Viscosity of Aqueous Polysaccharide Solutions and Selected Homogeneous Binary Mixtures

Abstract

The viscosity (η) of dextran (Dex), methyl cellulose (MC), hydroxypropylmethyl cellulose (HPMC), κ-carrageenan (KC), alginate (Alg), and carboxymethyl cellulose (CMC) was measured as a function of the shear rate (γ̇) over a broad range of concentrations both in salt-free water and in 0.1 M NaCl. The concentration (C) dependence of the Newtonian viscosity (η0) was found to be universal for neutral polysaccharides and anionic polysaccharides in 0.1 M NaCl when C was multiplied with the intrinsic viscosity. The dependence was compared with theoretical predictions assuming dominant hydrodynamic or dominant topological interactions. The effect of electrostatic interactions was observed for anionic polysaccharides in salt-free water but not at higher concentrations. Master curves of the shear thinning behavior at different concentrations were obtained when η/η0 was plotted versus τ. γ̇, with τ being a concentration-dependent time that characterizes the onset of shear thinning. Binary mixtures of two neutral polysaccharides (MC and HPMC), two anionic polysaccharides (Alg and CMC), and a neutral (Dex) and anionic polysaccharide (KC) were investigated as a function of the composition and the total polysaccharide concentration. The behavior of the first two mixtures was similar to that of a single polysaccharide with an intermediate intrinsic viscosity. Significant synergy was observed for the third type of mixtures in salt-free water demonstrating the important effect of electrostatic interactions between charged polysaccharides at low concentrations even in concentrated solutions of neutral polysaccharides.