KINETICS OF CARBONIZATION AND GRAPHITIZATION OF PBO FIBER

PBO [poly(p-phenylenebenzobisoxazole)] fiber has been shown to convert to an ordered carbon fiber without the need for stabilization. This a rticle presents the first detailed analysis of the carbonization and g raphitization behavior of this unique material. The carbonization proc ess was modeled as a series of free-radical reactions, and thermogravi metric analysis was used to determine an activation energy of 76 +/- 6 kcal/mol for the thermal initiation of free radicals. The initiation reaction data then were applied to determine the temperature dependenc e of the termination reaction. Additionally, the development of long-r ange order in the graphitizing fiber was examined. The spacing between graphene planes was shown to decrease with increasing treatment tempe rature and soak duration. Carbonized PBO fibers developed more long-ra nge order than carbon fibers produced from other polymers, which may p artially explain why these PBO-based fibers display excellent lattice- dependent properties. Finally, an Arrhenius analysis found the activat ion energy for graphitization to be 120 +/- 17 kcal/mol. (C) 1996 John Wiley & Sons, Inc.