RHEOLOGICAL PROPERTIES OF GUAR GALACTOMANNAN AND RICE STARCH MIXTURES- II - CREEP 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. Earlier steady shear experiments have shown an apparent upswing of the viscosity-shear rate profiles a t low shear rates, with higher filler concentrations (Rayment et al., 1995). In creep experiments, a low constant stress is applied to the s ample. In the present paper, the creep experimental data have been com pared to the steady shear how behaviour fitted by the yield stress mod ified Cross equation (introduced in Part I of this series). The appare nt zero-shear viscosity and yield stress parameters have been constrai ned in a number of ways in the model to establish the effect of these parameters on the modified Cross model. Although the creep data appear s to alter the precision of the modified Cross equation, due to the lo w shear rates accessed, the apparent upswing of the steady shear data at low shear rates appear to be supported by the data described in thi s paper. This lends further credibility to the scaled filler models in troduced previously. (C) 1998 Elsevier Science Limited. All rights res erved.