Analytical assessment to develop innovative nanostructured BPA-free epoxy-silica resins as multifunctional stone conservation materials

Olivia Gómez-Laserna; Paola Lanzafame; Georgia Papanikolaou; María Ángeles Olazabal; Sandra Lo Schiavo; Paola Cardiano

doi:10.1016/j.scitotenv.2018.07.188

Analytical assessment to develop innovative nanostructured BPA-free epoxy-silica resins as multifunctional stone conservation materials

Sci Total Environ. 2018 Dec 15:645:817-826. doi: 10.1016/j.scitotenv.2018.07.188. Epub 2018 Jul 19.

Authors

Olivia Gómez-Laserna¹, Paola Lanzafame², Georgia Papanikolaou², María Ángeles Olazabal³, Sandra Lo Schiavo⁴, Paola Cardiano⁴

Affiliations

¹ Department of Analytical Chemistry, University of the Basque Country (EHU/UPV), Barrio Sarriena s/n, E-48080, Leioa, Bilbao, Spain. Electronic address: olivia.gomez@ehu.eus.
² Department of Mathematical and Informatics Sciences, Physics and Earth Sciences, University of Messina, and INSTM CASPE (Laboratory of Catalysis for Sustainable Production and Energy), Viale F. Stagno d'Alcontres 31, I-98166 Messina, Italy.
³ Department of Analytical Chemistry, University of the Basque Country (EHU/UPV), Barrio Sarriena s/n, E-48080, Leioa, Bilbao, Spain.
⁴ Department of Chemical, Biological, Pharmaceutical and Environmental Sciences, University of Messina, Viale F. Stagno d'Alcontres 31, I-98166 Messina, Italy.

PMID: 30031339
DOI: 10.1016/j.scitotenv.2018.07.188

Abstract

Bisphenol A (BPA)-free epoxy resins, synthesized from low molecular weight cycloaliphatic compounds, may represents promising materials for stone conservation due to their very appealing and tunable physico-chemical properties, such as viscosity, curing rate and penetration ability, being also easy to apply and handle. Furthermore, alkoxysilanes have been widely employed as inorganic strengtheners since they are easily hydrolysed inside lithic substrates affording SiO linkages with the stone matrix. Taking into account the advantages of these two classes of materials, this work has been focused on the development of innovative conservation materials, based on hybrid epoxy-silica BPA-free resins obtained by reaction of 1,4-cycloexanedimethanol diglycidylether (CHDM-DGE) with various siloxane precursors, i.e. glycidoxypropylmethyldiethoxysilane (GPTMS), tetraethyl orthosilicate (TEOS) and isobutyltrimethoxysilane (iBuTMS), using the 1,8-diaminooctane (DAO) as epoxy hardener. Thanks to Raman spectroscopy the synthesis processes have been successfully monitored, allowing the identification of oxirane rings opening as well as the formation of the cross-linked organic-inorganic networks. In accordance with the spectroscopic data, the thermal studies carried out by TGA and DSC techniques have pointed that GPTMS is a suitable siloxane precursor to synthesize the most stable samples against temperature degradation. GPTMS-containing resins have also shown good performances in the dynamic mechanical analysis (DMA) and in contact angle investigations, with values indicating considerable hydrophobic properties. SEM analyses have highlighted a great homogeneity over the entire observed areas, without formations of clusters and/or aggregates bigger than 45 μm, for the cited materials, confirming the efficiency of GPTMS as coupling agent to enhance the organic/inorganic interphase bonding. The variations provided by the incorporation of nanostructured titania, specifically synthesized, inside the epoxy-silica hybrids have been also evaluated. According to all the collected results, the hybrid materials here reported have proven to be promising multifunctional products for potential application in the field of stone conservation.

Keywords: Alkoxysilanes; BPA-free; Conservation; Epoxy resins; Hybrid materials; Nanotechnology.