Fundamental studies of stabilization of polyacrylonitrile precursor, part 1: Effects of thermal and environmental treatments

A very significant element of the overall cost of manufacturing carbon fibers from polyacrylonitrile precursor is represented by the oxidative stabilization stage. In Part 1 of this study, the effects of temperature, time, and environment on the stabilization of polyacrylonitrile were examined using wide-angle x-ray scattering, density measurement, differential scanning calorimetry, and scanning electron microscopy. It was found that increases in soak time at a given soak temperature result in a parabolic increase in bulk density and an exponential decrease in remnant heat values. The presence of oxygen in the 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 a pure nitrogen environment. Oxygen also promotes the formation of a weak diffraction peak at 25° 2θ, while treatment in pure nitrogen environment shows no evidence of its formation. Finally, treatment in air environment led to the formation of a skin/core fiber morphology while treatment in pure nitrogen or pure oxygen environment did not. Reasons for this behavior are discussed.