Acidified ZnCl2 molten salt hydrate systems as hydrolytic media for cellulose I and II nanocrystal production: from rods to spheres

Abstract Exploring environmentally benign and economic methods for the preparation of nanocelluloses with controllable morphology would promote their industrial production and utilization. Herein, cellulose I and II nanocrystals (CNC I and CNC II) of rod and sphere shapes were prepared directly from microcrystalline cellulose (MCC, cellulose I) via treatment by acidified zinc chloride molten salt hydrates. Upon adding a small amount of HCl (0.50/0.75/1.0 M) to ZnCl 2 (55/60/65%), the levels of cellulose swelling and hydrolysis could be tuned. Rod-like CNCs I (length: 181.3–279.3 nm) were obtained with 55% ZnCl 2 . Rod-like CNCs with size reduction along with spherical CNCs were produced as ZnCl 2 concentration increased to 60%. Further raising the ZnCl 2 concentration to 65% resulted in CNC II with exclusively spherical shape (diameter: 25.8–292.3 nm). Under the same ZnCl 2 concentration, CNCs produced with high HCl concentration exhibited improved crystallinity (up to 68.4%) and thermal stability (T max up to 343.5 °C). Furthermore, spherical CNC II displayed excellent suspension stability and emulsifying ability to stabilize oil/water Pickering emulsions. The best one stabilized 26% more emulsion volume than the commercially available CNCs and the emulsions showed shear and heat stability. Therefore, this study provides a sustainable method for production of CNCs with tailored characteristics and broad application potentials. Graphical abstract