Are lignin-derived carbon fibers graphitic enough?
Single component lignin-derived carbon fibers have been under development for many years, but strength properties are still inferior to those of commercial carbon fibers. The extent of graphitization is an overlooked limitation to lignin-derived carbon fiber development, particularly for high-modulus fibers treated at high temperatures. The tensile moduli of commercial carbon fibers increase with temperature during graphitization, however, lignin-derived carbon fiber moduli stay the same or decrease. This review exposes the inability of lignin-derived carbon fibers to graphitize in a manner similar to commercial carbon fibers, thereby providing rationale for the aforementioned discrepancy in tensile moduli-temperature trends and offering possible tangible future areas of research and development.