Characterization of Commercial Synthetic Resins by Pyrolysis-Gas Chromatography/Mass Spectrometry: Application to Modern Art and Conservation

Abstract

To characterize a set of synthetic resins, a methodology by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) has been developed. The studied reference materials were commercial versions of a wide range of synthetic resins. For each polymer, the pyrolytic and chromatographic conditions were optimized to adequately resolve the fragment mixture in a short time. The proposed analytical method does not require previous treatment of the sample, and due to its high sensitivity, only a small sample quantity in the microgram range can be used. The pyrolysis temperature was found to have little effect on the obtained pyrograms. The summarized data set for the individual polymer materials, especially the characteristic fragments with a structure close to the monomeric unit, was useful to identify commercial synthetic resins. These materials were used in the art and conservation field, as binding media, paint additives, painting varnishes, coatings, or consolidants. Two case studies are introduced where direct Py-GC/MS and thermally assisted hydrolysis and methylation GC/MS were applied on art objects: first, a modern gluing material of a medieval reverse glass painting, and the second example, the binding medium of a painting by Georg Baselitz ("Senta", 1992/1993) from the Sammlung Moderne Kunst at the Pinakothek der Moderne, Munich.

A chemical study of organic materials in three murals by Keith Haring: A comparison of painting techniques

“…Various pyrolyzers have been used for this purpose based on several technologies, such as furnace, filament, and Curie point [1][2][3][4][5][6]. Analytical pyrolysis is the preferred technique for the molecular characterization of synthetic polymers.…”

Polyurethane coatings in twentieth century outdoor painted sculptures. Part II: comparative study of four systems by means of Py-GC/MS

“…The detection of heptanal is possibly due to the presence of aldehyde resins in the binder mixes [10]. In the same way, the presence of alkyd resins could be at the origin of the detection of adipic acid [11][12][13][14].…”

Multi-technique chemical characterisation of a 12–13th-century painted Crucifix

“…Py-GC/MS is particularly suitable for the analysis of synthetic polymers [12][13][14][15] or polymeric fractions of natural resins [16][17][18][19], whereas MALDI-TOF-MS has recently been shown to be efficient in fast and complete identification of historic paint binders. In fact, since a decade the use of new mass spectrometric techniques based on soft ionization, such as MALDI [20][21][22][23][24][25][26][27] or Electrospray Ionization (ESI) [25][26][27][28][29][30][31][32][33][34][35][36] for investigation of organic materials as present in polychrome artefacts or archaeological finds has significantly increased.…”