Fracture behavior of heat treated liquid crystalline polymers

ABSTRACTThermotropic polymers are thermally treated in air at temperatures Ta, where ΔT =Ta- Ts→n=40°C, and Ts→n is the solid-to-nematic transition. Samples are extruded thin films of a series of thermotropic random copolyesters termed B-N, COTBP and RD1000. The thermal treatment produces a second endotherm without changing Ts→n for B-N and RD1000. However, for COTBP Ts→n is significantly increased. Regardless of the complex thermal behavior exhibited by the thermotropes, the thermal treatment produces a significant increase in Young's modulus, more than 30% for B-N and over 100% for COTBP. The increase in mechanical modulus is correlated with a thermally-induced fiber-like morphology.