Organic−Inorganic Hybrid Compounds Containing Polyhedral Oligomeric Silsesquioxane for Conservation of Stone Heritage

Abstract

Alkoxysilane solutions based on tetraethoxysilane (TEOS) have been widely used for the consolidation of decaying heritage stone surfaces. TEOS-based products polymerize within the porous structure of the decaying stone, significantly increasing the cohesion of the grains of stone components. However, they suffer from practical drawbacks, such as crack formation of the gel during the drying phase due to the developing capillary force and dense gel fractures left inside of the stone. In this study, a TEOS-based stone consolidant containing functional (3-glycidoxypropyl)trimethoxysilane (GPTMS) and polyhedral oligomeric silsesquioxane (POSS) has been prepared in order to reduce gel crack formation during the drying phase. The addition of nanometer-sized POSS and/or GPTMS having a flexible segment reduces the capillary force developed during solvent evaporation. The properties of the TEOS/GPTMS/POSS composite solutions were compared with those of commercial products (Wacker OH and Unil sandsteinfestiger OH 1:1). The gelation time was similar to that of commercial consolidants, and the TEOS/GPTMS/POSS solution was stable over a period of up to 6 months. The addition of POSS and GPTMS provided a crack-free gel, while the gel from the commercial consolidants exhibited cracks after drying. The surface hydrophobicity of the treated decayed granite increased with the addition of POSS and GPTMS, and it was higher than that of the commercial product, implying the possibility of POSS and GPTMS as barriers to the penetration of water. This result implies that the TEOS/GPTMS/POSS solution showed a high suitability for the consolidation of granite heritage.

Nanomaterials in art conservation

“…The main inconvenience of using well-established commercial consolidation products (that is, ethyl orthosilicate solutions) is that, on drying, they tend to crack inside the pores of the stone inducing mechanical stresses on the silicate matrix 19 . By adding silica nanoparticles, flexible silanes or nanometresized polyhedral oligomeric silsesquioxane commentary to ethyl orthosilicate solutions, crack formation during the drying phase is reduced 20,21 .…”

TEOS–colloidal silica–PDMS‐OH hybrid formulation used for stone consolidation

“…Recently, researchers have suggested the use of hybrid compounds based on TEOS, polyhedral silsesquioxane (POSS) and (3‐glycidoxypropyl)trimethoxysilane (GPTMS), and also TEOS, silica nanoparticles and GPTMS as stone consolidant. The additives of POSS and silica nanoparticles provide a crack‐free gel 18, 19. The use of epoxy‐silica polymer has been suggested as stone consolidant 20.…”

Consolidation of Wall Paintings and Stone

“…The cracking issue has been recently tackled, for instance by adding nano-sized silica particles and functional silanes that reduce the capillary force developed during the evaporation of solvents Son et al 2009), or by designing a consolidant synthesis where the sol-gel transition occurs in the presence of a surfactant, so to avoid cracking as the gel dries within the stone pores (Mosquera et al 2008). Miliani et al (2007) studied particle-modified silica consolidants (PMC) filled with titania, alumina and silica nanoparticles.…”