CHARACTERIZATION OF TOBACCO LIGNIN BY ANALYTICAL PYROLYSIS AND FOURIER TRANSFORM-INFRARED SPECTROSCOPY

Two milled wood lignins (MWLs) were isolated from tobacco leaves (laminae) and midrib material according to the Bjorkman procedure. Prior to MWL isolation, the material was extracted with cyclohexane/ethanol and hot water to remove extractives which could interfere with this isolation. MWLs were obtained with a yield of 0.03% (leaves) and 0.06% (midribs) based on dry pre-extracted material. FT-IR spectroscopy was used for quality control and classification of the isolates. Both preparations fulfilled the spectroscopic lignin criteria of a GS lignin with low syringyl content, although the isolates were not pure. Besides carbohydrate impurities, the lamina material, especially, was contaminated with nitrogen and fatty acid-containing substances. Proteins and cutin are discussed as probable contaminants. Both MWLs were characterized with quantitative pyrolysis-gas chromatography using a resistant heating instrument. Curie-point pyrolysis-gas chromatography/mass spectrometry and pyrolysis-mass spectrometry were used for additional characterization of both MWL samples. The results show that the tobacco MWL contains up to 22% carbohydrate-type impurities. Small amounts of alkaloids, proteins and lipids were also detected as contamination. Results of previous studies on mineral acid residues could be corroborated: tobacco lignin contains approximately 10% 4-hydroxyphenylpropane, 78-82% guaiacylpropane and 10-13% syringylpropane moieties.