Environmental degradation of polymers for cultural heritage

Abstract

Plastic materials are used both for the protection of cultural heritage and as material for artworks. As for other materials, the durability and the maintenance of their initial properties are fundamental for the use of these materials. For the protection of the cultural heritage (particularly for stone artworks) the main important properties are the hydrophobicity, the UV transparency and the water vapour permeability that must be maintained even after a long exposure to the environmental conditions (UV irradiation, rain, temperature variations, etc.). When the polymers are used for the production of an artwork, the most important characteristics are the maintenance of the aesthetical appearance and the mechanical properties also in this case even after a long exposure to the environment. Fluorinated polymers have been used for their high hydrophobicity as a surface coating, but early fluoropolymer showed poor ability to stick to the stone. New compounds containing functional groups that can adhere to the stone surface have been developed, providing a more persistent protection but a rapid loss of water-repellent properties after accelerated and field (natural) weathering has been noted and deserves further study. In this work one new copolyfluorimer for the protection of cultural heritage and one typical polymer for the creation of artworks, polycarbonate, have been investigated by following the evolution of the above properties as a function of the UV irradiation time. The copolyfluorimer, only after more than 2000 hrs of UV irradiation at 50 °C, shows some. degradation phenomenon, while significant worsening of the molecular structure can be observed for the polycarbonate at lower irradiation times.