Origin of hydrophilicity of cellulose hydrogel from aqueous LiOH/urea solvent coagulated with alkyl alcohols

Surface and structural properties of cellulose hydrogel prepared from LiOH/urea solvent with alcoholic coagulation were examined. As coagulants, alcohols from methanol to butanol were employed. Alcohol with high water miscibility (MeOH, EtOH, 1-PrOH, 2-PrOH, and t-BuOH) gave a nano-porous structure consisting of a fibrous network of cellulose, while alcohol with low water miscibility (1-BuOH, 2-BuOH, i-BuOH) showed aggregation of a fibrous structure because of large shrinkage during the coagulation process. Congo red adsorption measurement showed that an increase in the carbon number of alcohol brought about a less hydrophobic surface. This is likely to occur because the alkali/urea/cellulose complex was formed during the coagulation process in the case of ethanol, propanol, and butanol, leading to a higher crystalline content of cellulose II, the surface of which is thought to be highly hydrophilic.