Thermal conductivity and thermal expansivity of in situ composites of a liquid crystalline polymer and polycarbonate

The thermal conductivity and thermal expansivity of extruded blends of a liquid crystalline polymer (LCP) and polycarbonate (PC) with volume fraction (V-f) of LCP between 0.09 and 0.8 have been measured as functions of draw ratios lambda ranging from 1.3 to 15. At V-f < 0.3, the LCP domains are dispersed in a PC matrix and the aspect ratio of the domains increases with increasing lambda. At V-f > 0.55, phase inversion has occurred and the LCP becomes the continuous phase. The axial thermal conductivity K-parallel to increases while the axial expansivity alpha(parallel to) decreases sharply with increasing lambda, as a result of the higher aspect ratio of the LCP fibrils and the improved molecular orientation within the fibrils. Since the transverse thermal conductivity and expansivity are little affected by drawing, the blends exhibit strong anisotropy in the thermal conduction and expansion behavior at high lambda. At V-f < 0.3, the behavior of K-parallel to is reasonably modeled by the Halpin-Tsai equation for short fiber composites. At high draw ratio (lambda = 15), all the blends behave like unidirectional continuous fiber composites, so K-parallel to and alpha(parallel to) follow the rule of mixtures and the Schapery equation, respectively.