Stabilizing effect of cetostearyl alcohol and glyceryl monostearate as co-emulsifiers on hydrocarbon-free O/W glyceride creams

The structure of a stable O/W cream is characterized by a more or less pronounced mixed crystal bilayer. The addition of co-emulsifiers in order to achieve a soft formulation often leads to a mixed crystal bilayer network of high viscosity and even phase separation. In order to ovoid this components of different chemical identities are used which often are not inert or harmless if they are absorbed. For this reason it seems to be interesting to use only components from one chemical family, e.g. to use only glycerides and their derivatives because in the case of absorption they are metabolized. The disadvantages of glyceride creams are, however, their low viscosity. The aim of this investigation was to find the optimum amount of co-emulsifier as consistency excipient for the basic formulation of an O/W glyceride cream. This was achieved by using differential scanning calorimetry; thermogravimetry, oscillation rheology and various stress tests. The amount of co-emulsifier used should not be too high, as it would crystallize increasingly during storage which gives the preparation an optical inhomogenity and a lack in softness which is needed for a suitable cosmetic acceptance. A slightly higher concentration than is necessary for the mixed emulsifier system can be advantageous, as the formation of a separate crystalline lipophilic network in the preparation increases its viscosity which will lead to a higher physico-chemical stability of the formulation. These results were obtained with the co-emulsifiers glyceryl monostearate (Imwitor 900), cetylstearyl alcohol (Lanette O), and PEG-20-glycerolstearate (Tagat S2) as O/W emulsifier. As oil phase a mixture of Miglyol 812 (caprylic/capric triglyceride) and Avocado oil was used.