Optimization of carboxymethylation reaction as a pretreatment for production of cellulose nanofibrils

We investigated the optimal reaction conditions for carboxymethylation as a pretreatment method for the production of cellulose nanofibrils (CNF). The influence of the reaction sequence, solvent composition, and presence of water in the reaction medium on the carboxymethylation of pulp was studied. We also investigated the effects of water in the reaction medium on CNF properties. The most effective carboxymethylation of pulp was achieved with non-solvent exchanged pulp and isopropanol. An increase in pulp consistency increased the carboxyl group content. The optimum reaction condition used only one-third the amounts of monochloroacetic acid and sodium hydroxide for the same level of carboxymethylation. The number of passes required for mechanical fibrillation of the pulp, the morphology and dispersion instability of CNF were all strongly influenced by the carboxyl content introduced during the carboxymethylation reaction. The number of mechanical treatment steps required to produce CNF decreased as the carboxyl content increased. Pulp with a high carboxyl content resulted in a more stable suspension due to the increased electrostatic repulsion between the fibrils.