Novel amphiphilic cellulose nanocrystals for pH-responsive Pickering emulsions

[Display omitted] •Benzyl-polyethyleneimine modified cellulose nanocrystals have been developed.•The amphiphilic cellulose nanocrystals can prepare pH-responsive Pickering emulsion.•Both benzyl content of nanoparticle and pH value affect the stability of emulsion.•The emulsification-demulsification and oil recovery can be achieved by adjusting pH.•Emulsifiers can be recycled and reused. Development of a green, recyclable emulsifier for pH-responsive Pickering emulsion would be of great importance to many industries. To this end, a novel emulsifier, benzyl-polyethyleneimine modified cellulose nanocrystals (Ben-PEI-CNCs), was developed via the periodate oxidation of cellulose nanocrystals and reductive amination. Ben-PEI-CNCs possess pH-responsive amphiphilicity due to the existence of hydrophilic amino and hydrophobic benzyl groups. The Pickering emulsions stabilized by Ben-PEI-CNC2 and Ben-PEI-CNC18 are very responsive to pH changes, and adjusting the pH from 3 to 7 effectively triggers oil-water separation and emulsification. Additionally, cyclic testing establishes the robustness of this process. Overall, this study demonstrates that Ben-PEI-CNCs can promote the transition from a stable emulsion to an unstable emulsion by adjusting the pH, allowing the recovery of oil and the recycling of the emulsifier.