Solution Copolymerization Of Acrylonitrile For Carbon Fiber

With the excellent characteristics such as low weight, high strength, high modulus, anti-high temperature, anti-erosion and so on, carbon fiber is widely used in the field of aeronautical and space technologies, transportation, sports supplies, civil construction, etc., making itself the most promising material in the coming decades.Several precursors can be used to produce carbon fibers, among which polyacrylonitrile (PAN) based carbon fibers has the best performance and share 90% in quantity. The production of PAN based carbon fibers can be divided into two steps:the production of PAN precursor and the pre-oxidation and carbonization of the precursor. The first step is the key point which can determine the quality of carbon fiber.In order to produce high molecular weight polyacrylonitrile, free-radical solution copolymerization of high concentration (about 50 wt%) of acrylonitrile (AN) as first monomer and itaconic acid (IA) as comonomer is carried out in dimethyl sulphoxide (DMSO), using low concentration (about 50 wt%) of azodiisobutyronitrile (AIBN) as initiator. The values of different factors such as temperature, the concentration of monomer, IA content in the monomer, and the concentration of AIBN are changed, the copolymer in those conditions in different reaction time is produced and the conversion of monomer was measured at each point of condition. Then, the viscosity average molecular weight of poly(AN-co-IA) prepared in each point of condition above was measured by Ubbelohde viscosity meter at 30℃, using DMF as solvent. The copolymer with viscosity average molecular weight of 300～1000 thousand was produced, and the curve of conversion-time at each condition was drawn by the experiments above. It has been demonstrated that both reaction rate and viscosity average molecular weight are increased by the increasing of monomer concentration, while the same thing is otherwise with IA content. Reaction rate will increase dramatically with the increading of either temperature or AIBN content, while again, the same thing is otherwise with viscosity average molecular weight. Though conversion increases dramatically along with the polymerization time, viscosity average molecular weight changes slightly.Though the time can make conversion increase, it has little effect on viscosity average molecular weight.Monobutyl Itaconate (MI, also named Itaconic Acid Monobutyl Ester) is also introduced as another potential comonomer in the free-radical solution copolymerization of acrylonitrile, using medium concentration AIBN as initiator and DMSO as solvent under different temperatures of 50℃,55℃,60℃, and 65℃. By using different ratio of AN/MI, a series of poly(AN-co-MI) are preparared under low conversion (below 10%) at each temperature. The accumulated average composition of the copolymer was determined by elemental analysis, and then both Fineman-Ross method and Kelen-Tudos method were applied to calculate the reactivity ratio of the copolymerization system. It shows that the result of Fineman-Ross method is unreasonable because it has a negative value, while that of Kelen-Tudos method is reasonable because the practical experimental points coincide with the theoretical curve under each temperature. It shows that temperature has tiny influence on reactivity ratio, the value of reactivity ratio is about rAN=0.66～0.71,rmi=8.35～7.44 in the range of 50～65℃, and with the increasing of the polymerization temperature, the reactivity ratios of AN and MI approach to unity, suggesting that the solution copolymerization of AN/MI has a tendency to ideal copolymerization.