Effect of the oxygen content and the functionality of spinnable pitches derived from ethylene tar by distillation on the mechanical properties of carbon fibers

Abstract

Three basic pitches were prepared by the distillation of ethylene tar at 200, 250, or 300 °C for 3 h. Spinnable pitches were produced from them using air-blowing followed by heat treatment at 330°C for 4 h and are designated P200AT, P250AT and P300AT, respectively. These three pitches, and stabilized fibers and carbon fibers produced from them were characterized by TG-MS, FT-IR, 13C-NMR, XRD, SEM, solubility tests and elemental analysis. The components and oxidation reactivity of the basic pitches, and its influence on the oxygen functionality and microstructures of the spinnable pitches and mechanical properties of the resulting carbon fibers were investigated. Results showed that with increasing distillation temperature the aliphatic carbon content and n-hexane and toluene solubility of the basic pitches decreased, while their aromaticity and planarity increased, and the oxidation reactivity reached a maximum at 250 °C. Of the three spinnable pitches P250AT had the highest softening point, highest carbon yield, oxygen content, and C=O content and the highest toluene insoluble fraction. However, the oxygen uptake of P250AT pitch fibers during stabilization was the lowest among the three. This led to a reduction of gas release during carbonization, and therefore the highest carbon yield, the smallest number of defects, the highest tensile strength and the lowest Young's modulus of all the carbon fibers.