Improving Wood Resistance to Decay by Nanostructured ZnO-Based Treatments

In this study, the maple wood surface was coated with nanostructured zinc oxide, grown on the surface by using a hydrothermal process, and furtherly treated with shellac varnish. Samples obtained both after ZnO treatment and after the final varnish application were characterized by different techniques, i.e., X-ray diffraction (XRD), scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDS), micro-FTIR with attenuated total reflectance (μ-ATR-FTIR), chromatic variation measurements, and contact angle determinations. Analytical results showed that the wood surface was covered by quite a homogeneous array of inorganic nanoparticles and that the natural resin forms a regular film over the ZnO nanostructures. An accelerated aging test was used to evaluate the protecting effectiveness of the treatments towards UV-induced decay of wood material. After the test, wood treated with ZnO and with the shellac/ZnO combination underwent a considerably lower chromatic change if compared to the untreated wood, suggesting an enhanced resistance of the treated maple to the decay due to light exposition. The presence of nanostructured ZnO protects from decay not only the wood substrate but also the shellac film. A microbiology test showed that growth of fungal species, e.g., common mold, is prevented on the wood surface treated with ZnO or with shellac/ZnO, indicating that the nanostructured zinc oxide also provides an effective protection from biodeterioration. The coating obtained by consecutive application of nanosized ZnO particles and shellac varnish combines the excellent aesthetical features and water repellence of the traditional finish with the protecting effectiveness of the nanostructured inorganic component

Stradivari's Varnish Revisited: Feature Improvements Using Chemical Modification

The most widespread varnish formulations used by master violin-makers of the "Italian Golden Age", including Antonio Stradivari, were based on mixtures of siccative oils (e.g., linseed oil) and natural resins (e.g., colophony). Similar formulations are still used for the finish of contemporary instruments. Although most precious violins made by Stradivari and other Cremonese Masters are kept in museums, several instruments are still played and their finish may undergo deterioration due to contact with the players. Moreover, the decay of the traditional varnish may occur due to mechanical stress and natural aging caused by environmental agents (e.g., exposure to uncontrolled light, humidity, and temperature changes). The main aim of this research work is to investigate the possible improvement of varnish resistance to the decay induced by different aging processes. For this purpose, the traditional varnish (linseed oil/colophony 3:1 w/w) was recreated in the laboratory following an ancient recipe and then it was functionalized with a cross-linking agent (3-Glycidyloxypropyltrimethoxysilane, GLYMO). Plain and functionalized varnishes underwent artificial aging (UV light, temperature, and humidity variations), and their properties were comparatively studied using different techniques. All the results suggest that the functionalized varnish displays improved resistance to the aging process and particularly enhanced photostability and increased hardness (resistance to scratches)

Silver Nanoparticles in the Cultural Heritage Conservation

Our cultural heritage is our invaluable social and environmental resource and concern. Moreover, it is a key global economic driver. However, they are subjected to deterioration process and aging. Particularly, microorganisms are nowadays considered harmful agents of biodeterioration of artistic materials due to the fact that their interactions with the material cause not only an esthetical damage due to their visible growth on the surface, but they may affect the interested materials in different ways and at different degrees via mechanical and biochemical processes leading to the formation of pitting, scaling and, in the worst scenario, to the loss of material by its detachment. To protect our shared tangible cultural heritage from biodeterioration and preserve it for future generations, several methods have been developed. Notably, using nanomaterials, with antimicrobial features, has been considered an interesting and economical method to preserve valuable heritage materials. In this chapter, we will present an overview of the decay mechanisms that participate in the deterioration of tangible artworks, in particular microorganisms’ colonization. Next, current works that have been developed to use silver nanoparticles to protect heritage items from microbial colonization and prevent their deterioration have been detailed

Durable Polymer Coatings: A Comparative Study of PDMS-Based Nanocomposites as Protective Coatings for Stone Materials

Nowadays, durable protective coatings receive more attention in the field of conservation for several reasons (they are cost effective, time consuming, more resistance, etc.). Hence, this study was focused on producing a multi-functional, durable coating to protect different stone materials, especially, Lecce stone, bricks, and marble. For this purpose, ZrO2-doped-ZnO-PDMS nanocomposites (PDMS, polydimethylsiloxane used as the binder) were synthesized by in situ reaction (doped nanoparticles were inserted into the polymer matrix during the synthesis of PDMS) and the performances of resulting coatings were examined by handling different experimental analyses. In particular, the study aimed to evaluate the durability properties of the coating along with the self-cleaning effect. As a result, the durability of the nanocomposite coating with respect to the well-known PDMS coating was assessed after exposure to two different ageing cycles: solar ageing (300 W, 1000 h) and humid chamber ageing (RH > 80%, T = 22 ± 3 °C, desiccator, 2 years). All the results were in good agreement with each other providing that newly prepared nanocomposite coating can be used as a durable protective coating for different stone materials

Heritage Conservation and Restoration: Surface Characterization, Cleaning and Treatments

Conservation is not the same thing as restoration [...

Enhanced Gd Doped TiO2 NPs-PDMS Nanocomposites as Protective Coatings for Bio-Calcarenite Stone: Preliminarily Analysis

The main objectives of this research are the development and characterization of pure and Gd-doped TiO2 nanoparticles (NPs) with low doping amounts (doping ions/Ti ratio varies between 0.1 and 3 mol%) and self-cleaning activity to be used when mixed with binder as protective coatings on monument surfaces. The prime objectives of this study are to synthesize nanopowders with controllable nanosize particles, spherical shape, anatase phase, and enhanced photo-response activity. Different coatings composed of as-synthesized nanoparticles and binder were applied to stone samples (Lecce stone). The developed coatings are intended to induce negligible colourimetric variation on the treated surface, have a good water repellence feature, and have a good distribution on the studied stone. XRD, DLS, SEM, and UV-Vis analyses were performed to analyze TiO2 NPs. The efficiency of the as-prepared NPs was estimated by testing their photocatalytic activity under UV and visible light. Chromatic measurements, static contact angle measurements, optical microscope observations, and SEM-EDS analysis were performed to analyze thin films applied to Lecce stone. The results showed that samples doped with low concentrations (≤1 mol%) of gadolinium in conjunction with PDMS can be considered as good candidates for protecting monument surfaces for this type of stone

Heritage Conservation and Restoration: Surface Characterization, Cleaning and Treatments

Conservation is not the same thing as restoration [...

Nanoparticle-modified shellac for protection of wood surface

Shellac has been widely used as a natural protecting material for wooden furniture and musical instruments, due to its excellent film-forming behaviour and aestethical effect, ease of application, high adhesion to the wood surface and protecting properties along with its nonpoisonous nature [1]. However, its application displays some limitations, such as the softness of the coating, photodegradation, and sensitivity to to pH variations [2-3]. In the present study, dewaxed natural shellac was modified by introducing different inorganic nanoparticles. Silicates nanoparticles as well as zirconium oxide nanoparticles were added with the aim of improving the film hardness, while zinc oxide nanoparticles were expected to improve the decay resistance and antifungal performances of the shellac matrix. Different shellac-based materials containing different amount (1, 2, or 3%) of silica, montmorillonite, zinc oxide, or zirconium oxide were prepared by dispersing nanoparticles in ethanolic solutions of shellac. Materials were characterised by performing different experimental analyses both on modified shellac films and on maple wood specimens treated by brushing. Properties of shellac-based materials were investigated by performing hardness and adhesion tests, moisture adsorption mesurements, thermogravimetric analysis, differential scanning calorimetry, UV and solar test, contact angle measurements, evaluation of chromatic variation, solubility and alkali resistance tests. X-ray, FTIR and SEM-EDS analyses were also carried out on films and treated wood specimens. Quality and thickness of the coating are important parameters when products are developed for the real case applications. Both native and modified shellac treatments on wood specimens provided good quality coatings whose thickness were very close to real applications (about 25 μm). Hardness measurements performed by international standard test indicated that the presence of zirconium oxide, silica and montmorillonite nanoparticles in shellac improves the hardness of the resulting coating. In addition, SiO2-shellac applied to wood specimens afforded an improvement of hydrophobic properties, while montmorillonite-shellac increased the base resistance property with respect to the native shellac. ZnO-shellac treatment preserved almost unaltered the chromatic properties (L*, a* and b* coordinates of the CIELAB space) with respect to native shellac, even after the solar ageing (1000h). [1] J. Wang, L. Chen, Y. He, Progress in Organic Coatings (62), 2008, 307–312. [2] W. H. Gardner, W. F. Whitmore, Industrial and Engineering Chemistry (21), 1929, 226-229. [3] M. Licchelli, M. Malagodi, M. Somaini, M. Weththimuni, C. Zanchi, Surface Engineering (29), 2013, 121-127

Improving the Protective Properties of Shellac-Based Varnishes by Functionalized Nanoparticles

Shellac is a natural varnish still known as one of the most elegant finishes for furniture and musical instruments, and currently used for restoration and refinishing of wooden antiques. However, it displays some limitations such as (i) sensitivity to alcoholic solvents (ii) softness of the coating, and (iii) considerable weathering due to photo- and bio-degradation. Hence, the main aim of this study was to improve the properties of shellac-based finish by introducing functionalized nanoparticles. Two inorganic nano-sized materials were considered: ZnO that was expected to reduce photo- and bio-degradation problems, and ZrO2 that was expected to improve the hardness of the varnish. Nanoparticles were synthesized and treated with a bifunctional silane coupling agent. Both plain and functionalized nanoparticles were extensively characterized using different experimental techniques. Functionalized nanoparticles were grafted on shellac through a reaction involving the epoxy-rings introduced on their surface. The resulting modified varnishes were applied on maple wood specimens according to traditional procedures. Different instrumental techniques and testing methods were used to characterize both nano-sized materials and the corresponding nanocomposites, as well as to evaluate the performance of the new coatings. The investigated composite materials display the same aesthetic appearance as plain shellac, while some other properties were improved. In particular, both nanocomposites are distinctly less soluble in alcohols than plain shellac and display antifungal properties. Moreover, coating containing functionalized ZnO nanoparticles displays photo-protection behavior, while shellac modified with ZrO2 nanoparticles exhibits a higher hardness when compared to the traditional varnish

Stone consolidation by treatment based on diammonium hydrogenphosphate and calcium hydroxide nanoparticles

Recently the interest in application of nanomaterials for preservation of Cultural Heritage increased. The study proposes a method for the consolidation of weathered calcareous stone (i.e. Lecce Stone) by diammonium hydrogenphosphate and calcium hydroxide nanoparticles providing hydroxyapatite. Stone specimens were artificially weathered by wetting-drying and freezing-thawing cycles and then treated with the products. The mineralization process affording hydroxyapatite was carried out at room temperature, by mimicking the growth mechanism of bone. Ca(OH)2 nanoparticles were synthesized and characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and dynamic light scattering (DLS). The progression of apatite in stone substrate was studied by XRD, its distribution by SEM-EDS. The Treatment efficacy was evaluated by tests as water capillary absorption, colorimetric measurements, tape test, resistance to salt crystallization and uniaxial compression. The results about biomimic formation of hydroxyapatite represent a promising method for conservation of calcareous materials as Lecce Stone