Composition-Dependent Viscosity and Properties of MCC/CNC Regenerated Cellulose Hydrogels Prepared Using TBAF/DMSO

Although microcrystalline cellulose (MCC) and cellulose nanocrystals (CNCs) possess the same cellulose backbone, it remains unclear whether they have similar effects on solution viscosity behavior in tetrabutylammonium fluoride (TBAF)/dimethyl sulfoxide (DMSO) and the properties of the resulting regenerated hydrogels. This study investigated the composition-dependent viscosity behavior of MCC/CNC solutions in TBAF/DMSO and the properties of the regenerated cellulose hydrogels. At 2.5% cellulose, the MCC solution achieved a maximum viscosity of 8.8 Pa·s at 2.5% TBAF, whereas the CNC solution reached 15.0 Pa·s at 5.5% TBAF. In mixed solutions, increasing the CNC content decelerated the viscosity increase, extending the time required for solution preparation and molding. After water-induced regeneration, the gel strength and cutting strength decreased from 70.8 to 33.6 N·mm and from 55.8 to 6.7 N·mm, respectively, as the formulation shifted from MCC-only to CNC-only. Conversely, the CNC-containing hydrogels exhibited higher optical transmittance than MCC-only hydrogels. Time-resolved photoluminescence measurements suggested composition-dependent local photophysical relaxation. Fourier-transform infrared spectroscopy revealed no formation of new covalent structures, while X-ray diffraction indicated that the regenerated hydrogels were predominantly amorphous. Thermogravimetric analysis revealed composition-dependent thermal degradation. These results demonstrate that controlling the MCC/CNC compositional ratio provides a means of balancing solution processability and regenerated hydrogel properties.