Introducing thermo-mechanochemistry of lignin enabled the production of high-quality low-cost carbon fiber

Producing green carbon fiber from lignin is not only attractive to biorefineries for valorizing lignin but also contributes to the decarbonization of multiple industries. However, the difficulty of obtaining high-quality lignin-based carbon fibers at low cost remains the bottleneck and barrier to its commercial application. Previous approaches for chemically modifying lignin or blending with co-precursors were ineffective in delivering the carbon fiber with the desired quality. We discovered that introducing thermo-mechanochemistry of lignin to carbon fiber processing is a facile and green approach to overcome this challenge. Thermo-mechanochemistry can be introduced by properly integrating thermal heating and mechanical tension force applied to the spun fiber, which can manipulate the ordinary lignin chemistry to control the microstructure evolution from lignin. Under the influence of this newly known chemistry, lignin can transform into an oriented structure that can easily be graphitized at low temperatures. In this work, three precursors consisting of lignin or lignin blends were used to produce the carbon fibers with average tensile strength and modulus of 2.45 GPa and 236 GPa, 2.11 GPa and 215 GPa, 2.2 GPa and 225 GPa, respectively, using a surprisingly low carbonization temperature of only 700 °C. The preliminary techno-economic analysis suggests a low production cost. The discovery of the thermo-mechanochemistry of lignin will alter perceptions of lignin-based carbon fibers and provide opportunities to produce commercially viable low-cost green carbon fibers, advancing lignin valorization. A surprisingly simple approach to increasing the mechanical properties of lignin-based carbon fiber by leveraging a newly discovered thermo-mechanochemistry of lignin.