A pyrolysis approach for characterizing and assessing degradation of polyurethane foam in cultural heritage objects

Abstract

Specific analytical tools are needed to investigate the composition and degradation processes of the synthetic materials in the cultural heritage, and recent advancements in pyrolysis-based analytical techniques have great potential for the characterisation of synthetic polymers. We applied evolved gas analysis mass spectrometry (EGA-MS) and double shot pyrolysis coupled with chromatography and mass spectrometry (Py-GC/MS) to investigate polyurethane foam micro-samples from the Italian popart sculpture "Contenitoreumano n.1" (1968) by Ico Parisi (1916-1996) and Francesco Somaini (1926-2005. The chemical analysis aimed to assess the chemical composition and of the state of preservation of the PU foam by acquiring information on its thermal degradation behaviour and identifying the pyrolysis products produced at different temperatures. A preliminary ATR-FTIR analysis was also carried out. The multi-analytical approach enabled us to identify the isocyanate and polyol precursors as 2,6-toluenediisocyanate and polypropylene glycol, respectively. The plasticizers used in the production of the PU foam were also identified in the first shot of a double shot Py-GC/MS experiment. A comparison of a sample of better preserved foam with a sample of degraded foam from the surface of the object highlighted that the more degraded part of the PU foam featured an increase in the thermal degradation temperature of the soft-fragments of the PU network, related to crosslinking phenomena. Moreover, loss of plasticizers and formation of NH2 functional groups was observed in the degraded foam.

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

“…In the last 10 years multi-shot pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) has been applied to maximize the information obtained from the analysis of single samples containing different components with a wide range of molecular weights [12,28]. In heritage science, Py-GC/MS has been used for identifying and discriminating between the additives used in the production of synthetic paints and for investigating degradation processes [20,21,29].…”

“…To date, EGA-MS has been mainly used to study reference materials in order to rationalize degradation pathways, or to disclose the nature of interactions occurring in composite materials, however it also provides insights into the nature and degradation of unknown samples [29][30][31].…”

Thermal Decomposition Behavior of a Chelating Resin Immobilizing Carboxymethylated Polyethyleneimine: Possibility of Estimation of Carboxymethylation Rate

“…16,17 Evolved gas analysis/ mass spectrometry (EGA/MS) is a powerful tool to analyze the thermal decomposition process of the polymer. [16][17][18][19][20][21] Recently, fragment-less ionization techniques, such as photo ionization and ion attachment ionization, has attracted attention. 20,[22][23][24][25] When such ionization techniques are applied, a thermalfragment peak in the obtained mass spectrum derives from a compound; therefore, chromatographic separation of compounds evolved from a sample in thermal decomposition is not required.…”

Plastics in Heritage Science: Analytical Pyrolysis Techniques Applied to Objects of Design

“…The analytes derived from the desorption/pyrolysis processes are directly analyzed by the mass spectrometric analyzer without chromatographic separation. This approach achieves information complementary to that from the Py-GC/MS analysis, such as the thermal features of the material, the decomposition temperature of the various fractions (as in a thermal analysis) and the extent of reticulation and depolymerization [33][34][35].…”

“…Each object (described in Section 2.1 and Table 1) had particular preservation issues: the rubber of the fan VE505 (1953), for example, shows a loss of elasticity, exudation and in some areas, embrittlement and decohesion. The polyurethane of Contenitoreumano is part of a very complex multi-material artefact of which very few copies have been made, all of which are now missing except for this polyurethane foam [33] that is the only 'original' element left from 1969. Again, very few copies were made, and it is affected by major structural damage for which it is very difficult to define a plan of action.…”