High-internal-phase pickering emulsions stabilized by ultrasound-induced nanocellulose hydrogels

The present work applied nanocellulose hydrogels for the first time to stabilize high internal phase emulsions (HIPEs, oil-in-water) with a 75% oil phase. Nanocellulose hydrogels are easily fabricated by ultrasonic treatments based on the physical entanglement between slender nanocelluloses. This ultrasound-induced hydrogel had reversible gelation properties. Small-angle X-ray scattering measurements revealed that ultrasonic treatments reduced the interfibrillar distance of hydrogels from 86.81 to 6.05 nm with increasing ultrasonic time from 10 to 90 min. Hydrogels with small interfibrillar distances showed the stronger gel strength. The influence of the hydrogel/water ratio (ranging from 2:8–8:2, w/w) in the aqueous phase on the formation and stability of HIPEs was investigated. Stable HIPEs could be prepared using hydrogel ratios ranging from 3 to 7. Nevertheless, the gel behavior of HIPEs depended on the hydrogel ratio level. HIPEs with strong gel strength showed the better physical and storage stability. The stabilization mechanism was clearly exhibited by the three-dimensional image from confocal laser scanning microscopy (CLSM): gaps between oil droplets were fully filled with the continuous network structure which was re-formed by dispersed hydrogels due to its reversible gelation property. This continuous network structure effectively solidified the surrounding oil droplets, preventing oil droplet aggregation and coalescence. The findings could extend the applications of unmodified nanocellulose in emulsion formulations in the food and pharmaceutical fields.