Lignin is the second most abundant and unique aromatic natural polymer in plants. It exhibits good UV-absorbing, antioxidant and biocompatibility due to its functional groups such as phenolic, ketone and other chromophores, thus making it an excellent candidate for the development of nature-inspired sunscreens. Experiments showed that a small amount of lignin could significantly enhance the UV-blocking performance of commercial sunscreens. The synergistic effect between lignin and chemical sunscreen was first observed. This effect was found to be even more obvious after UV irradiation. One of the main obstacles for developing lignin-based sunscreens is the dark color imparted by lignin. We demonstrated two effective methods to reduce the color. First method involves the modification of lignin through acetylation, followed by self-assembly in selective solvents to prepare uniform lignin colloidal spheres. An alternative way to whiten lignin is by exposing it to UV radiation in solvents producing peroxide. After radiation, the color could be reduced by 65%. Both whitening methods sacrifice the phenolic hydroxyl groups of lignin, which are not only responsible for scavenging free radicals, but also helpful for blocking UV radiation. In order to preserve the phenolic hydroxyl groups, lignin colloidal spheres were prepared without chemical modification and then blended with pure cream to develop lignin-based sunscreens. Sunscreen containing 10 wt% lignin colloidal spheres of about 50 nm exhibited sun protection factor (SPF) value of 15. Inspired by the high efficiency of acoustic cavitation for initiating the polymerization reactions, lignin/chemical sunscreen nanocapsules were successfully prepared by one-step high-intensity ultrasound. The lignin/chemical sunscreen nanocapsules present good photo, thermal, and storage stabilities. The SPF values of the creams containing 5 and 10 wt% lignin/chemical sunscreen nanocapsules reached 120 and 400 respectively, which are far higher than the SPF 60 exhibited by commercial sun cream containing &gt;30 wt% chemical sunscreens.

Fabrication of lignin nanoparticles for developing natural broad-spectrum sunscreens

255th National Meeting (2018)

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