Effect of carbonization conditions on microstructural properties of isotropic coal tar pitch-based general-purpose carbon fibers

The microstructures of carbon fibers can be significantly modified by understanding the carbonization conditions which improves the properties of fibers. The carbonization is a complex process of converting pitch fibers into carbon fibers through the evolution of gases and arrangement of molecules by polymerization reactions. Hence, the present study focuses on the synthesis of isotropic pitch-based carbon fibers and the investigation of microstructural properties with varying carbonization conditions at 1000 °C. The isotropic pitch is derived from coal-tar pitch through the utilization of a vacuum distillation technique. Various properties of isotropic pitch are studied to determine the flowability and optimum temperature range for melt-spinning into fibers. Subsequently, the stabilization process is conducted in an open atmosphere to retain fibers shape by introducing oxygen-containing functional groups. Time-dependent carbonization parameters such as heating rate and holding/soaking periods are used to optimize the conditions that yield superior microstructural properties. This research reveals that slower heating rates enhance the crystallite sizes while reducing defects. Conversely, longer holding times at carbonization temperature showed adverse effects on the microstructural properties. To assess microstructural, thermal and physical properties of the pitch and fibers, various characterizations are performed, including DSC, TGA, rheology, FTIR, XPS, Raman, XRD, and SEM.