Skin exposure to an appropriate amount of sunlight allows for vitamin D synthesis, thus strengthening the bones. However, excess exposure to sunlight can have a negative effect on the skin because of ultraviolet(UV) light. Recently, the destruction of the ozone layer has led to an increase in the amount of UV rays that reach the surface of the earth; and its negative effects such as corneal burn, cataract, and skin cancer have been widely discussed.
Zinc oxide has a high refractive index and high UV light scattering; therefore, it is frequently used in sunscreen cosmetics. However, these cosmetics could have problems including grainy texture, white effect, and decreased photocatalytic activity caused by the high composition of inorganic powders such as zinc oxide. To overcome these regulations and develop a better sunscreen cosmetics, zinc oxide coated with fatty acids, amino acids, lecithin, silica, and alumina has been used.
In this study, we aimed to develop a new composite powder to block UV rays that cause photoaging. We used micro sized zinc oxide, widely used in the cosmetics industry, coated with silica, frequently used for industrial purposes using sodium silicate. Hydrothermal method with sodium silicate and acid hydrolysis were used to coated silica. The process variables for the production of silica coated zinc oxide included the type of acid catalyst, pH, molar ratio of zinc and silicon, volume of solvent, reaction temperature, and reaction time. The physical and chemical properties of silica coated zinc oxide particles were analyzed by XRD, FT-IR, XPS, EDS, SEM and PSA.
Furthermore, we assessed the UV protection effect of the composite powder using UV-Vis and In-vitro test. We subjected the newly produced composite powder to user test to determine the advantages for practical use of this powder as a cosmetics, comparing with uncoated zinc oxide. The results show that the composite powder has a high UV protection effect, sensory feeling, adhension feeling, and spreadability for use in cosmetics.