Extraction of cellulose nanocrystals with redispersion ability via deep eutectic solvents enhanced with nickel chloride hydrate

Cellulose nanocrystals (CNCs) are difficult to redisperse after drying unless chemical modification or adding additives has been adopted. The production, transportation and application of CNCs in large-scale are restricted owing to the poor redispersion ability. To this end, CNCs with redispersion ability were successfully extracted by nickel chloride hydrate enhanced deep eutectic solvent (Ni-DES), which is composed of choline chloride and oxalic acid dihydrate, from microcrystalline cellulose. C 2 O 4 2− and Ni 2+ are integrated with each other owing to the incorporation of deionized water at the end of Ni-DES extraction. As a result, the particles of NiC 2 O 4 ·2H 2 O are found on the surface of obtained CNCs. The NiC 2 O 4 ·2H 2 O particles, which can be removed by acid-washing, are beneficial to the redispersion of dried CNCs because they can prevent the formation of hydrogen bond during CNCs drying, as demonstrated by the results of SEM, XRD and size distribution. In addition, the results of FTIR, XRD, SEM, and TEM reveal that the crystalline structure, chemical structure, and microstructure morphology of CNCs are scarcely varied during the drying and redispersion. Nevertheless, the slight flocculation of CNCs is unavoidable during the drying and redispersion, which is responsible for the insignificant depravation in the size and size distribution of redispersed CNCs. Fortunately, the satisfied redispersion ability of CNCs is obtained by Ni-DES extraction. It is obvious that using Ni-DES for the extraction of redispersible CNCs can provide a potential strategy for improving the economic and environmental viability of CNC industrial production and application.