Sunlight-curable boehmite/siloxane-modified methacrylic based nanocomposites as insulating coatings for stone substrates

An organo-modified boehmite (OMB) was used to prepare solvent-free, hydrophobic and thermal insulating sunlight curable nanocomposites, based on an innovative photo-polymerizable siloxane-modified methacrylic formulation. A deep analysis of the selected nano-filler was first performed by Wide-Angle X-ray (XRD), Scanning Electron Microscopy (SEM) and thermo-gravimetric analysis (TGA). Then, a small amount (i.e. 3 pph) of the nano-filler was dispersed in the organic formulation in presence of a mix of photo-initiators, the latter being able to activate the curing reactions upon sunlight exposure. The rheological behavior of the unfilled and nano-filled formulations was studied, verifying that the presence of the nano-particles does not hinder the field of application of the liquid product. The kinetics of the radical photo-polymerization reactions, induced by solar radiations, was, then, studied by both Fourier Transform Infrared spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC), in order to evaluate the effect of boehmite particles on the kinetics of reaction. Glass transition temperature, thermal conductivity, transparency, surface hardness, hydrophobicity and UV resistance of the systems, produced as thin samples on an aluminum substrate and photo-polymerized in air, were measured. The presence of boehmite nano-particles was found to increase the Shore D hardness of the polymeric matrix, to reduce its thermal conductivity and to increase the transparency of the nanocomposite film. The thermal insulating properties of the OMB filled coating, along with its excellent hydrophobic characteristics, suggested its potential applications in the field of construction/Cultural Heritage protection as hydrophobic/insulating coating. In order to explore this possibility, a preliminary experimental study was carried out assessing the protective performance of the nanocomposite when applied on calcareous stone substrates