Self-Assembly of Light-Colored UV-Absorbing Lignin–Starch Microcapsules

The aromatic polymer kraft lignin (KL) is an effective UV absorber that has recently emerged as a promising natural candidate for UV radiation filters in cosmetics. However, despite the excellent UV-blocking performance of KL, its dark color owing to chromophores and low solubility in aqueous environments are significant bottlenecks to its use in practical UV-shielding applications. Herein, the intrinsic problems associated with the color and dispersity of KL were resolved by fabricating a composite matrix of KL with short-chain glucan (SCG), which was obtained from the enzymatic cleavage of amylopectin in waxy maize starch, to employ its white color and hydrophilic nature; the composite matrix was fabricated via self-assembly into spherical microcapsules without the need for any toxic solvent or chemical modifications. We utilized the characteristics of the intermolecular interactions between KL and SCG which enabled their solubility in the aqueous γ-valerolactone/double-distilled water binary solvent. Notably, the J-aggregation state of KL allows for the even distribution of KL within the composite, significantly improving the UV-blocking properties with a broad absorption range and a UVA/UVB ratio of 0.9 at the critical wavelength (λc) of 387 nm, which are sufficient for practical use as a UV-blocking filter.