Fundamental Studies of Stabilization of Polyacrylonitrile Precursor

The purpose of this study was to examine the stabilization of polyacrylonitrile precursor. Currently, the stabilization of polyacrylonitrile is the limiting step in the production of carbon fibers because of its cost and time requirements. By furthering the understanding of the stabilization process, it may be possible to reduce the cost and time required, allowing the widespread use of carbon fiber in several industries to be achieved.

In this study, the effects of temperature, time, environment, and pressure on the stabilization of polyacrylonitrile were examined. Once fiber samples were heat treated, four experimental techniques were used to examine the samples. The techniques were (1) wide-angle x-ray scattering, (2) density gradient column, (3) differential scanning calorimetry, and (4) scanning electron microscopy.

Temperature and time were found to play important roles in the stabilization of polyacrylonitrile. Increases in both temperature and time were found to lower crystallinity, increase the bulk density, and lower the remnant heat. The presence of oxygen in the stabilization environment was found to promote the formation of an amorphous structure, higher density, and lower remnant heat values at lower soak temperatures and soak times than would be necessary in inert environments. Both pure oxygen environment and increased pressure were found to affect stabilization, but only after 60 minutes soak time, with 0 minutes soak time giving results similar to those of air environment at atmospheric pressure, for a given temperature. Based on the results, a possible progression for the thermos-oxidative stabilization of polyacrylonitrile is discussed, but despite the various analyses performed, it was impossible to quantify the fully stabilized state necessary for subsequent carbonization.