(424a) Study of Structural Characteristics of Lignin Fractions Obtained from Sequential Solvent Fractionation
Lignin, one of abundant polymeric materials in Earth, has heterogeneous and complex chemical structure, which can be big barrier for its valorization. Thus, recent researches of lignin valorization are interested in improving its homogeneity, and sequential lignin fractionation with organic solvents can be considered as one of the solution to overcome this problem. Because of different dissolving capacity of organic solvents, lignin can be separated as well as homogenized according to solvent fractionations. Therefore, the purpose of our study was to fractionate various lignins by molecular weight and analyze structural characteristics of them for their efficient utilization. In our study, milled wood lignin(MWL), soda lignin (SL), and organosolv lignin (OL) was fractionated successively with ethyl acetate (F1), methanol (F2), acetone (F3), and dioxane/water (95:5v/v, F4), and insoluble fraction was named for F5. The yields of each fraction of MWL were 7.7%, 26.7%, 9.2%, 56.4% with the absence of F5, whereas those of SL were 22.0%, 52.5%, 4.6%, 14.9%, 6.1%. In the case of OL, only F1, F2, and F4 were obtained 20.8%, 62.1%, and 17.1%. In GPC analysis, as dissolving capacity of solvent increased, its soluble fraction showed higher average molecular weight (Mw) in all lignins, only F5 of SL was not able to be analyzed due to its insolubility to GPC solvent. Methoxyl group contents of lignin fractions tended to decrease as compared with those of raw lignins, but didn't show any comparable tendency between them. Thermal degradation properties, determined by thermogravimetric analysis, showed that thermal stability of MWL fractions showed no specific differences between them, while that of SL fraction decreased as molecular weight increased. In the case of OL, thermal stability of F4 seemed to significantly decrease compared to other fractions. For detailed study of their structures, each fraction needs to be also introduced to other analyses such as DFRC, Pyrolysis-GC/MS, FT-IR and 2D-HSQC-NMR.