In this work we propose the use of isothermal thermogravimetry to evaluate the oxidative stability of a lipid and to evaluate how the glyceride composition affects the entire oxidative process, to ...quantify the oxidation undertaken by the lipid, and numerically compare the oxidative behaviour of different lipids. The innovative aspect of the present method lies in the acquisition of a prolonged "oxygen uptake" curve (4000-10,000 min) of a lipid under oxygen and in the development of a semi-empirical fitting equation for the experimental data. This provides the induction period (oxidative stability), and allows to evaluate the rate of oxidation, the rate and the magnitude of oxidative degradation, the overall mass loss and the mass of oxygen taken by the lipid upon time. The proposed approach is used to characterize the oxidation of different edible oils with different degrees of unsaturation (linseed oil, sunflower oil, and olive oil) as well as chemically simpler compounds used in the literature to model the autoxidation of vegetable oils and lipids in general: triglycerides (glyceryl trilinolenate, glyceryl trilinoleate and glyceryl trioleate) and methyl esters (methyl linoleate and methyl linolenate). The approach proves very robust and very sensitive to changes in the sample composition.
Acrylonitrile butadiene styrene (ABS) is a thermoplastic polymer widely used in several everyday life applications; moreover, it is also one of the most employed plastics in contemporary artworks and ...design objects. In this study, the chemical and thermal properties of an ABS-based polymer and its photo-degradation process were investigated through a multi-analytical approach based on thermal, mass spectrometric and spectroscopic techniques. LEGO
building blocks were selected for studying the ABS properties. First, the composition of unaged LEGO
bricks was determined in terms of polymer composition and thermal stability; then, the bricks were subjected to UV-Vis photo-oxidative-accelerated ageing for evaluation of possible degradation processes. The modifications of the chemical and thermal properties were monitored in time by a multi-technique approach aimed at improving the current knowledge of ABS photodegradation, employing pyrolysis online with gas chromatography and evolved gas analysis, coupled with mass spectrometric detection (Py-GC-MS and EGA-MS), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and corroborated by external reflection FT-IR spectroscopy. The multimodal approach provided new evidence on the two-step degradation pathway proposed for ABS, defining molecular markers for polybutadiene oxidation and styrene-acrylonitrile depolymerization. Moreover, the results highlighted the feasibility of correlating accurate compositional and thermal data acquired by bulk techniques with external reflection FT-IR spectroscopy as a non-invasive portable tool to monitor the state of conservation of plastic museum objects in-situ.
We present the results of a diagnostic campaign on three of Giuseppe Capogrossi’s abstract paintings from the 1950s and 1960s, conserved at the National Gallery of Modern and Contemporary Art in ...Rome. Non-invasive investigations by reflection FT-IR spectroscopy were carried out, followed by micro-destructive laboratory analyses using Py-GC-MS, and HPLC-ESI-Q-ToF. The investigations focused on identifying the binders used for both the preparation and the pictorial layers. In two of the paintings investigated, an industrial preparation was identified based on egg yolk, mixed with other organic materials (acryl resin, oil, animal glue). The paint media include the use of both oil and alkyd paint. In one of the three paintings, the presence of a styrene-acryl resin was observed. The results show the simultaneous use of traditional and innovative materials, confirming the complexity of the period in which the artist was active, characterized by the technical experimentation of both the artists and manufacturers. The research also contributes to a better understanding of Giuseppe Capogrossi’s artistic profile, from the point of view of executive techniques.
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•A mass spectrometry methodological approach is implemented to study oil curing.•Methyl linoleate is employed as a simplified model of an oil paint binder.•The molecular features of ...oxidative degradation and cross-linking are disclosed.•Curing of pigmented paint layers are studied with a new high level of molecular detail.•The composition of the cross-linked fraction depends on the pigment.
The structure of the polymeric fraction in an oil painting is believed to be strongly connected to the stability of the paint layers over time, but its molecular characterisation is extremely difficult given the complex composition of a vegetable oil-based polymer.
In this study we report the implementation of a methodological approach for the systematic mass spectrometric investigation of the molecular features of the products of oxidative degradation and cross-linking of oil paint layers upon curing. The approach is based on the use of methyl linoleate as a simplified model of an oil paint binder. Gas-chromatography coupled with mass spectrometry, solid phase microextraction gas chromatography mass spectrometry, flow injection electrospray mass spectrometry and evolved gas analysis mass spectrometry, are used to analyse the evolution of compounds produced over seven months of natural ageing, from the volatile products to the macromolecular and cross-linked fractions. The aim is to improve our fundamental molecular understanding of the curing process of oil paints, and to investigate the balance between oxidative degradation and cross-linking when specific binder-pigment combinations are in place.
Model paint layers were prepared using lead white and ultramarine blue as pigments. These two pigments are known to produce paint layers with different stability over time. The use of methyl linoleate as model oil binder greatly simplifies the mass spectral features of the lipid paint fraction, enabling the detection of products of oxidation and cross-linking with a new high level of molecular detail. Data clearly show that crucial differences between paints containing the two pigments establish with time, which are mostly related to the cross-linked fraction.
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•A technical study of paints based on ovalbumine-drying oil mixtures is carried out.•Detection of proteins can be hampered when these are applied in mixture with drying oils.•A new ...procedure with two hydrolysis steps was implemented for GC–MS analysis of proteins.•Ovalbumine affects the curing of linseed oil.•Hypothesis on copolymeristaion between drying oils and ovalbumine is proposed.
In this paper we present the technical study of protein-drying oil mixtures in the paint formulation of original manufacturers paint tubes from Fabbrica di colori per Belle Arti Maimeri dating back to the 1950s. The study is part of a wider research project aimed at understanding the chemistry of protein-drying oil mixtures, and how the oil curing in the presence of proteins may affects the protein analysis with mass spectrometric based techniques.
Tempera grassa, according to traditional Late Medieval and Renaissance painting techniques, entails the use, as paint binder, of a mixture of a drying oil with a water miscible medium, commonly egg. The paints analysed in this study were, according to technical documentation available at the manufacturer, based on a mixture of linseed oil, ovalbumin and mastic resin. All the components of the paints were detected but proteins proved very challenging. They could not be detected by pyrolysis coupled to gas chromatography-mass spectrometry, nor by using classical procedures for gas chromatography – mass spectrometry analysis of amino acids after hydrolysis. A new analytical procedure based on two subsequent hydrolysis steps assisted by microwaves was implemented and proved to be successful. The first step with trifluoroacetic acid was aimed at a partial hydrolysis of proteins into peptides, for their efficient extraction. The second with hydrochloric acid in the vapour phase was used for a complete hydrolysis of peptides into amino acids for the GC–MS analysis. Linking experimental results on the tempera grassa paints to data obtained on the curing of oil/protein mixtures in paint mock-ups, the hypothesis that copolymerisation of proteins and the oil has taken place is proposed, and a discussion on how this may affect protein detection is carried out.
Carbon black-based particles are widely employed as pigment and they are known to slow down the drying time of oil paints. In this work, the effect of amorphous carbon black on the mechanism and ...speed of autoxidation of a polyunsaturated oil was investigated. Moreover, the effect of the addition of aluminium stearate and zinc stearate was studied. These are two common additives used in the artists’ paint industry to facilitate pigment dispersion. The curing of the oil paints with and without the addition of the two stearates at 80 °C under airflow was followed by isothermal Thermogravimetry. The oxygen uptake profiles were fitted by a semi-empiric equation to comparatively study the kinetics of the oil oxidation and estimate oxidative degradation. Moreover, model paintings were left to cure at ambient conditions and Differential Scanning Calorimetry was then used to monitor their curing progress over time and to evaluate the stability of peroxides formed in the paint layers. Gas Chromatography–Mass Spectrometry was performed at 7 and 12 months of natural ageing of the model paintings, to investigate the non-covalently cross-linked fractions. Analytical Pyrolysis coupled with Gas Chromatography–Mass Spectrometry was used to characterise the whole organic fraction of the model paintings, including the cross-linked network. Amorphous carbon has an antioxidant effect and inhibits the radical chain propagation. The presence of aluminium and zinc stearates in the black paint affects the autoxidation process, by leading, in the first months, to a faster consumption of unsaturated moieties, and, accordingly, to accelerate and increase peroxides formation. After a few months though, the whole curing slows down, and active peroxides and radicals are still present even after 12 months.
Abstract Geopolymers have been recently proposed for restoration of built heritage to substitute traditional mortars. Local materials and industrial wastes from the Italian region Sicily showed their ...potential as low-cost aluminosilicate sources for the preparation of geopolymers. Here, a set of Sicilian clays was studied by Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC), and its mineralogical composition was evaluated by X-ray diffraction (XRD). The raw materials were used to prepare geopolymers by alkaline activation with or without the addition of silicate. The thermal degradation profile of the final materials was studied by TGA and compared with that of the precursors, and the energetics of dehydration were investigated by DSC. Two statistical analyses (made by Principal Component Analysis) were performed on the TG data of raw materials and geopolymers and on the TG data of geopolymers and their mineralogical composition, respectively. The last analysis in particular showed a correlation between the mineralogical composition of the materials and the samples' thermal properties. Additional studies of samples subject to accelerated aging by UV irradiation and exposure to acetic acid vapors highlighted the different effects of these two agents on the samples’ stability. Graphical abstract
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•A strong ovalbumin stabilization occurs as the water content decreases below 30 %.•In water-limiting condition, humidity changes stress the protein stability/structure.•Water phase ...separation occurs within protein-based paint layers.•Protein phase's water content is higher than the paint’s nominal value.
The role of water and hematite (Fe2O3) on the stability of ovalbumin-based model paint layers was investigated by means of DSC and FTIR. The aim of this research is to improve our understanding on the stability of paint layers based on proteinaceous media, assessing the water content and the pigment presence effects. Pigments may play a fundamental role in determining the structure of proteins in paint layers, thus affecting the possible interactions among proteins and the external environment, including humidity. Previous studies revealed that hematite affects the secondary structure of OVA in paint layers, although no experimental evidence of hematite/OVA covalent bonds has been reported in the literature. In this paper we investigate the synergic effect of water and hematite on OVA structure and stability. DSC analyses coupled with FTIR measures on protein hydration revealed that below 30 % of humidity the amount of water strongly influence the protein structure and stability: the less the water content, the higher the protein stability. Furthermore, our results suggest that a water phase separation occurs in the presence of hematite for which, in water-limiting condition, the hematite’s hydration shell becomes almost negligible if compared to the bulk water available for the protein hydration because of the high protein-water affinity. Accordingly, the protein phase humidity is higher than the sample’s nominal value. Paints at the same overall humidity exhibit different protein hydration state following the pigment/binder ratio, and in turn different resistance to damages throughout aging.
In this work, we propose to follow the crystallization capability of oils in oil-based paints, during curing, as an indirect index of the matrix status in the early stages of paint film formation ...that usually are indicative and crucial to understand the process evolution. To proof the concept, the oil crystallization properties were investigated through DSC measurements on samples of both unpigmented linseed oil and two model paints, composed by lead white + linseed oil (LWLO) and ultramarine blue + linseed oil (UBLO), at different ageing time at room and oxygen-limiting conditions. The results indicate that the curing process strongly affects the oil’s ability of forming crystals in the paint layers, and the proposed experimental approach is rather suitable and sensitive enough to discriminate differences between the action of pigments and environmental conditions. On the other hand, despite the simplicity and the potentiality, this approach is limited at the early stages of paint curing offering an index of the overall matrix status and therefore must be intended as a complementary method that has to be integrated with other approaches if the aim is to explore in detail the chemical and physical aspects of the curing process.
In this study, the chemistry of air-drying artist’s oil paint curing and aging up to 24 months was studied. The objective is to improve our molecular understating of the processes that lead to the ...conversion of the fluid binder into a dry film and how this evolves with time, which is at the base of a better comprehension of degradation phenomena of oil paintings and relevant to the artists’ paint manufacturing industry. To this aim, a methodological approach based on thermogravimetric (TG) analysis, differential scanning calorimetry (DSC), gas chromatography–mass spectrometry (GC–MS), and analytical pyrolysis coupled with gas chromatography and mass spectrometry (Py–GC–MS) was implemented. Model paintings based on linseed oil and safflower oil (a drying and a semidrying oil, respectively) mixed with two historically relevant pigmentslead white (a through drier) and synthetic ultramarine blue (a pigment often encountered in degraded painting layers)were investigated. The oil curing under accelerated conditions (80 °C under air flow) was followed by isothermal TG analysis. The oxygen uptake profiles were fit by a semiempiric equation that allowed to study the kinetics of the oil oxidation and estimate oxidative degradation. The DSC signal due to hydroperoxide decomposition and radical recombination was used to monitor the radical activity over time and to evaluate the stability of peroxides formed in the paint layers. GC–MS was performed at 7 and 24 months of natural aging to investigate the noncovalently cross-linked fractions and Py–GC–MS to characterize the whole organic fraction of the model paintings, including the cross-linked network. We show that the oil–pigment combination may have a strong influence on the relative degree of oxidation of the films formed with respect to its degree of cross-linking, which may be correlated with the literature on the stability of painting layers. Undocumented pathways of oxidation are also highlighted.
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