SPECTROSCOPIC COMPARISON OF ORGANOSOLV LIGNINS ISOLATED FROM WHEAT STRAW

Glycerol lignin (LIG-Gly), dimethylformamide lignin (LIG-DMF) and mixed solvents (glycerol and dimethylformamide) lignin (LIG-Gly, DMF) were isolated from wheat straw by organosolv pulping. The physical characterization of three different lignins isolated under laboratory conditions from wheat straw was performed. The structures of lignins were studied by three non-destructive (FT-IR, H-1 and C-13 NMR spectroscopy) methods. The examination of FT-IR and 1H NMR spectra did not show changes in the main structure of lignins, but based on 13C NMR spectra of lignin obtained from glycerol (LIG-Gly), C-alpha, C-beta and C-gamma in beta-O-4 and carbon-carbon bonds, such as beta-beta, beta-5, were observed. In the case of lignin that was obtained from mixed solvents (LIG-Gly, DMF), the signals for C-beta and C-gamma in beta-O-4 and beta-1, beta-5 and 5-5 type structures were detected. In the C-13 NMR spectra, signals relating to the ester groups obtained from the linkage of p-coumaric acids, ferulic acids and an ether linkage from ferulic acid and lignin were observed. In the lignin obtained from DMF (LIG-D), no fractures occurred.