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Characterization of solvent-fractionated lignins from woody biomass treated via supercritical water oxidation

Ho Seo, Jin, Jeong, Hanseob, Lee, Hyung Won, Choi, Cheol Soon, Bae, Jin Ho, Lee, Soo Min, Kim, Yong Sik
Bioresource technology 2019 v.275 pp. 368-374
Quercus mongolica, biomass, fractionation, glass transition temperature, hardwood, lignin, moieties, molecular weight, oxidation, solvents, thermal stability
Crude supercritical lignin (SCL) extracted from hardwood (Quercus mongolica) treated via supercritical water (SCW) oxidation was subjected to sequential fractionation with four organic solvents; five lignin fractions (F1−F4 and FIN) were thus obtained. The molecular weight (MW) of the fractionated lignins gradually increased as fractionation proceeded. However, the content of methoxyl groups and phenolic hydroxyl groups tended to decrease with increasing molecular weight of the lignins. The functional groups of SCL and the fractionated lignins were very similar based on Fourier-transform infrared analysis. The syringyl/guaiacyl ratio (S/G ratio) of the fractionated lignins increased with an increase in the MW. The thermal stability decreased with decreasing MW of the fractionated lignins, and all fractions except for F1 had a maximum degradation temperature of around 360 °C. The glass transition temperature (Tg) of the fractions increased from 83 °C to 137 °C with increasing MW.