Preparation of carbon fibers with excellent mechanical properties from isotropic pitches

Abstract

A novel isotropic pitch composed of linear methylene chains of polycondensed aromatic molecules was synthesized from naphtha-cracked oil through bromination and subsequent dehydrobromination (NB). Isotropic pitch-based carbon fiber obtained from the prepared NB yielded an unprecedentedly high tensile strength and elongation at break of 1500MPa and 3.2%, respectively, following carbonization at only 800°C for 5min. The aromatic components of NB were primarily condensed cyclic compounds containing three and four aromatic rings. In contrast, a pitch prepared by simple distillation (ND), was composed of compounds containing three to six aromatic rings, which carried the tensile strength of carbon fiber by only 700MPa with the similar fiber diameter. Interestingly, TOF-Mass analysis indicated that the molecular weight of the NB was higher than that of the ND. 13C-NMR analyses revealed that the NB pitch contained up to 18.8% aliphatic and naphthenic components compared to the 2.8% found in the ND pitch. Both isotropic pitches exhibited Bingham behavior above their softening temperatures. However, the linear chains of the NB pitch resulted in a higher degree of shear-thinning than was observed with the nonlinear ND pitch. This could result in a greater degree of molecular orientation during spinning.