Flow Properties of Lambda Carrageenan in Aqueous Systems

Abstract

Small amplitude oscillatory and steady shear measurements at 25°C were used to inves‐ tigate the rheological behavior of λ‐carrageenan solutions at pH 7.0 ± 1.0 without and with added sodium counterion. The dynamic moduli, G′(ω) and G″(ω), show the typical behavior of macromolecular solutions in which the viscous character predominates. The steady shear flow exhibits a Newtonian zero‐shear viscosity (η0 ) region followed by a shear‐thinning zone. Viscosity data can be well described by the Carreau‐Yasuda model. Without added Na+ , the intrinsic viscosity, [η], and the critical overlap concentration, C*, are 204 dL/g and 0.21%, respectively. With 20 mmol/dm3 Na+, [η] = 14.7 dL/g and C* = 0.38%. For concentrations below C*, the viscous character is more sensitive to the presence of added Na+ , and the opposite occurs when the concentration exceeds C*. The dynamic moduli and viscosity increase with the increase of polysaccharide concentra‐ tion, but they decrease with added Na+ , confirming the polyelectrolyte nature of λ‐carra‐ geenan. Empirical shift factors were used to obtain master curves for the dynamic moduli and apparent viscosity for different polysaccharide and added Na+ concentrations