Homogeneous melanin/silica core-shell particles incorporated in poly (methyl methacrylate) for enhanced UV protection, thermal stability, and mechanical properties

Natural melanin is abundant in wide ranges of sources, especially in dark colored animal fibers. Despite the unique features and functionalities, its extensive analyses and applications have greatly been hindered due to its serious self-aggregation. To tackle this issue, this study uses the Stöber method to encapsulate the melanin particles extracted from colored alpaca fibers with a thin layer of silica. It was observed that the melanin/silica core-shell particles (MSCPs) with 20 h encapsulation time provided excellent dispersity and optical performance. Different concentrations of MSCPs were then doped in poly (methyl methacrylate) (PMMA) through an in-situ polymerization process to obtain MSCP/PMMA bulk materials. The produced composite materials showed homogeneous appearance, controllable UV absorbance and visible light transmittance. The thermal stability, durability under UV, and mechanical properties of the fabricated composites were examined and the role of melanin on the obtained results was elucidated. It was observed that the PMMA samples with MSCPs showed excellent durability under UV even after 100 h irradiation. Testing the thermal stability and mechanical properties (hardness and elastic modulus) of MSCP/PMMA samples confirmed the positive effect of MSCPs presence in PMMA. These results demonstrated the applicability of natural melanin-based materials and composites in UV-protection related fields.