Effect of chemical structure and molecular weight on the properties of lignin-based ultrafine carbon fibers

Unlocking the effects of chemical structure and molecular weight of lignin on the properties of carbonized fiber can accelerate the development of lignin-based carbon fiber which was mainly limited by its complex structure. Hardwood kraft lignins (HKLs) with different structures and molecular weights prepared via heat treatment and fractionation processes were spun into ultrafine fibers using electrospinning technique at the assistance of 1 wt% polyoxyethylene (PEO), which was further removed during the carbonization process to eliminate the potential impacts. The structure and molecular weight of HKLs together with their influences on the thermal behavior, fiber morphology, crystal structure and mechanical performance of HKLs ultrafine fibers or carbonized ultrafine fibers were systemically investigated to provide an elaborate knowledge on the relationship between physico-chemical structure and properties of HKLs ultrafine fibers. Results suggest that a high molecular weight of HKL is beneficial to the formation of graphite-like crystallite, and the formed graphite-like crystallite and condensed structure of HKLs are crucial for the improvement of the mechanical performance of carbonized ultrafine fibers.