Oxidation and structural changes in NMMO-regenerated cellulose films

Carbonyl and carboxyl groups introduced by oxidative processes during production and purification of celluloses determine intra- and intermolecular interactions and thus application-related bulk and surface properties of cellulosic materials. We report a comprehensive approach to the quantification of carboxyl and carbonyl groups in cellulose films upon reconstitution from NMMO solutions. Measurements of the excess conductivity were combined with the determination of the molecular weight distribution, quantification of the carboxyl and carbonyl group content, crystallinity and film swelling in aqueous solutions. TEMPO-oxidized, NMMO-regenerated cellulose films were additionally analysed as a reference system for extensive cellulose oxidation. Our reported data demonstrate that dissolution of cellulose in NMMO results in the formation of onic acids, chain degradation, increased ionization and film swelling, whereas TEMPO-oxidation introduced carbonyl groups as well as onic and uronic acids causing a significantly increased charging, ion accumulation and swelling even at higher crystallinity.