Characterization of Sodium Carboxymethyl Cellulose Aqueous Solutions to Support Complex Product Formulation: A Rheology and Light Scattering Study

Abstract

Sodium Carboxymethyl Cellulose (Na CMC) is used for its thickening and swelling properties in a wide range of complex formulated products for pharmaceutical, food, home and personal care applications, as well as in paper, water treatment and mineral processing industries. To design Na CMC solutions for applications, a detailed understanding of the concentration-dependent rheology and relaxation response is needed. We address this here by investigating aqueous Na CMC solutions over a wide range of concentrations using rheology as well as static and dynamic light scattering. The concentration dependence of the solution specific viscosities sp could be described using a set of three power laws, as predicted from the scaling theory of polyelectrolytes. Alternatively, a simpler approach could be used, which interpolates between two power law regimes and introduces only one characteristic crossover concentration. We interpret the observed behavior as a transition from the non-entangled semi-dilute to the entangled concentration regimes; this transition behavior was not observed in the solution structure, as determined using static light scattering. Dynamic light scattering revealed three relaxation modes. The two fastest relaxations were assigned as the 'fast' and 'slow' relaxation modes typically

Diffusion and Viscosity of Unentangled Polyelectrolytes

“…Boris and Colby identified significant deviations from the Fuoss law for NaPSS in deionized (DI) water, and after a careful review of literature data, they concluded that much (but not all) of the observed behavior could be attributed to artifacts related to shear thinning and/or salt contamination . Deviations to stronger power laws have also been reported for other systems. ,,− Recently, an extensive analysis of literature data for the viscosity of unentangled NaPSS , in salt-free water showed that the power law exponent of the specific viscosity with concentration is an increasing function of polymer concentration and agrees with the Fuoss law only for c ≲ 0.05 M. The origin of the concentration dependence of the viscosity–concentration exponent could however not be established as viscosity and diffusion data were in apparent conflict. ,,, …”

Capillary breakup extensional rheometry of sodium carboxymethylcellulose solutions in water and propylene glycol/water mixtures

“…According to the results of measurements by Lopez et al ., at high DS values, sodium carboxymethylcellulose is molecularly dispersed in water, and the scaling exponent assumes the value of 3.4. Generally, an increase in the power‐law exponent value above 3.4 suggests the presence of interchain associations in an entangled solution of Na‐CMC . The lower values of the power‐law exponent observed in this study in the concentrated regime may indicate that the PG/water mixture is a “poorer” solvent than pure water.…”

Diffusion and viscosity of non-entangled polyelectrolytes

“…Boris and Colby 23 identified significant deviations from the Fuoss law for NaPSS in DI water, and after a careful review of literature data concluded that much (but not all) of the observed behaviour could be attributed to artefacts related to shear thinning and/or salt contamination. 23 Deviations to stronger power-laws have also been reported for other systems 27,29,[83][84][85] . Recently, an extensive analysis of literature data for the viscosity of non-entangled NaPSS 25 in salt-free water showed that the power-law exponent of the specific viscosity with concentration increases with increasing polymer concentration, and agrees with the Fuoss law only for c 0.05 M. The origin of the concentration dependence of the viscosity-concentration exponent could however not be established as viscosity and diffusion data were in apparent conflict.…”