Elucidate the difference of molecular structure of lignin from small-diameter bamboo

Although small-diameter bamboo represents a renewable biomass resource with high accessibility, systematic investigations into the molecular architecture of its lignin constituents remain limited. In this study, DES and ball-milling methods were employed to extract lignin from small-diameter bamboo and Moso bamboo, and the lignin structures obtained via these two methods were analyzed and characterized. The results show that the DES for extracting lignin is significantly more efficient than ball-milling. DES can promote the cleavage of the β-O-4 bonds in lignin, and subsequently, the lignin undergoes a condensation reaction, thereby increasing the phenolic hydroxyl group content and elevating the S/G ratio. For instance, in comparison with ML- Bm , DL- Bm exhibits a significantly reduced β- O -4 content of only 12.7%, while the phenolic hydroxyl group content reaches a high value of 6.23 mmol/g and the S/G ratio increases from 1.3 to 2.4. Furthermore, DES-extracted lignin exhibited enhanced molecular weight accompanied by an increased polydispersity index (Đ). The molecular weight of lignin exerts a more pronounced influence on the T g than does the hydroxyl group content. This work is of great significance for optimizing the lignin extraction process and its functional utilization, providing technical support for the upgrading of the bamboo industry and the development of the biomass economy. • Lignin was extracted from small-diameter bamboo by DES and ball-milling. • DES can promote the cleavage of β- O -4 bonds in lignin, thereby reducing its content. • DL- Bm has the lowest β- O -4 bonds content and the highest hydroxyl content.