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 ga lactomannan/water) have been studied. A number of equations have been proposed to describe the shear-thinning behaviour of 'random-coil' pol ysaccharides such as guar gum. However, on increasing particulate conc entration the system becomes more rate-dependent at low shear rates an d there is evidence of an apparent yield stress associated with this i ncrease in particulate inclusions. In the present paper, this flow beh aviour 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 suc h a model can lead to a prediction of the rheological behaviour of sim ilar systems when the proportion of the relative components is known. The present study determines the effect of particulate and composite p roperties on the apparent zero-shear viscosity and yield stress of gua r galactomannan and rice starch mixtures.