FACTORS INFLUENCING MICROSTRUCTURE FORMATION IN POLYBLENDS CONTAININGLIQUID-CRYSTALLINE POLYMERS

Four isotropic polymers, poly(butylene terephthalate) (PBT), polycarbo nate (PC), polyethersulfone (PES) and polysulfone (PSU), were blended by extrusion with a thermotropic liquid crystalline polymer (LCP) at d ifferent temperatures. The morphology of extrudates was observed by me ans of scanning electron microscopy and the intrinsic aspect ratio of LCP fibrils and particles separated from matrix resin was measured wit h an image analysis. Special attention was paid to the LCP fibrillatio n in these four matrices in a wide temperature range from 270 to 360 d egrees C and the internal relations among the effects of processing pa rameters, such as viscosity ratio, extrusion temperature, and LCP conc entration. The results show that the viscosity ratio of the dispersed LCP phase to the continuous phase is a decisive factor determining the formation of LCP fibrils, but its effect closely relates with the LCP content. In the range of viscosity ratios investigated, 0.004 to 6.9, and lower LCP content of 10%, significant fibrillation took place onl y at viscosity ratios below 0.01. It is predicted that the upper Limit of the viscosity ratio for LCP fibrillation will increase with increa sing LCP content. A comparison of the morphologies of LCP/PES blends w ith different LCP concentrations reveals that the LCP phase becomes co ntinuous at a concentration of less than 50%, and high LCP content doe s not always favor the formation of long and uniform LCP fibrils. The extrusion temperature has a marked effect on the size of the minor LCP domains. For fibril forming systems, the percentage of LCP fibrils wi th larger aspect ratios increases with increasing extrusion temperatur es. All these results are explained by the combined role of deformatio n and coalescence of the LCP dispersed phase in the blend.