In-situ microstructural changes of polyacrylonitrile based fibers with stretching deformation

In-situ wide-angle X-ray scattering technique was used to investigate the microstructural changes of polyacrylonitrile (PAN) based fibers with the macroscopic fiber strain. Crystalline phase, transition layer, and amorphous matrix were found coexistence in the PANFs. Tensile deformation induced the PAN-chain transformation from amorphous matrix to crystalline region through the transition layer. After the PANFs were oxidized into stabilized fibers (SFs), the SFs inherited the amorphous and crystalline phases of the PANFs, but the transition layer disappeared and a cyclized ladder structure was formed. Partial PAN chains were anchored to the relatively rigid ladder structure, leading PAN chains folding with tensile deformation. After the SFs were further carbonated into carbon fibers (CFs), two rigid turbostratic structures were formed in the CFs. A new structure model was proposed to describe the microscopic structure changes with macroscopic fiber strains as well as the structural development from PANFs to SFs then to CFs.