Increasing oxygen diffusion during rapid stabilization of a PAN precursor fibre and its impact on the microstructure and properties of carbon fibre

In this work, a polyacrylonitrile (PAN) copolymer containing 3 wt% methyl acrylate (MA) and 3 wt% itaconic acid (IA) is stabilised using thermal treatments designed to increase oxygen diffusion into the precursor fibre prior to carbonisation. Elemental analysis confirms the enhanced oxygen content in the PAN fibre, while FT-IR spectroscopy shows the formation of the more thermally stable cyclic ladder structure in preference to earlier termination of cyclization. Higher oxygen diffusion leads to a more distinct skin-core structure, reflecting heterogeneity of the filaments, with the skin being more ordered and graphitic, and the core remaining disordered and amorphous. Despite this, the mechanical properties exhibit a marginal improvement in individual tensile properties within increasing oxygen content. From synchrotron SAXS/WAXS studies, the apparent crystallite height (Lc) decreases with increased oxygen diffusion, density increases as well as increased orientation. These findings offer insights into how oxygen can be used to control the oxidation mechanism and tailor the carbon fibre microstructure and material properties, providing pathways for develop high-quality, low-cost carbon fibres on an industrial scale. © 2025 The Authors