Rheological properties of guar galactomannan and rice starch mixtures .1. Steady shear measurements

The effect of particulate inclusions, or 'fillers', on the rheological properties of a typical polysaccharide entanglement solution (guar galactomannan/water) have been studied. A number of equations have been proposed to describe the shear-thinning behaviour of 'random-coil' polysaccharides such as guar gum. However, on increasing particulate concentration the system becomes more rate-dependent at low shear rates and there is evidence of an apparent yield stress associated with this increase in particulate inclusions. In the present paper, this flow behaviour has been described with reasonable accuracy, by a yield stress modified Cross equation: eta = eta(infinity) + [eta(0X) - eta(infinity)]/[1 + (a gamma over dot(p)] + (tau(X)/gamma over dot) The use of such a model can lead to a prediction of the rheological behaviour of similar systems when the proportion of the relative components is known. The present study determines the effect of particulate and composite properties on the apparent zero-shear viscosity and yield stress of guar galactomannan and rice starch mixtures.