PREPARATION AND PROPERTIES OF SELF-REINFORCED POLYPROPYLENE LIQUID-CRYSTALLINE POLYMER COMPOSITES

A fast and potentially economic method for creating a composite materi al of polypropylene (PP) with liquid crystalline polymers (LCPs) was e xplored. The LCPs were dispersed in the PP matrix in a conventional ex trusion process and subsequently drawn in order to obtain a highly uni axially molecular orientation of the LCP fibres. The strongest mechani cal properties were found after rapid cooling of the blend, which was optimally exploited in thin filaments where cooling was fast enough to prevent fibre break-up and/or orientation relaxation. To enable the p roduction of extrudates which are thick enough to be cut into self-rei nforced pellets, a fused multi-filament technology was developed. In t his technology several thin filaments were extruded/drawn and rapidly cooled to a temperature between the crystallisation temperatures of th e LCP and the PP. After solidification of the LCP, the single filament s were fused to a multifilament strand and further cooled to room temp erature. The thick multifilament LCP reinforced PP strands were cut in to pellets and used in injection- and compression-moulding processes. This processing took place between the melting temperature of the PP a nd the LCP, with retention of the aspect ratio and the molecular orien tation of the LCP fibres.