Synthesis of lignin terpolymer submicron sphere for sunscreen application

Lignin is a natural anti-UV biopolymer, and the use of lignin as a sunscreen additive is an attractive strategy for lignin valorization. However, its dark color and the variation in anti-UV performance seriously hinder its application as a commercial sunscreen ingredient. In this study, modification of a commercial alkali lignin (AL) is undertaken to significantly improve its anti-UV performance and color. Two small molecule UV absorbers, dihydroxybenzopheone (UV0) and methylenebis-benzotriazolyl tetramethylbutylphenol (MBBT) were grafted onto the AL via atom transfer radical polymerization reaction, leading to a terpolymer, AL-g-UV0/MBBT (AUM). Subsequently, submicron spheres of AUM were assembled by the solvent shifting method. The physio-chemical properties of AUM and its submicron spheres were characterized. The results showed that the color difference value (ΔE) of AUM submicron spheres was significantly reduced to 16.73 from 72.21 with AL. Moreover, with the application of AUM spheres in sunscreen, the sun protection factor (SPF) was significantly improved to 46.2 at 10 % loading compared to 4.2 with AL at the same loading, and the ΔE was reduced to 45.59 compared to 65.86 with AL. This study provides useful information and insights into design and development of lignin-containing sunscreens.