Preparation and properties of injection-moulded blends of poly(vinyl chloride) and liquid crystal copolyester

Abstract

Blends of poly(vinyl chloride) (PVC) and a liquid crystal copolyester (LCP) were prepared by injection-moulding. The LCP used was a copolyester consisting of 60 mol% p-hydroxybenzoic acid (PHB) and 40 mol% poly(ethylene terephthalate) (PET). The mechanical and thermal properties and the morphologies of these blends were investigated. The results showed that the tensile strength and modulus of the blends tend to increase with increasing LCP content for the blends containing LCP content below 15%, and they decreased significantly with further increasing LCP content. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) showed that PVC and LCP are partially miscible for the blends with LCP content <15 wt% and miscible for the blends with LCP content >15 wt%. The torque measurements indicated that the viscosity ratio between the LCP and PVC matrix is much smaller than unity. This implied that LCP fibrillation is likely to occur in the PVC/LCP blends. However, scanning electron microscopy (SEM) observations revealed that fine fibrils are only formed in the skin layer of the blends containing LCP content <15 wt%. Two-phase morphology disappeared in the PVC/LCP blends containing LCP content above 15 wt% owing to the decomposition of LCP during processing.