CONNECTIONS BETWEEN THE MACRO AND MICROPROPERTIES OF STONE COATED WITH PROTECTIVE POLYMER/OXIDE NANOPARTICLES COMPOSITES

The development and analysis of polymer/oxide nanoparticles dispersions is increasingly capturing the interest of the scientific community, due to the fact that they could be applied on stone surfaces for imparting to them hydrorepellency, together with several useful traits given by the inorganic component. According to the approach followed, the material to be treated has been set as the central point and a constant attention to its problems and to possible alterations that can occur after the treatment with the nanomaterial has been operated. More in details, the research work concentrated first on evaluating the effects of the application of four kind of polymer/oxide nanoparticles dispersions, to be used as protectives for stone surfaces, on two type of calcarenite lithotypes that have been used as building material for artefacts. Calcarenites are typical Sicilian stones, and have been used in most of the stone artworks passed down to us, as well as for common constructions. Among the different lithotypes, Noto white type and Comiso have been chosen as representatives, due to their different porosity and mineralogical features. The work was conducted by analysing the contribution of each component of the system, through a systematic approach, using several laboratory and portable techniques. After the structural characterization of the coating itself, the performance of those colloidal systems has been studied upon application on the calcarenites, preferring non-invasive techniques and microdestructive techniques. However, the main aspect that has been attentioned, aside from the empirical aspect, is the study of interactions at the microscale between the polymer, the nanoparticles and the stone substrate. This perspective, which is not typical of the industrial attitude, has been of interest for speculation and may bring about new pathway which take a bottom-up approach, starting from the interactions between components at the molecular level in order to tune the macroscopic properties of the composite. The main research result has been brought by the 19F Direct Polarization Magic Angle Spinning (DP MAS) solid state NMR technique. This technique has permitted to see , at molecular level and with a high accuracy, that the polymeric film obtained when the dispersions were applied on the stone was different in chemical structure respect to when the monomers were left to polymerize in an open and flat mould. An initial hypothesis was that the nanoparticles had some interfering role in the curing process, varying it of a significant degree. Nevertheless, NMR results have proved that two different end products, characterized by two distinct NMR spectra, can be identified. The remarkable and unforeseen result of this research is that the stone porosity actually has a strong effect respect to the cross linking, leading to having a different bonding between the units, on the basis of the stone on which the polymer/nanooxide dispersions are applied. On the other side, nanoparticles addition has proved not to have an interfering part in this process, prompting to develop their usage in smart composites , in order to exploit their additional properties maintaining the waterproofing feature. An empirical approach at the problem under study has been important during the testing and evaluation of the practical performances of the protectives; nevertheless, the unexpected results coming from the microscale approach open new research lines and connection with the industrial fields. In fact, increasing the research in this pathway may lead to know more about how the stone substrate porosity acts as a confined environment towards polymerization processes of the polymer composites. This aspect is of utmost importance for chemists, but also for manufacturing companies can be a key asset, with the aim of developing new commercial products, upgrading existing ones or orienting their end-user handling.