PHYSICOCHEMICAL STUDIES OF LIGNINSULPHONATES: I. PREPARATION AND PROPERTIES OF FRACTIONATED SAMPLES

Abstract

High molecular weight ligninsulphonates were separated from other constituents of spent sulphite liquor by a method of dialysis allowing continuous removal of the dialyzates and their replacement by distilled water. The process was controlled by continuous analysis of the residue and dialyzate. The lower molecular weight ligninsulphonates in the dialyzates were separated from the carbohydrates by precipitating their barium salts with ethanol; four fractions corresponding to different times of dialysis were prepared in this manner. The ligninsulphonates in the dialyzed liquor were separated into four additional fractions by ultrafiltration through membranes of different pore sizes. The methoxyl, sulphur, and phenolic hydroxyl contents, neutralization equivalent weights, reducing powers, ultraviolet absorption spectra, diffusion coefficients, and number-average molecular weights of the eight fractions were determined. The molecular weights of the fractions range from 3700 to 58,000 but the integral molecular weight distribution curve indicates the presence of ligninsulphonates with molecular weights as high as 100,000.