Crack formation in mesophase pitch-based carbon fibres: Part I Some influential factors for crack formation

The crack observable in the transverse section of mesophase pitch-based graphitized fibres was studied to clarify its development on spinning, stabilization, carbonization and graphitization, and to find the factors influential on the development on spinning. The crack was already observed as an embryo in the as-spun fibre of radial texture, which increased the opening angle according to the extent of shrinkage due to carbonization and graphitization. The spinning temperature, length/diameter, diameter and wall material of the spinning nozzle and the kind of mesophase pitch were found influential in crack development, defining the transverse texture and the extent of longitudinal alignment along the fibre axis. Although the radial texture defined under an optical microscope tends to give a crack, not all of such textures carried the crack, suggesting the necessity of more detailed classification of the texture in terms of alignment, shape and size of domains observed under high resolution scanning electron microscopy (HR-SEM). The factors revealed as being influential on the textures appear to be related to the apparent viscosity, the perfectness of the radial orientation and die-swelling at the outlet of the nozzle to modify the texture defined through the nozzle. The interaction of the m esophase pitch with the nozzle wall and flow properties should be emphasized as factors controlling the texture on spinning.