Evaluation of behaviours of various size and shape zno powders in emulsions and their sun protection performance

ZnO is an active ingredient of commercial sunscreens and it protects skin from harmful UV radiation particularly in UVA. However, micron sized ZnO reflects and scatters the visible light, making the sunscreen appear white on the skin. According to previous studies, decreasing particle size to nanometer scale results in less scattering of visible light, leading to increase in transparency. However, nanoparticles can penetrate into the skin and also have a tendency to agglomerate in an unctrolled mmanner. The scientific objective of this study was to determine the effects of synthesis conditions on the production process of designed micron-size platelet-shaped zinc oxide with primary nanoparticles (MicNo) to ensure the UV filtration properties of ZnO nanoparticles while eliminating the nanoparticles' negative effects. Interrupted experiments were done at T1-T15 temperatures for 1-8 hours with 2 different zinc-sources such that the formation mechanism of MicNo could have been revealed. The tecnological objective of the study was to determine base formulation with thickeners for this designed MicNo particles to formulate a sunscreen. Furthermore, we compared the sun protection performances of designed MicNo particles with commercial ZnO powders in formulated sunscreens. It has been observed that MicNo particles dispersed in an aqueous xanthan gum thickener containing gel-like suspension and they are not settled down even after several months. Therefore xanthan gum was chosen as thickener for further formulation studies. Formulations with %0-%20 ZnO were prepared and sun protection tests were performed by an independent laboratory. Especially in the formulations with %20 ZnO, MicNo particles exhibited up to 2,5 times better sun protection factor while maintaining he higher transparency values with respect to commercially avaliable nano ZnO particles that are marketed as transparent UV filters.