Insights into lignocellulosic waste fractionation for lignin nanospheres fabrication using acidic/alkaline deep eutectic solvents

Abstract

Facile fractionation of lignocellulosic waste into useable forms is essential to achieve a multi-product treatment process especially when the resulting lignin streams are expected for high-value materials valorization. Despite acidic/alkaline deep eutectic solvents (DESs) are promising solvents for lignocellulosic waste fractionation, there is little information about their differences in the fractionation and lignin extraction profiles. In this work, four DESs that were cataloged to acidic types (formic acid-choline chloride, lactic acid-choline chloride) and alkaline types (monoethanolamine-choline chloride, glycerol-K₂CO₃) were investigated to compare their abilities of bamboo waste fractionation. Physicochemical properties of these resulting cellulose, lignin and derived lignin nanospheres (LNPs) were also assessed. Results showed that DESs could selectively extract lignin via cleaving lignin-carbohydrate linkages and lignin ether bonds. Acidic DESs pretreatments were more effective in biomass delignification (~95.0 %), while alkaline DESs showed better polysaccharide retention. Glycerol-K₂CO₃ LNPs exhibited much smaller sphere size (50-100 nm) while acidic DESs LNPs showed higher thermal stability due to higher extent of lignin condensation. In addition, MEA-ChCl could introduce amine groups onto lignin hydroxyl. This work provided insightful information for tailoring technique routes to selective lignocellulosic waste fractionation, while facilitating the downstream applications of the obtained cellulose/lignin.

Keywords: Deep eutectic solvents; Delignification mechanism; Lignin nanospheres; Lignocellulosic waste.