Carbon fiber is a lightweight, high-strength material valued for its exceptional strength-to-weight ratio, making it widely used in the aerospace, automotive, and sporting industries. However, carbon fiber production primarily depends on non-renewable precursors like polyacrylonitrile (PAN), raising significant environmental concerns. Lignin, a sustainable and abundant alternative with a high fixed carbon content, presents a promising solution but faces challenges due to its complex and highly variable structure. In this work, a softwood kraft lignin modified by bio-oil was melt-spun and subsequently processed into carbon fiber. The heating and tension condition of the fibers during the stabilization and carbonization processes were carefully controlled to activate the thermo-mechanochemistry of lignin and tune the structural changes. The carbon fiber obtained at a carbonization temperature of 700°C had a tensile strength of 2.08 GPa and a modulus of 197 GPa, meeting the U.S. Department of Energy (DOE) target for automobile-grade carbon fiber. The lignin-based short carbon fiber is directly incorporated into an epoxy resin matrix without surface sizing to fabricate a carbon fiber-reinforced polymer (CFRP) composite. The preliminary study shows that lignin-based CF has excellent interfacial competitivity with the polymer matrix, probably due to its reactive surface functional groups.
