Green solvent pretreatment for enhanced production of sugars and antioxidative lignin from poplar.

A promising pretreatment mediated by biomass-derived deep eutectic solvent (DES) with choline chloride to lactic acid was implemented to overcome the recalcitrant structure of poplar sawdust for effective enzymatic hydrolysis and valorized lignin. Results showed the DES applied was strongly selective towards removal of lignin and xylan while preserving cellulose. Under the optimal pretreatment condition (DES ratio: 1:2, temperature: 130 °C, time:1.5 h), the glucose yield from enzymatic hydrolysis was 75.8%. Chemical and structure changes of recovered lignin were evaluated to gauge its valorization potential. It indicated that the recovered lignin possessed molecular weight (4000-6000 g/mol), low polydispersity (PDI < 2.0), low quantity of β-aryl-ethers with no recondensation, and an abundance of phenolic OH groups. The excellent antioxidant capacity of lignin demonstrated its great value as a polyphenolic antioxidant. Overall, this work demonstrated an emerging biorefinery technology method for effective fractionation and valorization of lignocellulosic biomass.