Polyacrylonitrile carbon fiber is a carbon fiber made of polyacrylonitrile fiber, and is mainly used as a reinforcement for composite materials. Carbon fibers can be prepared from homopolymerized or copolymerized polyacrylonitrile fibers. In order to produce high-performance carbon fibers and increase productivity, copolyacrylonitrile fibers are often used in the industry as raw materials. The requirements for the raw materials are: impurities, less defects; uniform fineness, and the finer the better; high strength, less hair; the higher the degree of orientation of the chain molecules along the fiber axis, the better, usually greater than 80%; thermal conversion Good performance.
The process of preparing polyacrylonitrile fiber in production is: firstly copolymerizing acrylonitrile with other small amount of second and third monomers (methyl acetonate, methylidene dibutyl acrylate, etc.) to form a copolymerized polyacrylonitrile resin (molecular weight higher than 6) Up to 80,000), then the resin is dissolved in a solvent (sodium thiocyanate, dimethyl hydrazine, nitric acid, zinc chloride, etc.) to form a spinning solution of suitable viscosity, which is spun by wet, dry or dry-wet method. The silk is then made into polyacrylonitrile fiber by water washing, drawing, drying and heat setting. If the polyacrylonitrile fiber is directly heated and melted, it cannot maintain its original fiber state.
When preparing carbon fibers, the polyacrylonitrile fibers are first placed in air or other oxidizing atmosphere for low temperature heat treatment, that is, pre-oxidation treatment. Pre-oxidation treatment is a preliminary stage of fiber carbonization. The fibers are typically heated to about 270 ° C under air for 0.5 h to 3 h. The color of the polyacrylonitrile fibers gradually changes from white to yellow and brown, and finally black pre-oxidized fibers are formed. It is a result of a series of chemical reactions such as oxidation, pyrolysis, cross-linking, and cyclization, which form a heat-resistant ladder polymer after thermal oxidation of a polyacrylonitrile linear polymer. Then, the preoxidized fiber is subjected to a high temperature treatment at 1600 ° C for carbonization treatment, and the fiber further generates a reaction such as cross-linking cyclization, aromatization, and polycondensation, and removes hydrogen, nitrogen, and oxygen atoms, and finally forms a two-dimensional carbon ring. A carbon fiber having a planar network structure and a layer of coarse and parallel layered graphite structure.