The role of structural evolution of polyacrylonitrile fibers during thermal oxidative stabilization on mechanical properties

Abstract The effects of chemical and physical structural evolution of polyacrylonitrile (PAN)‐based carbon fibers precursor during thermal oxidative stabilization (TOS) on the mechanical properties of stabilized fibers were systematically studied. The results of Fourier transform infrared spectroscopy, wide‐angle X‐ray diffraction, and density gradient column showed that the PAN fibers treated with high temperature and for long time have higher extent of cyclization, oxygen content, and crosslinking content. The crystallinity and crystallite size decreased with the increase of TOS time and temperature, whereas the bulk density of the stabilized fibers increased. The mechanical property results indicated that the decrease in tensile strength was inseparable from the formation of the cyclic structure and the amorphization transition of the crystal structure. The fibers have better structural stability when the extent of cyclization was 80–83%, the crystallinity was 34–45%, and the bulk density of stabilized fibers was 1.33–1.35 g/cm 3 , but exceeding these ranges, a serious skin‐core structure appeared.