Kinetics of benzophenone-3 release from clay minerals or organosilicates for sun protection formulation

In this study, we evaluated the ability of three clay minerals and clay-like adsorbents, namely lipophilic organosilicates (OS_L), LAPONITE® and montmorillonite (MMT), to extend the duration and released amount of UV filter. With only 4 % of benzophenone-3 (BZ-3), it was possible to obtain new sunscreen formulations stabilized by intercalating BZ-3 within the lamellar structures of the three adsorbents. The kinetics of BZ-3 release was studied through a membrane-free method in sink conditions using four mathematical kinetic models. The kinetics demonstrated that BZ-3 was released from the three adsorbents in a continuous and homogeneous way when powders of BZ-3 and OS_L, LAPONITE® or MMT were combined at a similar dosage. We then focused on the effects of adsorbed BZ-3 on OS_L particles. The sun protection evaluation tests suggested that the formulation using BZ-3 and OS_L was executed accurately and efficiently. The F2 (OS_L-BZ-3) showed the most effective broad-spectrum formulation with a higher λc (371) and UVA/UVB ratio (0.57) comparatively to F1 (with only 4% BZ3). Rheological analysis of F2 (OS_L-BZ3) showed controlled viscosity, efficient spreadability, and enhanced structural integrity, which are key for uniform UV protection, stability, and consumer acceptability. The OS_L-BZ-3 formulation provided an increased protection range and improved sunscreen photostability with respect to current regulations.