Multibranch Strategy To Decorate Carboxyl Groups on Cellulose Nanocrystals To Prepare Adsorbent/Flocculants and Pickering Emulsions

A simple multibranch strategy was employed to increase the carboxyl contents on the cellulose nanocrystal (CNC) surface. The effects of various sequential grafting of ascorbic acid or citric acid on the morphology, microstructure, thermal stability, dye adsorption capability (methylene blue), and coagulation–flocculation capacity (model kaolin suspension) of the functionalized CNCs were investigated. Cellulose nanocrystals with multicarboxyl groups (CNC-g-AA-g-CA) showed better thermal stability (Tmax = 359.3 °C), and possessed the highest carboxylic groups of 4.073 mmol/g, which led to a high absolute ζ potential value up to 47.7 mV. Furthermore, the CNC-g-AA-g-CA exhibited excellent coagulation–flocculation capability to kaolin suspension with a turbidity removal rate of 91.07% and good cationic dye (methylene blue) removal rate of 87.8%, indicating that the CNC-g-AA-g-CA can be used as excellent adsorbent and efficient flocculants. In addition, CNC-g-AA-g-CA have good stabilizing effects on soybean oil/water Pickering emulsions, and the resultant Pickering emulsion volume can remain for 30 days or longer.