PAN fiber diameter effect on the structure of PAN-based carbon fibers

The oxidation reaction mechanism during the thermal stabilization process of polyacrylonitrile(PAN) fibers was studied to investigate why the skin-core structure formed easily after the thermal stabilization of PAN fibers was elaborated. And it was found that the heterogeneity of the fibers was poor. In order to achieve a uniform structure after the stabilization treatment, the fiber diameter was systematically reduced. Three PAN fiber samples with different diameters were selected, and they were treated by thermal stabilization and carbonized under the same conditions. The stabilized samples and carbon fiber samples with different diameters were analyzed by differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy, and elemental analysis. The results show that: the skin-core structure of the PAN fiber with the smallest diameter was completely eliminated by stabilization, and the heterogeneity was better. Meanwhile, C | N bonding also decreased, and the cross-linking reaction was easier to happen to form a large network molecular structure in the fiber with smaller diameter. The degree of graphitization of carbon fibers was higher when the diameter of fibers was reduced, and the relative carbon content increased. Crystallite size parameters were also affected when the diameter of fibers was reduced, with larger d002, lower Lc and increased La. In addition, the graphitization degree, as well as the carbon content was higher in the carbon fiber with smaller diameter.