Oxidation Behavior of Polyacrylonitrile Fibers Evaluated by New Oxidation lndex

Abstract

Oxidation conditions of the precursor polyacrylonitrile (PAN) fibers govern not only the performance but also productivity of the PAN-based carbon fibers. Here, the stabilization index (SI) was proposed to be a measure of the oxidation of PAN fibers. The SI was defined as the ratio of the shrinkage stress at 180°C after cooling to that at a high temperature up to which the samples was heated. The content of the chemically-bound oxygen in the oxidized fibers and the tensile strength of the carbon fibers were measured as a function of the magnitude of SI. The experimental results indicate that SI is an effective parameter to determine the optimum oxidation conditions of PAN fibers which finally give carbon fibers with high tensile strength. It was also shown that two step oxidation method in the atmosphere composed of equal volumes of oxygen and nitrogen was preferable to produce carbon fibers.