PHYSICOCHEMICAL STUDIES OF ALKALI LIGNINS. I. PREPARATION AND PROPERTIES OF FRACTIONS

Abstract

Alkali lignin was prepared by cooking periodate lignin with sodium hydroxide. Fractionation by gradual decrease of pH was not possible as most of the lignin was precipitated sharply at pH 4.4. Fractionation could be achieved by addition of non-solvents such as acetone, dioxane, or ethanol to an alkaline aqueous solution of the lignin, but the initial fractions when separated could not be redissolved. This difficulty was overcome by using barium chloride as a precipitant when all the fractions remained soluble. X-Ray analysis revealed no difference between the insoluble and soluble fractions.The intrinsic viscosity of the fractions ranged from 0.027 to 0.585 g−1 dl. Reduced viscosities were considerably increased at lower ionic strength indicating that the molecule was a polyelectrolyte. The fractions possessed nearly constant methoxyl content (13%), visible absorption (0.28 cm−1 l g−1 at 5460 Å), U.V. absorption (18 cm−1 l. g−1 at 2800 Å), neutralization equivalent (1.3 meq g−1), and electrophoretic mobility (−12.6 × 10−5 cm2 v−1 sec−1). The partial specific volumes of a high and a low molecular weight fraction were 0.63 and 0.68 g−1 ml respectively.