Fractionation of Alcell lignin by sequential solvent extraction

A prototype solvolytic lignin has been fractionated into three fractions by successive extraction with organic solvents of increasing hydrogen-bonding capacity. A comparison between the fractions and the starting lignin has been made in terms of methoxyl group content, fractionation yields, molecular weight distribution, alkaline nitrobenzene oxidation, and 1H and 13C NMR spectroscopy. The fractionation procedure was found to isolate fractions having distinct group functionalities and molecular weight distributions. In particular, the heterogeneity of ALCELL lignin is demonstrated from the data. A significant portion of this lignin, 27%, was found to be comprised of a very low molecular weight (Mw = 714 g/mol) fraction soluble in ether. This fraction had a lower polydispersity but a higher content of guaiacyl structures with saturated side chains than the higher molecular weight fractions