The influence of molecular structure and chemical composition of mesophase pitch on the stabilization process and mechanical properties of derived carbon fibers

The stabilization process is the most complex and time-consuming step in manufacturing high-performance mesophase pitch-based carbon fiber (MPCF), with the molecular structure of the mesophase pitch dictating its oxidative reactivity and final fiber properties. Here, four mesophase pitches with different molecular structures were prepared by precisely adjusting the ratio of three petroleum pitch fractions, and the influence of molecular structure and chemical composition of mesophase pitch on the stabilization reaction pathway, oxygen functional group evolution, and resultant mechanical properties of derived carbon fibers was comprehensively investigated. Quantitative structure–reactivity correlations reveal that the oxidative reactivity is governed by three jointly acting molecular descriptors: the aromatic index (I ar ), the alkyl index (I A ), and the H/C atomic ratio. Mesophase pitches with I ar = 0.66–0.72, I A > 0.45, and H/C > 0.60 achieve oxidation onset temperatures as low as 143 ℃ and maximum weight gains of 12.8 wt% during stabilization, whereas mesophase pitches with I A < 0.42 exhibit sluggish oxidation reactivity. The moderate aromaticity and sufficient aliphatic side chains are essential molecular features for designing mesophase pitch, which can significantly enhance oxidative reactivity, enabling the rapid, uniform stabilization process and the preparation of high-performance carbon fibers. Oxygen functional group evolution follows a temperature-dependent pathway: at 250–270 ℃, ketone, carbonyl, and ether groups form preferentially (C–O–C content up to 56.32%), while above 280 ℃ these convert into ester and anhydride structures (O–C O content increasing to 40.24%), which decompose during carbonization to produce structural defects and reduce the orderliness of carbon fiber. The microcrystalline order and mechanical properties of the carbon fibers are determined jointly by the microcrystalline structure and stabilization process of mesophase pitch. MPCF-1 achieves a remarkable tensile strength of 1742 MPa and tensile modulus of 206 GPa. This work establishes a quantitative structure-reactivity-performance framework and provides actionable molecular design guidelines for synthesizing high-performance spinnable mesophase pitch.