Application of a factorial design to the study of the flow behavior, spreadability and transparency of a Carbopol ETD 2020 gel. Part II.

A factorial design (2(3)) is applied to study the influence of three of the components of a cosmetic gel (the concentrations of Carbopol ETD 2020, ethanol and glycerine) on flow parameters (Casson's yield value (tau(c)), Casson's viscosity (eta(c)) and apparent viscosity at 125 s-1 (eta(ap.) 125 s-1), spreadability, and transparency. The first-order polynomial equation allowed by the model suitably accounts for the tau(c) and spreadability. Both depend on the concentrations of Carbopol and ethanol, and tau(c) also depends on the ethanol-glycerine interaction. The model explains to a certain extent the complex relationships that are established between the components and that influence eta(c) y eta(ap.) 125 s-1. Transparency is independent of the Carbopol concentration and it is also thought to be independent of the ethanol concentration. In addition, a high linear correlation has been found between the tau(c) and spreadability and other viscoelastic parameters of the gels that were previously determined (Int. J. Pharm. (2001)). The application of the technique of experimental design has been shown to be a very useful tool for formulating gels.