Flow Properties of Aqueous Solutions of Sodium Alginate

Abstract

The fiow properties of aqueous solutions of sodium alginate (Alg) were investigated and nonlinear viscoelasticity was mainly examined. The peculiar flow properties of the aqueous solutions of Alg were compared with the existing theories for non-Newtonian flow of concentrated polymer solutions and the experimental results of the aqueous solutions of methylcellulose. The non-Newtonian behavior of aqueous solutions of Alg was ebserved at shear rates lower than that calculated from Graessley's theory. This peculiar phenomenon was investigated from the relation between Graessley's characteristic times and the intermolecular interactions which are affected by the behavior of Alg in solution as a polyelectrolyte.A coaxial cylinder apparatus was onstructed to measure the normal stress in Couette flow. From the normal stress measurements, recoverable shear strain and fluid elasticity were obtained. As compared with aqueous solutions of methylcellulose, aqueous solutions of Alg showed remarkable fluid elasticity and behaved as Hookean body. ln aqueous solutions of Alg as well as so1utions of nonpolar polymers, the dynamic shear modulus was correlated with the normal stress difference in the low frequency and low shear rate regions, and the steady state shear compliance was inversely proportional to the second powers of concentration. The concentration dependence of normal stress coeMcient ceincided with that is predicted from Graessley's interpretation.