Effects of aromatic units, linkages, and end-groups of lignin on its UV shielding properties and color

Lignin holds significant promise as an ingredient for broad-spectrum sunscreen. However, its ultraviolet (UV) absorption and color rendering remain unclear due to its structural complexity. This study systematically investigated the correlation between structural characteristics (aromatic unit composition, linkage and side-chain end-group) of different lignins originating from typical lignocelluloses, and lignin properties (SPF and color), as well as lignin-based sunscreens performance (UV shielding, color and photostability). Results show that lignin color is mainly influenced by the content of G aromatic units and bulk density, while UV absorption is positively correlated with the type and content of side-chain end groups. Five lignin fractions were prepared to further clarify how lignin's structure influences its UV absorption performance and color. Additionally, the influence was further explained by elucidating the molecular orbitals and energy levels of lignin's specific structure with theoretical analysis. These findings hold significant importance for the development of high-performance lignin-based sunscreens.