Methoxy substitution in the α-carbon of lignin side-chain inhibits its condensation for light-colored lignin extraction.

Lignin is a natural macromolecular within woody plant. Its integrally isolation is a challenging because the conventional preparation causes its dark brown. Herein, we reported a method for extracting light-colored lignin using a mixed solvent of 1,4-dioxane and methanol in acidic conditions, achieved by introducing methoxy groups onto the α‑carbon of lignin side chains via nucleophilic substitution. The reaction declined the condensed structures of the extracted lignin so that the color of the product was light-yellow in the whiteness index of 68.2 (CIELAB color parameters L*, a* and b* values of 73.0, 4.1 and 16.3, respectively). Light-colored lignin can cater to consumer preferences and enhance the acceptability of lignin-based sunscreens. During the extracting, the separated lignin kept very well structurally with high purity (98 % lignin content). The lignin exhibited excellent antioxidant activity and biocompatibility for application in sunscreen. When 4 % of the separated lignin was added to the sunscreen, the color of the lignin-sunscreen was close to the skin tone, and its sun protection factor (SPF) increased from 16 to 40. Incorporating 6 % and 8 % lignin into sunscreens resulted in SPF values of 51 and 61, respectively, demonstrating significant potential for light-colored lignin to partially substitute chemical agents in sunscreens.