Light-colored lignin with high UV absorption for sunscreens by fractionation and bleaching

Abstract

Lignin, a versatile biopolymer, has a high UV-absorbing quality, which makes it a promising sustainable ingredient of sunscreens. However, its dark color has limited its application in cosmetics. To date, several methods of brightening lignin (e.g., bleaching) have been developed; however, most of them decrease its UV-absorbing activity. This work proposes a novel two-step treatment (fractionation followed by bleaching) for producing light-colored lignin with high UV absorption. Organosolv lignin was fractionated with methanol and subsequently bleached with NaOCl under mild conditions. The resultant lignin was characterized in terms of color, UV absorption, functional groups, and molecular weight. The dark technical lignin was successfully lightened, maintaining its high UV absorption property. When the light-colored lignin was blended with a base cream, the SPF value was considerably enhanced and became 9.52 at 3 % lignin, which is higher than those obtained with 5 % lignin reported in other studies. The ligninbased cream was also highly homogeneous and stable. In addition, cytotoxicity test using human skin cells demonstrated that the treated lignin was much more biocompatible than the untreated one. Overall, this study addresses significant obstacles to the development of lignin-based sunscreens, providing a promising path for effective, sustainable sunscreening agents that can reduce the environmental impact and skin irritation associated with conventional UV filters.