Biopolymers as stone protectives

In the last decades, natural organic products have been substituted by synthetic products in the field of Conservation of Cultural Heritage. Unfortunately synthesized products have sometimes some drawbacks, due to the fact that they have high costs of synthesis, or they are soluble in toxic solvents for man or environment, or they become irreversible once applied on the substrate. As a consequence, it appears clear that the use of new polymers derived from natural sources as protectives for lapideous materials would be very welcome. Lactic acid is produced starting from 100% annually renewable resources. Moreover, under appropriate conditions, polymers of lactic acid can be completely biodegraded. They are widely used in packaging and medical devices, and in this work they were proposed as stone protectives. They were tested on samples of two Apuan Marbles having different conservation state: one of them was specifically quarried for this experimentation, while the other one was obtained by an ancient front quarry, probably used in Roman Age. Samples of the two marbles were characterised and treated with an homopolymer of lactic acid and two co-polymers between lactic acid and Fluorolink D-10H, a low weight perfluoropolyether, with the aim to improve hydrorepellence properties. Treated materials were subjected to artificial ageing, both with thermohygrometric cycles and UV exposure. Colour changes and protective efficacy were evaluated after treatment and monitored during the artificial ageing cycles.