Comparative and structural characterization of organosolv and alkali lignins from abaca fiber

In this study, one organosolv lignin preparation and two alkali lignin preparations were extracted with 95% ethanol, 1% NaOH from abaca fiber, and 17.5% NaOH from the fiber holocellulose, respectively. The three lignin preparations were compared using spectroscopic and degradative techniques. The very small chemical differences between the one organosolv lignin and two alkali lignin preparations were mainly that the organosolv lignin contained 3.70% neutral sugars and 1.88% uronic acids. The two alkali lignin preparations, however, were relatively free of neutral sugars and had lower uronic acid content. The weight-average molecular weights (M-W) of the lignins ranged between 2,160 and 3,340. All three lignin preparations showed a large proportion of syringyl units and fewer guaiacyl and p-hydroxyphenyl units. The lignin preparation B, extracted with 1% NaOH at 25 degrees C for 0.5 h, is mainly composed of beta-O-4 and beta-beta ether bonds, together with some beta-beta and beta-5 carbon-carbon linkages between the lignin structural units. Furthermore, it was found that p-coumaric acids and uronic acids were esterified to lignin, while ferulic acids are etherified to lignin molecules.