Effect of the addition of hydroxyl-terminated polydimethylsiloxane to TEOS-based stone consolidants |
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Authors: | Ramón Zárraga Jorge Cervantes Carmen Salazar-Hernandez George Wheeler |
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Institution: | 1. Department of Chemistry, University of Guanajuato, Noria Alta S/N, 36050 Guanajuato, Mexico;2. Historic Preservation Program, Columbia University, 1172, Amsterdam Avenue, New York 10027, USA |
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Abstract: | Hybrid stone consolidants prepared from tetraethoxysilane (TEOS) and α,ω-hydroxyl-terminated polydimethylsiloxane (PDMS-OH) have been considered as one of the most promising approaches to improve the effectiveness of traditional alkoxysilane-based formulations. They have emerged as response to the negative reports commonly found in the literature: the resulting silica gel phase (SiO2) tends to develop fractures and fissures inside the stone as the gel shrinks during the drying stage. In this work, we employed SEM, solid-state 29Si NMR spectroscopy and compressive tests to characterize SiO2-PDMS hybrid gels. We report the morphological characteristics exhibited by gels prepared in vitro and in situ. It was found an appreciable reduction of gel fracture for hybrids prepared from 5% w/w of PDMS. As TEOS polycondenses, PDMS-OH is chemically incorporated into the gel matrix via Si-O-Si bonds. The inclusion of these elastic chains provides the necessary flexibility to resist the stress imposed by capillary pressure. Additionally, an important hydrophobic character is imparted to the stone. |
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