Morphology and physical properties of In-situ composites based on specialty EP and TLCP

Abstract

Several isotropic engineering plastics were in-situ reinforced with a commercially available thermotropic liquid crystalline polymer(LCP), Vectra. Binary and ternary LCP blend systems were investigated in terms of thermal, rheological and physical properties, crystallization kinetics, and phase morphology. The effect of a third component on the mechanical performance of in-situ composites was discussed as well. An incorporation of Vectra A-950 reduced Tg of both polyarylate(PAR) and polysulfone(PSF), and had a profound influence on the rheological properties. Particularly in the vicinity of crystal-nematic transition temperature, LCP increased the melt viscosity and produced non-zero yield stress. However, it decreased the melt viscosity of matrix resin above the crystal-nematic transition temperature, acting as a processing aid. The tensile strengths of the PAR/LCP blend fibers were increased with increasing spin draw ratio and LCP content. Spinning temperature had a profound influence on the tensile strength; increasing the spinning temperaturefrom 300 to 340$^\circ$C notably decreased the tensile strength of the blendfiber. With PAR/LCP blend fiber spun at 300$^\circ$C an abrupt reduction in tensile strength was observed at the blend ratio 50/50. Incorporating a third component, a multiblock copolyesterether, however, substantially improved the tensile strength at this particular composition, preferably at the usage level ca. 2 phr. SEM studies of fractured surface of PAR/LCP fiber revealed that blockcoploymer improved interfacial adhesion and lead to more homogenuous mixing. Tensile strength and modulus of as-spun PSF/LCP blend fibers were increased as LCP content and spin draw ratio were increased, which was more prominent with LCP rich blend. The compositional moduli of as-spun blend fiber were well fitted to the additivity rule of mixture. The wide angle X-ray diffraction patterns attributed the increased tensile strength to the enhanced molecular orient...