Study on the effects of electron beam irradiation on the stabilization of polyacrylonitrile and their carbon fiber application

Abstract

Polyacrylonitrile (PAN) is one of the most widely used in textiles and producing a fibrous precursors of carbon fibers. PAN fibers are particularly suitable to produce high performance carbon fibers due to their high melting point and a great carbon yield (>50% of the original precursor mass). Moreover, the PAN polymer is also attempted to fabricate various compositions with nanoadditives such as nanosilica, nanomagnetite, nanohydroapatite and carbon nanotubes. Carbon fibers are manufactured by controlled oxidative stabilization, carbonization and graphitization of PAN precursor fibers. Oxidative stabilization process takes long time due to the key process in the process of converting PAN fiber to high performance carbon fiber. To accelerate the stabilization process, fibers can be crosslinked by photo-stabilization. Ionizing radiation generates free radicals in PAN, which aid cyclization and crosslinking. This dissertation deals with the investigation of PAN fibers stabilized with various doses of beam irradiation. The effects of electron beam on the chemical, thermal and mechanical properties were analyzed. It was found that electron beam irradiation could induce chemical reactions so that the structural change which was transformed C$\equiv$N bonds into C=N bonds by changing PAN into their cyclized structure observed. Stabilizaion index values were increased with increasing the electron beam irradiation dose. This dissertation also deals with the investigation of highly effective method of pretreatment PAN fibers. The method consists of exposure the PAN precursor to electron beam at various doses, and then the fibers are thermal stabilized. Electron beam pretreatment was enhanced inducing chemical reactions that converted the structure and affected the physical properties of the PAN fibers. Carbon fibers are prepared through carbonization process at various carbonization temperatures. The degree of carbonization and mechanical properties of carbon fibers increases with the increase of carbonization temperature. Thermal treatment for stabilization of electron beam pretreated precursor enhanced the degree of carbonization and mechanical properties of carbon fibers. The prepared carbon fibers are expected to be applied in automobiles, sporting equipment, turbine blades, ressure vessel, transportation, and so on. First of all, this dissertation establishes the industrial application feasibility of producing carbon fibers from electron beam irradiation technique.