Control Of Pan-based Carbon Fiber Graphite-Like Structure And Its Effect On Properties

PAN-based carbon fiber has excellent mechanical properties,and its properties are closely related to carbon fiber’s graphite structure.Studying the factors affecting carbon fiber graphite-like structure and establishing control measures for graphite-like structure can improve the performance of carbon fiber.In this paper,the adjustment of PAN stabilized fiber structure was studied by NMR and optical density.The influencing factors of carbon fiber graphite-like structure were studied by means of Raman and XRD.The relationship between carbon fiber graphite structure and properties was studied,and the following conclusions were obtained.1.Stabilization conditions have different effects on the chemical structure of the stabilized fiber and the radial distribution of the structure.Increasing the degree of stabilization reaction,such as increasing the stabilization temperature and prolonging the reaction time,will increase the cyclization rate and relative oxygen content in the stabilized fiber and reduce the content of hydrogen-containing aromatic carbon;2.The chemical structure of the stabilized fiber will affect the carbonization process.Stabilized fibers with lower cyclization rate and oxygen content will facilitate the stacking of graphite-like sheets,while stabilized fibers with lower hydrogen-containing aromatic carbon content will facilitate the growing of graphite-like layers.Increasing the drafting in the stabilization stage is beneficial to increase the orientation degree of the carbon fiber crystallite.Under certain carbonization conditions,the difference in the radial structure distribution of the stabilized fiber will not be inherited to the carbon fiber;3.Carbonization determines the final graphite-like structure of carbon fiber.The drafting of fiber at low-temperature carbonization stage can increase the chemical structure diversity of carbon fiber,and make the crystallite size larger and the orientation of crystallites higher.Increasing the high-temperature carbonization temperature will make the chemical structure of carbon fiber more regular,and the crystallite size will increase significantly,and the degree of orientation will increase.The introduction of medium-temperature carbonization will alleviate the rearrangement reaction,which is beneficial to form more uniform graphite-like layer and to increase the size and orientation of the crystallites;4.The regular chemical structure can bring high modulus to carbon fiber,but the structure with high chemical structure diversity can bring high strength to carbon fiber;high degree of orientation,large crystallite,high crystallinity can increase carbon fiber modulus,and the fine crystallization and large microcrystalline cross-sectional area are beneficial to increase the strength of the carbon fiber.In order to prepare high strength and high modulus carbon fibers,it is necessary to adjust the graphite-like structure to a suitable degree.5.The carbon fiber prepared by regulation has the characteristics of suitable chemical structure diversity,high crystallite orientation,large crystallite cross-sectional area and crystallinity of about 64%.We got the medium modulus and high strength carbon fiber with the modulus of 300GPa and the strength of 7.0GPa.