Rheology of Sodium Polyacrylate as an Emulsifier Employed in Cosmetic Emulsions

A set of emulsions containing sodium polyacrylate as emulsifier was prepared. The effect of pH, temperature, and polymer concentration on sample stability was studied. Stability of the sample was evaluated through rheology and the morphology techniques. The sample containing 2% (w/w) sodium polyacrylate exhibited more evident changes in storage G' and loss G '' moduli with respect to 1% and 1.5% (w/w) samples, evidencing a more structured elastic material, even at high temperatures at which a more stable sample is assumed. For most of the systems studied, the storage modulus (G') was always higher than the loss modulus (G '') which is attributed to the formation of a strong network arising from the polymer interacting with the oil and aqueous phases; the complexity of this network is related to the action of pH and temperature. These results reveal the conditions at which the polyacrylate offers the best advantages in industrial cosmetic applications, that is, pH levels near 6.5, with a 2% (w/w) polymer concentration and a temperature of 25 degrees C.