EPR spectroscopy applied to the study of the TEMPO mediated oxidation of nanocellulose

Two different methods of pH control were used in the synthesis of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) oxidized cellulose nanocrystals (CNC) and the reaction kinetics and degree of oxidation were investigated. In method I the media pH was controlled by addition of NaOH solution. The effect of the oxidant concentration (sodium hypochloride, NaClO) on the final degree of oxidation and crystallinity of the samples was investigated. Conditions for obtaining an optimum balance between high crystallinity and degree of oxidation were selected from those results. In method II, pH was fixed by using a buffer solution. Electron spin resonance (ESR) spectroscopy offered direct information of the decay of TEMPO concentration under these conditions. The kinetics of the reaction was determined, finding a direct correlation between these results and those corresponding to the decay of the NaClO concentration and the advance of the CNC degree of oxidation. Differences found between the two methods were analyzed.