Study On Copolymerization Of Acrylonitrile For Carbon Fiber

Carbon fiber has excellent performances such as high strength, high modulus, anti-high temperature, anti-erosion and so on. So it has been developing rapidly in recent decades.There are several precursors to produce carbon fibers, in which polyacrylonitrile (PAN) based carbon fibers has the best performance and is 90% in quantity. The production of PAN based carbon fibers is divided into two steps. The first step is the production of PAN precursor. The second one is the pre-oxidation and carbonization of PAN precursor.The copolymerization of PAN for spinning is a key step in the production of PAN based carbon fibers. It will affect the next technics. The original structure and performance of polymer directly influence the final performance of carbon fibers. According to literatures, various monomers have been used in the copolymerization of PAN based carbon fibers, however acrylonitrile (AN)/ normal butylmethacrylate (NBMA)/ itaconic acid (ITA) solution copolymerization has not been seen yet. In this work, the AN/ NBMA/ ITA terpolymer had been prepared in solution. The copolymerization mechanism of AN/ NBMA/ ITA system had been deeply researched.The reactivity ratio is very important parameter for copolymerization reaction. It is significant to the study of reaction mechanism and control in production. The reactivity ratios for the copolymerization system of AN/NBMA in DMSO solution with AIBN as an initiator were determined, based on KT method, by fitting the calculated curve with the experimental data. And according to the figure of monomer-polymer, it was analysed qualitatively that the activity of NBMA was higher than the activity of AN.With the same method, the reactivity ratios for the solution copolymerizationsystem of AN/NBMA/ITA were determined. Compared reactivity ratios obtained from two levels of monomer concentration, 20% and 25%, it found that changing of monomer concentration affected reactivity ratios less.The preliminary polymerization condition and process were researched, including homopolymer of AN, homopolymer of NBMA, homopolymer of ITA and copolymer of AN/NBMA. On the base of these experiments, the terpolymer of AN/NBMA/ITA was researched using orthogonal analysis. It found that temperature and initiator concentration were primary factors which affected copolymer of AN/NBMA/ITA. Compared various factors, the optimum conditions and the best ratio of monomers of AN/NBMA/ITA solution copolymerization were confirmed. A novel PAN based copolymer was synthesized.The AN/NBMA copolymers and AN/NBMA/ITA terpolymers were tested and analysed by scanning electron microscope(SEM). The SEM results about various ratio AN/NBMA copolymers and AN/NBMA/ITA terpolymers were compared. The morphology of copolymers were studied. NBMA and ITA can loose the molecule structure of AN, relax the exothermic reaction and play a role in catalytic cyclization. All these help the oxygen molecule permeating to the fiber in the process of pre-oxidation , get internal and external structure of fiber even uniform after pre-oxidation ,and improve final mechanics performance.The various ratio AN/NBMA/ITA terpolymers were tested and analysed by differential scanning calorimeter(DSC). It found that the glass transition temperature(Tg) of PAN copolymer descended with NBMA content increasing. When ITA content increased, the Tg variation tendency of the copolymer was not so obvious as NBMA, the influence of NBMA to copolymer was better than ITA.