Whiten Lignin-Based Sunscreen via Fractionation and Ultrasonic Cavitation

Lignin exhibits good potential in natural sunscreens, but its dark color is still an obstacle. Herein, a strategy combining ultrafiltration and ultrasonic cavitation is developed to whiten enzymatic hydrolysis lignin (EHL). Results show that fractions with the smallest molecular weight possess the lightest color due to the lower bulk density and fewer surface chromophores. The hydrophobic aromatic skeleton and abundant phenol and carboxyl groups endow the fraction with good dispersibility and reactivity. Oil chemical sunscreen actives are effectively emulsified and encapsulated via ultrasonic cavitation. As-prepared capsules have an average diameter of 269 nm and a whiteness index of −15, representing 71% and 63% whiteness improvement compared to EHL and EHL-based capsules. The capsule-based sunscreen approaches white even under a dosage of 10 wt %. The sun protection factor of the sunscreen reaches 96 and maintains good performance at both room and high temperatures.