Abstract
Ethanol extraction of lignocellulosic biomass under mild conditions has re-attracted considerable attention since a light-colored lignin with low molecular weight can be obtained. Unfortunately, the yield of isolated lignin for the ethanol extraction process is very limited. To enhance the extraction efficiency of lignin from poplar, ultrasound was used to assist the ethanol extraction and the isolated lignin was analyzed in terms of structure features and functional properties. As expected, increasing the ultrasonic power and ultrasonic time led to higher lignin yields during the ultrasound-assisted ethanol extraction (UAEE) process. The chemical structure of the isolated lignin (UAE-L) was almost completely retained, the C-O (mainly β-O-4) linkages in the lignin only exhibited a slight decrease, while the C-C (β-β, β-5, and β-1) linkages were nearly unchanged. The UAE-L was light in color and had more phenolic hydroxyl groups, less carbohydrate impurities, lower molecular weight and narrower polydispersity as compared to the poplar MWL. The UAE-L could scavenge more 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH·), displaying a stronger antioxidant activity. Moreover, the UAE-L showed good UV-absorbing properties in both UVA and UVB regions. These results indicated that the UAE-L has great potential for replacing the commercial synthesized antioxidant and anti-UV ingredients.
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