Depletion Effects and Stabilization of Pickering Emulsions Prepared from a Dual Nanocellulose System

Nonadsorbing cellulose nanofibrils (CNF) are shown to induce stabilization of dilute oil-in-water Pickering emulsions formed by interfacial adsorption of highly charged TEMPO-oxidized CNF (TOCNF). The correlative interactions that occur upon sequential addition of the two types of nanofibrils (TOCNF and CNF) afford control of the properties of the obtained emulsions. For instance, the emulsions undergo (1) creaming of nonflocculated droplets at low CNF concentrations, (2) destabilization by depletion flocculation at intermediate concentrations of the nonadsorbing CNF, and (3) stabilization by formation of a fibrillar network and gelation above a critical CNF concentration (∼0.15 wt %). The observed phenomena are reproduced in TOCNF-stabilized emulsions of varying droplet sizes (3.6, 6.9, and 11 μm). The interactions induced by the presence of CNF in TOCNF-based Pickering emulsions allow tailoring emulsion stability, most useful in fully green, all-cellulose foodstuff, cosmetic, and pharmaceutical formulations.