Ionically crosslinked cellulose nanocrystals by metal nitrates for the preparation of stable emulsions with tunable interface properties

Abstract

AbstractBiologically extracted cellulose nanocrystals (CNCs) are rod-like and amphiphilic materials with surface-exposed (hydrophilic sites) and hidden (hydrophobic sites) hydroxyl groups. These physicochemical characteristics make CNCs suitable for use as emulsifying agents to stabilize emulsions. Stable oil-in-water emulsions, using sulfated (i.e., –$${{\text{SO}}}_{3}^{-}$$ SO 3 - ) CNCs that were ionically crosslinked with alkaline-earth (i.e., $${{\text{Mg}}}^{2+}$$ Mg 2 + ) or transition-d-block (i.e., $${{\text{Zn}}}^{2+}$$ Zn 2 + ) metal cations, were developed without the use of any synthetic surfactants or prior functionalization of pure CNCs with hydrophobic molecules. Various emulsion surface properties such as interfacial tension, surface charge, surface chemistry, as well as rheology were characterized. Ionically crosslinked CNCs (iCNCs) adsorbed at the interface of an oil and water and fortified the emulsion droplets (5–30 µm) against coalescence by lowering the interfacial tension from 65 mN/m (i.e., pure CNC mixture with oil) to 25 mN/m (i.e., iCNC mixture with oil) and reducing zeta potential with surface charge values (–30 mV to –10 mV), ideal to maintain droplet layer assembly at the water–oil interface. This study provided an alternative approach to achieve particle-stabilized and surfactant-free emulsions by using divalent metal nitrates to develop “clean” emulsion-based technologies for applications in many industries from agriculture to food to pharmaceuticals.