Investigation of spinning performance based on the evolution of spinnable pitch components

Spinnable pitch prepared by air-blowing thermal polycondensation is rich in free radicals and various intermolecular interactions, making it unstable and prone to change during storage. Spinnable pitch was separated into tetrahydrofuran soluble (THFS) and tetrahydrofuran insoluble (THFI) fractions. THFS fraction contained a high heteroatoms content, the content decreased and the average molecular weight increased with storage time. THFI fraction exhibited a high free radical concentration, with increasing oxygen and sulfur content. Both THFS and THFI fractions generated oxygen-containing functional groups such as sulfoxide, carbonyl and hydroxyl groups. Spinnable pitch underwent oxidation, crosslinking, polymerization and other reactions during storage due to heteroatoms and free radicals, the average molecular weight increased. Consequently, the softening point, viscosity, and flow activation energy of the spinnable pitch increased, more non-melting particles, while phase angle decreased, indicating that a transition from viscous to elastic components, easy to brittle. Eventually, spinning stability and continuity of spinnable pitch reduced, resultant carbon fiber defects increased, and performance decreased. This study provides insights into improving the stability of spinnable pitch and optimizing carbon fiber performance.