Insight into the self-assembly process of bamboo lignin purified by solvent fractionation to form uniform nanospheres with excellent UV resistance.

Lignin exhibits some antioxidant and UV protection due to its large number of phenolic hydroxyl and methoxy groups, which can be used in the field of sun protection. However, its complex macromolecular structure, high polydispersity, low solubility and deep coloration limit their development in the sunscreen field. In this work, we purified and separated lignin by solvent fractionation so that its phenolic hydroxyl content could be retained or even increased without modification. Consequently, by controlling environmental factors, lignin rapidly self-assembles into nanospheres without changing its structure, which not only achieves the standard of light-colored lignin but also meets the requirement of high sunscreen performance. It was measured that the lignin nanospheres formed by this method could meet more than 90% of UV blocking, especially for ultraviolet (UVA) fragments, when mixed with commercially available creams. It not only promotes the application of lignin in the field of sun protection, realizes the sustainable development of lignin, but also alleviates the problem of solid waste treatment and disposal. [Display omitted] • Lignin fractions with different molecular weight, functional groups and solubility were obtained by solvent fractionation. • The union of solvent fractionation and self-assembly avoids the modification of lignin and promotes the synthesis of NPs. • Lignin sunscreens block UV rays up to 90% or more, especially for the UVA portion. • Compared with other methods for reducing lignin color rendering, it is simpler and environmentally friendly. • 30g of bamboo chips can meet the synthesis demand of sunscreen and realize the resource utilization of solid waste. [ABSTRACT FROM AUTHOR]