Periodate-chlorite oxidation for dicarboxylcellulose (DCC) production: activation strategies for the dissolution and visualization of oxidized groups distribution

There are different activation pathways for the oxidation of cellulose by the periodate-chlorite system: thermal activation, chemical activation and cellulosic pulp activation using chemical or mechanical pretreatments. This study aimed to compare the different possible activation methods applied on cellulose, focusing on their effects at the molecular scale (cellulose chain oxidation and degradation) and at the cell wall scale (visualization of oxidized groups locations). It is shown that the activation pathway has an influence on the relation between cellulose carboxylation and depolymerization. A method for analyzing the distribution of carboxyl groups at fiber surface and in the depth of the fiber wall was also developed, including sodium-to-silver ion exchange and SEM imaging with chemical contrast. Important differences in carboxyl group distribution were observed between the diverse activation treatments. Dissolution ability of oxidized PHK pulp at 3% in an alkaline aqueous solution was also assessed. The comprehensive comparison of the activation methods revealed that the combination of mechanical pretreatment and the addition of inert salt during the periodate stage, despite causing only slight oxidation activation, enhances the dispersity of carboxyl groups. This results in a higher dissolution ability in alkaline solvent while maintaining the cellulose DPv (viscosity-average degree of polymerization).