Development of Methylene Bis-Benzotriazolyl Tetramethylbutylphenol-grafted lignin sub-microspheres loaded with TiO2 for sunscreen applications

Lignin serves as a promising Ultraviolet (UV) absorber within sunscreen industry. However, the commercial development of lignin-containing sunscreens faces challenges due to their low sun protection factor (SPF) and dark color in cosmetics industry. In this study, dual modifications on the chemical and physical structures of lignin were conducted to address these challenges. Initially, methylene bis-benzotriazolyl tetramethylbutylphenol (MBBT) was grafted onto alkali lignin (AL) through an atom transfer radical polymerization reaction, resulting in a polymer of AL-graft-MBBT₃ (AL-g-MBBT₃). The sunscreen prepared with 10% AL-g-MBBT₃ displays outstanding sun protection performance with a SPF of 42.93 and a light color with a color difference value (ΔE) of 45.6, in contrast to 10% AL with a SPF of 4.74 and a ΔE value of 49.5. Subsequently, AL-g-MBBT₃ was transformed into normal submicron spheres (AL-g-MBBT₃ N) and TiO₂-loading submicron spheres (AL-g-MBBT₃/TiO₂). The sun protection performances of 10% AL-g-MBBT₃ N@C and AL-g-MBBT₃/TiO₂@C sunscreens obviously surpass that of AL-g-MBBT₃@C sunscreen, achieving SPFs of 60.38 and 66.20, respectively. Additionally, there is a considerable improvement in the color of these sunscreens, with ΔE values of 41.8 and 36.3, respectively. These results provide valuable insights into exploring lignin's high-value applications in sunscreen.