A feasible approach efficiently redisperse dried cellulose nanofibrils in water: vacuum or freeze drying in the presence of sodium chloride

Cellulose Nanofibrils (CNFs) were exposed to a certain amount of sodium chloride (NaCl) before being subjected to two types of drying methods (freeze drying and vacuum drying). The effect of two drying methods on water redispersibility of CNFs was investigated by characterizing product morphology, particle size distribution, water stability, and surface chemistry. The results showed that vacuum drying was favorable for the redispersion of CNFs with NaCl resulted in more homogenous fibril structure with lower mean particle sizes and higher water stability. Fourier transform-infrared spectroscopy (FT-IR) and Energy-dispersive X-ray Spectroscopy (EDX) experiments indicated that vacuum drying at pH 8 was more conducive to complexation between Na+ and carboxyl, hydroxyl groups favorable for CNF redispersion. Furthermore, NaCl is cheap, and the process is very straightforward which does not require any organic solvents or hazardous chemicals. Therefore, vacuum drying with NaCl may be considered as a green and economically feasible method for preparation of water redispersible dried CNFs.