Microplastics prepared from commercial marine antifouling paints were weathered by UV-C irradiation representing between 25 and 101 days of real-time, outdoor exposure. Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy of the degraded paint particles showed that weathering induced chemical changes in the material, including the release of volatile components and the formation of hydrophilic groups. The chemical changes and increased reactivity of the paint binder were associated with alterations in their physical properties and increased leaching of metals in freshwater conditions. Changes in the spectra obtained from weathered paint samples reduced their match with spectra of unaged materials, resulting in a poorer similarity index, the Score when using automatic identification tools for microplastics. The results suggest that spectra of weathered, as well as pristine paint microplastics, should be consulted when applying analytical pipelines to identify microplastics extracted from natural matrices.