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

Abstract

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 wereinvestigated. In method I the media pH was controlled by addition of NaOH solution. The effect of theoxidant concentration (sodium hypochloride, NaClO) on the final degree of oxidation and crystallinity ofthe samples was investigated. Conditions for obtaining an optimum balance between high crystallinityand degree of oxidation were selected from those results. In method II, pH was fixed by using a buffersolution. Electron spin resonance (ESR) spectroscopy offered direct information of the decay of TEMPOconcentration under these conditions. The kinetics of the reaction was determined, finding a direct cor-relation between these results and those corresponding to the decay of the NaClO concentration and theadvance of the CNC degree of oxidation. Differences found between the two methods were analyzed.