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A thermotropic liquid-crystalline polymer (TLCP), a copolyester with a 60/40 molar ratio of p-hydroxy benzoic acid and poly(ethylene terephthalate), was blended with a styrene/ethylene butylene/styrene thermoplastic elastomer with a twin-screw extruder. The rheological behavior, morphology, and mechanical properties of the extruded strands of the blends were investigated. The rheological measurements were performed on a capillary rheometer in the shear rate range of 5-2000 s Ϫ1 and on a plateand-plate rheometer in the frequency range of 0.6 -200 rad s Ϫ1 . All the neat components and blends exhibited shear thinning behavior. Both the shear and complex viscosities of all the blends decreased with increasing TLCP contents, but the decrease in the shear viscosity was more pronounced. The best fibrillar morphology was observed in the extruded strands of a blend containing 30 wt % TLCP, and a lamellar structure started to form at 40 wt % TLCP. With an increasing concentration of TLCP, the tensile modulus of the blends was greatly enhanced, whereas the tensile strength was almost unchanged. The elongation at break of the blends first slightly decreased with the addition of TLCP and then sharply dropped at 40 wt % TLCP. The tension set measured at 200% deformation slightly increased with increasing TLCP contents up to 30 wt %, over which the set value was unacceptable for a thermoplastic elastomer. A remarkable improvement in the dynamic mechanical properties of the extruded strands was observed in the blends with increasing amounts of TLCP.

ABSTRACT:The mechanical and dynamic mechanical properties of thermoplastic polyurethane (TPU) elastomers reinforced with two types of aramid short fibers, m-aramid (Teijin-Conex) and copoly(p-aramid) (Technora), were investigated in this study with respect to the fiber loading. In general, both types of composites exhibited very similar stress-strain behaviors, except that Technora-TPU was stronger than Conex-TPU. This was primarily due to the intrinsic strength of the reinforcing fibers. Both types of fibers reinforced TPU effectively without any surface treatment. This could be attributed to good fiber-matrix interactions, which were revealed by the broadening of the tan ␦ peak in dynamic mechanical analysis. Furthermore, the morphologies of cryogenically fractured surfaces of the composites and extracted fibers, investigated with scanning electron microscopy, revealed possible polar-polar interactions between the aramid fibers and TPU matrices.

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