Polymers, Colloids & Interfaces, Invited lecture

The evolution of polymer chemistry in the preservation of monuments

M. L. Santarelli1,2, M. P. Bracciale1,2
1Dept. Chemical Engineering Materials Environment, University of Rome Sapienza, 2CISTeC- Research Centre in Science and Technologies for the Conservation of Historical-Architectural Heritage, University of Rome Sapienza -

Conservation science was born around the 1970s when, with the increasing of the pollution in the atmosphere, evident signs of deterioration were observed on the surface of the monuments in relation to the action of acid rains. Currently, around 60 forms of material degradation are defined due to the interaction of water and air (polluted and not) on monumental surfaces [1]. Considering in Europe the presence about 3,500,000 monuments, the preventive conservation of monumental surface is an important goal both of cultural and economic nature.
Since the 1970s, a close interaction was established between conservation scientists and producers of coatings. A coating should allow at the masonry to breathe, without altering the appearance and showing a high compatibility and reversibility. Many studies identified two categories of coatings as protectives and consolidants: silica-based polymers and acrylic-based polymers [2].
The family of siloxane resins can be distinguished in resins polymerizing in situ and polymerized resins to be applied directly by brush or spray. Among the most famous products, ethyl silicate is certainly applied as a consolidant on various materials.
Acrylic-based polymers are generally MMA/EMA copolymers. Surely the most applied product is Paraloid (Rhom & Haas) for its reversibility and transparency characteristics.
The technical-scientific evolution helped a deeper knowledge of the nature of ancient materials and their decay, increasing the knowledge of their chemical interaction and compatibility with coatings, identifying strengths and weaknesses of their nature and function.
Lately, the diffusion of new nanostructured polymers has led towards a new interest in these new materials, whose properties seem to match well with the conservative needs. However, it is still necessary a full understanding of their characteristics and their behavior in the time.
Some experiments have shown a full applicability of cleaning systems on painted surfaces based on hydrogels, while the application of polymeric composite and hybrid systems are still under study (Fig. 1), especially to increase the self-cleaning, anti-microbial and hydrophobic behavior [3].

[1] ICOMOS-ISCS, www.icomos.org/publications/monuments_and_sites/15/pdf/Monuments_and_Sites_15_ISCS_Glossary_Stone.pdf, 2008.
[2] M. Sadat-Shojai, A. Ershad-Langroudi, J. Appl. Polym. Sci.,2009, 112, 2535-2551.
[3] F. Sbardella, L. Pronti, M. L. Santarelli, J. M. Asua Gonzàlez, M. P. Bracciale, Coatings, 20188, 283-297.
[4] NN. Rosyadah Ahmad, H. Mukhtar, DF. Mohshim, R. Nasir, Z. Man. Rev Chem Eng, 2016, 32, 181–200.