Synthetic materials in art: a new comprehensive approach for the characterization of multi-material artworks by analytical pyrolysis

Jacopo La Nasa,Maria Perla Colombini,Francesca Sabatini,Francesca Modugno,Greta Biale,Ilaria Degano

doi:10.1186/s40494-019-0251-4

Jacopo La Nasa, Maria Perla Colombini + Show 4 more

Open Access

https://doi.org/10.1186/s40494-019-0251-4

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Journal: Heritage Science	Publication Date: Feb 16, 2019
Citations: 34	License type: open-access

Affiliation: University of Pisa

Abstract

Modern art materials introduced since the end of XIX century include a large number of formulations of synthetic polymers and pigments, whose degradation processes and best preservation conditions are a major issue in heritage science. Analytical pyrolysis coupled with gas chromatography and mass spectrometry (Py-GC/MS) is widely used for the characterisation of polymeric materials and organic pigments, however the interpretation of the pyrograms obtained from samples containing different analytes is not straightforward. To improve our understanding on how these materials behave in complex matrices, we used evolved gas analysis coupled with mass spectrometry (EGA-MS) and multi shot Py-GC/MS to highlight and analyse the different fractions in a sample from a pop-art made of painted polyurethane (PU) foam. The study represents a proof of concept to evaluate EGA-MS potential in studying composite modern art materials in combination with multi-shot pyrolysis. The aim of the investigation was establishing the composition of the PU formulation, the paint binder and the pigments, thereby contributing to planning the stabilisation and conservation of the object. The polymers and the class of synthetic organic pigments present in the paint were assessed by determining their specific pyrolysis products and through comparisons with data in the literature. EGA-MS analysis provided both thermal and chemical information in one analytical run, so that we could select four temperatures for use in multi-shot Py-GC/MS analysis and thus to selectively study the different fractions evolved at different temperatures. Information on the various components of the mixture was obtained, including additives and organic pigments, separating them on the basis of their different thermal degradation temperatures. The multianalytical approach included also non-destructive ATR-FTIR and enabled us to characterize in detail different synthetic materials: polyether-based polyurethane produced by the polyaddition of 2,6-diisocyanate toluene, hexamethylene diisocyanate and polypropylene glycol, vinyl paint, and a mixture of β-naphthol and mono-azo as pigments. HPLC–DAD and HPLC–ESI–MS analyses confirmed the pigments, and provided a positive identification of two β-naphthols (PO5 and PR1) and two monoazo pigments (PY1 and PY3).

Highlights

Preserving modern and contemporary artworks and design objects is emerging as a major issue in conservation science, due to the wide range of new techniques and materials for artists that have been introduced since the end of the nineteenth century [1, 2]
This study further explores the advantages of introducing evolved gas analysis coupled with mass spectrometry (EGA-MS) in the field of heritage science and examine its potential in combination with multi-shot pyrolysis to investigate modern artistic materials
The multianalytical approach enabled us to characterize in detail, at a molecular level, a complex sample from a three-dimensional work of art made up of different synthetic materials: polyurethane foam painted with a vinyl paint containing organic pigments

Summary

Introduction

Preserving modern and contemporary artworks and design objects is emerging as a major issue in conservation science, due to the wide range of new techniques and materials for artists that have been introduced since the end of the nineteenth century [1, 2]. The combination of more than one material in the same artwork makes the conservation of synthetic polymers in heritage objects a critical issue, due to possible interactions between components, which are characterized by different degradation pathways and a different durability. Some classes of synthetic organic pigments (SOPs) are labile and vulnerable to fading and photo-oxidation phenomena [3]. The knowledge of their exact composition, in terms of both major and minor components, is mandatory to disclose the chemical behaviour of a specific SOP over time [4]. The identification of organic pigments is further complicated by the lack of information generated by their generic trade names and by the frequent commercialization of the same compound under different names and vice versa; scarce attention was often paid to the purification steps [5]

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