Injection molded poly/copolyesters

Table 6.3 Mechanical properties of injection-molded poly/ copolyesters...

In Figure 16, results of Jackson and Kuhfuss show the effect of molding temperature and polymer morphology weight on the mechanical properties for poly(ethylene terephthalate) modified with p-hydroxybenzoic acid. "The temperature at which the PHB copolyesters are injection molded affects the orientation of the liquid-crystal polymer chains and, therefore, affects the mechanical properties. 

In this and the following two sections we consider the data for a PLC and for different blends of that PLC with isotactic polypropylene (PP). The PLC used in this study was liquid crystalline copolyester PET/0.6PHB, where PET = poly (ethylene terephthalate), PHB = p-hydroxybenzoic acid and 0.6 is the mole fraction of PHB in the copolymer, manufactured by Unitika Ltd, Kyoto, Japan. The content of the PLC in the blends with PP was varied from 0 to 20 wt%. The samples were prepared by injection molding. PP, resin VB65 llB, was supplied by Neste OY, Finland. 

Skin/core morphologies are common in blends of LCP s and thermoplastic polymers and they play a significant role in defining the properties of both extruded and injection molded samples. Usually, LCP s in the skin have a higher degree of orientation than in the core when the blends are extruded or injection molded (Husman et al. 1980 Hedmark et al. 1989 Lee 1988). Baird et al. (Baird and Mehta 1989 Baird and Sukhadia 1993) observed a skin/core morphology in blends of PA 66 with HBA/HNA and 40 PET/60 PHB and 20 PET/80 HBA copolyesters. More LCP fibers were present in the skin than in the core for both systems. Isayev and Swaninathan (1994) also reported shell-core structure in the fracture surfaces of injection molded blends of HNA/HBA liquid crystalline copolyesters and poly (etherimide). 

Another method of reducing the melting points of the higher-melting polyterephthalates of substituted hydroqulnone is to Introduce flexibility into the pol3naer chain by preparing them as copolyesters with poly(ethylene terephthalate). The properties of injection-molded test bars are described in an earlier paper in this series, and the properties of melt-spun fibers are disclosed in a... 

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