DYNAMIC RHEOLOGIC MEASUREMENT OF THE INTERACTION BETWEEN XANTHAN GUM AND COLLOIDAL MAGNESIUM ALUMINUM SILICATE

An oscillatory shear device was used to measure the dynamic rheology of dispersions of xanthan gum (XG), magnesium aluminum silicate (MAS), and mixtures of the two. XG exhibited linear behavior up to about 50% strain, while the linear range for MAS was much more restricted. Storage modulus (G') values for MAS were nearly constant over a wide range of frequencies and the loss tangent was low, indicative of rigid structure. The structure of XG depended on concentration, and no yield value was evident. XG effectiveness in reducing sedimentation is ascribed to liquid structure and high apparent viscosity at low shear. The addition of XG to MAS dispersions extended the strain at which G' remained constant. The loss modulus (G") increased in value as a function of XG concentration while G' was generally reduced at low frequencies but raised at high frequencies. The loss tangent was increased. These changes point to a reduction in structural rigidity and an increase in flexibility.