Lignin-Based Carbon Fibers from Hybrid Poplar and Corn Stover: Renewable Aqueous Solvents for Lignin Fractionation and Solvation

Because of the growing interest in cellulosic bioethanol, lignin from agriculture residue sources has drawn attention as a renewable and inexpensive material for value-added applications. Similar to Kraft lignins, the heterogeneity and impurities of these biorefinery byproduct lignins present significant challenges that negatively impact their economic viability as precursors. The ALPHA process was developed as a means of both controlling the molecular weight and reducing the metallic impurities of technical lignins through the use of aqueous, renewable solvents. Previous work has demonstrated that higher molecular weight cuts of Kraft lignin, purified via ALPHA, produce carbon fibers with the best tensile strength and Young’s modulus of any lignin to date. This same approach of lignin purification is being applied to lignins isolated via alkaline pulping from hybrid poplar wood chips and corn stover. The resultant ALPHA-processed lignin fractions are being prepared into spinning dopes -- using the same ALPHA solvents as for the fractionation/purification step – and then dry-spun into fibers. The effect of lignin molecular weight and purity on spinning, stabilization, and fiber properties will be reported, and results compared against a commercial softwood Kraft lignin.