Lignin: A Review on Structure, Properties, and Applications as a Light-Colored UV Absorber

Lignin is a promising UV-shielding material to substitute the synthetic absorbers in a composite due to its excellent UV-shielding property. The chromophores group of lignin is responsible for the UV-shielding property of composites, but it brings an undesirable dark color. This perspective is the first to review the recent progress on fabricating light-colored UV-shielding composites that contain lignin; we provide a clear picture of the concept of light-colored UV-absorbing lignin composite materials that can be used in food packaging, healthcare products, and solar panel protection. The UV-absorbing and photostability mechanisms are introduced by correlating UV absorption with intrinsic factors, like phenolic substructures and molecular weight of lignin. Extrinsic factors that affect the UV-shielding properties and color of lignin, such as the extraction process, chemical modification method, and obtained size of lignin, are also systematically discussed in this perspective. By summarizing recent studies on the synergetic effect between the lignin and the second constitute materials, this perspective discusses the benefits of lignin to the composite's overall properties, such as stability under UV radiation, mechanical property, dispersity, and water permeability.