Processing and characterization of blends of polyarylate and a thermotropic polymer

Blends of polyarylate and a thermotropic copolymer of HBA/HNA (75/25) were studied for their general phase behavior and mechanical properties. The compatibility of the two polymers has been analyzed using DSC and polarizing optical microscope. Polyarylate has been found to give incompatible blends showing a two phase morphology up to 20% by weight of LCP. Low composition blends (1- 4% LCP) show a decrease in T_g of the polarylate phase as shown by the DSC traces of the blends. Mechanical properties of the fibers prepared by melt drawing of these biphasic blends have been analyzed using SEM images of the fracture surface. Estimates of the aspect ratio of the reinforcing LCP fibrils were obtained from the counts of the pulled out fibrils on the fracture surfaces and their average diameters. It is seen that the aspect ratio of the fibrils increases with the decrease in the corresponding number of pulled out fibrils as the concentration of LCP increases from 1% to 15% by weight. An optimum melt shear rate of 150-200 sec^-1 and a temperature of 300°C has been shown to give favourable morphologies for enhanced mechanical properties of the composite fibers. Melt viscosity of the blends measured for capillary flow decreased with increasing LCP composition at a steady shear of 100 sec^-1 showing over a 12 fold drop at 5% level of LCP. All blends showed Newtonian behaviour of the matrix in the shear rate region of 10 to 200 sec^-1. Blends with 1% by weight of LCP however showed a shear thinning behavior up to about 100 sec ^-1.