(43c) Lignin Fractionation for Quality Carbon Fiber

Qiang Li^1,2*, Cheng Hu^1,2, Mengjie Li^1,2, Joshua S. Yuan^1,2*

¹Synthetic and Systems Biology Innovation Hub, Department of Plant Pathology and Microbiology, Texas A&M University, College Station, TX 77843, USA

²Department of Chemical Engineering, Texas A&M University, College Station, TX 77843, USA

*For correspondence: Qiang Li: liqerlee@tamu.edu; Joshua S. Yuan: syuan@tamu.edu

Lignin represents a promising alternative of polyacrylonitile (PAN) polymer as precursor to synthesize carbon fiber, because of the abundance, low cost, and high carbon content of lignin polymer. Lignin is a main waste from both paper industry and lignocellulosic biorefinery, and converting lignin waste into carbon fiber has been sought after for several decades with attempt to return economics and build sustainability of both areas. Nevertheless, the poor mechanical performance remains to be a major barrier for commercial applications of lignin-based carbon fiber. We have established that the low mechanical performance was attributed to the chemical heterogeneity of lignin polymer, including diverse interunitary linkages, various functional groups, different molecular weight, and polydispersity. Recent advancements of our group in fractionation technologies showed the great potential to reduce lignin heterogeneity and thus enhance lignin carbon fiber performance. We have developed a series of fractionation technologies to process industrial lignin, including 1) partly degradation of lignin using laccase-mediator system and autohydrolysis treatment; 2) solvent fractionation using different organic solvents with different solubility of lignin; 3) physical fractionation by dialysis tube according to lignin molecular weight; 4) lignin precipitation against water with gradient pH. All these fractionation have trimmed lignin chemistry and reduced lignin heterogeneity by deriving lignin fraction with more β-O-4 linkage, less hydroxyl groups, higher molecular weight, and less polydispersity index (PDI). The resultant carbon fiber was found to have both enhanced mechanical performance and electrical conductivity. Mechanistic study have revealed that the improvement in lignin heterogeneity has improved the molecular interactions of lignin with guest molecules, and thus enhanced the growth of the crystallite structures in carbon fiber, resulting in carbon fibers with improved performances. Overall, fractionation of lignin represents a simple and efficient way to regulate lignin chemistry and boost the quality of lignin carbon fibers, which paved an avenue to transform the bioeconomy and the sustainability of biorefinery and paper industry.