Preparation of isotropic pitch precursors for general purpose carbon fibers (GPCF) by air blowing—I. Preparation of spinnable isotropic pitch precursor from coal tar by air blowing

A QI-free coal tar pitch with a softening point around 80°C was air blown in an autoclave at 330°, 360° and 380°C, respectively, for various periods in order to prepare a pitch precursor for GPCF. Air blowing markedly increased the softening point and contents of solvent insoluble fractions such as BI, QI, as well as atomic CH ratio. The pitches blown at 360°C for 2 to 4 h showed excellent spinnability into thin fibers of 12 to 14 μm in diameter at a wide range of 255° to 330°C. Structural characterization by NMR, FT-IR and elemental analysis on the blown pitches showed that distillation of lighter fractions, aromatization and polymerization of the remaining fractions due to oxidative dehydrogenation raised their softening points. Although all blown pitches stayed completely isotropic, further heat treatment at 380°C under N2 flow for 14 to 21 h allowed generation of mesophase spheres in the isotropic matrix. After the carbonization at 600°C, all pitches showed anisotropic texture, suggesting that blown pitches maintain fusibility and reactivity to follow the growth and development of mesophase spheres in the successive carbonization.