High-value utilization of kraft lignin: Color reduction and evaluation as sunscreen ingredient

Dark color of lignin puts brakes on its development as sunscreen ingredient. In order to address this issue, the color of lignin was whitened by facile and economical approach via solvent fractionation and follow-up acetylation. After the two-step treatment, the color of lignin was highly lightened by 313.5% owing to the separation of dark-colored condensed structures and the blocking of free hydroxyls. The UV absorbability of the light-colored lignin was investigated, which indicated that the UV absorbance of the light-colored lignin are not as strong as commercial sunscreen actives under certain wavelengths, however it presented broad-spectrum absorbability and obvious synergistic effects with the commercial sunscreen actives. Based on that, lignin-based sunscreen was prepared by blending light-colored lignin with an SPF15 lotion, and the SPF of the as-prepared lignin sunscreen was boosted from 15.3 to 75.2 under a lignin addition amount of 8%. The as-prepared lignin sunscreen is stable enough under UV irradiation and exhibits outstanding color performance, which make it possible to satisfy the daily requirement of consumers. Briefly, an effective approach was demonstrated in this work to prepare light-colored lignin, which makes lignin a green alternative to replace synthetic sunscreen actives and imparts lignin potentials in cosmetics applications.