Rheological behavior of sun protection compositions during formulation

Abstract

Rheological properties of cosmetic products are related to the products’ sensory attributes and to performance. In literature there is a lack of information on the influence of physicochemical interactions during processing of complex systems. This study is focussed on the interactions between the ingredients of cosmetic compositions during formulation in respect to their flow behavior. The rheological behavior of model cosmetic compositions based on polyvinyl alcohol solutions and containing natural plant extracts in glycerol and olive oil, UV screens (TiO2), synthetic UV absorber, emulsifier (Carbopol 2050), preservative (Bronopol) and fragrance was studied. The flow properties of compositions containing natural UV absorbers were compared to those of compositions with synthetic ones. All the compositions exhibited shear thinning rheological behavior that can be described by the power-law rheological model. It was proved that the emulsifier’s addition thickens the compositions; the addition of Bronopol leads to slight degree of thixotropy avoided by pre-shearing the samples for one minute. The fragrance addition in EtOH solution lowers the composition’s apparent viscosity; the addition of fine TiO2 as UV-screen even in quite tiny quantity of 0.2% mass increases the consistency of basic 10% PVA samples, lowering in the same time the flow index. The compositions containing glycerol extracts are more stable than those with olive oil extracts and they preserve their properties longer.