Properties of thermotropic liquid crystalline polyester-engineering plastic blends

Abstract

Binary blends of thermotropic liquid crystalline polyester (TLCP) and flexible chain polymer (FCP) were prepared in molten state. The TLCP adopted as the reinforcement were copolyesters of ethylene terephthalate and 60 mol% p-hydroxybenzoic acid (ET-HBA) and p-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid (HBA-HAN). The FCP adopted as the matrix were polycarbonate (PC) and PET. Thermal/mechanical properties, morphology, and rheological properties of the blends were investigated by differential scanning calorimeter (DSC), polarizing optical microscope (POM), capillary rheometer and scanning electron microscope (SEM). The P(ET-HBA)/PC blends were known to be partially compatible by thermal analysis and the surface transesterification reaction were observed between the two polymers at high temperature by POM. SEM studies revealed that the P(ET-HBA) component formed finely dispersed spherical domains with diameters of 0.2-2.0 microns in the PC matrix and the inclusions were deformed from the spherical droplets to fibrils as the blends were oriented in varying the draw ratio. The interfacial adhesion between the polymers was quite good and therefore it was confirmed that the LCP could act as a reinforcement of PC. The P(HBA-HNA)/PET blends were completely incompatible and the interfacial adhesion between the two polymers was poor and therefore dewetting of the dispersed phase was observed in the oriented blends. The mechanical properties of the blends were enhanced remarkably due to the well developed rod-like microfibrils embedded in teh PET matrix. The skin-core morphology was observed in the injection molded specimens similar to the case of the fiber glass reinforced plastics. From the rheological measurements minimum melt viscosity was observed at about 50% LCP concentration though the viscosity of the blend was largely dependent upon the shear rate, temperature, and composition. The dynamic storage modulus crossed over the dynamic loss modulus at 60% Lc...