Change in the Mechanical Properties of Liquid-Crystalline Thermoplastic Polymers at High Temperatures

The change in the modulus of elasticity and tensile strength of initial and heat-treated liquid-crystalline polyester fibres after annealing at a temperature 20-40°C higher than the melting point of the crystallites in the polymers was investigated. It was shown that from 50 to 90% of the initial values of the strength characteristics were preserved. In heating above the melting point of the crystallites, LC polyester fibres can melt into a monolith with preservation of elevated mechanical properties, which permits production of self-reinforced composites. The fibres melt as a result of cooperative molecular movement, and preservation of the strength indexes is ensured by the cross-links formed at high temperatures. Selection of the temperature—time conditions of heat treatment and molding is especially important for production of high-strength self-reinforced composites by melting of LC polyester fibres into a monolith.