Solid acid facilitated deep eutectic solvents extraction of high-purity and antioxidative lignin production from poplar wood.

Pure deep eutectic solvents (DESs) system of choline chloride (ChCl)/Lactic acid (Lac) were demonstrated to be an effective strategy for extraction of lignin. In this study, two kinds of different promising solid acid (SA) with DESs were designed to promote the pretreatment of lignocellulose. The SA of phosphotungstic acid (HOPW) and iron bromide (FeBr) were introduced into DESs to extract poplar wood lignin and evaluate the antioxidant activity. It was found that 82.2% and 80.9% of lignin were obtained from poplar wood under HOPW-ChCl/Lac acid and FeBr-choline ChCl/Lac system with 4 h and 8 h, respectively. The lignin fractions with a high purity (>89%), low molecular weight (Mw 1800-2000 g/mol). Besides, the antioxidant activities of lignin fractions were better than butyl hydroxyanisole (BHA). Therefore, DES lignin has prominent antioxidant activity and could developed a potential natural cosmetics and food packaging.