Behavior of Some Rheological Modifiers Used in Cosmetics Under Photocatalytic Conditions

Abstract

This work studies the photocatalytic degradation of some water‐dispersed rheological modifiers upon UV irradiation of suspended TiO₂, an inorganic pigment used as sunscreen in solar creams and gels. The photocatalytic activity of titanium dioxide is a matter of concern in the field of cosmetics, since it causes the undesired photoinduced degradation of organic compounds. The glyceryl polymethacrylate + propylene glycol Lubrajel® DV showed a lower decrease in viscosity than cellulose derivatives upon irradiation in the presence of TiO₂, most likely due to higher stability under photocatalytic conditions. As a consequence, use of Lubrajel instead of modified cellulose is preferable when the photocatalytic stability of the rheological modifier is an important issue. Moreover, the degradation of phenol and salicylic acid, chosen as model organic molecules, was studied in the presence of both TiO₂ and the modifiers under illumination. The purpose was to assess the photocatalytic activity of titanium dioxide under conditions simulating those of the real cosmetic product. The presence of the rheological modifiers protects both phenol and salicylic acid from photocatalytic degradation.

Keywords:

• Photocatalysis
• Photochemistry
• Rheology
• Liporamnosan®
• Methocell®
• Natrosol®

Acknowledgments

We are indebted to Prof. Ezio Pelizzetti for useful discussion and precious suggestions and to an anonymous referee for his helpful comments on the manuscript.