Photoprotective properties of alpaca fiber melanin reinforced by rutile TiO₂ nanoparticles: A study on wool fabric

Melanin/titanium dioxide (TiO₂) composite systems are introduced as efficient UV absorbers. Natural melanin particles were extracted from the pigmented alpaca fibers and the spindle-like rutile TiO₂ nanoparticles were synthesized through a two-step sol-gel method at room temperature. The composites of melanin/TiO₂ were prepared via electrostatic attraction force. In order to understand the UV absorption features of melanin and melanin/TiO₂ composite systems, the prepared particles were applied to the surface of wool fabrics. Then, the UV protection and photostability of functionalized fabrics were assessed based on photoinduced chemiluminescence (PICL) emission, UV reflectance spectra, photoyellowing and ultraviolet protection factor (UPF). It was observed that the photostability of treated fabrics enhanced significantly, implying the generation of less free polymeric radicals in the substrate under UV irradiation. Among different synthesized composites, the proportion of melanin/TiO₂ 1/4 was the most efficient ratio inducing 80% reduction in the PICL emission peak intensity compared with untreated wool samples. The presence of melanin particles significantly enhanced the UPF values of fabrics where 30% increment was observed for wool samples after treating with melanin/TiO₂ 1/4 compared with pure TiO₂. Having some advantages such as nontoxicity, eco-friendly and feasible synthesis approach, the prepared bio-organic/inorganic composite structures can be of some potential applications in photoprotecting and free radical quenching purposes.