Study On Structure And Properties Of Thermotropic Liquid Crystalline Polymer And Its In-situ Composites

In this paper, a commercialization liquid crystalline polymer (LCP) was used to prepare polypropylene / liquid crystalline composites (PP/LCP) without and with compatibilization (MAH) and nylon / liquid crystal composites (PA/LCP). The flow properties, mechanical properties and heat resistance of the composites were test to study the modified role of liquid crystal polymer in PP/LCP composites and PA/LCP composites. Meanwhile, the composites were analyzed by differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) to study the effect of liquid crystalline polymer on the structure property and morphology development of PP and PA.Study found that liquid crystalline polymer is a high-strength, super toughness material. It has great tensile strength and impact strength. The injection temperature and pressure have little effect on the tensile properties of liquid crystalline polymer, but a lot on the impact strength. Temperature has the more effect on the impact strength. Experiment obtained that the most suitable processing temperature is 290℃. In addition, the injection temperature and pressure changes do not affect on the crystallization of LCP and the generation and distribution of liquid crystalline micro-fiber.For the PP/LCP composites, the addition of LCP change the flow properties of the composites better, the the flow properties of the composites are higher than both of the pure component. In mechanical properties, liquid crystalline polymer plays the role of improving both of the polypropylene's strength and toughness. 10 quotient content of LCP has the largest improvement on the strength and toughness of polypropylene. At this time, the tensile strength of PP/LCP composite has been increased by 4.7% compared with the PP, and the impact strength was 20%. The LCP improved the heat deflection temperature and the melting temperature of PP, but reduced the degree of crystallinity of PP. 15 content of LCP improve the heat deflection temperature and melting temperature by 5℃and 3℃,but the degree of crystallinity of PP from 38.33% down to 31.67%. After adding compatibilizer, the effect of LCP on PP was significantly improved. In the 3 quotient compatibilizer content, the tensile strength of the PP/LCP composite increased 23.8% than that of PP, the impact strength was increased by 49%, the heat deflection temperature and melting temperature increased by 5℃and 3℃,the degree of crystallinity of PP from 31.67% up to 35.12%.For PA/LCP composites materials, the addition of LCP change the flow properties of the composites better, the flow properties of the composites are higher than PA by122%. In mechanical properties, a small amount of LCP (content of less than 25%) play an enhanced role in nylon matrix, the largest increase of tensile strength by 14.2%. A large amount of LCP(content of more than 25%) play a toughening role in nylon matrix. In addition, the addition of LCP decreased the heat deflection temperature and the melting temperature of PA, the 20% LCP decreased them by 13℃and 3℃. A small amount of LCP (less than 10%) can improve the degree of crystallinity of nylon. When the content of LCP is 5%, it improved the degree of crystallinity of PA from 36.6% to 39.01%.In the composites'near-surface layer (away from the surface of 0.2mm), the LCP gradually became a rod-like or flake structure formation as its content increases, and the rod-like or flake structure has a slight orientation; in the composites'shear layer (away from the surface of 1mm), the LCP has a micro-fiber structure and a well orientation; in the composites'core layer (away from the surface of 1.8mm), there is no micro-fiber and no orientation, the LCP only has a granular structure. Compatibilizer can improve the fiber-forming properties of the LCP.