Effect Of Comonomers On Pre-oxidation Of Polyacrylonitrile

Carbon fibers have high strength and modulus, which have been generally used in the fields of high-tech, chemistry, transportation and some other important industries. Polyacrylonitrile(PAN)-based carbon fibers have been applied to all kinds of fields because of its excellent properties and high production. The pre-oxidation is a key technology which determines the performance of carbon fibers and has been recognized as an important bridge between precursors and fibers. For these reasons, researchers devote to studying the changes of structures and properties during pre-oxidation, as well as their influencing factors. In this paper, PAN homopolymer and its copolymers with acid (IA)、 methyl acrylate (MA)、acrylic amide (AM) comonomers were synthesized by aqueous deposited polymerization. The effects of comonomers on the pre-oxidation were discussed in this study.The change of the color during heating showed that polymers have conducted some chemical reactions.FTIR spectra analysis showed that oxidation happens first, followed by cyclization and the last was dehydrogenation during oxidative stabilization. FTIR and DSC analysis showed that the pre-oxidative can be promoted by IA and AM, especially IA, but inhibited by MA. The extend of stabilization was evaluated by data of FTIR, the sequence of oxidation of different copolymers as follows:P(AN-co-IA)>P(AN-co-AM)>PAN> P(AN-co-MA).DSC analysis indicated that the cyclization of the initial temperature and exothermic rate were reduced, concentration of heat was eased by the introduced of IA in P(AN-co-IA) copolymers. With increasing of IA, the rate of exothermic reaction decreased gradually with a broadened exothermic peak. The activation energy (Ea) of PAN and its comonomers were obtained from Kissinger and Ozawa method. The Ea of cyclization reaction was significantly reduced with the introduction of IA. It was indicated that P(AN-co-IA) was more dominant in dynamics. It was also found that the Ea of cyclization reduced with the increasing of IA content gradually at low temperature, but increasing with the increasing of IA content at high temperature.