Comparative analysis of the structures and properties of cellulose hydrogels prepared using different solvent systems

Abstract

Numerous studies have investigated the use of cellulose hydrogels produced via the dissolution-regeneration method. However, using different cellulose solvents, a comprehensive comparison of their structures and properties has yet to be reported. In this study, we prepared cellulose hydrogels using six different solvents: LiCl/N,N-dimethylacetamide (DMAc), 1-butyl-3-methylimidazolium chloride, NaOH/urea, ZnCl₂/AlCl₃, LiBr, and Ca(SCN)₂ solutions with the same cellulose concentration and evaluated their structure, transparency, and mechanical properties. Depending on the cellulose solvent used, significant differences in volume shrinkage were observed during regeneration and washing with water. The cellulose hydrogels prepared from LiCl/DMAc and NaOH/urea solutions showed the most significant volume shrinkage during regeneration and washing. Greater volume shrinkage resulted in a higher solid cellulose content in the hydrogel. A positive correlation exists between solid content and both elastic modulus and strength. The cellulose hydrogel prepared from LiCl/DMAc showed excellent mechanical properties: compressive modulus of 332 kPa, tensile modulus of almost 1000 kPa, and ultimate tensile strength of 523 kPa. The cellulose hydrogels prepared from LiBr and Ca(SCN)₂ solutions showed negligible volume shrinkage and lower solid content. However, the elastic modulus and strength of the hydrogels were relatively high despite their solid content due to the three-dimensional network structure composed of nanofibers. Moreover, the transparency was higher for the hydrogels prepared from LiCl/DMAc with amorphous cellulose and a uniform internal structure. These findings could assist in customizing the material properties of cellulose hydrogels.