Synthetic lignin derived from ferulic acid for UV-blocking sunscreen

Conventional lignin, a dehydrogenated polymer derived primarily from hydroxycinnamic alcohol monomers, exhibits relatively low antioxidant and ultraviolet (UV)-blocking activities due to its structural imperfection. Herein, we demonstrated that the dehydrogenated polymer of ferulic acid (an unconventional lignin precursor) (FAL) had excellent antioxidant and UV-blocking properties. Structural characterization showed that FAL contains abundant dihydrobenzofuran and butyrolactone structures, free phenolic hydroxyl groups, and cinnamic acid end groups. Such structural characteristics endow FAL with much higher antioxidant activity and broader and stronger UV absorptivity (especially UVA) than conventional lignins. Our investigation showed that FAL could significantly improve the UV-blocking property of commercial SPF30 and SPF50 and render a relatively light color. These versatile properties make the FAL a potential ingredient for application in sunscreen products. This work is enlightening not only for exploring better antioxidant and UV-blocking polymers from the dehydrogenated polymers of phenolic compounds but also for biosynthesizing more advantageous lignin in plants.