Fiber drawing from blends of polypropylene and liquid-crystalline polymers

This paper discusses the drawing of polypropylene (PP) fibres, blended with liquid crystalline polymer (LCP) at a w/w ratio of 100/10, with the aim of enhancing fibre mechanical performance. After melt extrusion, the blended fibres consist of LCP fibrils surrounded by a PP matrix. These fibrils are, however, split after conventional one-stage drawing, and the tensile properties of the polyblend fibres are poorer than those of the corresponding pure PP fibre. By contrast, two-stage drawing, under carefully optimised conditions, can bring about same enhancement of fibre mechanical performance. In view of the very different structural properties of PP and LCPs, the use of a compatibilising agent has been studied to promote adhesion between the PP and LCP phases in the drawn fibres. It is shown that, whilst a compatibilising agent may indeed promote adhesion across the interface between the two phases, it will also increase LCP fibril fragmentation during the drawing process, with consequent impairment of fibre., mechanical performance. A strategy is outlined for overcoming fibril fragmentation during drawing, using compatibilising agents which are themselves liquid crystalline.