A Rheological Study of the Effect of Bentonite on Heated Emulsions

Abstract

Summary The rotational viscometer having a variable speed drive can be used to give a viscosity curve expressed in fundamental units. Two viscosity curves which will characterise the consistency of a pharmaceutical cream base, at a given temperature, can be obtained in a reasonable time for control purposes. The consistency of autoclaved emulsions prepared with and without bentonite has been determined quantitatively and the results tabulated. Emulsions prepared without bentonite showed shear-rate thinning both before and after autoclaving. 5 A change in type of viscosity from shear-rate thinning to uniform plastic flow occurred when an emulsion containing bentonite was autoclaved. 6 The entire viscosity curve is necessary to characterise shear-rate thinning whereas uniform plastic flow can be characterised by two factors: “plastic viscosity” and yield value.