New aspects in the oxidative stabilization of PAN-based carbon fibers: II Original Research Article

A model detailing the development of morphology in copolymer PAN (polyacrylonitrile) fibers during oxidative stabilization was recently proposed (Gupta and Harrison, Carbon, 1996, 34, 1427). Some of the main features of this model are: (a) a two-step oxidative stabilization process wherein reactions initiate in the amorphous phase, and progress to the crystalline phase at high temperatures; (b) intramolecular cyclization reactions dominating the early part of the stabilization process, intermolecular cross-linking occurring at higher temperatures and in the presence of oxygen; (c) macroscopic shrinkage along the fiber axis primarily being an entropy-driven process, with “chemical” effects serving to modify the entropic response; and (d) a final heat treatment temperature (HTT) of ~ 380 °C seemed to be necessary in order to effect complete oxidative stabilization. In the current work, results from tensile testing and X-ray experiments help in validating the proposed model. Studies on isothermal stabilization indicate no benefits when compared to a rapid and more effective constant temperature ramp process. Additionally, for stabilization in argon, dehydrogenation is a slow process, leading us to believe that stretching of precursor fiber could be carried out over a wide temperature range.