The Use of Sodium Chlorite in Post-Oxidation of TEMPO-Oxidized Pulp: Effect on Pulp Characteristics and Nanocellulose Yield

Presence of aldehydes on cellulose nanofibers (alternatively called nanocellulose) produced from TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyle)-oxidized pulp could interfere with the grafting of selected compounds on the carboxyls group of the oxidized pulp or of the nanofibers produced from such pulps. A simple protocol, called post-oxidation, utilizing sodium chlorite under acidic conditions has been developed for TEMPO-oxidized native cellulose to oxidize the aldehydes to carboxyls. The chemical nature, degree of polymerization, nanocellulose yield, and brightness stability of the post-oxidized pulp was characterized and compared with those of pulps prepared by the post-oxidation methods published in the literature. A sodium chlorite charge of 10% was sufficient for the oxidation of the TEMPO-oxidized pulp, which had a residual aldehydes content of ∼100 mmol/kg. We had observed an increase in degree of polymerization, nanocellulose yield, and brightness stability due to post-oxidation. It was found that aldehyde groups contributed significantly to the brightness reversion and yellowing of the TEMPO-oxidized pulp.