Investigation of Semisolid Lipophilic Preparations by Small Strain and Continuous Shear Viscometry and Their Application to Texture Profile

Abstract

The effects of grade variation of white soft paraffin on the rheological properties of paraffin ointment BP, simple ointment BP, and some nonpharmacopoeial paraffinic and emulsion preparations were investigated by continuous shear and creep viscometry. The creep curves were analyzed to determine discrete and continuous spectra of retardation times and transformed mathematically to determine dynamic parameters such as storage and loss compliances. The elastic properties of the white soft paraffins influenced the properties of preparations made with these paraffins. There was no general correlation between viscosity data for the preparations, possibly due to some specific interaction such as that described for hard paraffin and liquid paraffin. Dilution of white soft paraffin with liquid paraffin shortened the retardation times but did not significantly alter the type of retardation spectrum involved (bimodal), while emulsification radically altered the retardation mechanisms. The utility of the types of viscometry and various analyses of the creep curves is discussed in terms of correlation with sensory data for texture profile evaluation. It is concluded that small strain experiments are important in texture profile evaluation.