Macromolecular orientation in the flow of poly(vinylidene fluoride)-polymer liquid crystal blends

Blends of thermoplastic engineering polymers (EPs) with polymer liquid crys tals (PLCs) can show properties close to those of PLCs but at affordable pr ices, While several EP + PLC blend paris have been reported in the literatu re, there is a need for more, and for those in which the blend properties d o indeed approach those of pure PLCs. We have studied blends of poly(vinyli dene fluoride) (PVDF) containing 5, 10, 15 and 20 weight% of a longitudinal PLC, namely PET/xPHB, where PET is poly(ethylene terephthalate). PHB is p- hydroxybenzoic acid, and x is the mole fraction of the LC component (here P HB) in the copolymer. For all compositions, a significant drop in viscosity with respect to purr PVDF is observed. We are observing the channelling ef fect predicted theoretically by our extension of the statistical-mechanical theory of Flory [25]: the rigid PLC sequences in the PLC chains cause orie ntations not only of those entire chains but also of the neighbouring PVDF chains. The crystallization of PVDF is clearly affected by the presence of the PLC. The nucleation effect causes an increase in the crystallization te mperature of PVDF. Al the same time, vr, observe a decrease in the PVDF cry stallization rate, clearly caused by the perturbation of the structure of t he thermoplastic matrix by the PLC chains. Optical microscopy, wide angle X -ray scattering and Raman spectroscopy all confirm the existence of orienta tion not only of the spherulites but also of the PLC chains in the PVDF mat rix. (C) 1998 Elsevier /Science Ltd. All rights reserved.