THE MECHANISM OF SKIN-CORE MORPHOLOGY FORMATION IN EXTRUDATES OF POLYCARBONATE LIQUID-CRYSTALLINE POLYMER BLENDS

The mechanism of skin/core morphology development and LCP (liquid crys talline polymer) fibril formation in polycarbonate/LCP blends was stud ied. A certain minimum concentration of the LCP phase must be present for the formation of continuous LCP fibrils in the extrudates. A skin- core morphology characterizes the PC/LCP extrudates. Short LCP fibrils are formed in the capillary converging entrance section, through the elongation of LCP domains and their coalescence. Continuous fibrils we re formed in the skin of extrudates emerging from cylindrical capillar ies, through the coalescence of the short fibrils, provided the shear stresses are high enough and the LCP viscosity is equal or lower than that of PC. Increasing capillary length enhances the LCP lateral migra tion and fibrils formation. The high interfacial tension stabilizes th e LCP fibrils. In the core region the short fibrils recoil or breakup, resulting in spherical or elongated droplets. Long and continuous fib rils cannot be formed in a zero length capillary, even at high flow ra tes.