OXIDATION BEHAVIOR OF POLYACRYLONITRILE FIBERS EVALUATED BY NEW STABILIZATION INDEX

The shrinkage stress of the precursor polyacrylonitrile (PAN) fibers during oxidation was measured under various conditions, and was found to decrease with cooling the fibers from certain oxidation temperatures, depending strongly on the degree of oxidation, and to become constant below 180 degrees C. Here, the stabilization index, SI, was proposed to be a measure of the oxidation of the PAN fibers, which was the ratio of the shrinkage stress at 180 degrees C in cooling to that at the high temperature at which the samples were heated. The experimental results indicated that the SI value reflected the changes of the chemical structure in the fibers by oxidation, and was an effective parameter in determining optimum oxidation conditions. The SI value was shown to be useful in controlling the continuous production line of the oxidized fibers to produce carbon fibers with high performance.