The Heat-Treatment And Surface Modification Of Thermotropic Liquid-Crystal Polyarylate As-spun Fiber

As a kind of microfibre self-enhancement polymer materials, thermotropic liquid-crystalline polyarylate have many excellent characteristics such as high strength, high modulus, low viscosity, easy process etc. It has been widely used in the field of advanced science, which attracts most attention from science and industry community. Recently, although our country has carried on positive exploration in TLCP industrialization, the research and development of TLCP remain at lab-development stage. Because the key technologies are mastered by foreign companies, and most of the important polymerized monomers and polymerized technologies depend on import. So there exist many problems to solve the TLCP industrialization, such as high price on raw matierals, production cost and spinning process controls, industrial equipment etc. How to obtain the TLCP fiber with high strength, high modulus, and high temperature resistant at a relative low cost, is still the main research direction in our country. It is desperately needs more LCP researchers to study and develop it.In this thesis, we studied the heat-treatment and surface modification of TLCP as-spun fiber. Firstly, the macro-kinetics of solid phase polymerization of TLCP fiber was exploried and the effects of heat treatment on surface appearance and thermal properties was disscussed. The second part is about the TLCP fiber surface modification with Friedel-Craft reaction. Finally, we studied the effects of different twisting on the tensile properties of TLCP as-spun fiber. The main research achievements were as follows:(1) When the heat-treating temperature was220℃, in the initial stage of heat treatment the fibre strength significantly increased. At the later stage the increasing of strength became slow; but the weight loss constantly increased and ultimately reached balance. The main influence on the increasing of fiber tensile strength came from the growth of molecular weight and crystallinity of fiber at the early stage(before9h) of heat-treating process. In the later stage the fiber tensile strength increased mainly from the growth of molecular weight of aromatic polyester. The heat-treating temperature had a significantly influence on the weight loss rate of fiber. And the temperature was higher; the increasing speed of polyarylate molecular chain was faster. About250℃was the critical heat-treating temperature. In the post-treatment production for TLCP fiber, the heat-treating temperature should be as high as possible when there was no adhesion appearence. The initial and later apparent activation energies of TLCP fiber were respectively38.4kJ/mol and94.4kJ/mol.(2)The decomposition temperature of as-spun fiber was509.7℃. The high decomposition temperature means the good heat resistance for the as-spun TLCP fiber. At the same heat-treating temperature, the melting point of fiber was increased along with the thermal treatment time going on. Under the condition of the same treatment time, the melting point of fiber was higher at the higher heat-treating temperature. Besides, the heat-treating temperature has more evident influence on as-spun fiber compared to the heat-treatment time. The surface of TLCP fiber became rough and unsmooth after the heat-treating, which was resulted from the constant escaption of the small molecular by-products from the fiber interior in the solid-phase polymerization of TLCP fiber. When the fiber was heat-treated for9h at280℃the fiber surface appeared fibrillation and was heavily damaged. The reason was that the adhesion appeared between the single fibers at higher temperature. This indicated that the mechanics of TLCP fiber would be heavily decreased due to the damage of the fiber surface if the heat-treating temperature was overhigh and the treatment time was overlong.(3) When the surface of TLCP fiber was modified by means of the Friedel-Craft reaction, the interfacial shear strength between the single TLCP fiber and epoxy resin could be effectively improved. The interfacial shear strength of the modified fiber improved52%campared to that of the unmodified fiber, the optimal reaction time was40min for the modification of fiber. The surface of single TLCP fiber had no obvious etches and damage phenomenon. This indicated that the mechanics of TLCP fiber would not be significantly affected.(4) For the TLCP fiber bunch, the tensile properties of the fiber were obviously influenced by the twisting. With the twist increasing, the strength of TLCP fiber bunch was first increased, and then decreased. At the optimal twisting, the variation tendency of strength with the linear density was the same as that of the strength. When the linear density of the TLCP fiber bunch was52.50tex and the twist was130Tm, the maximum strength of the fiber bunch was9.14cN/dtex. For single TLCP fiber, adding a certain twisting then twisting back again could enhance the strength. When exceeded the threshold of twisting, the strength of fiber would decrease. For non-twisting single TLCP fiber, the strength was increased with the linear density increasing. When the linear density was1.39tex, the maximum strength of the single fiber was11.3cN/dtex.