Evaluating of the oxidative behaviors of isotropic pitch fractions for optimal the mechanical properties of isotropic pitch-based carbon fibers

Abstract

Oxidative stabilization plays an extremely important role in maintaining shape and structural integrity and preventing inter-filament fusing of isotropic pitch fibers during the subsequent carbonization. However, the actual chemical processes and mechanism of the stabilization reaction are complex and as yet poorly defined because of the complexity of the isotropic pitch. In the study, an isotropic pitch synthesized through the co-carbonization of aromatic-rich distillate oil and polyethylene glycol was fractioned into seven fractions by n-heptane, toluene, and their mixtures. The chemical structure and oxidative reaction features of each pitch fraction were systematically analyzed and investigated by FT-IR, 13C NMR, TG-DSC, SEM, etc. The results revealed that the light pitch fractions with more and longer alky side chains attached to the aromatic nucleus exhibit higher oxidative reactivity and appear to induce a higher content of oxygen uptake to achieve stabilization as compared with the heavy pitch fractions. The stabilization reactions of the pitch fractions were carried out in multiple stages, which was confirmed by the conversion of oxygen-containing functional groups ketones and aldehydes to anhydrides and esters as oxidation temperature increased from 150 ℃ to 290 ℃. Three commercial isotropic pitches produced from petroleum-based raw material were oxidized under different conditions. The results confirmed that it is feasible to predict and optimize the stabilization process by tailoring the pitch components.