Constructing the pyrolysis kinetic model of mesophase pitch for improving mechanical properties and thermal conductivity of carbon fibers

Mesophase pitch has become a superior precursor of high thermal conductivity pitch-based carbon fibers due to its high aromaticity, high carbon content and ability to be graphitized. However, mesophase pitch is prone to pyrolysis during melt spinning, which leads to structural defects such as pores in the carbon fiber, thus inhibiting the continuous improvement of carbon fiber properties. In this paper, a kinetic model was built by revealing the pyrolysis of petroleum-based mesophase pitch, establishing an association between pyrolysis weight loss and spinning process and spinning state. The results indicate that the pyrolysis products of petroleum-based mesophase pitch mainly consist of high-temperature volatile components and small molecules produced by continuous decomposition of macromolecules. When the pyrolysis weight loss of mesophase pitch is less than 2.2 wt%, it has good spinnability, and the surface and cross section of spun fiber are smooth and defect-free. Ultimately, the carbon fibers show a tensile strength of 3.09 GPa, a tensile modulus of 855 GPa, and a thermal conductivity of 727 W·m⁻¹·K⁻¹. It is demonstrated that the pyrolysis kinetics model of petroleum-based mesophase pitch is reliable for guiding the optimization of melt spinning processes and enhancing the physical properties of carbon fibers.