Effect of aromatization degree of mesophase pitch on cracks and mechanical properties of mesophase pitch-based carbon fibers

The aromatization degree of MP is closely related to the orientation of carbon fibers, which determines their properties. To investigate the effect of the aromatization degree of MP on the properties of carbon fibers, this study prepared MP with varying aromatization degrees using the self-pressurization/N-blowing two-stage thermal condensation method with refined coal tar pitch as raw material. Mesophase pitch-based carbon fibers (MPCFs) were obtained through melt spinning, pre-oxidation, and carbonization processes. Results show that the C/H atomic ratio rises from 2.067 to 2.318 as the aromatization degree of MP increases. After carbonization at 1300 ℃, the microcrystalline structure of MPCFs becomes ordered, with obvious axial radiation in the cross-section. The carbon layers in MPCFs are tightly stacked in parallel, significantly improving tensile strength and modulus. When the C/H atomic ratio of MP exceeds 2.262, the resulting MPCFs exhibit a maximum tensile strength of 1389 MPa and a maximum tensile modulus of 167 GPa. However, when the C/H atomic ratio of MP exceeds 2.318, the excessive aromatization degree makes the MPCFs structure prone to cracking due to circumferential volume shrinkage, and the appearance of cracks reduces the tensile strength of MPCFs.