Small-angle x-ray scattering analysis of carbon fiber voids considering void length distribution

The analysis method proposed by Ruland et al. is widely used to analyze the void lengths in carbon fibers, but it could not apply to mesophase pitch-based carbon fibers. We thought that the reason for the inability to analyze pitch-based carbon fibers was the length distribution of voids that Ruland neglected. We investigated an analytical method that considers the length distribution of voids in carbon fibers. The proposed new method could be applied to various carbon fibers from polyacrylonitrile and mesophase pitch. The analysis results revealed that the average length of voids in mesophase pitch-based carbon fibers is not only long but also widely distributed. On the other hand, the voids of carbon fibers tend to be longer as the crystallite length is longer in both polyacrylonitrile-based and mesophase-based carbon fibers. It suggests that the growth of void length is strongly influenced by the growth of crystallites in the plane direction.