Synthesis of Planar-Type ZnO Powder in Non-Nano Scale Dimension and Its Application in Ultraviolet Protection Cosmetics.

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.