Study On The Structure Of Polyacrylonitrile-based Carbon Fiber Precursor And Pre-oxidation Process

Carbon fiber is a special fiber with chaotic layer graphite structure formed by high temperature carbonization of polymer,and has extremely high theoretical tensile strength.At present,the highest tensile strength of industrial carbon fiber is far from the theoretical value.The structural changes in the carbon fiber production process have always been an important research issue.This paper studies the crystal structure and voids structure of PAN precursor filaments in different production stages,and also conducts pre-oxidation simulation experiments on PAN precursor filaments to study the changes in the crystal structure and voids structure of PAN fibers during the production process.The pre-oxidation simulation experiment was carried out to study the changes of PAN fiber crystal structure and microporous structure during the production process.The results show that the shape of the micropores of the PAN precursor will change in different production stages.The pores of PAN fibers are almost spherical after being stretched in the coagulation bath and boiling water.After high-temperature steam stretching,the voids become elliptical and oriented in the stretching direction.After high temperature steam stretching,the(100)crystal plane of PAN fiber is partially destroyed,and the high stretching ratio promotes the stretching orientation of the molecular chain.The orientation promotes the further crystallization of the fiber and makes the crystal area of the fiber more perfect.Maintaining tension can increase the cyclization temperature of the PAN macromolecular chain.The PAN precursor maintains a good crystal structure and orientation in the early stage of pre-oxidation(below 240°C),and the micropores in the fiber are sharp and narrow in the late stage of pre-oxidation(270°C).At the same time,the PAN macromolecular chain forms a trapezoidal structure,so that the fiber maintains a better crystal orientation.The aspect ratio of the voids of the pre-oxidized fiber decreases.Affected by the decomposition orientation,the micropore morphology is slightly rounded,but the void orientation is enhanced,and the fiber as a whole maintains a good orientation.