The Preparation And Properties Of Liquid Crystal Polyarylate Fiber

The liquid crystal polyarylate fiber (LCP fiber) with high strength and modulus, great heat resistant and good creep resistant has been researched for more than30years, and industrialized in the1990s. With the successful development of the superfine LCP fiber, dyed LCP fiber, this kind of fiber has been received more and more attention recent years. The liquid crystal polyarylate was first studied in1972, and attracted many research institutions and companies because it’s large amount using in plastics industry. In the1990s, The Kuraray Japan purchased the fiber patent from Hoechst Celanese Corporation and then mass-produced the fiber. Nowadays the production capacity has reached1000t per year. In our country the research of the liquid crystal polyarylate started in1980s, however there are still no commercial LCP fiber up to now.In this thesis, the molecular weight of fiber-grade polyarylate was adjusted by solid-state polymerization, and the thermal performance and rheology behavior of different molecular weight polyarylate were analysised. For different molecular weight polyarylates, different spinning equipments such as spinneret and quench device were designed and technology to prepare low denier as-spun fiber, and then the mechanical properties, structure and the failure mechanism of the as-spun fiber were studied. The properties of the as-spun fiber were improved by heat treatment, two heat treatment methods were employed, they were dynamic continuous heat treatment and static heat treatment. Fiber’s mechanical properties, thermal properties and crystal properties before and after thermal treatment were studied. These researches would be valuable=for the commercial production of LCP fiber.(1) The liquid crystal polyarylate has excellent thermal properties, the initial decomposition temperature and melting point are520℃and286℃respectively. The resulted polyarylate exhibited liquid crystal behavior between Tm and Tj. The molecular weight of the polyarylate can be increased by solid-state polymerization. (2) The high molecular weight polyarylate requires a higher spinning temperature and larger diameter spinneret. A special quenching hole in the spinneret, and a quenching unit under the spinneret were designed, to get low denier as-spun fiber. Since the viscosity of low molecular weight liquid crystal polyarylate is low, the spinning temperature is low, the diameter of the spinneret is small.(3) The diameter of the high molecular weight LCP fiber is about60μm, the breaking strength, Young’s modulus and the breaking elongation are8.43cN/dtex,370.43cN/dtex and2.70%respectively. The diameter of the low molecular weight LCP fiber is about40μm, the breaking strength, Young’s modulus and the breaking elongation are5.47cN/dtex,290.14cN/dtex and1.87%respectively.The fiber mechanical properties for both low and high molecular weight LCP show a slight increase after dynamic heat treatment.The time of the static heat treatment is longer than that of dynamic heat treatment, for the low molecular LCP fiber, the breaking strength, Young’s modulus and the breaking elongation change greatly from5.47cN/dtex,290.14cN/dtex,1.87%to16.56cN/dtex,359.45cN/dtex,2.74%after static heat treatment; For the high molecular LCP fiber, the breaking strength, Young’s modulus and the breaking elongation change greatly from8.43cN/dtex,370.43cN/dtex,2.70%to17.80cN/dtex,387.83cN/dtex,3.01%after static heat treatment.