Effect Of PAN Fiber Diameter And Gradient Temperature Stabilization On Carbon Fiber Structure And Properties

Study on improving mechanical properties of polyacrylonitrile(PAN)-based Carbon Fibers from two aspects.On the one hand,PAN precursor prepared high-properties carbon fiber must have a good structural basis,so improving the original structure of PAN fiber is very useful.On the other hand,from the stabilization and carbonization to explore the best process to reduce structural defects,and complete the structure with each reaction stage.In this paper,two kinds of the domestic wet spinning PAN precursor(12K)with different diameter used to prepare carbon through the self-designed continuous experimental line of stabilization and carbonization process.The reaction degree and structural change of the process fibers during the stabilization and carbonization with 4-stage gradient heating and 6-stage gradient heating process were studied by mechanical properties analysis such as density,tensile strength and physical and chemical structure analysis such as DSC,FTIR,EDS,Raman etc.As well as the effect of gradient temperature setting and temperature change on the fiber density and the tensile strength of carbon fiber,the characteristics of the two kinds of stabilization processes and the advantages of the 6-stage gradient stabilization process.The differences of the two kinds of PAN precursor structures with the same composition and different diameter were studied,and the difference of the reaction degree under the same stabilization and carbonization process was also studied.Focuses on the differences in the radial structure of the two kinds of pre-oxidized fibers,and the structure and properties of the final carbon fiber were compared.The results of PAN precursor analysis show that the smaller diameter of the original wire has the characteristics of high crystallinity,high orientation,high molecular chain regularity and small crystallite size,giving it higher reaction activation energy and higher starting temperature,reflecting the characteristics of fine denier,fine crystallization in PAN fiber.The results shown by the continuous experiment with wet spinning PAN precursor that the 6-stage gradient stabilization process has lower stabilization initiation and termination temperature and more temperature gradient,so that the fiber has a lower degree of stabilization reaction.The final stabilization fiber relative to the degree of cyclization,oxygen content slightly lower than the 4-stage gradient stabilization.However,due to the multi-stage temperature setting and the lower reaction temperature,the reaction is more gentle,ease the concentration of heat concentration,which is conducive to the improvement of stabilization fiber structure,and the final carbon fiber has a higher density,more completed structure,high mechanical properties.In addition to the termination temperature,the mechanical properties of carbon fiber are relatively insensitive to other temperature changes,indicating that the 6-stage gradient heating process has good controllability for each stage of the reaction.The experimental results of the two kinds of PAN precursor under the same preparation process show that the lower relative cyclization degree of PAN precursor in the early stage.The later stage tends to be the same,and the oxygen content is lower in each stage.But the distribution of radial oxygen elements in the pre-oxidized fiber,the distribution of the radial order degree is more uniform,the core structure is smaller,the defects are reduced,and inherited the high orientation of PAN precursor;The final carbon fiber has high crystallinity,high degree of orientation,high degree of graphitization,large crystallite size,low porosity,and high tensile strength(5.11GPa).