Natural Sunscreens Based on Nanoparticles of Modified Kraft Lignin (CatLignin)

Commercial chemical sunscreens have a high content of synthetic ultraviolet (UV) actives that have caused widespread damage to marine ecosystems and may have adverse health effects in humans. In the present work, safer bio-based sunscreens with lignin UV absorbers were developed to address this issue. Partly demethylated and otherwise altered kraft lignins, the so-called CatLignins with abundant phenolic hydroxyl auxochromes and catechol units, outperformed regular kraft lignins as sunscreen UV absorbers in terms of sun protection factor (UVB-SPF) and UVA-UVB transmittance. Converting lignins to nanoparticles significantly enhanced sunscreen performance. The best lignin sunscreen, containing nanoparticles of hardwood CatLignin, had a UV transmittance of only 0.5-3.8% over the entire UVA-UVB region compared to 2.7-51.1% of a commercial SPF 15 sunscreen. Lignin-based sunscreens are particularly suitable for dark-tinted SPF cosmetics.