Polymers and volatiles: Using VOC analysis for the conservation of plastic and rubber objects

There is an acknowledged need for improved conservation of plastic and rubber objects within collections, including improved methods of condition assessment, material identification, and better understanding of material degradation. This reflects the inherent instability and wide-ranging formulations of many such objects and also the relative lack of knowledge in this field. Analysis of volatile organic compounds (VOCs) is a useful method for understanding the chemical processes involved in polymer degradation and for the identification of materials. Conservators and curators have used odor analysis to identify historical plastics for many years, and techniques ranging from acid detection strips to laboratory-based techniques such as solid-phase microextraction-gas chromatography-mass spectrometry have been used to characterize plastic and rubber materials and to understand their degradation. VOC analysis also has potential as a technique for bulk material identification, as a complementary tool to spectroscopic analysis of the surface. A significant advantage of VOC analysis is its potential to be non-invasive, avoiding destructive sampling or even contact with an object. However, there is a greater potential for VOC analysis to be of benefit within conservation than is currently being exploited and significant scope for future research. In fields such as construction or waste management, there is also significant research into analysis of VOC emissions from plastic and rubber materials. The goal of this paper is to systematically review research from a range of fields including conservation, polymer degradation, and plastics recycling and it includes the use of VOC analysis to understand the causes of damage to plastic and rubber objects, to provide evidence of degradation and to monitor degradation progress, and to identify materials and distinguish between different formulations. Summaries of relevant studies are given, and volatile markers of object damage and polymer degradation and key volatile identifiers of a particular material are highlighted

Method development for measuring volatile organic compound (VOC) emission rates from spray foam insulation (SPF) and their interrelationship with indoor air quality (IAQ), human health and ventilation strategies

The polyurethane foam industry is projected to reach a worldwide value of up to $74bn by 2022 and with airtightness of new and retrofitted properties continually increasing, an important question arises: what is the impact of these materials on the indoor air quality (IAQ), occupants’ health and indoor environment? As the foams are made in-situ through an exothermic reaction between two chemical mixtures (side A and side B), volatile organic compounds (VOCs) are emitted during their application and curing process. Current research, commercial practices and governmental advice suggests that emissions decrease over time and 8-24 h after application are usually sufficient for residents to return safely to their properties. However, there is still a lack of case studies and a fundamental absence of robust analysis on how ventilation strategies affect long term off-gassing rates and chemical emission quantities. The emission rates from SPF materials could have a direct impact on IAQ if they exceed the occupational exposure rates recommended by NIOSH, or other professional associations. But the difficulty in recording these emission rates is evident as there is still a lack of an international standard for their quantification. To address this issue, we have developed an analytical methodology for measuring some of the composition materials of the foams and residual products associated with their application. The experiment consisted of two stages- active air sampling of spray foam emissions and spiking desorption tubes with a standard solution in order to develop calibration curves. The solution included SPF compounds, or by-products from their application, associated with possible acute impact on health: 1,4 dioxane, chlorobenzene, dibutyltin dilaurate, triethyl phosphate and bis(2-dimethylaminoethyl)ether. We managed to detect five of the chemicals of interest through air sampling and produce calibration curves for 1,4 dioxane, chlorobenzene and triethyl phosphate, which would allow us to quantify the emission rates at the next stage of research. The results of the experiments successfully demonstrated proof of concept quantitative methodology for the compounds of interest. With further research and experiments, this technique has the capacity to be developed into an international standard for measuring VOCs from spray foam emissions and other buildings products. This would provide scientists and industry professionals with the tools to further develop retrofit and ventilation strategies in order to provide healthier buildings

Influence of Particle Size on Optical Constants From Pellets Measured With Terahertz Pulsed Spectroscopy

Particle size is shown to influence both the overall value and the measurement precision of the refractive index and absorption coefficient of a sample diluted with high density polyethylene (HDPE) powder and compressed in a pellet. However, excessive grinding of a sample before it is mixed with HDPE powder can result in the formation of large particle clusters. These aggregates can induce internal scattering of the terahertz pulse within the pellet as well as lead to different mechanical properties of the pellet, which may change the distribution of air pores. These phenomena result in extracted optical constants with low accuracy and precision. The present work introduces a simple experimental procedure to improve the precision and accuracy of optical constants from spectroscopic pellets. This procedure consists of moderately grinding the sample powder in fine HDPE powder with a pestle and mortar. The standard deviation of the refractive index of Prussian blue has been observed to reduce from 0.14 to 0.02 following this procedure

Optical Coherence Tomography for Examination of Parchment Degradation

A novel application of Optical Coherence Tomography utilizing infrared light of 830 nm central wavelength for non invasive examination of the structure of parchment, some covered with iron gall ink, is presented. It is shown that both the parchment and the ink applied are sufficiently transparent to light of this wavelength. In the study, Spectral OCT (SOCT) as well as Polarisation Sensitive OCT (PS-OCT) techniques were used to obtain cross-sectional images of samples of parchment based on scattering properties. The second technique was additionally employed to recover the birefringence properties and the optical axis orientations of the sample. It was shown that freshly produced parchment exhibits a degree of birefringence. However, this property declines with ageing, and samples of old parchment completely depolarise the incident light

The Development of a SPME-GC/MS Method for the Analysis of VOC Emissions from Historic Plastic and Rubber Materials

Analytical methods have been developed for the analysis of VOC emissions from historic plastic and rubber materials using SPME-GC/MS. Parameters such as analysis temperature, sampling time and choice of SPME fibre coating were investigated and sampling preparation strategies explored, including headspace sampling in vials and in gas sampling bags. The repeatability of the method was evaluated. It was found that a 7 d accumulation time at room temperature, followed by sampling using a DVB/CAR/PDMS fibre, with a sampling time of 60 min at room temperature was a suitable strategy for the detection of VOC emissions from a wide range of historic plastic and rubber artefacts. For 20 mL vials, a sample size of 50 mg was found to be appropriate and grinding the samples improved the repeatability of the analysis and yielded higher levels of emissions. A non-destructive adaptation of the method that could be used directly on historic objects in a museum environment is also presented. The detected emissions improve understanding of ongoing degradation processes within historic plastic and rubber materials, in addition to providing information on material composition

Viability of laser cleaning of papyrus: Conservation and scientific assessment

There has been a growing interest in laser cleaning applications for a variety of organic materials such as paper, parchment, textiles, and leather during the last decade. However, archaeological organic materials, notably papyrus, have rarely been investigated. This contribution examines whether removal of burial encrustation can be justified in view of its short-term and long-term effects on the substrate. To examine this, tests using mock objects have been performed. Using artificially soiled and archaeological papyrus samples, optimization of laser cleaning parameters using a picosecond laser (1064 nm, various operating conditions) was attempted. Optimization was based on colorimetry, optical microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and cellulose degree of polymerization data, both before and after accelerated degradation. In papyrus, there is no clear damage threshold, and substrate degradation can always be observed and is comparable in treated (cleaned) and untreated (soiled) objects. Therefore, the decision on whether to clean papyrus using lasers is predominantly based on aesthetic and treatability (e.g. need for consolidation) criteria

Effects of NO2 and acetic acid on the stability of historic paper

This research investigates degradation of historic paper in polluted environments during long-term dark storage. In an innovative experiment, degradation rates at realistic pollution levels are compared with degradation rates in the absence of pollution, using a set of real historic papers. The most abundant pollutants in repositories in post-industrial environments are taken into account: acetic acid and nitrogen dioxide. Their action was assessed in terms of reduction of ‘handling’ (as defined by decrease in degree of polymerisation) and ‘display’ (as defined by discolouration) lifetimes. Extrapolations to room conditions enabled lifetime predictions in conditions that are comparable to a real archival or library repository environments while prediction uncertainties were analytically evaluated to assess the significance of conclusions. While 10 ppb of NO2 does reduce the handling lifetime of almost all types of paper, their predicted lifetimes were still assessed to be several millennia, with the exception of acidic paper. Acetic acid at concentrations that are typical for archival and library repositories (<100 ppb) has significantly less effect than NO2 while it does not affect display lifetimes. From a conservation management perspective, it needs to be addressed whether the predicted reductions in otherwise significant handling lifetimes are of real concern and whether air filtration in archival and library repositories is justified

Analytical robustness of quantitative NIR chemical imaging for Islamic paper characterization

Recently, spectral imaging techniques such as Multispectral (MSI) and Hyperspectral Imaging (HSI) have gained importance in the field of heritage conservation. This paper explores the analytical robustness of quantitative chemical imaging for Islamic paper characterization by focusing on the effect of different measurement and processing parameters, i.e. acquisition conditions and calibration on the accuracy of the collected spectral data. This will provide a better understanding of the technique that can provide a measure of change in collections through imaging. For the quantitative model, special calibration target was devised using 105 samples from a well-characterized reference Islamic paper collection. Two material properties were of interest: starch sizing and cellulose degree of polymerization (DP). Multivariate data analysis methods were used to develop discrimination and regression models which were used as an evaluation methodology for the metrology of quantitative NIR chemical imaging. Spectral data were collected using a pushbroom HSI scanner (Gilden Photonics Ltd) in the 1000-2500 nm range with a spectral resolution of 6.3 nm using a mirror scanning setup and halogen illumination. Data were acquired at different measurement conditions and acquisition parameters. Preliminary results showed the potential of the evaluation methodology to show that measurement parameters such as the use of different lenses and different scanning backgrounds may not have a great influence on the quantitative results. Moreover, the evaluation methodology allowed for the selection of the best pre-treatment method to be applied to the data. © (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Climate change mitigation strategies for mechanically controlled repositories: The case of The National Archives, Kew

A computer based building simulation model was developed to examine the energy load and environmental management in The National Archives Q1 repository building in Kew, UK to optimise environmental management and examine the impacts of climate change. The need to accurately simulate the hygrothermal environment inside the archive building which houses mainly paper-based records led to the choice of EnergyPlus as the modelling software. The study presents the simulation results of five environmental strategies which predict energy saving potential as high as 43% without significantly affecting the quality of the preservation environment. The effect of climate change is predicted to have little impact on the archive environment due to the filtering effect of the air conditioning system. On the other hand, an increase in total energy load by 15% and 24% is predicted under the worst case climate change scenario in 2050 and 2080, respectively, if the current environmental management practice is continued into the future. However, the identified energy saving strategies could represent possible mitigative solutions in reducing future energy load against the impact of climate change

Dose-response functions for historic paper

Paper degradation has been studied extensively over the past few decades from both the conservation and the material science perspectives. This review focuses on the quantifiable impacts of the environment and material composition, from the viewpoint of long-term storage of historic paper-based collections. Therefore, temperature, relative humidity and their variation, and pollution are of major interest while photoinitiated processes are covered only briefly. New experiments comparing the effects of the most abundant indoor pollutants (NO2, acetic acid and formaldehyde) and the effects of fluctuating temperature and relative humidity are also presented as part of the discussion. This work highlights the need for revision of the existing dose–response (damage) functions for paper and their further development