Cross-infection effect of polymers of historic and heritage significance on the degradation of a cellulose reference test material

Review of recent advances on the use of mass spectrometry techniques for the study of organic materials in painted artworks

The study of painted artworks using scientific methods is fundamental for understanding the techniques used in their creation and their appropriate conservation. The ethical constraints involved in the handling of, and sampling from, these objects has steered recent developments in the field of Heritage science towards a range of new non-invasive/non-destructive spectroscopic techniques capable of providing important insights into their elemental or bulk chemical compositions. Due to the inherent complexities of heritage artefacts, however, their organic components are especially difficult to study in this way and their identification and degradation pathways are thus often best investigated using mass spectrometric (MS) techniques. The versatility, sensitivity and specificity of MS techniques are constantly increasing, with technological advances pushing the boundaries of their use in this field. The progress in the past ten years in the use of MS techniques for the analysis of paint media are described in the present review. While some historical context is included, the body of the review is structured around the five most widely used or emerging capabilities offered by MS. The first pertains to the use of spatially resolved MS to obtain chemical maps of components in cross-sections, which may yield information on both inorganic and organic materials, while the second area describes the development of novel sample preparation approaches for gas chromatography (GC)-MS to allow simultaneous analysis of a variety of components. The third focuses on thermally assisted analysis (either with direct MS or coupled with GC-MS), a powerful tool for studying macromolecules requiring zero (or minimal) sample pre-treatment. Subsequently, the use of soft ionisation techniques often combined with high-resolution MS for the study of peptides (proteomics) and other macromolecules (such as oligosaccharides and triglycerides) is outlined. The fifth area covers the advances in radiocarbon dating of painting components with accelerator MS (AMS). Lastly, future applications of other MS techniques to the study of paintings are mentioned; such as direct analysis in real time MS (DART-MS) and stable isotope ratio MS (IRMS). The latter, having proven its efficiency for the study of lipids in archaeological artefacts, is envisioned to become a valuable tool for this area, whereas DART-MS is already being utilised to study the surface composition of various museum objects. Rapid technological advances, resulting in increased sensitivity and selectivity of MS techniques, are opening up new approaches for paintings analysis, overcoming the fundamental hurdle of sample size available for destructive analysis. Importantly, while the last decade has seen proteomics applications come to the fore, this review aims to emphasise the wider potential of advanced MS techniques for the study of painting materials and their conservation.

The Effect of Synthetic Polymer Foams on Cellulosic Material Degradation

Polymeric materials are widely used at present as auxiliary materials in the preservation of tangible cultural heritage in museums, galleries, or libraries. The desired properties of such materials include chemical inertness and long lifetime, which are verified by accelerated aging tests. This work has tested three color types of PE foam Plastazote^® LD45 (white, grey, and black), which is recommended for use in the field of cultural heritage preservation. The volatile organic compounds released from the foams after artificial aging and their influence on lignocellulosic materials were investigated. The cellulosic materials were artificially aged in close contact with the foams. All foams released organic acids ranging from acetic acid to hexanoic acid. White foam released organic acids to an extent higher by an order of magnitude compared to the grey and black types. A great influence of white foam on the properties of cellulosic materials was observed. There were large differences in the rate of degradation between the types of foams tested, indicating the need to develop a test method in order to determine the suitability for use in the preservation of culture heritage objects.

Special Aspects of Nitrocellulose Molar Mass Determination by Dynamic Light Scattering

The dynamic light scattering method was successfully applied to determine the molar mass of nitrocellulose. The methodology of nitrocellulose fractionation in acetonic solutions is described in detail; six polymer fractions with monomodal distribution were obtained. It was shown that the unfractionated colloxylin with polymodal molar mass distribution had mass average molecular mass values of 87.3 ± 14.1, 28.3 ± 7.3, and 0.54 ± 0.17 kDa when investigated by the dynamic light scattering method. The viscometric method only provided integral viscosity average molar mass equal to 56.7 ± 5.8 kDa.

Machine learning-assisted non-destructive plasticizer identification and quantification in historical PVC objects based on IR spectroscopy

Non-destructive spectroscopic analysis combined with machine learning rapidly provides information on the identity and content of plasticizers in PVC objects of heritage value. For the first time, a large and diverse collection of more than 100 PVC objects in different degradation stages and of diverse chemical compositions was analysed by chromatographic and spectroscopic techniques to create a dataset used to construct classification and regression models. Accounting for this variety makes the model more robust and reliable for the analysis of objects in museum collections. Six different machine learning classification algorithms were compared to determine the algorithm with the highest classification accuracy of the most common plasticizers, based solely on the spectroscopic data. A classification model capable of the identification of di(2-ethylhexyl) phthalate, di(2-ethylhexyl) terephthalate, diisononyl phthalate, diisodecyl phthalate, a mixture of diisononyl phthalate and diisodecyl phthalate, and unplasticized PVC was constructed. Additionally, regression models for quantification of di(2-ethylhexyl) phthalate and di(2-ethylhexyl) terephthalate in PVC were built. This study of real-life objects demonstrates that classification and quantification of plasticizers in a general collection of degraded PVC objects is possible, providing valuable data to collection managers.

Material Analysis and a Visual Guide of Degradation Phenomena in Historical Synthetic Polymers as Tools to Follow Ageing Processes in Industrial Heritage Collections

Identifying the most vulnerable plastics and monitoring their deterioration is one of the main problems within heritage collections with historical synthetic polymers. Gathering and interpreting data about material and degradation phenomena in a collection reveals its conservation needs. A systematic survey of the collection can help towards this purpose. Surveys aiming at inspecting and documenting damages rely on several tools in order to fulfill their purpose. Firstly, objective descriptions of the damages that may appear, and secondly, the means of acquiring and interpreting material information. To address these needs, this article presents (a) a visual damage catalogue of degradation phenomena in plastic and rubber materials, and (b) the implementation of Fourier-transform infrared spectroscopy (FTIR) and pyrolysis–gas chromatography–mass spectrometry (py-GCMS) for the identification of analytically challenging rubber materials and of blooming phenomena. The damage catalogue is based solely on visual and olfactory signs, so that the assessment is independent of possible causes of damages and underlying processes, with the purpose of allowing objectivity to prime over interpretation. The limitations of the use of FTIR in the identification of heavily compounded rubbers in museum surveys is highlighted, and examples are presented. The use of py-GCMS on these cases conveniently allowed the identification of the constituting monomers of several rubber materials where FTIR could not provide a univocal classification of the material present. The study of several cases of blooming allowed the identification of diverse compositions and origins, showing that the description of a degradation phenomenon is only the first step towards its understanding. Unveiling the nature of a particular case of blooming is particularly critical when conservation treatments, such as the removal of a (potentially protecting) layer, are planned. For this purpose, attenuated total reflection-FTIR (ATR-FTIR) as a surface technique was particularly useful.

Novel markers to early detect degradation on cellulose nitrate-based heritage at the submicrometer level using synchrotron UV-VIS multispectral luminescence

Cellulose nitrate (CN) is an intrinsically unstable material that puts at risk the preservation of a great variety of objects in heritage collections, also posing threats to human health. For this reason, a detailed investigation of its degradation mechanisms is necessary to develop sustainable conservation strategies. To investigate novel probes of degradation, we implemented deep UV photoluminescence micro spectral-imaging, for the first time, to characterize a corpus of historical systems composed of cellulose nitrate. The analysis of cinematographic films and everyday objects dated from the nineteenth c./early twentieth c. (Perlov's collection), as well as of photo-aged CN and celluloid references allowed the identification of novel markers that correlate with different stages of CN degradation in artworks, providing insight into the role played by plasticizers, fillers, and other additives in stability. By comparison with photoaged references of CN and celluloid (70% CN and 30% camphor), it was possible to correlate camphor concentration with a higher rate of degradation of the cinematographic films. Furthermore, the present study investigates, at the sub-microscale, materials heterogeneity that correlates to the artworks' history, associating the different emission profiles of zinc oxide to specific color formulations used in the late nineteenth and early twentieth centuries.

A Smart Archive Box for Museum Artifact Monitoring Using Battery-Less Temperature and Humidity Sensing

For the first time, this paper reports a smart museum archive box that features a fully integrated wireless powered temperature and humidity sensor. The smart archive box has been specifically developed for microclimate environmental monitoring of stored museum artifacts in cultural heritage applications. The developed sensor does not require a battery and is wirelessly powered using Near Field Communications (NFC). The proposed solution enables a convenient means for wireless sensing with the operator by simply placing a standard smartphone in close proximity to the cardboard archive box. Wireless sensing capability has the advantage of enabling long-term environmental monitoring of the contents of the archive box without having to move and open the box for reading or battery replacement. This contributes to a sustainable preventive conservation strategy and avoids the risk of exposing the contents to the external environment, which may result in degradation of the stored artifacts. In this work, a low-cost and fully integrated NFC sensor has been successfully developed and demonstrated. The developed sensor is capable of wirelessly measuring temperature and relative humidity with a mean error of 0.37 °C and ±0.35%, respectively. The design has also been optimized for low power operation with a measured peak DC power consumption of 900 μW while yielding a 4.5 cm wireless communication range. The power consumption of the NFC sensor is one of the lowest found in the literature. To the author’s knowledge, the NFC sensor proposed in this paper is the first reporting of a smart archive box that is wirelessly powered and uniquely integrated within a cardboard archive box.

Development of a gel permeation chromatography method for analysing cellulose nitrate in museums

This article describes the development of a suitable Gel Permeation Chromatography method for cellulose nitrate plasticised with camphor (celluloid) found in cultural heritage. Current sample preparation and dissolution methods, apart from focusing on native, nonderivatised cellulose, require long preparation times, and often employ solvents that induce degradation. This study aims to develop a systematic method for sample preparation of cellulose nitrate that uses the least sample amount possible, is nondegrading, and can be applied on differently aged samples. This is investigated through identification of a suitable solvent system and a statistically designed experiment testing the critical variables affecting the analysis, namely sample condition, sample, and salt concentration (lithium chloride) in N,N-dimethylacetamide. The use of 0.1% sample was inadequate for analysis because it did not fully dissolve in any salt concentration, while the 0.3% negatively impacted the analysis with its high molecular weight distributions. The 0.2% cellulose nitrate in a solution of 0.5% lithium chloride in N,N-dimethylacetamide offered the most consistent and repeatable molecular weight data. This method miniaturised the sample as much as possible and is suitable for museum objects in various ageing conditions.

ZnO/polyaniline composite based photoluminescence sensor for the determination of acetic acid vapor

In this study, we report a novel ZnO/polyaniline (PANI) nanocomposite optical gas sensor for the determination of acetic acid at room temperatures. ZnO nanorods, synthesized in powder form were coated by PANI (ZnO/PANI) by chemical polymerization method. The obtained nanocomposites were deposited on glass substrate and dried overnight at room temperature. Structure and optical properties of ZnO/PANI nanocomposite have been studied by using X-ray diffraction, transmission electron microscopy, scanning electron microscopy, diffuse reflectance and photoluminescence spectroscopy. Tests towards acetic acids were performed in the range of concentrations 1-13 ppm. The adsorption of acetic acid on the sensor's surface resulted in the decrease of ZnO/PANI photoluminescence. The response and recovery time of the sensor were in the range of 30-50 s and 5 min, respectively. The developed sensors showed sensitivity towards acetic acid in a range of 1-10 ppm with the limit of detection of 1.2 ppm. Specially designed miniaturized sensing system based on integrated sensing layer, light emission diode as excitation source and optical fiber spectrometer was developed for the measurement of the sensor signal. The developed sensing system was applied for the investigation of some real sample assessment including the evaluation of storage conditions of ancient cellulose acetate films, which during the degradation are releasing acetic acid. The obtained results suggest that the developed novel optical ZnO/PANI nanocompsite based sensor shows great potential for acetic acid determination in various samples.

Effect of environmental conditions on the durability of polycarbonate for the protection of cultural heritage sites

Polycarbonate is a good material for covering and protecting cultural heritage sites because of its durability, mechanical properties, and transparency. However, polycarbonate degrades under environmental weathering with a significant decrease of physical and mechanical properties and loss of transparency. In this work, the contemporary presence of ultraviolet irradiation and different temperature and moisture conditions have been taken into account to study the environmental degradation of this polymer with regard to its mechanical and optical properties. The photo-oxidation reactions cause a decrease in the molecular weight and the formation of many oxygenated species. The hydrolytic scission, instead, gives rise to a remarkable reduction in the molecular weight. These two different degradation mechanisms do not seem interconnected because at the lowest degradation temperature and high humidity levels, the reduction of the molecular weight is more pronounced than that observed at the highest temperature but at a lower humidity level. Transparency decreases with the degradative processes, but even after severe degradation the loss of transparency is only about 10%. The yellowness index increases during the first stages of degradation, which has been attributed to the fast formation of carbonyl groups due to photo-oxidation.

Gas chromatography/mass spectrometry techniques for the characterisation of organic materials in works of art

The power of GC/MS to resolve, characterise and quantify complex mixtures of organic compounds with high sensitivity has made it an indispensable analytical tool to address detailed questions about the chemical constituents of works of art. This paper provides an overview of the technique and its particular suitability to material studies of art and historical artefacts, and reviews its diverse research applications concerning the organic composition of artists’ and conservation materials. Options with regard to sample preparation by chemical derivatisation, pyrolysis techniques, and methods for the analysis of volatile organic compounds are discussed, as well as various approaches to the treatment and interpretation of data. The greatest value is gained from GC/MS when it is used as a complementary technique, informed by and in synergy with other methods of analysis.

Analytical Approaches Based on Gas Chromatography Mass Spectrometry (GC/MS) to Study Organic Materials in Artworks and Archaeological Objects

Gas chromatography/mass spectrometry (GC/MS), after appropriate wet chemical sample pre-treatments or pyrolysis, is one of the most commonly adopted analytical techniques in the study of organic materials from cultural heritage objects. Organic materials in archaeological contexts, in classical art objects, or in modern and contemporary works of art may be the same or belong to the same classes, but can also vary considerably, often presenting different ageing pathways and chemical environments. This paper provides an overview of the literature published in the last 10 years on the research based on the use of GC/MS for the analysis of organic materials in artworks and archaeological objects. The latest progresses in advancing analytical approaches, characterising materials and understanding their degradation, and developing methods for monitoring their stability are discussed. Case studies from the literature are presented to examine how the choice of the working conditions and the analytical approaches is driven by the analytical and technical question to be answered, as well as the nature of the object from which the samples are collected.