Some limitations of continuous shear methods for the study of pharmaceutical semi-solids

Abstract

The limitations of the Ferranti Shirley viscometer are reviewed and discussed. An experimental study of four pharmaceutical materials indicates that the apparatus is restricted to a qualitative use for semi-solids because of effects due to evaporation, sweep time selection and shear fracture. When the above effects are gross, the rheograms demonstrate obvious peculiarities. If they are slight, they could escape unnoticed physically and yet lead to incorrect interpretation. The rheograms obtained for such materials are not reproducible for a once sheared sample and hence their quantitative interpretation would be meaningless. Transient tests or oscillatory studies are suggested as alternative methods of examination.