Carbon fibers derived from environmentally benign, ethanol-fractionated corn-stover lignin†

Corn stover (CS), the non-grain portion of corn, is among the top three agricultural residues produced globally and the largest in the U.S. CS comprises 75% of all agricultural residues in the U.S. and is an excellent non-food source of sustainable biomass. However, studies of its conversion into carbon fibers are scarce because lignin derived from CS does not possess the needed purity and molecular weight (MW) for precursor fiber spinning and final carbon-fiber properties. Through application of our Aqueous Lignin Purification with Hot Agents (ALPHA) process aqueous ethanol was used to simultaneously clean and fractionate corn-stover lignin to produce a liquefied precursor. Fractionation enabled higher MW components to be used for successful dry-spinning of thin CS precursor fibers. Furthermore, the higher MW also increased glass transition temperature of the precursor lignin, which reduced stabilization time to 9 hours, an impressive four-fold improvement as compared to prior studies using unfractionated corn-stover lignins. Carbon fibers from higher MW lignin fractions displayed a tensile strength of 1.0 ± 0.1 GPa, double that of previous carbon fibers derived from corn-stover lignin. These carbon fibers possess a specific modulus of 48 GPa (g⁻¹ cm³), about 50% greater than that of glass fibers, establishing their novelty as a low-cost reinforcing material suitable for potential applications such as ultrahigh temperature thermal insulation, electrostatic dissipation, and ablative composites.