Calcium ion-mediated ionic cross-linking of carboxymethyl cellulose: Concentration-dependent structural evolution and physicochemical properties

To address the performance limitations of carboxymethyl cellulose (CMC), This study investigated the cross-linking of CMC with varying concentrations of anhydrous calcium chloride (CaCl₂) and the resulting effects on the structural and physicochemical properties of CMC. It was demonstrated that Ca²⁺ chelated with the carboxylate groups (-COO^-) of CMC chains, thereby yielding a physical ionic cross-linked network. Crosslinking transformed CMC from a crystalline to an amorphous structure, resulting in a rougher and more porous surface. As the calcium chloride concentration increased, the particle size of the cross-linked CMC samples increased, the apparent viscosity decreased, and thermal stability improved significantly. At a CaCl₂ concentration of 2.0%-2.5%, the samples exhibited ideal physicochemical properties and structural integrity, whereas 3.0% CaCl₂ concentrations led to excessive cross-linking and local aggregation. Steady-shear and dynamic rheological characterization based on apparent viscosity (η), storage modulus (G'), and loss modulus (G″) further confirmed concentration-dependent differences in structural stability under dynamic shear conditions. These findings highlight the importance of controlling calcium chloride concentration for tailoring CMC properties in practical applications.