Physicochemical structure characteristics and biological activities of low temperature EDA/urea pretreated lignin

For high-value utilization of low temperature EDA/urea pretreated lignin (EUL), its physicochemical structure characteristics and biological activities were demonstrated. After pretreatment, the UV absorption of lignin was dramatically improved, indicating stronger UV resistance potential. Molecular weight and polydispersity index of EUL were significantly reduced from 2318 to 1421 g/mol and 1.44 to 1.20, respectively. The ester bond in lignin was broken due to EDA reaction with lignin carbonyl group and the C-H stretching vibration absorption strength of hydrophobic alkane in aromatic methoxy group and methyl and methylene in side chain was increased at 2852 and 2923 cm-1, suggesting that the hydrophobicity of lignin was improved. EUL exhibited the highest DPPH scavenging activity and Staphylococcus aureus inhibitory properties. It is speculated to be applied as novel UV protection, antioxidant and antibacterial agent in daily life. This research will lay a theoretical foundation for high-value utilization of low temperature EDA/urea pretreated lignin.