Cream-colored lignin nanoflowers via ethanol/water fractionation: Sustainable UV-blocking additives for sunscreen

Lignin possesses intrinsic ultraviolet (UV) shielding properties, making it one of the most promising natural materials for eco-friendly sunscreen development. However, the wide molecular weight distribution, complex structure, dark color, and poor dispersibility of industrial sulfonated lignin (LS) have hindered its commercial application in cosmetic formulations. In this study, a green and efficient antisolvent approach using ethanol was developed to simultaneously fractionate LS and fabricate lignin nanoflowers (LSNFs). The results revealed that the low-molecular-weight fraction, LSNF₃, exhibited a high density of oxygen-containing functional groups (phenolic hydroxyl content = 2.12 mmol/g), superior antioxidant activity (RSI = 6.45), and a significantly lighter appearance-with brightness and whiteness values increased by 253.5 % and 286.2 %, respectively, compared to LS. Molecular dynamics simulations further elucidated the self-assembly mechanism of nanoflower formation. Finally, LSNFs were incorporated into cream and SPF15 sunscreen formulations. The SPF value of 10 % LSNF₃/Sunscreen reached as high as 67.8, demonstrating a green and cost-effective pathway for the application of lignin in the field of sun protection.