A comparison of crystallite and pore structures in different polyacrylonitrilebased carbon fibers

Homemade polyacrylonitrile-based carbon fiber and the T300B, T700SC and M55JB products of Toray were investigated and compared by WAXD and SAXS. The WAXD results show that, the Lc, d002, Lc/d002 and pore content of the homemade carbon fiber were all between that of T300B and T700SC, and its La value was close to that of T700SC. The SAXS results suggest that the cylindrical pores with a m value (length of semi-major axis) less than 5nm were 99.72% in T700SC, and there were no pores with m value around 30nm, which was better than that of homemade carbon fiber and T300B. There was a large number of pores with m≈7-15nm in M55JB, as a result, the strength of M55JB was less than that of T700SC. The pores in T700SC and M55JB had the ratios of m to pore radius larger than that of the homemade carbon fiber . The pore orientation angle of homemade carbon fiber, and Toray T300 and T700 carbon fibers are all about 21-22. However, the pore orientation angle of M55JB graphite fiber is 8°, less than that of the others. In order to improve the performance of homemade carbon fiber, efforts should be made to increase the degree of graphitization, to reduce the d002 and pore content and to increase degree of densification. The number of larger pores should be reduced and eliminated, and the number of smaller pores should be increased from the spinning of the precursor fiber through stabilization and carbonization.