Physical Properties of Carboxymethyl Cellulose (I): Solubility, Conformation and Supramolecular Aggregation

Carboxymethyl cellulose (CMC), commonly used as the sodium salt (NaCMC) and also known as cellulose gum, carmellose or E466, is an ionic cellulose ether widely used in foods, pharmaceuticals, drilling fluids, detergents, paper products and lithium-ion battery slurries. Its physical properties depend strongly on the degree and pattern of substitution, which control crystallinity, water solubility, chain conformation, supramolecular aggregation and rheology. The aim of this article is to review current understanding of these relationships. We focus on how average degree of substitution and chemical heterogeneity determine whether CMC is molecularly dissolved or forms colloidal aggregates. A compilation of experimental results indicates that, for samples with approximately fewer than one carboxymethyl group per anhydroglucose unit, most chains are molecularly dissolved while a smaller fraction forms fringed-micelle aggregates. Block-like unsubstituted sequences promote crystallinity, aggregation, thixotropy, and physical gel formation. More uniformly substituted samples exhibit smooth shear-thinning behavior. We also discuss the methods used to characterize CMC, its historical development and industrial applications, and common limitations in the literature. We conclude by providing recommendations for measuring and reporting degree of substitution, molar mass, intrinsic viscosity, solubility, and aggregate content.