Preparation of carbon fibers from low-molecular-weight compounds obtained from low-rank coal and biomass by solvent extraction

The practical use of carbon fibers is limited by their high price mainly due to the high price of precursors. We have examined a high temperature solvent extraction method to prepare carbon fiber precursors from low-rank coals and biomass, using a lignite from Australia and rice straw. 1-methylnaphthalene at 350℃ was used for the extraction and some of the extract in the solvent was precipated at room temperature. The soluble fractions at room temperature were obtained for use as the precursors by solvent evaporation. They were spun into fibers by a centrifuge spinning system and were then were extracted by cyclohexane to increase the softening point, stabilized by a temperature-programmed thermal treatment in air from 80℃ to 330℃ and carbonized at 1 000℃ for 1 h in N₂ to obtain carbon fibers. The carbon and oxygen contents of the final carbon fibers were 92 and 6.0 wt%, respectively, similar to those of commercial carbon fibers. The fiber diameter was around 4-6 μm. The soluble fractions were found to be promising low-cost precursors for carbon fibers.