Effects of Colloidal Silica on the Apparent Viscosity of White Petrolatum

Abstract

Three grades of colloidal silica (Cab-0-Sil CDL-5, M-5', and EH-5) of different particle size and specific surface were added to white petrolatum in concentrations of 0925%, O. 5%, 1.0%, .and 2. 0% by weight in an attempt to determine the effect of particle size and concentration of the silica on the rheological properties of the petrolatum. Rheological properties were determined with a modified Stormer viscosimeter. Increasing concentrations of silica within a particle size grade caused an increase of apparent viscosity of the petrolatum at almost all rates of shear. The effect of particle diameter on apparent viscosity was found not to be strictly in order of decreasing particle size, as was expected, although the largest particle size grade (CDL-5) was the least effective of the three grades used. A possible explanation for the anomalous results would be either that the initial dispersion of the Cab-0-Sil in white petrolatum was not complete due to the limitations of the ointment mill used, or that subsequent particle agglomeration took place. In general, the apparent viscosity at all shear rates increased with aging of the samples, an effect that probably indicates structural reformation of white petrolatum with time.