Effect of oxygen-introduced pitch precursor on the properties and structure evolution of isotropic pitch-based fibers during carbonization and graphitization

Two ethylene tar-derived isotropic pitch-based fibers were prepared from nitrogen-distilled pitch (NDP) and air-blown pitch (ABP). The resultant fibers were carbonized at different temperatures to investigate the effect of the oxygen-introduced pitch precursor on the properties and structure evolution of fibers during carbonization and graphitization. The tensile strength of the ABP-derived carbon fibers (A-CFs) was higher than that of the NDP-derived carbon fibers (N-CFs) below 1200 °C because more gas was released from the N-CFs during carbonization. However, the mechanical properties of the A-CFs and N-CFs decreased significantly at 1400 °C, which resulted from defects that were produced by the removal of oxygen-containing gas. Above 1400 °C, the mechanical properties improved slightly, and the interlayer spacing decreased with an increase in heat-treatment temperature for two series fibers as a result of the rearrangement and development of microcrystallites. The A-CFs had a lower Young's modulus and a higher electrical resistivity than the N-CFs, because the cross-linked structure in the oxygen-introduced pitch precursor impeded the orientation of its fibers during carbonization and graphitization.