Lignin Analysis by Permanganate Oxidation. II. Lignins in Acidic Organosolv Pulps

Abstract

Summary The permanganate oxidation method was used to analyze residual lignins in Norway spruce (Picea abies) organosolv pulps. The pulps were produced by ethanol water solvolysis catalyzed by 0.005M or 0.01M H2SO4 at 175 °C. Condensation reactions of residual lignin occurred at a significant rate when the ethanol volume fraction was 0% but not when it was ≥ 51 %. There was selective removal of uncondensed guaiacyl units when mixtures of 51 %, 76%, and 91% ethanol were used. The condensed units in the native lignin were less reactive and accumulated in the fibers. They constituted > 60 % of the C9 units by the time 80 % delignification was achieved. A limited amount of results are presented for a kraft pulp with hopes of enhancing the credibility of permanganate oxidation as an analytical tool for residual lignins.