Kinetic study and real-time monitoring strategy for TEMPO-mediated oxidation of bleached eucalyptus fibers

The present work aims at glimpsing the rate-determinant process parameters of TEMPO-mediated oxidation of bleached kraft cellulose for developing kinetic models and real-time monitoring tools. This may contribute to the scaling up of this reaction, frequently used as precursor of the production of cellulose nanofibers. For this, the effect of temperature, TEMPO and NaBr contents, and surface area of the fibers was assessed by means of a total experimental batch of 18 combinations, monitoring the carboxyl content (CC) of the samples and the NaOH consumption during oxidation. The obtained data was used to calculate the kinetic constant as a function of the conditions, as well as correlating the CC with the NaOH consumption, obtaining a strong linear correlation between these parameters. It was found that similar correlations could be used regardless process conditions, except for the case of TEMPO, which was found to protect the fibers from depolymerization and, thus, having different behavior at increasing TEMPO contents. Overall, the obtained results in the present study reveal the suitability of upscaling TEMPO-mediated oxidation, as well as having a deeper understanding on how the key parameters involved in the reaction affect the reaction path and, thus, contributing to the industrial deployment of oxidized cellulose and nanofibers.