Nanocomposite hybrids of cashew apple bagasse-derived lignin with photoprotective properties for sunscreen applications

Abstract

Prolonged exposure to ultraviolet (UV) radiation can cause significant damage to the skin and immune system. There has consequently been an increasing emphasis on the development of biodegradable and sustainable materials that offer UV protection, reflecting increased awareness of health and disease prevention. Due to its high concentration of phenolic groups, lignin has emerged as a promising candidate for natural UV protective materials. This study therefore aimed to produce nanocomposites of lignin from cashew apple bagasse, due to its wide availability and high lignin content, combined with zinc or titanium oxides for sunscreen application. Fourier transform infrared (FTIR) spectroscopy and X-ray analysis confirm interactions between lignin and zinc/titanium oxides. The resulting nanocomposites are stable, as indicated by their zeta potential (−32 mV to −48 mV). Lignin nanocomposites (LigZnO and LigTiO2) exhibited similar antioxidant activity, though lower than that of lignin alone. Although lignin nanocomposites exhibited low sun protection factor (SPF) values in an emulsion base, they enhanced SPF in a commercial sunscreen. LigZnO (15.9) and LigTiO2 (15.7) boosted the effectiveness of commercial UV absorbers (Parsol MCX and avobenzone), outperforming formulations with lignin alone or commercial ZnO and TiO2. The synergistic interaction between LigTiO2, LigZnO, and organic UV blockers reinforced thixotropy, making lignin nanocomposites a promising additive for sunscreen formulations. Their low cost and sustainable synthesis add value to nanomaterials while mitigating agro-waste disposal.