Improving the spinnability of mesophase pitch and its carbon fiber performance by modifying toluene solubles content in the precursor

Toluene solubles (TS) play a crucial role in mesophase pitch (MP), but their influence on the spinnability of MP and the properties of carbon fiber remains unclear. In this work, a solvent extraction method is employed to regulate the TS content in MP for improving its spinnability, and the MPs with different TS contents are prepared. The results show that TS, characterized as a small molecule (I_OS = 0.337) with an alkyl side chain length index (Abs1460/Abs1380) of 2.012, can significantly improve the flowability of the system. Following comprehensive characterization, a unique molecular structure model is constructed. The removal of a portion of TS increases the regularity of the microcrystalline structure to a certain extent (d₀₀₂ = 3.447 Å, L_c = 8.86 nm), further optimizing the spinning performance of compounded MPs with different TS contents, and improving the tensile strength and thermal conductivity of their carbon fibers. The compounded sample MP-TS-17, containing 17 wt% TS, shows superior spinning performance at a high rotary speed of 315 rpm, accompanying with an average and even diameter of 12.60 μm. The carbon fiber derived from MP-TS-17 perform an impressive tensile strength of 2.39 GPa and a high thermal conductivity of 612 W·m⁻¹·K⁻¹. Compared with the carbon fiber from the raw material MP, its mechanical strength and thermal conductivity are improved by 97.4% and 120%, respectively, demonstrating a promising approach for preparing high-performance petroleum-based mesophase pitch carbon fiber.