Improving the aging properties of silicone-acrylate copolymers nanocomposites for encapsulation of outdoor exposed stone substrates

Abstract

In the preservation of cultural heritage items, the use of polymeric materials for the consolidation and protection of artifacts with historical and artistic value is widely accepted. In the case of stone conservation, application of polymeric materials is a settled technique used to minimize the rate of stone decay and to strengthen stone deteriorated by processes of weathering, effects of atmospheric pollution or inappropriate interventions. In recent years a new class of composite material is offered by polymeric nanocomposites systems, based on organic polymers and inorganic nano-particles [1, 2]. These systems show a great interfacial area per volume between nano-particles and polymer, with higher properties compared to the unmodified resin. Nanocomposite systems based on silicone-acrylate copolymers and different amounts of the modified nano-silicon dioxide (nano-SiO2) (1, 2 and 4 wt %) were tested as protective and encapsulating agents for the outdoor exposed stone substrates. Conservation and encapsulation efficiency of these treatments was evaluated through physical investigations (resistance to ultra violet, freeze-thaw aging resistance and accelerated ageing resistance to artificial climate). The results have evidenced that the nano-scale dispersion of low amounts of the modified nano-SiO2 into the polymeric matrix enhances the encapsulating and protective action of the outdoor exposed stone substrates. In fact, the outdoor exposed stone substrates treated with the nanocomposite systems exhibits a more marked reduction in resistance to ultra violet, freeze-thaw aging resistance and accelerated ageing resistance to artificial climate with respect to stone treated with the neat silicone-acrylate copolymers and B72 polymer, a commercial copolymer ethyl methacrylate/methyl acrylate (EM/MA).