Research On The Strategies For Alleviating The Skin-core Structure Of Pre-oxidized Polyacrylonitrile Fibers

Because of the unique properties-excellent mechanical properties high specific strength,high specific modulus,superior temperature resistance,corrosion resistance and so on,polyacrylonitrile-based(PAN-based)carbon fiber is an ideal reinforcement for composite materials.The pre-oxidation process is of vital importance step in the preparation of PAN-based carbon fibers.However,the diffusion resistance of oxygen into PAN fiber and the uncontrollable evolution of pre-oxidation reactions are primary reasons of the formation of skin-core structure,which make the final performance of carbon fiber degrade.Therefore,the physical and chemical structure of PAN fiber has been deeply studied,which is of great significance for alleviating the skin-core structure of the pre-oxidized PAN fiber and preparing high-performance PAN-based carbon fiber.In the present work,the effects of the modification by KMnO₄ and the pre-oxidation atmospheric pressure increase on the radial structure homogeneity of pre-oxidation fibers were studied through Fourier transform infrared spectroscopy(FTIR),scanning electron microscopy(SEM),wide-angle X-ray diffraction(WAXD),Raman spectroscopy and so on.(1)By adjusting the modification conditions and the pre-oxidation process parameters,the modified PAN fibers and pre-oxidation PAN fibers were obtained.The relationship between the physicochemical structure and the mechanical properties of modified PAN fibers,as well as the effects of PAN fiber modification on radial structure homogeneity of pre-oxidation PAN fibers were studied.The results showed that during the KMnO₄ solution modification process,PAN fibers underwent not only undergo partial cyclization reactions,but also partial hydrolysis reactions.When the degree of cyclization was 2.5%,it is effective to weaken the formation of the skin-core structure.(2)The influence of atmospheric pressure on the evolution of the physicochemical structure and the skin-core structure in the pre-oxidation process has been studied in detail.The results showed that the atmosphere pressure had a significant negative effect on the cyclization reaction,while a positive effect on the oxidation reaction(especially the oxygen uptake reaction)and the formation of radial homogeneity of pre-oxidation fibers.The cyclization reaction first occurs in the amorphous region.Increasing the atmospheric pressure during the pre-oxidation process can effectively improve the radial homogeneity of the pre-oxidized fibers,thereby weakening the formation of the core-skin structure.