L ignin-based carbon fibers for composite fiber applications

Carbon fibers have been produced for the first time from a commercially available kraft lignin, without any chemical modification, by thermal spinning followed by carbonization. A fusible lignin with excellent spinnability to form a fine filament was produced with a thermal pretreatment under vacuum. Blending the lignin with poly(ethylene oxide)(PEO)further facilitated fiber spinning, but at PEO levels greater than 5 por cent, the blends could not be stabilized without the individual fibers fusing together. Carbon fibers produced had an over-all yield of 45 por cent. The tensile strength and modulus increased with decreasing fiber diameter, and are comparable to those of much smaller diameter carbon fibers produced from phenolated exploded lignins. In view of the mechanical properties, tensile 400-550 MPa and modulus 30-60 GPa, kraft lignin should be further investigated as a precursor for general grade carbon fibers.