Polyvinyl resins, in particular poly(vinyl acetate) emulsions (PVA), are widely used in contemporary paintings as binding media, because of the optimum mechanical and optical properties these polymers confer on the paint layers. A study has been carried out to chemically characterize samples of PVA resins prepared as coating films from commercial products currently available from fine arts suppliers. For this purpose, a new method has been based on "on-line" silylation-pyrolysis using hexamethyldisilazane as derivatisation reagent in pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS). This proposed procedure leads to unambiguous identification of this type of binder and improves conventional direct Py-GC-MS. PVA media used in three contemporary paintings from a private collection and from the Museum of Fine Arts of Málaga (Spain) have been successfully identified with this procedure. As a second step of this work, a study devoted to the characterization of changes in the chemical composition of the PVA commercial products studied has been carried out. Effects induced in the specimens by three different types of artificial accelerated ageing process--thermal, UV light, and in an SO(2)-polluted chamber--were compared.
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.
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