Inorganic and hybrid inorganic-organic systems for conservative treatments of stone and wood materials

Inorganic and hybrid inorganic-organic systems for conservative treatments of stone and wood materials The research has focused on the synthesis, characterization and application of inorganic and hybrid inorganic-organic systems for conservative treatments of stone and wood. The wood preservatives synthesized and tested for biocidal activity are polyamidoamines functionalized with hydroxyl and siloxane groups, while the coatings applied on the stones are water based TiO2 nanosols with photocatalytic and self-cleaning properties. Firstly is reported the synthesis of amidoamines by addition reaction between an α,β-unsaturated amide (2-propenamide or N,N'-methylenebisacrylamide) and an amine (ethanolamine or diethanolamine). Their synthesis is a simple system for the study of polyamidoamines. The characterization of the starting reagents and the products of addition was made by means of different techniques (ESI-MS, NMR, FTIR and Raman spectroscopy). The model amidoamines synthesized by aza-Michael addition have allowed the study of the main parameters that influence the reaction It was verified that the reaction proceeds better in water compared to alcohol, and that at 55 °C the reaction takes place relatively quickly (about 4 h). Polyamidoamines under different reaction conditions were then synthesized. The polymers were functionalized with OH groups (PAAOH) and siloxane groups (SiPAA, SiPAAOH). The various polymers were characterized by spectroscopic techniques (ESI-MS, NMR, FTIR, Raman) and with thermal analysis. Polymers were applied on wood samples and their efficacy against fungi and termites has been verified according to UNI EN. The interaction with the substrate, the depth of penetration and the colour changes induced by the treatment were also investigated. The investigations showed that the polymerization reaction for the polymers with hydroxyl side chain is favoured when the amide is completely dissolved in the solvent and added slowly into the solution containing the ethanolamine, in particular when using water or methanol as the solvent. The measurements carried out on the polymers obtained without solvent at 90 °C show that the reaction proceeds up to completeness in less than 3 hours. As regards the polymers functionalized with siloxane, it is noticed that with increasing EtA/APTES ratio the effectiveness of polymerization increases. The DSC has allowed to evaluate the glass transition temperature of the polymers in the range 109 ÷ 120 °C. The hybrid polymers have been incorporated in the lignocellulosic structure of the wood and subjected to heat treatment (103 ± 1 °C for 18h) in order to increase the crosslinking. The high degree of crosslinking (DOC Degree of Condensation) within the wood has been demonstrated by 29Si-NMR spectra. Thanks to electron microscopy SEM it has been possible to verify the successful impregnation of wood specimens with different treatments. The preparations were applied as a protective coating on wood samples (sapwood of Pinus sylvestris) and tested for efficacy against biotic attack, both xilophagous insects and fungi, and resulted effective. After aging tests the polymers with siloxane functionality (SiPAA, SiPAAOH) are effective on wood-decay fungi. Finally, the synthesis and characterization of sol-gel TiO2 based coatings for the photocatalytic self-cleaning of biocalcarenites, are reported. Nanocrystalline titania sols in acid and basic aqueous environments have been prepared by sol-gel, processing titanium isopropoxide with two complexing agents, acetic acid and malonic acid and different peptizers, i.e. acetic acid, nitric acid and triethylamine. To verify the photocatalytic activity, gold nanoparticles have been added to the sol obtained by acetic acid. The effectiveness of the photocatalytic sols was verified by evidence of degradation of dyes, methyl orange (MeO) and methylene blue (MB), under UV-Vis irradiation. In accordance with the rules on cultural heritage, the harmlessness of coating towards the substrate has been investigated. XRD, Raman and TEM measurements on the corresponding titania powders have revealed nanocrystalline particles of anatase (5-6 nm) and of brookite in lesser amount. DLS and ELS-IEP analyses have indicated that preparations with acetic acid, acetic/nitric acids or malonic/triethylamine (basic) gives stable sols. The catalytic photoactivity of the sols under UV irradiation for the degradation of the anionic azo-dye MeO is much faster with acid sols than with the basic one. The cationic MB dye is completely photodegraded only by the basic TiO2 sol, on which the dye is adsorbed with the formation of trimeric species. Coatings at different pH were applied to biocalcarenites typical of southern Italy (Comiso, Modica, Noto and Lecce stones) used in the Baroque period of interest for cultural heritage. Satisfactory results are obtained by photodegradation under UV irradiation of Modica and Comiso stones coated by acid sol. The colour difference before and after the treatments is acceptable. The coatings do not alter the intrinsic properties of Modica and Comiso stones in the capillarity absorption of water, do not prevent the salts crystallization and leave unchanged the stone characteristics. The sol, used alone or with a silica interlayer, is promising for application in limestone protection. On Pietra di Lecce all the acidic sols showed good photocatalytic activity. All the coatings slightly reduce the capillarity water absorption. Colorimetric analyses show that the coatings do not significantly alter the original colour of the stones. The photocatalytic activity for MeO stain degradation is comparable for all the coatings: the addition of gold nanoparticle improves the cleaning in the first minutes, but the purple coloring prevents its use. On Pietra di Noto, both acid and basic titanium coatings do not alter the proprieties of the stone as the color difference measured is very small and capillarity absorption coefficient are comparable for treated and untreated samples. Referring to durability of the stone, the resistance to salt crystallization is generally improved. As concerns the self-cleaning properties, both TiO2 coatings exhibit a good photodegradation activity of methylene blue and methyl orange dyes. Both nanosols are suitable for harmlessness protection of Pietra di Noto, but the basic one exhibits better performances in term of filmogenic properties, colour changes, water absorption, durability enhancement and photocatalytic degradation of organic dyes and then it should be preferred for calcarenite substrates. The results highlight the compatibility of the treatments with respect to the properties of the calcarenite stones, showing no chromatic changes, no alteration of physical properties, an improvement of the resistance to salts crystallization and good photocatalytic activity on both dyes. This study has revealed that the basic sol is particularly suited for the self-cleaning of carbonatic stones, widely employed in ancient and modern architecture, opening perspectives for further applications.