Rheological Properties and Gelation Behavior of Chitosan in a Weakly Alkaline NaHCO₃/Urea Aqueous Solution

Sustainable polymer materials derived from renewable resources have become increasingly important in addressing environmental challenges. Chitosan, a derivative of chitin, offers exceptional potential due to its unique biological and physicochemical properties. However, its practical application has been limited by the harsh conditions typically required for dissolution and processing. Here we demonstrate a novel approach using NaHCO3/urea aqueous solution as a weakly alkaline solvent system that enables efficient chitosan processing under mild conditions. Through comprehensive rheological analysis, we reveal that the sol–gel transition of chitosan in NaHCO3/urea aqueous solution is governed by the synergistic interplay of hydrogen bonding, hydrophobic interactions, and chain entanglements. The gelation behavior exhibits strong dependence on chitosan concentration and molecular weight, with higher values promoting robust network formation at lower temperatures. Notably, we discover a reversible sol–gel transition mechanism that enables precise control over material properties through temperature modulation, while maintaining long-term stability despite modest changes in molecular characteristics during storage. These findings advance our understanding of polysaccharide self-assembly in weakly alkaline media and establish a new paradigm for developing controllable chitosan-based materials under environmentally friendly conditions.