Synthesis of isotropic carbon fibers from pitch precursors

Pitch is widely used as a binder and an impregnant in the production of bulk carbon and graphite materials, with heavy liquid products and bottoms from crude oil processing representing an alternative source of these materials. The suitability of carbon fibers synthesized from a wide range of isotropic pitch precursors for fiber production was investigated. The higher the softening point of the pitch, the greater the stabilization rate at which the fibers could be processed. An increase in fiber diameter reduced the maximum achievable stabilization rate. Weight gain increased with increasing carbon content in the precursor pitch during stabilization while the axial contraction was less for those fibers from pitches of higher carbon content. The combined effects of stabilization and carbonization gave carbon yields of 50-86% of the green fibers, with a corresponding axial contraction of 28-12%. The net carbon yield on conversion from pitch to carbon fiber increased with carbon content of the parent pitch, suggesting that the pitches with higher heteroatom content lost more material due to gasification. Similar relationships were observed between axial contraction and heteroatom content, and between axial contraction and carbon content. The tensile strength of the derived fibers was in the range 0.1-1.1 GPa, and increased with increasing molecular size, aromaticity, and decreasing heteroatom content in the precursor, while the electrical resistivity of the fibers decreased with these properties.