Enhancing the tensile strength of isotropic pitch-based carbon fibers by improving the stabilization and carbonization properties of precursor pitch

A unique isotropic pitch composed of linear chains of polycondensed aromatic molecules was synthesized through the bromination and subsequent dehydrobromination of mixed naphtha-cracked oil (NCO) and quinoline-insoluble free coal tar (CT). Isotropic pitch-based carbon fibers obtained from the co-carbonization of an NCO/CT mixture via bromination and dehydrobromination exhibited an unprecedentedly high tensile strengths and elongations at break of 1800 and 2050 MPa, and 3.2 and 2.8% following carbonization at 800 and 1100 °C for 5 min, respectively. The aromatic components derived from the co-carbonization process were primarily condensed cyclic compounds containing four or five aromatic rings. These substructures enhanced the tensile strength of the carbon fibers up to 2050 MPa, which is a level much higher than that reported for carbon fibers derived from naphtha-cracked oil-based isotropic pitch. TOF-MS analyses indicated that the molecular weight of the NCO/CT derived pitch was higher than that of the NCO derived pitch. Both isotropic pitches exhibited Bingham behavior above their softening temperatures. However, the linear chains of the higher aromatic units of the NCO/CT derived pitch resulted in a higher degree of shear-thinning than was observed with the NCO derived pitch, resulting in a higher degree of molecular orientation during spinning.