Structure of Carbonized Acrylic Fibers.

Abstract

The structure of carbons derived from acrylic fibers was analyzed by examination of structural peculiarities, i.e., anisotropy and distortions in the crystal. Changes in the structure of these fibers during the carbonization process and their dependence on stabilization conditions were investigated. During the carbonization process, a fiber structure was developed through a process whereby carbons in unorganized regions were gradually incorporated into crystallites as the carbonization temperature was increased. A marked increase in the fractions of crystallites and a discontinuous increase in the density of unorganized regions were observed at temperature of about 800°C, where growth of carbon layers associated with nitrogen elimination took place. Regularity in carbon layer stacking normal to the layer plane markedly increased at 1100°C. The microvoids in carbonized fibers were not those present in the stabilized fibers. At early stages of the carbonization process, the microvoids quickly disappeared, and at 800°C, they were recreated during the development of the carbon structure. Stabilization of the acrylic fibers minimizes loss of mass during the carbonization process. However, crosslinks formed by the stabilization prevented growth of carbon crystallites. Hence, as the degree of stabilization increased, the stacking height and the fractions of the crystallites in the carbonized fibers decreased, while the density and the fractions of unorganized regions increased. When the density of the stabilized fibers exceeded about 1.4g•cm-3, the excess oxygen uptake was eliminated as decomposition gases formed during the carbonization process, and the fractions of the microvoids in the carbonized fibers was increased.