SHEAR-DEPENDENT RHEOLOGICAL PROPERTIES OF STARCH BENTONITE COMPOSITE GELS/

Rheological properties of starch/bentonite gels (5.3-8.2% solids, 0-10 0% starch) were investigated at sheer rates 0.0083-0.33 s(-1) (Brookfi eld viscometer). Prior to these measurements the strain introduced dur ing preparation of the gel was kept as low as possible. Under these co nditions six different types of structural units could be identified i n the gel: bentonite particles associated in a band-type structure; ba nds coated with starch polymers; bundles of bands interlaced and envel oped by starch polymers (strands), individual bentonite platelets disp ersed in a polymer matrix; starch polymer networks; and swollen granul es. A power-law model was fitted to the experimental viscosity data: m u(app) = K gamma(n-1). In all cases n was found to be less than 0.5. I ts value decreased with the ability of the structural components to re orient under applied shear. K was found to be proportional to the comp action and/or entanglement of the structural units. These trends in K and n were further confirmed by the index of thixotropy (IT) and compl ex modulus of shear elasticity (G) measurements.