Colloidal aqueous dispersions of 2 to 5 % (weight) of hydroxypropylmethylcellulose (HMPC 4000) yield pseudoplastic mucilages and gels. Rotational viscosimetry in the cone-plate arrangement enables rapid and reproducible evaluation of the transitional region between pseudoplastic and plastic deformation, characterized by Herschel-Bulkley equation. To the traditional Ostwald’s two-parameter relationship it adds a third one, revealing a deviation from the beginning of the coordinates of the rheogram caused by the limiting yield stress. The obtained equations make it possible not only to estimate apparent and real viscosity, but also the area under the curve of the pseudoplastic rheogram. The actual precondition of integration, however, is the estimation of the limiting yield stress as the shear rate for the zero shear stress. Experimental estimation of the bottom margin for the integration of the area under the curve makes mutual comparability of rheograms possible. At a temperature of 32 °C, analysis of variance demonstrated a significant diminution of this area in the presence of about 2% of pilocarpinium chloride.

        Key words: rotational viscosimetry – mucilages and gels – pseudoplastic properties – rheogramme equation – pilocarpinium chloride