Oil-in-water Pickering emulsions stabilized by nanostructured cellulose: comparison of cellulose nanocrystals and nanofibrils

Abstract

Nanostructured celluloses, in the form of nanofibrils (CNFs) and nanocrystals (CNCs), obtained through TEMPO-mediated oxidation, by controlling the intensity of the process (changing catalyst concentration and processing time), were tested in the stabilization of Pickering emulsions, fabricated through high-pressure homogenization (HPH). Results showed that both CNFs and CNCs provided an efficient steric and electrostatic stabilization of the oil-in-water emulsions. Remarkably, the strong inter-droplet interactions, observed when CNFs were used as stabilizers, because of fibrils entanglement in the continuous phase, resulted in a 3D fibrous network emulsion, with higher viscosity than CNCs-stabilized emulsions, and higher tendency towards flocculation. However, the HPH treatment significantly affected the nanofibrils interfacial layer, promoting the emulsifying ability of CNFs, and increasing stability against coalescence. In contrast, CNCs-stabilized emulsions exhibited, along with lower viscosity, higher interfacial activity and emulsion stabilization capability, without any phase separation during 10 months of refrigerated storage. Remarkably, the HPH treatment did not significantly change the emulsifying ability of CNCs. Therefore, it can be concluded that nanocelluloses with tailored emulsifying properties can be easily obtained through the regulation of the process intensity of TEMPO-mediated oxidation of pulp cellulose, opening the way to the production of new ingredients for the food and cosmetic industries.