Evaluating polyacrylonitrile precursor structure effects on carbon fiber production

Polyacrylonitrile (PAN) precursor fiber with different draft ratios can affect the crystal and microporous structure of the produced carbon fiber. A high draft ratio for PAN fiber preparation was revealed beneficial for high crystal orientation and few defects in the fiber. In this research, pre-oxidation PAN fibers and carbon fibers were investigated with differential scanning calorimetry (DSC) and synchrotron radiation (wide-angle X-ray diffraction (WAXD)/small-angle X-ray scattering (SAXS)). The thermal analysis of DSC profiles indicated that PAN fiber with a high draft ratio is beneficial for the cyclization reaction. The WAXD data demonstrated that PAN fiber with a large draft ratio is beneficial for high crystal orientation; however, the resulting carbon fiber has reduced orientation. This is due to PAN fiber with a high draft ratio having a smaller crystal size, and the crystal structure is not well maintained during the simulated pre-oxidation process. SAXS data reveal that a high draft ratio results in PAN fiber micropores with a large aspect ratio and high orientation. However, the micropore structure could not be maintained in the pre-oxidation process, resulting in corresponding carbon fiber with a decreased aspect ratio and lower crystal orientation. These findings contribute to our understanding of the relationship between PAN fiber production and carbon fiber structure, demonstrating that PAN fiber structural maintenance is also important when producing carbon fiber.