Structure and properties of deep eutectic solvent lignin degraded by H2O2

In order to improve the reaction activity of lignin and increase its utilization rate. Lignin extracted from poplar wood powder by deep eutectic solvent was degraded with hydrogen peroxide (H2O2) and sodium hydroxide (NaOH) to obtain degraded deep eutectic solvent lignin (DES-lignin). The structures of DES-lignin and degraded DES-lignin were characterized by gel permeation chromatography (GPC), elemental analysis (EA), Fourier transform infrared spectroscopy (FT-IR), two-dimensional nuclear magnetic resonance spectroscopy (2D-HSQC NMR), and thermogravimetric analysis (TGA). The results indicated that the phenolic hydroxyl group of degraded DES-lignin increased by 39.62% and Mw and Mn decreased by 49.12% and 47.83%, respectively. C content decreased by 1.13%. The relative strength and S/G increased by 25.76% and 13.5%, respectively. The polymerization degree, β-O-4 linkages, and β-β linkages were decreased by 10.82%, 4.8%, and 4.2%, respectively. The residual residue increased by 8.3% at 800 °C. It showed that degraded DES-lignin had the advantages of strong activity, more reaction sites, narrow molecular weight distribution, less condensation structure, and thermal stability, which was more conducive to the high-value utilization of lignin.