Property Evolution Governed by Processing Parameters in Polyacrylonitrile Fibers With Increasing Tow Size During Stabilization

ABSTRACT The development of large‐tow carbon fibers, valued for their low cost and processability, remains a global research priority. This study systematically investigates the applicability of process conditions optimized for 25 K PAN‐based carbon fibers to the production of 50 K large‐tow fibers, focusing on their structural evolution and correlated performance. Thermal analysis revealed similar thermal behavior for both fiber types, evidenced by comparable initial stabilization temperatures, which is attributed to their identical precursor composition. However, density testing and morphological analysis (SEM/OM) reveal that 50 K fibers exhibit greater stabilization sensitivity and more pronounced core‐shell structural differences during stabilization—their core indentation depth increases by 16% compared to 25 K fibers (128 vs. 110 nm). This structural non‐uniformity is directly correlated with uneven heat distribution during the exothermic stabilization process. Despite these structural differences, both fibers demonstrated excellent performance stability. Composite material testing results indicate that performance fluctuations for both types can be controlled within 4%. In summary, this study confirms that existing 25 K process conditions can be effectively extended to 50 K large‐tow carbon fibers production. It provides critical theoretical and technical support for scaling up efficient manufacturing while maintaining performance standards.