Key words: delignification, supercritical fluids, lignin, hydrogen peroxide, oxidation
Transformation of functional groups of lignin in the course of low-temperature delignification by hydrogen peroxide in the medium of supercritical (SC) CO2 during the preparation of pulp fiber semi-product was studied. Molecular-mass characteristics of lignins are affected by the oxidation. The analyses of functional groups demonstrate that both oxidation and substitution processes are taking place. Oxidation in SC-CO2 leads to the formation of water- and alkali-soluble lignin species, while the degree of oxidation of the latter is mild or low due to a relatively low oxidant consumption.