Sequential solvent fractionation of heterogeneous bamboo organosolv lignin for value-added application

Value-added utilization of lignin is affected by its heterogeneous nature. In this case, bamboo organosolv lignin was successively fractionated with organic solvents of increasing dissolving capacity (i.e., ether, ethyl acetate, methanol, acetone, and dioxane/water) to obtain homogeneous preparations. The starting lignin and the fractions obtained were compared in terms of molecular weight distribution and functional groups by a set of chemistry and spectroscopy technologies. It was found that the yield of the five fractions obtained was 2.80%, 39.85%, 18.64%, 23.38%, and 13.30%, respectively. The lignin fraction extracted with ethyl acetate contained homogeneous materials of low molecular weight whereas the lignin fraction extracted with acetone was composed of a mixture of medium and high molecular weight materials. As evidenced by sugar analysis, there was strong association between hemicelluloses and lignin in the preparations with different molecular weights. Spectroscopy analysis indicates that with increasing the dissolving capacity of solvent, the contents of methoxyl, phenolic, and aliphatic hydroxyl groups in the extracted lignin fractions were decreased. The lignin fraction extracted with ethyl acetate, having a high radical scavenging index (RSI), will be a good feedstock as stabilizer. The results above suggest that the sequential solvent fractionation provides a promising way to prepare lignin with homogeneous structure and good functional properties for potential application.