Lignin condensation inhibition and antioxidant activity improvement in a reductive ternary DES fractionation microenvironment by thiourea dioxide self-decomposition

Abstract

Deep eutectic solvents (DESs) as promising green solvents can efficiently remove the lignin component in lignocellulosic biomass. Herein, novel ternary DESs formed by choline chloride (ChCl), thiourea dioxide (TD) and lactic acid (LA) were designed to efficiently dissolve the lignin and reduce the condensation reaction through the existence of a reductive microenvironment in fractionation processing. Compared to binary DESs (ChCl/LA), ternary DESs (ChCl/TD/LA) can efficiently reduce the condensation degree (DC) of lignin and improve the biological activity of lignin. Under optimum conditions (a DES ratio of 1 : 0.5 : 0.5, 130 °C and 4 h), the proportions of lignin and hemicellulose removed amounted to 69.77% and 47.71%, respectively. In addition, the hydroxyl (3.80–4.63 mmol g⁻¹) and carboxyl (2.59–2.93 mmol g⁻¹) contents of ternary DES lignin were higher than those of binary DES lignin, and the antioxidant activity (IC₅₀ = 49.82–43.18 mmol L⁻¹) was also better.