Abstract:

Sunscreen products can reduce the damage caused by UV rays, reducing tanning, inflammation and skin cancer. However, chemical sunscreen is more toxic, and the existing physical sunscreen is not stable and has poor sunscreening effect. Therefore, the development of a sunscreen formula with sunscreen function and emulsion stability has attracted extensive attention. In this work, a Pickering emulsion stabilized with calcium alginate microspheres loaded with titanium dioxide nanoparticles （Alg@TiO₂ microspheres） was designed to be used as a sunscreen component. By emulsification-gel method, the Pickering emulsion stabilized by hydrophobic TiO₂ nanoparticles was used as a template, and the internal aqueous phase was gelled. The TiO₂ nanoparticles were fixed on the surface of calcium alginate microspheres. The prepared microspheres were characterized by scanning electron microscopy, elemental analysis, thermogravimetric analysis and wettability. The effects of oil/water ratio and microsphere content on Pickering emulsion were investigated, and the type of emulsion was explored, and the long-term storage stability was tested. The results of SEM and elemental analysis showed that the Alg@TiO₂ microspheres were spherical in shape and contained TiO₂ nanoparticles on the surface, and the size of Alg@TiO₂ microspheres was approximately 2-6 μm. TGA results showed that the content of TiO₂ nanoparticles in Alg@TiO₂ microspheres was 43%. Wettability test showed that the three-phase contact angle between the microspheres and oil and water was 120°. When the oil/water ratio was 1∶1 and the mass fraction of microspheres was 3%, stable Pickering emulsion was formed with the largest emulsion volume fraction and the smallest droplet diameter. The emulsion type was water-in-oil type （W/O type）. The emulsion remained stable after 100 days at room temperature, facilitating the shelf life of the emulsion cosmetics. In UV absorption tests, the Pickering emulsion showed superior sunscreen performance compared with the other three types of sunscreens, including a commercially available sunscreen. This Pickering emulsion has been demonstrated to be easy to be cleaned as shown in skin surface cleaning experiments. The Pickering emulsion with high stability and excellent sunscreen performance as a sunscreen component is expected to promote the application of Pickering emulsions in daily chemical industry and promote the research and development of new cosmetics.

Key words: sunscreen, TiO₂ nanoparticle, Pickering emulsion, calcium alginate microsphere