RESUMO
ZnO is one of the most widely used inorganic sunscreens, owing to its fine particle size and UV light shielding capability. However, powders at nanosizes can be toxic and cause adverse effects. The development of non-nanosized particles has been slow. The present work investigated synthesis methods of non-nanosized ZnO particles for ultraviolet protection application. By altering the starting material, KOH concentration, and input speed, the ZnO particles can be obtained in different forms, including needle type, planar type, and vertical wall type. Cosmetic samples were made by mixing different ratios of synthesized powders. The physical properties and the UV blockage efficacy of different samples were evaluated using scanning electron microscopy (SEM), X-ray diffraction (XRD), particle size analyzer (PSA), and ultraviolet/visible (UV/Vis) spectrometer. The samples with 1:1 ratio of needle-type ZnO and vertical wall-type ZnO exhibited superior light blocking effect owing to improved dispersibility and prevention of particle agglomeration. The 1:1 mixed sample also complied with the European nanomaterials regulation due to the absence of nanosized particles. With superior UV protection in the UVA and UVB regions, the 1:1 mixed powder showed potential to be used as a main ingredient in UV protection cosmetics.
RESUMO
In this study, a [0001]-plane planar-type ZnO ceramic powder material with a high aspect ratio ranging from 20:1-50:1 is synthesized using the electrolyte collected from zinc air battery power generation. This high aspect ratio may be due to the Zn(OH)2-4 anion dissolved in the electrolyte. The obtained planar-type ZnO exhibits excellent formulation stability and applicability, even when formulated as a cosmetic with a single inorganic ingredient. Compared to commercial ZnO or TiO2 powders, relatively better protection against infrared and ultraviolet (UV) radiation is realized due to its asymmetric characteristics, with a width of approximately 1 µm and thickness of tens of nm. The synthesized planar-type ZnO is mixed with nanosized ZnO or TiO2 commercial powders and formulated into various combinations to achieve a high UV protection rate and heat-blocking effect. In particular, the addition of planar-type ZnO to nanosized TiO2 powders increases the heat-blocking effect, and improves the applicability and formulation stability of the cosmetic formulation, despite the decrease in turbidity. Among all the ceramic powder combinations examined in this study, the best UV protection rate and heat-blocking effect are obtained when the synthesized planar-type ZnO is mixed with microsized and nanosized TiO2.
