Study by ESR of kinetics TEMPO-mediated oxidation of nanocellulose

J. M. BUFFA; M. A. GRELA; MIRTA I. ARANGUREN; VERÓNICA L. MUCCI

Dübendorf

Workshop; Workshop COST Action FP1105; 2015

COST Action

TEMPO-mediated oxidation of cellulose nanocrystals (CNC) has been widely used as a selective oxidation of the C6 carbon to obtain carboxyl groups.  By this method, high degrees of oxidation (DO) can be obtained with only a catalytic amount of TEMPO and other inexpensive reagents, such as NaClO, NaBr and NaOH. The dependence of the DO with the amount of NaClO has been already reported [ref] as well as some theoretical approaches on the kinetic of the reaction [ref], but with no quantitative experimental information.In this work, we measured the evolution of TEMPO concentration through the reaction by the use of electron spin resonance (ESR) sprectroscopy. The correlation between this concentrations,NaClO concentration (determined by yodimetry) and DO (by conductimetric titration) is presented. By the use of reported procedure with optimized amounts of NaClO, we were able to obtain CNC with a DO of 26%, but for the kinetic measure we introduced a new way to study the reaction. Using a pH 10 buffer, we were able to eliminate the necessity of NaOH aliquots, maintaining the pH approximately constant, making possible for us to determine TEMPO concentration continuously. All three quantities determined (TEMPO and NaClO concentration and DO) were fitted using the same phenomenological constant in an exponential function.