Calcitic-based stones protection by a low-fluorine modified methacrylic coating

Eleonora Pargoletti,Luisa Annunziata,Giuseppe Cappelletti,Valeria Comite,Hermes Farina,Marco Aldo Ortenzi,Valentina Sabatini,Paola Fermo

doi:10.1007/s11356-021-15515-9

Abstract

Atmospheric pollutants, such as NOx, SO2, and particulate matter, together with water percolation inside the stone pores, represent the main causes of cultural heritage decay. In order to avoid these undesired phenomena, the application of protective coatings represents a reliable solution. In this context, the present study focused on the synthesis of low-fluorine content methacrylic-based (MMA) polymeric resins characterized by seven F atoms (namely F7 monomer) in the lateral chains. Four different percentages (1.0, 2.5, 5.0, and 10.0%) of the present monomer were adopted to obtain a final polymeric structure showing the desired hydrophobicity, processability, and structural and thermal stability (even after accelerated UV aging tests). MMA_F7(1.0) seemed to be the optimal one; therefore, it was further applied onto Candoglia marble. Specifically, the treated substrates showed good surface hydrophobicity, water repellency, and water vapor transpirability. No color variation was observed even after a 1.5-year exposure in a real polluted environment (Monza Cathedral). Interestingly, the application of this coating hindered the atmospheric nitrates penetration inside the stones and, at the same time, it limited the sulfates (gypsum) formation, thus revealing a very promising marbles protection resin.

Highlights

In recent decades, the achievement of a certain degree of surface hydrophobicity has been one of the main challenging issues to deal with especially in the field of cultural heritage protection (Mosquera et al 2014; Pino et al 2017; Aslanidou et al 2018; Eyssautier-Chuine et al 2018; Lettieri et al 2018)
As clearly visible in NMR spectra comparison (Fig. 3) and in Table S1, the experimental values of F7/methyl methacrylate (MMA) molar ratios are fully in accordance with the theoretical ones evidencing the actual insertion of the fluorinated monomers into the MMA matrix
Low-fluorine content (F7) methacrylicbased polymers were synthesized aiming at applying them as Candoglia marble protective coatings

Summary

Introduction

The achievement of a certain degree of surface hydrophobicity has been one of the main challenging issues to deal with especially in the field of cultural heritage protection (Mosquera et al 2014; Pino et al 2017; Aslanidou et al 2018; Eyssautier-Chuine et al 2018; Lettieri et al 2018). Calcitic-based substrates, such as Candoglia or Botticino marbles widely used for cultural heritage monuments, are among the materials that can be damaged by these external agents, leading to their irremediable decay. The Milan Cathedral, one of the most famous monuments worldwide, is mainly composed by calcitic marble (80–85% CaCO3 and the 15–20% other minerals (Dino et al 2019)). This important monument preservation against physicochemical deterioration induced by atmospheric pollution has to be guaranteed (Manoudis et al 2009a; Goffredo 2013; Jroundi et al 2017; Ruffolo and La Russa 2019)

Methods

Results

Conclusion