Preparation Of Melt-processable Polyacrylonitrile-based Carbon Fiber Precursors

Since 1970,carbon fibers(CFs)have been widely used in aerospace,automobile,windmill,sports goods and other fields due to its excellent specific strength,specific modulus,and lightweight performance.In recent years,the global demand for CFs increased year by year,and the application of CFs increased sharply.Polyacrylonitrile(PAN)has become the most important industrial precursor of CFs,accounting for 90%of global CFs production.Currently,PCFs precursors have to be prepared by solution spinning process due to its particular structure,costly and severe pollution.If melt spinning could be realized in whole or in part,it would undoubtedly greatly reduce the production cost of PCFS,the consumption of water and electricity and the discharge of wastewater.However,the melting temperature of PAN was higher than its decomposition temperature,and the PAN fibers were melted twice at the pre-oxidation treatment temperature.To prepare PAN based carbon fibers by melt spinning,special spinning process to reduce PAN melting point and matching thermal stabilization technology to prevent the fusion of the PAN fibers at the temperature of the preoxidation treatment were needed.Ultraviolet(UV)radiation referred to electromagnetic radiation with a wavelength of 10-400 nm.PAN fibers irradiated by UV generated crosslinked structures and induced cyclic reactions at a lower temperature.In this experiment,UV irradiation technology was introduced into the preparation of PAN-based CFs.The chemical structure and types and mechanisms of free radicals produced by UV irradiated were studied.A new plasticizer with UV crosslinking property was prepared.PAN fibers were cross-linked by UV irradiation to solve the problem that melt-spun PAN fibers melted at the temperature of pre-oxidation treatment.The experimental results showed that the chemical reactions of PAN induced by UV irradiation mainly occurred in amorphous regions.Alkyl radicals,polyenyl radical,peroxide radicals,and polyimide radicals were produced in PAN fibers by UV irradiation.Free radicals were interconnected to form cross-linked structures,or attacked the cyanide group to initiate cyclization.With the temperature increasing,the concentration of free radicals induced by UV irradiation decreased,and the oxidation reaction of the fiber intensified.When it reached the glass transition temperature,the molecular chain unfroze,and the degree of oxidation of the fibers increased greatly.It confirmed that the active groups formed by the combination of oxygen and free radicals induced the early cyclization reaction instead of the free radicals generated by UV irradiation.A novel plasticizer with UV crosslinking property was prepared.The results showed that plasticized melt-spun PAN fiber could keep excellent shape-stability at 260℃for 24 h when the composition of ABP in plasticizer reached 2 mol%,15wt% of the plasticizer was incorporated and the precursor was irradiated by UV irradiation for 30 min.The obtained PAN-based CFs have a tensile strength up to 0.81 GPa and Young’s modulus up to 120 GPa.