Suppressing photo-oxidative degradation: Biomimetic allomelanin enhances the UV-aging resistance of polyvinyl alcohol films

1,8-Dihydroxynaphthalene-derived allomelanin nanoparticles (AMNPs) were incorporated into poly(vinyl alcohol) (PVA) films at low loadings of 0.1–0.7 wt.% to regulate their mechanical, optical, photothermal, and UV-aging properties. The 0.3 wt.% film exhibited the best measured strength–ductility balance, with a tensile strength of 103.8 MPa and an elongation at break of 102.1%, while retaining partial visible transparency. Increasing the AMNPs loading enhanced UV attenuation and photothermal heating but reduced visible-light transmittance. The 0.5 and 0.7 wt.% films reached steady-state temperatures of 60.7 and 62.4 °C, respectively. In the curcumin photodegradation test, the 0.3 wt.% film limited degradation to 6% after 50 min of UV exposure, whereas the 0.5 and 0.7 wt.% films nearly completely suppressed degradation. After 120 h of laboratory UV irradiation, the AMNP-containing film showed less surface roughening than neat PVA. These results reveal composition-dependent performance windows: 0.3 wt.% favors mechanically robust and partially transparent UV-protective films, whereas 0.5–0.7 wt.% favors stronger light shielding and photothermal conversion.