Effect of Oxygen Concentration on Skin–Core Structural Evolution of Polyacrylonitrile Precursor Fibers During Thermal Oxidative Stabilization

Thermal oxidative stabilization (TOS) of polyacrylonitrile‐based precursor fibers (PFs) is a critical procedure in carbon fiber production, and oxygen concentration exerts a profound influence on the structural evolution of PFs during this process. In this work, PFs were thermally stabilized at 300°C under nitrogen, air, and pure oxygen atmospheres to investigate the effect of oxygen concentration on the formation of radial structural gradients. The chemical, physical, and mechanical properties of the fibers were systematically characterized via Fourier transform infrared spectroscopy, elemental analysis, simultaneous thermal analysis, x‐ray diffraction, optical microscopy, scanning electron microscopy, tensile testing, and nanoindentation. The results reveal that rising oxygen concentration facilitates oxygen uptake and oxidative dehydrogenation reactions propagating toward the fiber interior in the middle stage of TOS (240°C–260°C), which in turn makes heat‐resistant crosslinked structures migrate to the middle region in the late stage of TOS (260°C–300°C). In contrast, when such crosslinked structures are widely distributed and concentrated in the fiber skin region, both the carbon yield and mechanical performance of the fibers can be significantly enhanced. This study clarifies the function of oxygen concentration in TOS and provides guidance for optimizing TOS parameters in carbon fiber manufacturing.