blends are resistant to hydrocarbons, alcohols, organic acids, inorganic aqueous salts and mild acid or base solutions. PC/polyester blends present superior chemical resistance over polycarbonate. This makes PC/polyester blends suitable for utilizations requiring resistance to intermittent contact with fuels or oils. 

These blends find different applications (automobile industries, sporting goods, electrical...) due to their good thermal properties, toughness and chemical resistance (33). 

Among thermoplastics alloys the combination of PP and PET offers some advantages over the pure components. PET may enhance the stiffness of PP at higher temperatures while the polyolefin could facilitate PET crystallization. Non-compatibilized and compatibilized PET/PP blends were prepared. Main compatibilizers used were PP-acrylic acid copolymer, maleic anhydride modified PP (PP-g-MA), hydrogenated SBS block copolymer (SEBS-g-MA) and linear low-density polyethylene (LLDPE-g-MA) (34). 

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Table 7.9 Effect of use of isopropenyl 2-oxazoline on the properties of ABS/PET blends (Based on data in Modern Plastics International, February 1994)...

Blends of PBT with polycarbonates have been widely used for car bumpers. Interest in PBT/PET blends and PBT/ASA has arisen because of the good surface finish possible even with glass-reinforced grades. Copolyesters based on PBT but with some longer chain diol or acid are also now produced. 

Rgure 8 Effect of Flame Retatdant Type Impact Modified 2/1 PC/PET Blend Art ... 

Table 6 shows the flamability characteristics of an impact modified 2/1 polycarbonate/PET blend containing 6 % of the various flame retardants. The composition containing the brominated phosphate 60/4 is the only one which is V-0 by the UL-94 vertical burn test. At 10 % add-on, the all-bromine containing resin is V-1 and at 13 % add-on the all-phophorus containing resin is V-0. 

Table 6. Flame Retarding Impact Modified 2/1 Polycarbonate/PET Blend...

Yoda [28] investigated the activity of 20 catalysts in the transesterification reaction of PET and poly(ethylene isophthalate) (PEI) and found the same order of reactivity as for the transesterification of DMT with EG. The most effective catalysts were the acetates of Zn, Pb(n) and Hg(n), together with Co(m) acety-lacetonate and Sb203. Titanium catalysts were not included in Yoda s study, but are known to be effective catalysts in PET blending [46],... 

Figure 13.6 (a) Elongation as a function of wind-up speed for partially oriented yarn, (b-d) Stress-strain curves of fibers of PET blends with 3% copolyester of 1,4-phenyleneterephthalate and p-oxybenzoate (CLOTH) and 3% copolymer of 6-oxy-2-naphthalene and p-oxybenzoate (CO), spun at 3500, 4000 and 4500 m/min (1) PET control (2) 3 % CLOTH (3) 3 % CO the loci of the theoretical extensions of the PET control are shown as dashed curves [17]. From Orientation suppression in fibers spun from melt blends, Brody, H., J. Appl. Polym. Sci., 31, 2753 (1986), copyright (1986 John Wiley Sons, Inc.). Reprinted by permission of John Wiley Sons, Inc. 

Figure 20.3 Polarized micrographs of the PHB/PEN/PET blends for various compositions (mol %)...

Figure 20.4 The melting temperature ( ) and melting enthalpy ( ) as a function of PEN content for the PEN/PET blends...

Figure 20.7 The effect of pre-heating temperatures and blend composition on the melting temperatures of the PHB/PEN/PET blends , 260°C O, 280 °C A, 300 °C...

Figure 20.9 The 1H-NMR spectrum at 300 MHz, showing the assignments of the absorptions for the PHB/PEN/PET blends dissolved in cf-trifluoroacetic acid [21]. From Kim, S. H., Kang, S. W., Park, J. K. and Park, Y. H., J. Appl. Polym. Sci., 70, 1065-1073 (1998), Copyright (1998, John Wiley Sons, Inc.). This material is used by permission of John Wiley Sons, Inc...

The log G versus log G" plots of the various PHB/PEN/PET blends are presented in Figure 20.16, where and the slopes of the plots are measures of the homogeneity of the system [35], If the slope is zero, then the blend system is heterogeneous, and if it approaches 2, it means that the blend system is tending to a homogeneous system. The slopes of the plots in Figure 20.16 increase with the addition of excess PHB to the blend system. 

Figure 20.18 DSC curves of the P(HB80-ET20)/PET blends 1, pure PET 2,19/81 3, 41/59 4, 68/32 5, pure P(HB80-ET20) compositions in wt%...

ET40)/PET blends, and in the 100/0 wt% P(HB80-ET20)/PET blend. This is because of either (a) a high content of rigid rod-like liquid crystalline component, or (b) an enthalpy which was too small to detect. The dependence of Tg on the blend composition can be evaluated by using the Gordon-Taylor Equation [37],... 

Table 20.3 Results obtained for the equilibrium melting temperatures from the Hoffman-Weeks plots of the P(HB60-ET40)/ PET and P(HB80-ET20)/PET blends...

Conclusively, the calculated Avrami exponents reveal a three-dimensional growth of the crystalline regions for each blend. The rate of crystallization of each blend increased with the decrease in crystallization temperature, and the rate of crystallization of the (PHB80-PET20)/PEN blend was faster than that of the (PHB 80-PET20)/PET blend. 

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