Rheological properties of guar galactomannan and rice starch mixtures II. Creep measurements

Abstract

The effect of particulate inclusions, or ‘fillers’, on the rheological properties of a typical polysaccharide entanglement solution (guar galactomannan/water) have been studied. Earlier steady shear experiments have shown an apparent upswing of the viscosity-shear rate profiles at low shear rates, with higher filler concentrations (Rayment et al., 1995). In creep experiments, a low constant stress is applied to the sample. In the present paper, the creep experimental data have been compared to the steady shear flow behaviour fitted by the yield stress modified Cross equation (introduced in Part I of this series). The apparent zero-shear viscosity and yield stress parameters have been constrained in a number of ways in the model to establish the effect of these parameters on the modified Cross model. Although the creep data appears to alter the precision of the modified Cross equation, due to the low shear rates accessed, the apparent upswing of the steady shear data at low shear rates appear to be supported by the data described in this paper. This lends further credibility to the scaled filler models introduced previously.