Synthesis of lignin based composites of TiO₂ for potential application as radical scavengers in sunscreen formulation

Titanium dioxide (TiO₂) is added in sunscreens due to its ability to absorb ultraviolet (UV) light. However, upon irradiation of UV light, reactive oxygen species particularly hydroxyl radical which can damage human skin will be generated. In this study, lignin/TiO₂ composites were employed to quench the hydroxyl radicals generated by the TiO₂. The lignin was extracted from oil palm empty fruit bunch (OPEFB) via kraft and soda pulping processes. The kraft lignin composite was labelled as KL/TiO₂ whereas the soda lignin composite was labelled as SL/TiO₂. The lignins and the composites were characterized by FTIR, UV spectroscopy, ¹³C NMR, SEM, EDX, and XRD. The relative hydroxyl radical production of composites and TiO₂ were compared through photo-oxidation of coumarin to 7-hydroxycoumarin as a test medium. The effect of types and amounts of lignin used were studied. The KL/TiO₂ composite showed the least radical production due to higher phenolic hydroxyl content of kraft lignin. The activity of the hydroxyl radicals will be quenched when it abstract hydrogen atoms from the phenolic hydroxyl groups.