Positive Effect of Isotropic Components on the Elongation at Break of Mesophase Pitch-Based Carbon Fibers

Mesophase pitch (MP) is a discotic liquid crystal composed of various planar aromatic macromolecules characterized by high aromaticity, high carbon content, and ease of graphitization. During the melt-spinning process, MP is susceptible to shear-induced alignment in the spinneret, producing carbon fibers with large and highly oriented graphite layers. This contributes to a high tensile modulus, increased brittleness, and low elongation at break, thereby limiting their applications. To address these issues, this study prepared MP containing isotropic components via the thermal polycondensation method and investigated the mechanisms by which these isotropic components influence the mechanical and thermal properties of mesophase pitch-based carbon fibers (MPCFs). The results indicate that the isotropic components maintained the disordered graphite microcrystalline structure during heat treatment, suppressing the alignment and growth of graphite crystallites, which leads to a reduction in tensile modulus and thermal conductivity. However, the dispersed disordered graphite crystallites extend the crack propagation path, yielding carbon fibers with a higher tensile strength of 2.62 GPa, a moderate tensile modulus of 729 GPa, and an improved elongation at break by 24.6%. This work offers valuable theoretical insights into enhancing the elongation at break of MPCFs and broadening their application scenarios.