MIcrobial Alteration and preservation of Monuments in urban area (MIAM) – MIAM

The preservation of built cultural heritage in an urban polluted area is a socio-economic challenge for municipalities. Indeed, stone buildings are continuously exposed to chemical (pollutants such as NOx, CO) and biological (fungi, bacteria, algae) actions that lead to different alteration patterns. Despite important recent progress in the development of nanobiotechnology, nanofabrication and polymerization techniques, the willingness of scientists to design novel materials to prevent stone degradation remains a high research priority. To overcome the environmental damage and to avoid the use of common non-environmentally-friendly biocide reagents for stone restoration and consequently their toxic effect on aquatic and human health, it can be of prime importance to develop new hybrid coatings with respect to « green chemistry process ». In order to propose suitable conservation treatments, our project aims at discriminating the biological and pollution contributions in limestone and marble alteration and evaluating their synergic effects by a multidisciplinary approach. Such coatings will be designed according to the successive following steps: I) Comprehension of the microbial influence on stone degradation, II) identification of the microbial communities on stone surfaces as a function of atmospheric conditions, III) the synthesis of epoxy bio-based monomers along with permanent antimicrobial coatings according to the cationic photopolymerization under visible light illumination with natural dyes, IV) the synthesis of removal coatings via a “click-chemistry” process (PhotoDiels-Alder) from two kinds of precursor, i.e. one containing maleimide group and a second one derived from anthracenyl function derived from natural dyes and V) the study of the durability and the mechanical resistance of the coatings deposited on stone substrates, and their resistance in real atmospheric conditions.
Our motivation is to propose, in a reduced time, new low cost antimicrobial coatings from bio-based compounds according to“environmentally-friendly chemistry” with strong mechanical and permanent antimicrobial properties. We definitely avoid as far as possible the use of petroleum-based monomer, solvents or other hazardous molecules to respect the common environmental standards.
In conclusion, the major breakthroughs of this project compared to literature investigations are:
1) Comprehension of limestone and marble alteration as a function of the composition of the microbial communities and pollutants; 2) The design of new permanent protective coatings according to the analysis of the living microbial communities present on stone monument as a function of seasons and pollutants; 3) The elaboration of bio-based coatings according to a cationic photopolymerization process under visible light or sunlight irradiation in air conditions; 4) The design and the easily conception of «environmentally-friendly» bio-based materials in a reduced time; 5) The use of natural dyes which play a double role (photosensitizer for the initiation of the polymerization and promoter of reactive oxygen species under visible light illumination) lead to a permanent antimicrobial coatings and 6) Development of removal protective coatings via antracenyl/maleimide based molecules.