Fluorinated and perfluorinated polymers as protective and reinforcing agents for stone artefacts

Synthetic macromolecular compounds are widely accepted by scientific, technical and historical community for the conservation and restoration of works of art, because these materials have good cohesive, adhesive and water repellent characteristics. However, among polymers available on the market, few compounds are completely eligible as ideal products for the application on artefacts of relevant historical and artistic importance. In fact, even if the synthetic polymers are highly stable in consideration of their commercial use, if we consider their stability in a very long term, as required for their use on works of art, some problems are present. The main problem to be solved using this materials in the conservation is their stability for a long time to UV irradiation, heat, oxygen and chemical agents. The totally or partially substitution of hydrogen with fluorine in the organic compounds, usually increases the chemical stability of the molecules, due to the high stability of the C-F bond. On the contrary some perfluorinated polymers, having a very high stability, show a high diffusion inside the stone. Aim of this article is a critical evaluation of the performances of different fluorinated materials, in particular perfluoropolyethers, fluoroelastomers and some partially fluorinated acrylic polymers. The synthesis, photo-stability, hydrophobic properties and transport properties of water vapour in the tested polymers will be exposed in order to evaluate their efficiency as protective or reinforcing agents for stone artefacts. The performances of these polymers on stone materials (biocalcarenites) will be also reported.