Effects of Oxygen Partial Pressure on Multiscale Structures and Properties of Polyacrylonitrile Fibers during Preoxidation

A comprehensive understanding of how preoxidation parameters affect preoxidation behavior is a significant research topic in the development of high-performance carbon fibers (CFs). This study systematically investigated the influence of oxygen partial pressure on the evolution of multiscale structures and properties of polyacrylonitrile (PAN) fibers during preoxidation. By adjustment of the ratio of nitrogen gas/air/oxygen, a gradient oxygen partial pressure environment (0/14.78/16.23/19.00/21.11/23.11/25.10 kPa) was constructed. Combined with Fourier transform infrared spectroscopy (FTIR), X-ray Diffraction (XRD), elemental analysis (EA), scanning electron microscopy (SEM), and Raman spectroscopy, the influence of oxygen partial pressure on the chemical structure, aggregated structure, and morphological structure of PAN fibers was analyzed. The research results indicate that oxygen can significantly promote dehydrogenation and oxidation reactions, which play a decisive role in forming stable aromatic structures. Higher oxygen partial pressure can facilitate oxygen diffusion, increasing the oxygen content in the fibers from 0.78 to 10.78% and reducing the optical density difference (ΔOD) from 3.389 to 2.547% by improving the uniformity of radial reactions. However, excessive oxygen can inhibit the cyclization reaction by capturing free radicals. This study provides a theoretical basis for optimizing the preoxidation process parameters to improve the performance of CFs.