Fractionation of ALCELL(R) 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 H-1 and C-13 NMR spectroscopy. The fractionation procedure was found to isolate fractions having distinct group functionalities and molecular weight distributions. In particular, the heterogeneity of ALCELL(R) lignin is demonstrated from the data. A significant portion of this lignin, 27%, was found to be comprised of a very low molecular weight (M(w) = 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.