Light Color Dihydroxybenzophenone Grafted Lignin with High UVA/UVB Absorbance Ratio for Efficient and Safe Natural Sunscreen

To solve the poor absorbance on ultraviolet A (UVA) radiations and dark color, alkali lignin (AL) was modified via atom transfer radical polymerization (ATRP) grafting of 2-4-benzoyl-3-hydroxyphenyl acrylate (BHA). The color of AL was whitened 86% and the UVA/UVB absorbance ratio of AL-g-BHA improved to 1.2, while the reported highest value was 0.9. The excellent UV-blocking performance of AL-g-BHA was demonstrated in sunscreen. Sun protection factor (SPF) value of the sunscreen containing 10 wt % of optimal AL-g-BHA reached 59. Nanoscale AL-g-BHA normal and reverse micelles (LBNM and LBRM) were fabricated to investigate the effect of microstructure on the sunscreen performance. When BHA chains were packed inside, the SPF value of sunscreen containing 10 wt % of LBNM decreased to 28. In contrast, the SPF value of sunscreen containing 10 wt % of LBRM with BHA chains distributing on the surface was up to 244. Both AL-g-BHA and corresponding micelles exhibited good biocompatibility.