Effects of electron beam irradiation on the skin-core structure and thermochemical properties of polyacrylonitrile fibers

In this study, the skin-core selective mechanism of electron beam irradiation on the radially heterogeneous structure of polyacrylonitrile (PAN) precursor fibers is systematically revealed for the first time. This is achieved by integrating multi-scale characterization techniques, including synchrotron radiation microfocused wide-angle X-ray scattering, in-situ microfilm infrared spectroscopy, and wide-angle X-ray scattering. The study confirms that irradiated and non-irradiated PAN fibers exhibit distinct cortex-core structures, with the (100) crystal planes in the cortex showing higher crystallinity, crystal size, and degree of orientation compared to the core layer. As the irradiation dose increases, the cortex's crystallinity decreases, grain size reduces, and degree of orientation slightly diminishes, while crystal face spacing remains nearly unchanged, and core structure parameters show minimal variation. This differential evolution between cortex and core structures enhances oxygen diffusion efficiency to some extent, laying the foundation for improving the uniformity of PAN fiber pre-oxidation processes. Further studies reveal a synergistic effect between irradiation and heat treatment: 200 kGy is the optimal irradiation dose for achieving a 62% cyclization rate at 250 ℃, while 500 kGy provides the best carbon yield at 1 000 ℃, reaching 50.5% (a 12.25% increase over non-irradiated samples). Through rational adjustment of irradiation conditions, PAN fibers' pre-oxidation and carbonization processes can be optimized, providing new experimental evidence for developing high-performance PAN-based carbon fibers.