Preparation Of PAN Used For Carbon Fiber

Carbon fibers with many premium properties are becoming the indispensable material used for military and civilian fields. Among the three comerciailized carbon fibers, polyacrylonitrile (PAN) based carbon fiber has been predominantly developed for its combination properties. However, its precursor has been a bottle neck for China's carbon fiber industry, for which excellent performance PAN resin and reasonable spinning process are needed. The factors affecting resin performance include appropriate average molecular weight, molecular weight distribution, comonomers in the right amounts, high purity and less polymer structure defect. During the preparation of PAN used for carbon fiber, comonomer proportion, evocating agent, reaction temperature, reaction time and polymerization processs were studied at great length. These researchers made a major contribution to production of carbon fiber. However, in order to prepare PAN resin with excellent properties, other sides of polymerization like engineering problems must be researched in the interest of production.Polymerization is a very complicated process. It is necessary to know about the reaction rule so as to crucially adjust production method. In the process, in order to prepare high average molecular weight and narrow molecular-weight distribution PAN, smooth and steady polymerization and high conversion ratio are requisite. As a result, understanding the influences of polymerization process and other factors is important. Preparation of PAN is an addition reaction. After the start of reaction, evocator initiates copolymerization in many spots. During polymerization, conversion ratio and molecular weight varies from time to time, which acts in accordance with objective laws. The reaction laws are studied by analyzing conversion ratio and viscosity-average molecular weight of the products. Some engineering factors involving heat and mass transfer in the polymerization, such as stir speed, nitrogen protective mode, nitrogen pressure and so on, have much influence on average molecular weight and molecular weight distribution, and the quality of PAN resin at last.For preparation of copolymer, acrylamide(AA) is used for the second monomer, azobisisobutyronitrile(AIBN) is used for evocator and dimethyl suIfoxide(DMSO) is used for solvent in this paper. The conversion ratio could be more than 95%, and viscosity-average molecular weight could be up to 240,000. In this paper, the conversion ratio, viscosity-average molecular weights, viscosity of the products at different time were studied for analyzing the polymerization process. Through comparing the actual reaction conditions with the theoretical trends, it was found that the classic theory formula was not applicable for the high concentration and high conversion ratio when the conversion ratio reached over 50%. So we initiated with the concentration to amend the classical formula. After amendment, the conversion ratio in 5 hours reached 95%, and coincided with the actual maximum conversion rate. The molecular chain structure was analyzed through the thermal performance and elemental analysis. The results showed that, the second monomer played an important role in the cyclization mechanism, and made a transition of the radical cyclization to the ionic cyclization. The more appropriate the content of the second monomer was, the more easily the reaction could be carried out. Accompanying with variation of the content of the second monomer, the structure of molecular chains changed. To prepare the high-quality polyacrylonitrile resin, engineering factors should be taken into account, including the stirring rate, heating rate, nitrogen conservation style, pressure. It was found that slow heating rate, stirring speed of 160r/min, sealed protection was helpful for the preparation of high-quality polyacrylonitrile resin.