DETERMINATION OF PHENOLIC HYDROXYL GROUP CONTENT OF MILLED WOOD LIGNINS (MWLS) FROM DIFFERENT BOTANICAL ORIGINS USING SELECTIVE AMINOLYSIS, FTIR, H-1-NMR, AND UV SPECTROSCOPY

Milled wood lignins (MWL's) were isolated from 42 plant species, the majority of them tropical hardwoods. The phenolic hydroxyl group content of MWL's was determined by selective aminolysis of the aromatic acetoxy groups, and the results were correlated with data of FTIR, H-1-NMR, and UV spectroscopy. Before FTIR and H-1-NMR spectroscopy the lignins were acetylated. MWL's isolated from tropical heartwoods show a tendency to higher phenolic OH group contents than those isolated from sapwoods. Various techniques are described, which are suitable to enhance resolution and to evaluate quantitatively the acetoxy bands of FTIR spectra. Good correlations were obtained from data derived from absorbances ("heights") of FTIR spectra without mathematical resolution enhancement. The H-1-NMR spectra calibrated by wet chemical OMe determination gave slightly better correlations than FTIR. UV ionization spectroscopy (DELTA epsilon(i) method) was the less satisfactory technique. Linear equations are presented which permit the calculation of phenolic OH contents from various spectroscopic data. The total hydroxyl group contents of the MWL's are also reported.