Effect Of PAN-Based Carbon Fiber Structure On Graphitization

In the preparation of PAN-based carbon fiber, the change of pre-oxidation and carbonization conditions can influence the structures and also its mechanical properties. The graphitization of the carbon fiber can significantly improve tensile modulus of the fiber, but reduce its tensile strength. Therefore the regulation of the initial structures of carbon fiber can achieve the regulation of fiber structure in graphitizing process. To improve the modulus of carbon fiber, reducing carbon fiber strength loss at the same time is an important foundation for producing high strength and modulus carbon fiber.In this thesis, Raman spectrum and X—ray diffraction were mainly used to characterize the structure of carbon fiber and graphite fiber. Temperature dependence of carbon fiber structures was studied systematically. Based on the study of the effect of primary crystallite structures of carbon fiber on high temperature graphitization, the relationship between carbon fiber microcrystal structure and graphite fiber structure, properties and fiber structure was established.The results showed that:With the increase of carbonization temperature, the change range of the carbon chemical structure and micro crystal structure appeared at 1300?, The degree of graphite is greatly improved, and the graphite structure integrity is enhanced. In the radial direction, the structure of the core is different, and the crystallite structure is more perfect. The carbon fiber with higher initial graphite degree achieved relatively higher degree of graphite after high temperature treatment, and the graphite structure is relatively perfect. The distribution of the radial structure is uniform, and the homogeneity is better in the process of the graphitization, the degree of graphite is small in the range of radial distribution. Carbon fibers with better initial crystallite structure are relatively easier form of larger degree of orientation in the subsequent process of graphitization. A graphite structural parameter K for carbon fiber is proposed and is found that carbon fibers with K about 1.3 is relatively easier to graphitization with higher tensile strength. By controlling of the stabilization and carbonization, a carbon fiber with K=1.27 was prepared and subsequently graphitized at 2200?, and the tensile strength and modulus of the result fiber are 4.5GPa and 360GPa respectively, which corresponding to a tensile strength retain percentage of 80% and modulus increase of 1.2 times.