Elastic moduli of a liquid crystalline polymer and its in-situ composites

The elastic moduli of a liquid crystalline polyesteramide (LCP) and polycarbonate/LCP in-situ composites with 10 to 80 wt% of LCP have been measured as functions of draw ratio lambda from 1 to 15 by an ultrasonic method. For the LCP, the sharp rise of the axial Young's modulus E(3) and the slight decreases of the transverse Young's modulus E(1) and the axial (C-44) and transverse (C-66) shear modulus with increasing lambda result from the alignment of chains along the draw direction. E(1). C-44, and C-66 follow the lower bounds calculated using the series coupling scheme of the aggregate model. Although E(3) lies close to the lower bound at low lambda, it follows the upper bound calculated according to the parallel coupling scheme at lambda > 3. The elastic moduli of the composites have similar draw ratio dependences as those of the LCP. The strong increase in E(3) with increasing lambda arises from the higher aspect ratio of the LCP domains in the composites and the improved molecular orientation within the domains. The reinforcement effect on the other moduli is much weaker, with E(1) and C-44 of the composites only 5 to 30% higher than those of polycarbonate at lambda = 15. Since C-66 of the LCP decreases to a value below that of polycarbonate at lambda > 2, there is a positive reinforcement effect at low lambda but a negative effect at high lambda.