High internal phase emulsion stabilized by cellulose nanocrystals and amine compounds

High internal phase emulsions (HIPEs) possess unique semi-solid characteristics and find extensive applications in food, medicine, and other fields. HIPEs stabilized by cellulose nanocrystals (CNC) not only show high safety and good stability, but also has good biocompatibility and biodegradability. However, Large amounts of CNCs are usually necessary to stabilize the HIPEs due to the rather strong hydrophilicity of the CNC surface. Herein, amine compounds were utilized to modify the CNC surface instead of commonly used ionic surfactants. The results indicate that hydrogen bonding serves as the main molecular interactions between amine molecules and the CNC surface. A combination of 0.1wt% CNC and 0.1 mM aliphatic primary amine could stabilize Pickering emulsions with an oil-water ratio of 1:1 (v/v). The usage of CNC is about 20-fold lower than that of emulsions without amines. When combined with 1 mM aliphatic primary amine, stable HIPEs with an oil-water ratio of 8:2 (v/v) were formed, with a stability exceeding 6 months. All the HIPEs stabilized by CNC and amine compounds exhibit a solid-like structure dominated by elasticity. With the synergistic effect of CNC and amine compounds, the commercially available olive oil, soybean oil, and canola oil can all form stable emulsions. In addition, porous materials were successfully prepared by freeze-drying the prepared high internal phase emulsions. The present work reveals that HIPEs can be well stabilized by CNCs and amines at very low concentrations through hydrogen bonds. The results are also inspirable to develop eco-friendly HIPEs in cosmetics and food science.