High-quality renewable carbon fiber produced from melt-spun softwood kraft lignin using short stabilization time and ultra-low carbonization temperature.

Although lignin-based carbon fiber is of great interest, its poor tensile properties have been a significant hurdle to developing commercial applications. Additionally, the difficulty of melt-spinning lignin with high glass transition temperatures and prolonged stabilization times required for spun fibers negatively impacts the production costs. The present study describes highly effective and environmentally friendly approaches to overcome the challenges in developing commercially relevant lignin-based carbon fiber to reduce fiber production costs and increase mechanical properties. We showed that softwood kraft lignin modified using an aqueous light bio-oil was not only melt-spinnable, but its spun fiber could be stabilized within 4 h compared to the tens of hours required for other melt-spun fibers. We also demonstrated that introducing thermo-mechanochemistry to control the spun fiber during stabilization and carbonization is highly effective in significantly improving carbon fiber's tensile properties. In this study, the carbon fibers produced using a stabilization temperature of 300 °C and a carbonization temperature of 700 °C had a tensile strength of 2.08 GPa and a tensile modulus of 193 GPa. The process-property-structure relationships of lignin-based carbon fiber under the influence of thermo-mechanochemistry were also investigated. This study provides practical approaches to obtain market-desired green and low-cost carbon fiber.