Characterization of fractionated hardwood kraft lignin with organic solvents

Hardwood kraft lignin was fractionated with various organic solvents to obtain more homogeneous lignin. Using organic solvent solubility, hardwood kraft lignin was clearly separated into six fractions (F1-F5 and FI) by molecular size. Compared with hardwood kraft lignin, the molecular weight (MW) distribution of each fraction was in a relatively small range and the MW of each fraction (F1-F5) gradually increased from Fl to F5. In addition, thermal stability of the fraction was improved by increasing MW and the resulting glass transition temperature also increased with increasing MW. As a result of Fourier-transform infrared (FT-IR) analysis, the functional groups of each fraction, except for FI, were very similar. The methoxyl group contents of fractionated lignins from F1 to F5 were 6.2 mmol/g, 2.4 mmol/g, 2.0 mmol/g, 1.9 mmol/g, and 1.6 mmol/g, respectively. Furthermore, the methoxyl group and phenolic OH group contents tended to decrease with increasing MW. It was confirmed by the result of pyrolysis gas chromatography/mass spectrometer (Py-GC/MS) analysis that there were many sulfur-bonded structures in the F1 fraction. © EBSCO Information Services 2018. All rights reserved.