Characterization of polyvinyl resins used as binding media in paintings by pyrolysis–silylation–gas chromatography–mass spectrometry

Abstract

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.

Microbial deterioration of Mowilith DMC 2, Mowilith DM5 and Conrayt poly(vinyl acetate) emulsions used as binding media of paintings by pyrolysis-silylation-gas chromatography–mass spectrometry

“…At the same time, the suitability of pyrolysis-gas chromatographymass spectrometry (Py-GC-MS) as a complementary technique for evaluating biodeterioration processes was considered. For this purpose, a method based on the on-line derivatization of samples with hexamethyldisilazane (HMDS) was applied [16]. This method is based on the formation of trimethylsilyl ethers and esters, and has been proposed as an alternative to other commonly employed derivatization reagents such as tetramethyl ammonium hydroxide, to improve the detection of hydroxylated compounds and to avoid isomerization and unwanted alkylation reactions.…”

Determination of the plasticizer content in poly(vinyl acetate) paint medium by pyrolysis–silylation–gas chromatography–mass spectrometry

“…The effects of ageing are fairly known and have been extensively reported, including increased brittleness, loss of tensile strength, darkening, yellowing and loss of translucency among others [1][2][3][4].…”

“…Previous studies have shown that Py-GC-MS can be successfully used to identify monomers and plasticizers used in acrylic and vinyl resin based products [1,3]. Alternatively, Domé nech et al have recently optimized an ''on-line'' derivatization method using hexamethyldisilazane (HMDS) as a derivatization reagent for the study of acrylic and vinyl resins as well as some of the additives present in different commercial formulations.…”

“…Alternatively, Domé nech et al have recently optimized an ''on-line'' derivatization method using hexamethyldisilazane (HMDS) as a derivatization reagent for the study of acrylic and vinyl resins as well as some of the additives present in different commercial formulations. According to these studies, trimethylsilylation of the carboxylic acids present in both types of resins contributes to a better repeatability in results comparing to direct pyrolysis [1,23]. However, the application of this instrumental technique in the study of ageing of PVAc materials is scarce.…”

“…These test specimens were analyzed with ''on-line'' silylationpyrolysis using hexadimethyldisilazane (HMDS) as a derivatization agent in Py-GC-MS [1], and 1,4-dibromebenzene was applied as an IS for quantification purposes. This latter reagent has been proposed by Moldoveanu [24] as an IS for the quantification of the analysis of pyrolisates from tobacco samples by Py-GC-MS.…”