Protection Efficacy of Fluorinated Acrylic Copolymers Applied on Historical Italian Marbles.
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Protection Efficacy of Fluorinated Acrylic Copolymers Applied on Historical Italian Marbles. Tommaso Poli, Lucia Toniolo CNR-ICVBC, National Council of Researches-Institute for the Conservation and Valorisation of Cultural Heritage. P.za L. Da Vinci, 32 - 10133 Milan, Italy ABSTRACT Use of polymeric materials to protect stone started in the 1960’s but the study and knowledge of the complex and multiple interactions between stone and polymers has been carried out only recently. In a previous paper [1] the problems related to the efficacy of a stone treatment (film formation, deep penetration and coating behavior) has been addressed. In this paper performance after a thermal and a simulated solar UV ageing has been evaluated. In particular the issues related to stability and durability of two fluorinated acrylic copolymers applied on two different Italian marbles, Carrara and S. Giuliano, have been investigated. The specimens characterized and treated with two new partially fluorinated acrylic copolymers, 2,2,2-trifluoroethyl methacrylate / methyl acrylate (TFEMA / MA) and trifluoromethyl-2,2,2trifluorethyl methacrylate / methyl acrylate (HFIMA / MA), have been artificially aged in two different ways: with a long simulated solar UV ageing of 1000h and a thermal one at the same temperature (about 50°C) usually reached in the UV chamber, in order to separate the two ageing contributions (photochemical and thermal). After the ageing most of the testing methodologies suggested by UNI-Normal Italian protocol for evaluation of stone protective coatings, including capillary water absorption, static contact angles and colour variation, have been carried out. Slightly better protective efficacy was found for the HFIMA/MA before and after the two ageing. The important contribution of the thermal component in the worsening of the shielding efficacy has been assessed. INTRODUCTION A class of protective polymers, based on fluoro-acrylic structures, has been prepared and tested on natural stone during the last five years [2, 3]. The main characteristics of these products are the presence of fluorine, the acrylic backbone and an easy and relatively low cost synthetic process [4]. Other interesting features are enhanced water repellency [5, 6] and durability, overall transparency and high solubility [7, 8]. During this experimental work many copolymers have been studied, prepared and tested on Noto calcarenite [3, 9, 10] and Candoglia marble [10, 11, 12]. In this work two of the best performing fluorinated acrylic copolymers have been tested on different marbles, Carrara and S. Giuliano, in order to highlight the relationship among performance, molecular structure and substrate characteristics. In this paper the ageing behaviour of the same copolymers has been studied with particular attention to the thermal contribution in the UV ageing. EXPERIMENTAL DETAILS
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The copolymers The two copolymers tested are the 2,2,2-trifluoroethyl methacrylate / methyl acrylate (TFEMA / MA) and the trifluoromethyl-2,2,2-trifluorethyl
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