Sugar-derived bio-based resins as platforms for the development of multifunctional hybrids with potential application for stone conservation

This research is focused on the design of a bio-based epoxy-silica hybrid, enriched with SiO2 nanoparticles, to be used in stone conservation. For this purpose, isosorbide, a sugar derivative coming from renewable sources, was selected for the development of epoxy thermosets that were functionalized adding fixed amounts of silicaforming mixtures, to gain hybrid organic-inorganic networks. Fourier Transform Infrared (FTIR), Attenuated Total Reflection Infrared (ATR-FTIR) and Raman spectroscopies were exploited to follow the synthetic procedures, whereas the homogeneity of the networks was ascertained by scanning electron microscopy/energydispersive X-ray spectroscopy (SEM-EDS). The materials were investigated by thermogravimetric (TG-DTA), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and contact angle measurements. Once the proper epoxy-silica product was identified, specifically synthesized nanoparticles were incorporated. The obtained nanocomposite showed excellent thermo-mechanical (Tonset, Tg and Tα of 327, 55.9 and 70.1 ◦C, respectively) and hydrophobic (105◦) properties making it a potential candidate for stone conservation.This work has been financially supported by the project PHETRUM (CTQ2017-82761-P) from the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) and by the European Regional Development Fund (FEDER). The authors gratefully acknowledge Open Access funding provided by University of Basque Country. P. Irizar gratefully acknowledges his predoctoral grant from the MINECO (PRE2018-085888). O. Gomez-Laserna is grateful to the projects IT-742-13 for Consolidated Research Groups, funded by the Basque Country Government, and PHETRUM (CTQ2017-82761-P) from the MINECO for her post-doctoral contract. P. Cardiano thanks the Italian Ministry of University and Research (MIUR), PON R&I project AGM for CuHe (ARS01_00697), for Contact Angle measurements. The authors are grateful to the technical support provided by the Raman-LASPEA laboratory, the Nuclear Magnetic Resonance laboratory and to the Macrobehaviour, Mesostructure, Nanotechnology: Unit of Materials and Surfaces of The Advanced Research Facilities of the SGIker (UPV/EHU, MICINN, GV/EJ, ERDF and ESF)

Bio-based hybrid nanocomposites as multifunctional sustainable materials for stone conservation

This study was aimed at developing a sustainable versatile bio-based epoxy-silica material to be potentially employed as hydrophobic and biocidal consolidating product in the field of stone conservation. For this purpose, two hybrid formulations containing 2,2,4,4-tetramethyl-1,3-cyclobutanediol diglycidylether (CBDO-DGE), a cycloaliphatic epoxy precursor derived from the arnica root, together with (3-glycidyloxypropyl)trimethoxysilane (GPTMS) and octyltriethoxysilane (OcTES) as silica-forming additives, were chosen as the basis of the multifunctional material to be finely adjusted and gain biocidal properties. With this goal in mind, different synthetic strategies based on ionic liquids (ILs), essential oils (EOs) and nanoparticles (NPs) doping have been employed. Specifically, dimethyloctadecyl[3(trimethoxysilyl)propyl]ammonium chloride (QAS), tetradecyl phosphonium chloride (QPS) and thymol, as well as cerium-TiO2 NPs and thymol-loaded SiO2 NPs were incorporated into the starting hybrid formulations, during the sol-gel process, to investigate their influence on the network formation. First, distribution studies by scanning electron microscopy/energy-dispersive X-ray (SEM-EDS) analysis were performed, whereas the suitability of each formulation to match the main requirements for a stone conservation material was evaluated in terms of thermostability, hydrophobicity and inhibition of the microbiological growth by a combination of TG-DTA, DSC, dynamic mechanical analysis (DMA), with contact angle and disk-diffusion measurements, respectively. Based on the data analysis, it was observed that the direct incorporation of ILs and EOs had an adverse effect on the ability of GPTMS to act as a coupling agent. This resulted in decreased thermal stability and a 50 % reduction in glass transition temperatures, along with the retention of hydrophilic behavior. In contrast, the inclusion of NPs did not significantly interfere with the hybrid network formation, and effectively maintained the thermo-mechanical and hydrophobic properties of the hybrids within satisfactory parameters. Consequently, both nanocomposite materials were further tested on stone samples by artificial ageing experiments under acidic atmosphere. In view of the results, the hybrid enriched with thymol-loaded SiO2 NPs demonstrate the most suitable thermo-mechanical and hydrophobic properties (Tonset, Tα and CA values of 276 °C, 54 °C and 100°, respectively), as well as a proper biocidal capability against bacteria. Furthermore, the developed material provided effective stone protection, resulting in a 92 % reduction in material loss, while preserving the substrate chromatic characteristics (ΔE 2.23). These findings suggest that the proposed treatment meets the first main requirements for stone conservation.This work has been financially supported by the projects PHETRUM (CTQ2017-82761-P) and DEMORA (PID2020-113391GB-I00) from the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) and the Spanish Ministry of Science and Innovation (MICINN), respectively, as well as by the European Regional Development Fund (FEDER). The authors gratefully acknowledge Open Access funding provided by University of Basque Country. P. Irizar gratefully acknowledges his predoctoral grant from the MINECO (PRE2018-085888). The authors are grateful to the technical support provided by the Raman-LASPEA laboratory, the Nuclear Magnetic Resonance laboratory and to the Macrobehaviour, Mesostructure, Nanotechnology: Unit of Materials and Surfaces of The Advanced Research Facilities of the SGIker (UPV/EHU, MICINN, GV/EJ, ERDF and ESF)

The potential of in situ Raman spectroscopy in the study of the health of cement-based materials of modern buildings during restoration works

Although Raman spectroscopy is a common technique for the analysis of cement-based materials in the research studies or in the field of Cultural Heritage to carried out multianalytical studies, it is not generally used as unique technique of a research or to carry out analysis during ordinary restoration works of modern urban buildings affected by environmental stressors. The disadvantages associated with Raman spectroscopy as fluorescence limits its implementation beyond research studies, more in the case of in situ equipment. However, the technological development allows high-quality results with in situ equipment, so its use could be useful during restoration works. Thus, this work demonstrates how the implementation of the correct methodology could lead to useful and fast results during restoration works. The proposed methodology is based on the use of in situ analysis (screening) on the scaffolding, followed by the sampling of layers based on the previous screening and a posterior exhaustive laboratory analysis. The research has been conducted during the restoration works of a reinforced concrete building in which the attack of atmospheric acid gases (CO2, SO2, and NOx) was identified as the main affection suffered, and the fixed sulfates were the most important intermediary compounds of decaying processes. Many of the pollutants and decaying compounds were even identified during the in situ analysis, improving the anticipation and responsiveness. Therefore, this methodology allows the understanding of the chemistry of the materials to evaluate its health state in a fast and reliable way.Spanish Agency for Research AEI (MICINN/FEDER-UE), Grant/Award Number: PID2020-113391GB-I0