| Abstract: | The rheological behavior of carboxymethyl starch aqueous systems has been studied under continuous and oscillatory shear conditions. The systems examined exhibited shear-dependent properties, typical of dispersions having a weak degree of particle aggregation. A transition in the rheological properties was observed with increasing concentration and/or decreasing temperature, as a consequence of formation of a three-dimensional continuous network in the disperse phase under rest conditions. The shear-dependent behavior changed from shear-thinning to plastic and a finite plateau appeared in the low frequency region of mechanical spectra. A rheological model was proposed for the correlation of both shear-thinning and plastic data, thus making possible an objective definition of the rheological transition. Oscillatory flow data confirmed the results obtained in continuous shear conditions, that is, the frequency dependence of the complex viscosity was almost parallel to the dependence of the steady shear viscosity on the rate of shear. Moreover, the high strain sensitivity of the viscoelastic quantities and their analysis in terms of relaxation spectra clearly indicated the moderate degree of connectivity of the structural network. © 1992 John Wiley & Sons, Inc. |
