Condensation of Lignin in Dioxane-Water-HCl

Abstract

Black spruce sawdust, when treated batchwise, in accordance with the principles of the gel degradation theory, with dioxane: H₂O:HCl (90:8:1.8 by volume) at various extents of lignin solubilization, gave a series of lignin fractions. The undialyzed lignin preparations, characterized by Klason lignin, methoxy contents, microanalysis, and U.V. absorptivity, were found to be reasonably uniform in composition. Gel permeation chromatography with a combination of refractive index (RI) and Low Angle Laser Light Scattering (LALLS) detection gave fractions that qualitatively resembled those obtained by the degradation of synthetic model polymer gels. In efforts to quantitatively correlate molecular weights (M _w) of these lignins with the existing gel degradation models, however, the problems of lignin fluorescence, association and recondensation were encountered. During the batchwise dioxane:H₂O:HCl extraction of wood, irreversible recondensation of the lignin fragments took place, limiting analysis of the results in the context of the gel degradation theory, revealing however, a salient feature of delignification.