Thermoplastic copolyesters processing

Copolyester elastomers can be processed by conventional thermoplastic melt processing methods such as injection molding and extrusion. They require no vulcanization. These polymers can be processed successfully with low-shear processes such as laminating, rotational molding, and casting. 

Polymer blending represents important route for the development of new pol)nneric materials with improved physical and processing properties and optimal cost performance. Thermoplastic copolyester elastomers are generally used as modifiers, i.e. the minor phase... 

There are two classes of polyolefin blends elastomeric polyolefin blends also called polyolefin elastomers (POE) and nonelastomeric polyolefin blends. Elastomeric polyolefin blends are a subclass of thermoplastic elastomers (TPEs). In general, TPEs are rubbery materials that are processable as thermoplastics but exhibit properties similar to those of vulcanized rubbers at usage temperatures (19). In TPEs, the rubbery components may constitute the major phase. However, TPEs include many other base resins, which are not polyolefins, such as polyurethanes, copolyamides, copolyesters, styrenics, and so on. TPEs are now the third largest synthetic elastomer in total volume produced worldwide after styrene-butadiene rubber (SBR) and butadiene mbber (BR). 

Liquid Crystal Polymers Thermoplastic aromatic copolyesters with highly ordered structure. Has good tensile and flexural properties at high temperatures, chemical, radiation and fire resistance, and weatherabil-ity. Processed by sintering and injection molding. Used to substitute ceramics and metals in electrical components, electronics, chemical apparatus, and aerospace and auto parts. Also called LCP. 

Ecoflex (poly(butylene adipate-co-terephthalate)), a commercialized aliphahc-aromatic copolyester from BASF, was characterized to be an ideal random copofymer with 44 mol% of BT units. The glass transition occurs at 30°C, and the melting point is 110-115°C [86]. The physical and mechanical properties of this soft thermoplastic are similar to those of LDPE, and it can be processed on convenhonal equipment for LDPE. 

These thermotropic liquid-crystalhne polymers have high melting points but can be melt-processed like other thermoplastics. The macroscopic orientation of the extended-chain crystals depends on the orientation imparted by flow during processing (molding, extrusion, etc.). Because of the fibrous nature of the extended-chain crystals, these plastics behave as self-reinforced composites, with excellent mechanical properties, at least in the chain direction. This is illustrated in Table 4.3 for molded specimens of a hquid-crystalline copolyester of ethylene glycol, terephthalic acid, and / -hydroxybenzoic acid [14]. In the direction parallel to the flow, the properties listed in Table 4.3 favorably compare with ordinary crystalline thermoplastics (nylons, polyesters) reinforced with up to 30% glass fibers. 

These ordering processes appear to be far more general and have been observed in a nonliquid crystalline copolyester (LPE-8) derived from a mixture of sebacic acid, biphenol and hydroquinone (62/38 BP/HQ) (See Figure 3), as well as in a thermoplastic elastomer based on copolyester units and recently reported on by Fischer [20]. 

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