POLY(LACTIC ACID)-BASED POLYMERS FOR  THE PROTECTION OF MONUMENTAL STONE HERITAGE

Andrea Pedna1,3*, Giulia Giuntoli 1,2, Luca Rosi1, Marco Frediani1, Barbara Sacchi2, Emma Cantisani2, Maria Perla Colombini3, Piero Frediani 1,2

1 Department of Chemistry, University of Florence, via della Lastruccia 3-13, 50019 Sesto Fiorentino, Italy

2 ICVBC-CNR, via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy

3 Department of Chemistry and Industrial Chemistry, University of Pisa, via Risorgimento 35, 56126 Pisa, Italy

*apenda@unifi.it

ABSTRACT 

The application of a water repellent protective is a common practice in the conservation of monumental stone exposed to an open air. Commercial synthetic polymers often do not satisfy the requirements for application in Cultural Heritage. Therefore scientific community takes interest in the development of new products with suitable properties.

Our research was devoted to the synthesis and characterization of modified Poly(Lactic Acid) (PLA) for a potential application in the protection of stone surfaces. Chain-end fluoro-functionalized PLAs and lactide/mandelide copolymers were synthesised by Tin(II) 2-ethylhexanoate-catalyzed ring opening polymerization. The polymers were characterized by NMR, FTIR, GPC and DSC and tested as protective coating for stone. Performances were evaluated by capillary water absorption tests and CIE-Lab* colour measurements on selected marble samples. Furthermore, the photo-stability of polymers was investigated by accelerated UV ageing.

The treatment with the polymers caused negligible colour changes of the treated stone. Furthermore modified PLA showed a significant improvement in performance over PLA in terms of film formation and water repellence.

The polymers showed an interesting photo-stability with slight changes of both chemical-physical properties and coating performance up to 1000 hours ageing.

Key-words:  synthesis, polymers, coating, ageing, marble