Commercial poly(vinyl acetate) (PVAc) paint formulations for artists include a number of compounds in addition to the PVAc polymer and pigments to improve the physical and chemical properties of the resulting product. Among the most common additives are surfactants, coalescing agents, defoamers, freeze-thaw agents and thickeners. These products significantly influence the behaviour of the dried film. Nevertheless, they are usually difficult to detect with conventional analytical methods given their low concentration. In order to identify these additives, present in the dried film as minor components, an analytical method based on in situ thermally assisted pyrolysis-silylation gas chromatography-mass spectrometry (GC-MS) using hexamethyldisilazane as a derivatisation reagent is proposed. This method improves the conventional GC-MS analysis performed by direct pyrolysis and enables the simultaneous identification of the PVAc binding medium and the additives included by the manufacturer in the commercial paint. Five different commercial PVAc paints have been analysed, namely, armour green, burnt umber, oriental red, raw umber and white from Flashe. Internal plasticiser VeoVa consisting of C(10) fatty acids with highly branched chains has been recognised from the MS spectra. On the other hand, the differences found in the additive content of the studied paints, in particular the poly(ethylene glycol)-type surfactant, are in good agreement with their mechanical properties.
This work proposes a multi-method approach that combines advanced microscopy (SEM/EDX, AFM) and spectroscopy (UV-vis and FTIR) techniques. This approach not only characterises the behaviour of the additives of two commercial poly(vinyl acetate) (PVAc) and acrylic emulsion paints but also simultaneously characterises the changes in chemical composition and morphology observed in the paint films as a result of ageing due to the paints being exposed to an intense source of simulated daylight. In parallel, a series of mechanical tests were performed that correlate the chemical changes in composition and the changes observed in the films' mechanical properties. This work was a comparative study between both types of acrylic and PVAc paints. The results obtained are of great interest for the modern paint conservation field as they provide valuable information on the mid- and long-term behaviours of these synthetic paints.
This paper presents a study of thin films of the commercial ketone resins Laropal K80, Keton N and MS2A, attempting to reproduce the pictorial layers and protective finishes commonly present in contemporary paintings. Chemical and morphological changes due to the degradation effect of environmental agents have been specially considered. For this purpose, three different accelerated ageing processes were applied to a series of specimens prepared from the studied commercial products: thermal, UV light and ageing in an SO(2)-polluted chamber. Spectroscopic techniques such as FTIR spectroscopy and UV-Vis spectrophotometry were applied in combination with microscopic examination techniques, namely, AFM and scanning electron microscopy energy dispersive X-ray microanalysis (SEM-EDX). Chemical changes due to UV light and thermal ageing are in good agreement with those previously reported in the literature. Bleaching exhibited by the three commercial products after exposure to a SO(2)-saturated atmosphere has been related to the diffusion of SO(2)-rich water vapour into the film. This effect was particularly strong in the MS2A resin due to the higher content of hydroxyl groups in this product.
a b s t r a c tCommercial formulations of poly(vinyl acetate) (PVAc) and acrylic dispersions and paints commonly used by artists include a number of additives such as surfactants, coalescing agents, defoamers and thickeners, which are designed for improving shelf-life, as well as chemical and physical properties of the resulting product. Recent studies have shown that additives present in paints play an important role in the alteration processes undergone by the painting during ageing and further in cleaning tasks planed in conservation interventions. However, the identification of additives is a difficult task due to the elusive character of these substances present at low concentration in the paint.In this context, a four-step approach is proposed that includes analysis of paint samples together with analysis of their water extracted products by pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) and pyrolysis-silylation-gas chromatography-mass spectrometry (Py-silylation-GC-MS). This analytical strategy enables a better characterization of common additives present in commercial PVAc and acrylic paints and dispersions. In particular, the analysis of water soluble extracts, which are mainly composed by paint additives, avoids the interference of the major polymer pyrolizates. Experimental conditions concerning sample preparation and instrumental working conditions of both Py-GC techniques are optimized.Both acrylic and PVAc paints presented poly(ethylene oxide) (POE) type fragments dominating the background of their pyrograms, especially when derivatized by means of hexamethyldisilazane (HMDS). For the first time, additives such as alkyl sulfate and alkyl ether sulfate with C 10 and C 12 alkyl chains, poly(ethoxylate) fatty alcohol and octylphenyl poly(ethoxylate) surfactants were identified, as well as polyvinyl alcohol (PVOH) protective colloids, hydrophobically modified ethoxylated urethane (HEUR) thickeners an defoamers. Their major fragments and corresponding mass spectra are discussed.
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