1,720,989 research outputs found
Water-repellent properties of fluoroelastomers on a very porous stone: Effect of the application procedure
No full textA fluorinated elastomeric material with enhanced hydrophobic properties has been studied as a protec- tive coating on Lecce stone. The polymer has been applied, as a butyl acetate solution, on stone specimens according to two different methodologies, i.e. brushing and capillary absorption.
The application performed by brush (amounts equal or greater than 50 g/m2 ) induces the formation of a superficial film, which prevents condensed water from penetrating but, at the same time, considerably reduces the vapour permeability.
On the contrary, when the fluoroelastomer solution is applied by the capillary absorption technique (amounts in the 25–75 g/m2 range), reduction of vapour permeability is acceptable but a poor protection against water penetration is observed. It can be due to a deeper penetration of the polymeric material, which is more homogeneously dispersed in the stone without forming a hydrophobic coating on the surface
Anti-graffiti nanocomposite materials for surface protection of a very porous stone
No full textThe preservation of stone substrates from defacement induced by graffiti represents a very chal- lenging task, which can be faced by applying suitable protective agents on the surface. Although different anti- graffiti materials have been developed, it is often found that their effectiveness is unsatisfactory, most of all when applied on very porous stones, e.g. Lecce stone. The aim of this work was to study the anti-graffiti behaviour of new nanocomposite materials obtained by dispersing montmo- rillonite nanoparticles (layered aluminosilicates with a high-aspect ratio) into a fluorinated polymer matrix (a fluorinated polyurethane based on perfluoropolyether blocks). Polymeric structure was modified by inducing a cross-linking process, in order to produce a durable anti- graffiti coating with enhanced barrier properties. Several composites were prepared using a naturally occurring and an organically modified montmorillonite clay (1, 3, and 5 % w/w concentrations). Materials were applied on Lecce stone specimens, and then their treated surfaces were soiled by a black ink permanent marker or by a black acrylic spray paint. Several repeated staining/cleaning cycles were performed in order to evaluate anti-graffiti effectiveness. Colorimetric measurements were selected to assess the anti-graffiti performance. It was found that the presence of 3 % w/w organically modified montmorillonite in the polymer coating is enough to induce a durable anti-graffiti effect when the stone surface is stained by acrylic paint. Less promising results are obtained when staining by per- manent marker is considered as all the investigated treatments afford a reasonable protection from ink only for the first staining/cleaning cycle
Shellac/nanoparticles dispersions as protective materials for wood
No full textWood is a natural material that finds numerous and widespread applications, but is subject to different decay processes. Surface coating is the most common method used to protect wood against deterioration and to improve and stabilize its distinctive appearance. Shellac is a natural resin that has been widely used as a protective material for wooden artifacts (e.g. furniture, musical instruments), due to its excellent properties. Nevertheless, diffusion of shellac-based varnishes has significantly declined during the last decades, because of some limitations such as the softness of the coating, photo-degrdn., and sensitivity to alc. solvents and to pH variations. In the present study, different inorg. nanoparticles were dispersed into dewaxed natural shellac and the resulting materials were investigated even after application on wood specimens in order to assess variations of the coating properties. Analyses performed by a variety of exptl. techniques have shown that dispersed nanoparticles do not significantly affect some distinctive and desirable features of the shellac varnish such as chromatic aspect, film-forming ability, water repellence, and adhesion. On the other hand, the obtained results suggested that some weak points of the coating, such as low hardness and poor resistance to UV-induced ageing, can be improved by adding ZrO2 and ZnO nanoparticles, resp
Stradivari’s Varnish Revisited: Feature Improvements Using Chemical Modification
Full text linkThe 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)
Chemical characterization of wood samples colored with iron inks: insights into the ancient techniques of wood coloring
No full textIn the past, the practice of dyeing wood was very widespread, for instance for obtaining substitutes for rare and expensive ebony, which was used for all marquetry techniques and especially for making inlays to decorate musical instruments. This study focuses on two traditional wood-dyeing procedures carried out with iron–gall dye and iron–logwood dye, respectively. In order to reproduce the ancient techniques, preparation of dyes and their application on two different wood species (poplar and pear) were carried out according to typical ancient recipes and traditions. Wood samples were dyed using mixtures similar to two of the most important historic iron inks, and several specimens (approximately 7 mm in size) were taken and investigated in order to: (1) gain a better insight into the processes involving the dyes and the wood matrices, (2) analyze the effects of the treatments on the anatomical wood structures, (3) evaluate the level of penetration of the dyestuffs into the samples. The analyses were performed after each step of the dyeing procedures, both on the wood samples and on the solutions. Various reaction processes were hypothesized after a micro-Fourier transform infrared spectroscopy analysis, performed in transflection and attenuated total reflection mode. The effects of the various treatments on the wood samples were studied by means of stereomicroscopy, polarized optical microscopy and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The results obtained suggested that both treatments cause alterations in the outer 300 μm of the wooden samples, and that a higher level of penetration was obtained with the hematein complex than with the iron-gall ink
Surface treatments of wood by chemically modified shellac
No full textShellac is an animal resin, which has been widely used as a decorative lacquer for wooden handicrafts in the last centuries. It still finds application as wood sealer and finisher because of its peculiar properties. However, there are also some limitations, such as sensitivity to alcoholic solvents and to pH variations and considerable tendency to chromatic variations upon ageing. The aim of this work is to improve some features of shellac by inducing a cross-linking in its structure. Two new materials were obtained by addition of a polyamine and a polyaziridine to shellac, and their performance were studied by different experiments. The varnish obtained by addition of polyaziridine shows a considerably improved performance when compared to plain shellac. In particular, it preserves almost unaltered the chromatic properties of shellac varnish and it shows an increased resistance to alcohols, to basic agents and to artificial ageing caused by a long lasting UV irradiation
Experimental characterization of oil-colophony varnishes: A preliminary study
No full textHistorically, the varnishes had the aim to protect the bowed musical instruments by the
external agents and to confer them an aesthetic value. During the 17th and 18th century, in
Italy, the bowed instruments, especially violins, were generally covered by a layer of varnish
made with several natural materials such resins, oil or hide glue: i.e., instruments by the great
violin maker Antonio Stradivari were covered often with a layer of varnish made of linseed oil
and colophony in the ratio 3:1, respectively. The main aim of this work was to study the
modifications that occur in those kinds of varnishes, after exposing them to some factors of
degradation. In order to study the different properties of organic coatings and their suitable
compositions, different mixtures of linseed oil and colophony were recreated in the laboratory
following an ancient recipe: linseed oil and colophony were mixed together with different
ratios (50/50 and 75/25, respectively) and then, they were applied on Maple wood samples and
on glass slides for experimental purposes. In order to investigate the different external factors
which cause the varnish layer degradation, samples were analyzed by different techniques
before and after different ageing processes (thermo-hygrometric cycles, exposition to UV lamp
and to acid vapors). Out of strong experimental evaluation, all the results suggested that the
composition of 75/25 (oil: colophony) is much better as a varnish for musical instruments
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