The Effect Of γ-Ray Irradiation Of Polyacrylonitrile Fibers On Oxidation And Carbonization Processes

Carbon fibers are now widely used as a reinforcing component in the preparation of lightweight composite materials because of their high strength, high elastic modulus, and low density. The polyacrylonitrile fibers as the most important precursor to make high performance carbon fiber need go through oxidization and carbonization processes. The stabilization is usually carried out at150-300℃, during which the molecular chain random motion increased, to affect the comprehensive performance of carbon fiber. However, the traditional stabilization usually adopts slowly heating way to control the exothermal heat, which will lead to high costs of time and energy. Therefore, shortening reaction time and lowering the temperature to reduce the cost of making carbon fibers became a matter in the industrial production.To be aimed to solve these problems, y-ray irradiation treatment is explored previous to the process of stabilization to change the structure of the PAN fiber, inducing molecular chain cyclizaton and crosslinking, in order to prevent the PAN chains from disorienting and to shorten the stabilization time.(1) The difference of structure and performance is discussed between the modified fiber and the unmodified fiber. After y-ray irradiation modification, the color of the fiber became darken, combined with IR and Elemental Analysis it can be concluded that the number of oxygen functional groups and the degree of cyclization structure increased. Through XRD analysis it is found that the orientation of crystal area slightly declined for the modified fiber. With the help of DSC and TG analysis, it is learned that the exothermic peak took place earlier and more gently, and the thermal stability increased, resulting in a higher carbon yield for the modified fiber. The mechanical property of modified fiber has dropped, but the breaking elongation has increased by13%.(2) The influence of y-ray irradiation on the oxidization process was evaluated. Through tensile strength test it is found the breaking elongation of modified fiber has greatly improved. Through applying tension on the fiber tows during stablization, it is found that the tension to break greatly improved, and maximumly increased by50%. So that it is possible to apply high tension during the stablization process to maintain high orientation, so as to make high performance carbon fiber. The DSC test found that the degree of cyclic structure improved. With the help of element analysis and volume density test, it is found that to achieve the same stablization degree, the heat treatment time for the modified fiber was shortened nearly7minutes, by12%.(3) The carbonization process of the stabilized y-ray irradiation fiber was studied. Through tensile strength test it is found that the mechanical strength of the carbon fiber derived from modified fiber was greatly improved, and maximumly improved to2.986GPa from2.575GPa. Compared with the unmodified one, the volume density of the carbon fiber through modification was improved, meaning probably a decrease of defects. The XRD test shows that for both of the carbon fibers the orientation degrees of crystal area were improved with increase of the applied tension during stabilization, moreover, that for the modified PAN fiber was improved more profoundly. The SEM analysis found that the surface morphology of the carbon fiber from modified fibers was rougher with more evident groove structure.