TEMPO-mediated oxidation of microcrystalline cellulose: limiting factors for cellulose nanocrystal yield

Cellulose nanocrystal (CNC) production suffers, among other problems, from low yields. The focus of this study was to investigate the universal effect of charge density, centrifugation, and mechanical treatment as limiting causes of yield. Microcrystalline cellulose (MCC) was used as the starting material in order to eliminate the relatively arbitrary yield losses caused by the hydrolysis conditions. To disintegrate MCC into nanocrystals, high surface charge in the form of carboxylic groups was introduced by TEMPO-mediated oxidation, after which the material was mechanically treated, and separated into fine and coarse fractions. The fine fraction collected as supernatant after separation by centrifugation had a yield of 17-20% independent of the mechanical treatment method or time used. The particle sizes of these fractions did not significantly differ from each other, which raises questions on the efficiency of the mechanical treatment (sonication) and centrifugation in traditional CNC production. The results imply that radically new approaches in preparation are needed for truly meaningful increases in the CNC yield.