Strategy for the preservation of plastic artefacts in museum collections

Final Report Summary - POPART (Strategy for the preservation of plastic artefacts in museum collections)

Executive Summary:
The POPART project focussed on four priorities dealing with the preservation of plastic collections in museums: the identification of polymers, the collection survey, the degradation assessment and the active conservation.
Prior to any preservation decision, the first step is the identification of the different types of plastics in order to suggest correct treatment, storage strategies and risk assessment. Tools and methodologies for identification the polymer constituting plastics art objects in museums were developed and tested within the Popart project. In order to assess the advantages and limitations of those analytical approaches, a sample collection of plastics artefacts of about one hundred standard and reference plastic objects representing the major polymer families was assembled (SamCo : Sample Collection). Spectroscopy in the IR region (NIR and FTIR) was investigated and a data base of spectra was produced. Some destructives tests such as pyrolysis gas chromatography-mass spectroscopy (Py-GCMS) analysis as well as Evolved Gas Analysis was applied to cover and evaluate the broad spectrum of possibilities that are offered to museum staff, scientists or conservators. A NIR spectrometer having an appropriate data base was introduced by a SME partner.
The second task of this project focussed on surveying and monitoring collection. A reference survey form has been established and used in five museums for identifying the condition and the most common visible deterioration of plastics based objects collections. Analyses were carried out to characterised deposits found on some objects and off gassing products. In order to assess and monitor changes and degradations during natural ageing in different environmental conditions, a reference object made of different polymers in a shape of a doll so called Polly was conceived. During the project duration significant changes were observed for some polymers. Polly constituents were also used for the development of dose-response functions for historic plastic materials. The third task addressed polymers degradation such as cellulose esters, PVC, PUR among others. Those polymers were thermally or photo chemically aged and then characterized by using chemiluminescence, thermogravimetry, differential scanning calorimetry, Fourier Transform Infrared spectroscopy, and Headspace Solid Phase Micro Extraction (SPME) coupled to GCMS for volatile organic compound characterisation. Kinetics and thermodynamic parameters were appraised. Lastly, the project addresses repair and interventive conservation of plastics which was so far underdeveloped. A large number of cleaning techniques were evaluated. Some exploration on consolidation processes using different products on deteriorated polyurethane foam. The outputs of this project are widely accessible through publication and on the web. The POPART project has responded to research needs for the investigation and conservation of plastic artefacts. Yet, much more will have to be done. Hopefully, the collaborations and sharing of knowledge renewed or developed within Popart will continue and extend in the future.

Project Context and Objectives:
Nowadays museums contain an increasing amount of plastic objects in their collections. In the last twenty years, conservators, restorers and scientists have been confronted with the vulnerability of plastics and were aware that a better understanding into plastics was needed in order to establish a proper approach into the preservation of plastics, to understand their degradation phenomena, to estimate risk and to define appropriate conservation treatments.

*First objective : Identification of polymer artefacts

Prior to any conservation or treatments decision for collections made on synthetic polymer, the main issues are to identify the different types of plastics in order to suggest adapted treatment and storage strategies. Some plastics can be harmful when in contact with other materials; some are sensitive to cleaning with water, etc. Unfortunately identification of the plastic in an object is not a simple matter. Plastics are a huge family of materials that includes many different polymers often complex, which can make identification a real challenge. Therefore, a proper and correct identification of plastic objects requires specific analytical techniques and needs the support of reference materials. It is necessary first to gather a collection of well characterized reference materials representing new and degraded plastics found in museum collections. Then, some partners will performed chemical analysis of this collection on their lab equipments using invasive or non invasive technics such as FTIR, FTIR-ATR, NIR spectroscopy, Py-GCMS, chemiluminescence, DTA and TS. This will contribute to evaluate suitable analytical tools for the identification of plastics. Results will be collected and compared in order to evaluate the quality and complementarities of analytical tools and methods and possibly calibrate some equipment. These data will be made web available.

*Second objective : Condition report, monitoring and survey methodology

During ageing, many polymers exhibit chemical and physical degradation in the form of discolouration, change in opacity, crazes, cracksThe first step consisted in the creation of a survey form that fits to plastic collections requirements. Based on the proposed survey form, conservators will investigate a few museum collections. All kind of deterioration/alteration will be reported in the survey form that will serve for assessing the frequency and deteriorations found in collections. This will also allow ranking degradation level of polymer objects and establishing typology of objects and their deteriorations.
Surveys will help to determine further priority and provide samples for analysis of degradation products and for cleaning. Analysis will be carried out to identify the nature of deposits found on some objects and off-gassing products. Reference artefact that suffers of discoloration or physical changes will be monitored in order to better assess the impact of the environment. Monitoring of plastic artefact will be done along the period of the project in order to record changes during natural ageing by using non invasive spectroscopic characterisation and sampling if necessary.

*Third objective : Assessement of plastic degradation

Most plastics conservators and scientists agree that the 4 synthetic polymers which require attention in all collections are: cellulose nitrate, cellulose acetate, poly(vinyl chloride) and polyurethane. The objective is to perform a quantitative assessment of the degradation of such polymers based on the evaluation of kinetic parameters from isothermal and nonisothermal runs. Chemiluminescence and Thermal analysis (DSC, TGA) will be apply on a serie of malignant polymers as well as polymers from the reference collection. Of particular interest is whether or not the breakdown of some plastics during thermal degradation, produces hazardous chemical VOCs. SPME/GC/MS analysis will provide with a list of off gassing products from polymer during natural ageing.

*Fourth objective : Conservation treatment, cleaning strategies

Repair or active conservation of plastics is very underdeveloped and will be addressed in this project. Some exploration on consolidation will be attempted for very fragile artefacts (PUR foam) or coating on objects that are requiring a protective layer. Almost all plastics artworks need surface cleaning during their useful lifetime. However, many plastics are highly sensitive, especially when attacked by organic liquids, aqueous solutions and water itself; inappropriate treatments may result in irreversible damage. This project will evaluate mechanical, aqueous and non-aqueous cleaning techniques for their effectiveness at removing dust in a quantitative way, which has not been carried out before and to present the results as guidelines for professional conservators. All the data and knowledge gathered will be discussed. From these results, a strategy for identifying, exhibiting, storing, documenting and cleaning plastics objects in museum will be established

*Fifth objective : Dissemination

A lot of information dealing with conservation of plastic collection is scattered. One of the objectives is to built a web site that gathers any relevant information from the project and to implement there the new knowledge gained. Conference-workshops and a conference preprint will allow to disseminate the outputs of the projects to the community and the public.

Project Results:
*First objective : Identification of polymer artefacts

To achieve a valid comparison of the various invasive and non-invasive techniques proposed for the identification and characterisation of plastics, a sample collection (SamCo) of plastics artefacts of about 100 standard and reference plastic objects was gathered. SamCo was made up of two kinds of reference materials: standards and objects. Each standard represents the reference material of a pure plastic; while each object represents the reference of the same plastic as in the standards, but compounded with pigments, dyestuffs, fillers, anti oxidants, plasticizers etc. Three partners ICN, V&A and Natmus collected different natural and synthetic plastics from the ICN reference collections of plastic objects, from flea markets, antique shops and from private collections and from their own collection to contribute to SamCo, the sample collection for identification by POPART partners. At a 2-day meeting (24 and 25 of January 2009) at RCE, Natmus together with V&A participated in selecting the most suitable materials for SamCo.
Standards and references were collected and made ready for the SamCo for 6 EU partners.
SamCo is consisting of 30 standard materials of the resin kit (commercially bought by each partner of the Round Robin test) and 66 examples of reference resins and plastics objects. According to the DOW, all SamCo boxes were send to partners in February /March 2009. A FileMaker Pro database was developed by RCE to catalogue SamCo and all the analysis performed by the partners. SamCo boxes are available for analysis at partners institutes. A Round Robin test for the identification of plastic objects from the reference collection (SamCo) was set up to evaluate all analytical techniques used. The principal techniques for identification were FTIR, Py-GCMS, NIR and Raman. SamCo was analyzed by each partner using non-invasive and minimally invasive analytical techniques, with and without portable devices. The techniques were classified as follows: bench top (in the laboratory), transportable (invasive but can be used outside the laboratory) and handheld (especially mend to be to be used outside the laboratory).
To validate the results, a blind test was also implemented. Thirty-five samples of plastics (whose identity was kept hidden from the participating laboratories) were used to compare the accuracy and limitations for identification between the various analytical techniques.
The results of the analyses were used to compare and evaluate the ease and usefulness of the various techniques. The identification of plastic artefacts encompasses the evaluation of analytical techniques and methodologies. Analytical techniques, from the non-invasive (no sampling) NIR, UV-Vis, FTIR handheld and Raman handheld to the invasive (micro-sampling 0.6 mm2 or less) were included. The FTIR bench top and Py-GCMS techniques were also evaluated on their ease of use and the quality of their results. In general, FTIR was found to be a very adequate technique for most plastics identification. According to the results of the analyses performed by the partners, all were able to conclusively identify all the plastics included in the SamCo collection, and in some cases partners reporting on seeing features from other components other than the main resins, either inorganic (e.g. fillers, pigments) or organic (e.g. colorants).
Some difficulties of sampling were mentioned, but these were more to do with the specific sampling procedures available. For example, those partners who used a Golden Gate attenuated total reflectance (ATR) accessory could squeeze the more rigid plastics into thin films in order that better contact was made with both diamond surfaces, and hence obtain better resolved spectra. FTIR was shown not to be ideal for mixed or complex plastics because a spectral feature of some other component might obscure spectral features that can identify one component. Thick enough laminates can, however, be cross-sectioned to analyse each layer individually. Additives like fillers, plasticizers, colorants, stabilisers, anti-oxidants, and ultra violet absorbers can therefore only be identified if their concentration is high enough, depending on the nature of the additive, and nature of the polymer (but in some cases is possible for concentrations under 5% w/w). Given that it would be impossible to process most polymers into useful objects without additives, and that additives can affect the long-term stability of the plastic to such a high degree, the inability of FTIR to identify these components in typical situations is clearly a significant limitation, for any kind of study into ageing and/or degradation.

Bench top instruments and/or transmission mode of operation might offer a better resolution than portable instruments used in ATR/transmission mode, which might help when similar polymers can be discriminated only by very small absorption bands. By comparison bench instruments such as the bench Perkin Elmer at L-C2RMF and the bench Bruker Hyperion 3000 at GCI and the bench Perkin Elmer at RCE all institutions reported subtle differences between the three types of polystyrene and between Nylon 6 and 6,6 measured in standards. However, these small differences can only be clearly observed in standard reference materials and not always obvious in compounded objects. The absorption bands of the compounding materials such as fillers, stabilisers and pigments can obscure the small differences in the fingerprint region absorptions in the FTIR spectrum between different polymers of the same family. Therefore compounded objects can be equally identified using portable and bench top instruments.

The transportable FTIR using invasive sampling used by RCE was not able to distinguish between samples of polystyrene general purpose, high and medium impact, or between different polymers belonging to the same family, like Nylon 6 and Nylon 6,6. Furthermore, identification using FTIR (either bench top, handheld or transportable) is based on comparing data of the spectra by a library search on the computer. Depending on the amount of reference standards in the database and the skills of the scientist, better results will be obtained. For the identification of complex mixtures and additives Py-GCMS has to be used. Though not all partners have access to or could perform Py-GCMS, this technique provided complete and detailed identification of all plastics analyzed. Evolved Gas Analysis (EGA) proved to be a valuable complementary technique to PY-GCMS. Raman spectroscopy is an efficient tool for the identification of plastics, but bench equipment is much more efficient than the portable instruments tested. Most polymers could be successfully distinguished and identified. The two portable instruments tested were found to be promising but not yet as reliable as the bench instrument with almost half of the samples yielding illegible spectra. The shape and colour of the samples were also found to have a significant influence on the quality of the spectra. As the Raman technique has only been used by GCI and RCE, no inter-laboratory comparison could be made. Initial findings indicate this approach to be good. With a reliance of the production of a good and extended reference database. The more reference spectra, the more reliable the result.
Spectroscopic and chromatographic techniques such as Fourier transform infrared spectroscopy (FTIR) and pyrolysis gas chromatography mass spectrometry (Py-GCMS) are extremely useful for the identification of organic materials. Since the 1990s, spectroscopic techniques have improved significantly in terms of the size of sample required, the speed of analysis, the user interface, and portable/mobile instrumentation. The use of these spectroscopic methods has become widespread in conservation, and is likely to increase further with the recent development of handheld instruments (FTIR, Raman and Near Infrared (NIR)) for rapid, non-invasive, insitu analysis.
Although Raman spectroscopy has improved on many of the problems it had initially with fluoresce coming from additives in the plastics, and both NIR and Ultra violet- Visible spectroscopy (UV-Vis) have become more sensitive and more useful, the most widely used technique for identifying plastics is still FTIR. The technique is highly versatile, and also permits the analysis of surface-deposited degradation products, polymer bond changes, depth profiling and the monitoring of polymer loss. For the identification of complex mixtures of plastics and additives, however, Py-GCMS offers many advantages over FTIR. The main disadvantage to this technique seems to be the lack of low-cost models and the additional resources needed for its maintenance.

A scheme with analytical techniques and possibilities for identification/characterization is documented in the book Preservation of Plastic Artefacts in Museum Collections, edited by Bertrand Lavedrine, Alban Fournier and Graham Martin, published by Editions du CTHS, 2012, ISBN: 978-2-7355-00770-2. Results were also presented and four practical workshops conducted for conservators and conservation scientists at the POPART International conference in Paris in March 2012. All data of the plastic objects after identification were submitted to the SamCo Filemaker Pro database. Photographs and general information about the reference standards and reference objects of SamCo were registered. Data of the FTIR spectra of the plastics were submitted to the database as Microsoft Word files and results of the PY-GCMS analyses were submitted as chromatographic bitmaps. All results are available on the Poaprt website.

-Characterisation techniques

Several additional analytical techniques were utilised in the POPART project to provide additional information for characterising many of the polymers, and which would be used to monitor changes in chemical, mechanical and physical properties on ageing and/or after cleaning treatments. These include ultra violet-visible spectroscopy (UV-Vis), Thermo-gravimetric analysis (TGA), Differential Scanning Calorimetry (DSC), Dynamic mechanical analysis (DMA), Tensile-stress strain analyser (TSS) and Dielectric Spectroscopy (DS).

FTIR imaging and NIR hyper spectral cameraimaging, useful for surface characterisation, Size Exclusion Chromatography (SEC), Solid Phase Micro extraction (SPME) GCMS and Chemiluminescence (CL) were all used for the characterising the chemical changes in plastics on ageing.

NIR spectroscopy has a significant potential in the field of organic material characterization and greatly enhances heritage collection management replacing destructive and micro-destructive methods. One aspect of NIR spectroscopy is the use of this technique for quantitative imaging of chemical properties and damage mapping on plastic objects. As with NIR imaging, the technique of FTIR imaging can be used to quantify change of chemical properties in the polymer structure. It can used to measure and locate oxidation products on the surface of degraded plastic objects.
The analyses of spectra in the UV-Vis-NIR region may be exploited for manifold purposes. The UV-Vis spectral region is dominated by the absorption bands of the chromophores groups, which are responsible of the colour of the material. In some polymers the insurgence or the disappearance of bands in the UV-Vis interval may be related to degradation of the polymeric chains (e.g. due to photo-induced reactions), and the UV-Vis spectrum may inform about the conservation state of the material. Moreover, the spectrum in the Vis range (380-780 nm) is the basis of colorimetric analysis, which is used for quantifying and monitoring the chromatic alterations (discoloration, yellowing, darkening, etc.) due to the ageing processes. Finally, the NIR region (800-2500 nm), characterized by the overtones and combinations bands of the fundamental vibrations of molecular groups, can be useful for discrimination and characterization purposes.
The UV-Vis-NIR spectral characterisation of the SamCo collection by means of non-invasive reflectance spectroscopy has been completed. All the spectral data have been entered in the FileMaker Pro database template provided by RCE. This way an archive of absorption spectra in 350-2500nm range, measured by means of non invasive reflectance spectroscopy (FORS), is now consultable through a common interface accessible by the Popart website, making comparison and exchange of data among different laboratories easier.
The acquisition of highly-resolved reflectance spectra in the UV-Vis region is also useful to investigate photo-induced phenomena of selected polymers before they become visually appreciable at the naked eye. To fully exploit NIR spectroscopy for identification purposes, setting up of a library of spectra of plastic materials with known composition is necessary. For the purpose of the proof-of-concept, an NIR spectral library was built using the Samco collection.
An Automated Spectral Matching Algorithm tool has been developed for identification of NIR spectra of plastic materials using the spectral database. Spectral Matching compares the shape of a spectrum with each spectrum in the library and assigns a degree of match using a proprietary algorithm.
However, the success of this method for unknown samples largely depends on the number of further samples included in the training set: by inclusion of sufficient and representative variation (in composition, colour, size, thickness, physical nature, condition and age) in each polymer type the robustness of the method can be enhanced.
A statistical identification routine was programmed by Morana RTD d.o.o. and built into a demo MORANA NIR software, in order to produce a user friendly application for use by personnel not trained in complex statistical methods, such as curators and conservators.
The MORANA NIR application was tested on a blind set of historical samples. 80% of the unknown samples were correctly identified. This result further supports the need for an application, designed specifically for historical and degraded plastic materials. The result can be further improved by expanding the database of plastics, on which the identification is based.
Dielectric Spectroscopy (DS) is the investigation of the dipolar nature of materials through the study of the physical phenomenon known as dielectric relaxation. When applied to polymers, it provides information about the segmental mobility of a polymeric chain, allowing to study the dynamics of polymers with different molecular architectures.
Plastic objects exposed in museums are continuously subjected to physical and chemical agents that influence their constitutive properties. Almost all those agents, in particular heat, light and moisture, have effects on the polymeric chain structure and, as a consequence, they may affect the dielectric properties of the material. As plastic consists of polymeric materials plus some kind of additive or filler, dielectric characteristics are in principle suitable parameters to monitor the materials changes (ageing, deterioration etc.). Actually, in many other applicative fields (e.g. industry, quality controls, etc.) a relevant literature exists concerning the detection and quantification of polymers degradation due to water absorption, to heat and to the exposure to UV radiation. For example, the effect of ageing on polymers used in cables or in transformers as insulating materials has been studied by DS, i.e. by studying the frequency-dependent characteristics of their dielectric properties as a function of temperature, UV exposure, water absorption. Thus, starting from the experience gained in other technological sectors, a new research line aimed at investigating potentialities and limits of DS applied to diagnostics on cultural heritage has been established.

The overall results obtained can be summarized as follows:

DS is rather weak when used alone in robustly identifying the polymer type. Perhaps, dielectric measurements performed over a very broad band could allow to determine some kind of dielectric fingerprint useful to discriminate selected classes of polymers, but the intra-species differences are expected to be a limitation in using DS for identification purposes.
Preliminary tests confirmed that DS is promising in detecting and/or monitoring ageing or deterioration phenomena in plastics. Dielectric properties are indeed very sensitive to changes in the polymer chain structure and to several physical parameters (for example, temperature and humidity). Therefore, DS is eligible to be used as working principle in customized instrumentation for monitoring the conditions of a plastic artifact during its lifetime, allowing to detect molecular changes due to deterioration before they become visible.
The experimental work conducted at IFAC-CNR was dedicated to investigate potentialities and limits of DS as working principle for novels portable tools tailored for museum applications. The results obtained from measurements on different sets of samples, as well as from test on different instrumental concepts (based on time domain and frequency domain) made it possible to draw the following conclusions:
a) DS appeared to be scarcely suitable to be used as unique tool for identification of unknown plastics, resulting to be a poorly effective technique for discrimination between selected groups of polymers. Nevertheless although the discriminating power of DS is not comparable to that of other techniques, it can provide useful complementary indications
b) DS showed to be instead more promising for an early detection of the deterioration phenomena in polymers, and monitoring plastic materials due to the exposure of artifacts to the environment.
Based on the results of the first year of research the subsequent activity has been devoted to designing a customized instrumentation, working in the time-domain and giving information about the low-frequency region (0.1-100Hz) which is expected to be more informative for plastics classification, as well as for characterisation of the degradation state of the material. This prototype was intended as the first step toward the realisation of a portable device, suitable for in-situ measurements on objects, without constraints due to their shape/thickness. At present the development of a portable instrumentation, suitable for on-site monitoring in museums, has not yet been completed. Indeed the phase of testing of the TDDS system has turned out to be longer than initially planned, and further tests on standard samples are needed. The measurement tools developed during the POPART project currently allow to take measurements on flat samples, with limitations concerning the shape (disk/plate) and the surface conditions.

*Second objective: Condition report, monitoring and survey methodology

The first step was the production of a survey form that was set through a collaboration among Victoria & Albert Museum, IFAC-CNR, LC2RMF, ICN (now called RCE) and Natmus. Such a form was used for the successive survey of collections in different museums. Moreover, it can constitute a useful guide for conservators and curators to evaluate the conservation state of their own collections. Of course, the form might be modified and adapted to the needs and situation of each collection.

As a successive step, the collections of the following museums were surveyed:

-Victoria & Albert Museum (V&A), London, U.K.
-Stedelijk Museum, Amsterdam, The Netherlands
-Musée dArt Moderne et dArt Contemporaine (MAMAC) Nice, France
-Musée dArt moderne, St. Etienne, France
-Musée Galliera, Paris, France

At the V&A approximately 200 objects were surveyed. Good or fair conservation conditions were found for about 85% of the objects, whereas the remaining 15% was in poor or even in unacceptable (3%) conditions. In particular, crazing and delamination of polyurethane faux leather and surface stickiness and darkening of plasticized PVC were observed. The situation at the Stedelijk Museum in Amsterdam was particularly favourable because a previous survey had been done in 1995 so that it was possible to make a comparison with the Popart survey in 2010. A total number of 40 objects, which comprised plastics early dating from the 1930s until the newer plastics from the 1980s, were considered and their actual conservation state compared with the 1995 records. Of the objects surveyed in 2010, it can be concluded that 21 remained in the same condition. 13 objects containing PA, PUR, PVC, PP or natural rubber changed due to chemical and physical degradation while works of art containing either PMMA or PS changed due to mechanical damages and incorrect artists technique (inappropriate adhesive) into a lesser condition.
6 works of art (containing either PA or PMMA or both) changed into a better condition due to restoration or replacements. More than 230 objects have been examined in the 3 museums in France. A particular effort was devoted to the identification of the constituting plastics materials. Surveys have been undertaken without any sophisticated equipment, in order to work in museums everyday conditions. Plastics hidden by other materials or by paint layers were not or hardly accessible, it is why the final count of some plastics may be under estimated in the final results. Another outcome is that plastic identification has been made at a general level only, by trying to identify the polymer family each plastic belongs to. Lastly, evidence of chemical degradation processes that do not cause visible or perceptible damage have not been detected and could not be taken in account in the final results.

Nonetheless, some micro-samples has been undertaken on selected objects, either when plastic identification was unsure by naked eye observation only or when degradation products visible on the surface require further analyses. Thanks to CRCC, a few environmental analyses have also been performed in SPME-GCMS in order to measure volatile organic compounds (VOCs) inside some wrappings and storerooms.
The conservation state of the overall objects examined was a little worse than that found in London and Amsterdam as indicated by the above figure. The most damaged artefacts resulted constituted by cellulose acetate, cellulose nitrate and PVC.

One of the main issues that is of interest for conservators and curators is to assess which kinds of plastics are most vulnerable to deterioration and to what extent they can deteriorate under the environmental conditions normally encountered in museums. Although one might expect that real time deterioration could be ascertained by a careful investigation of museum objects on display or in storage, real objects or artworks may not sampled due to ethical considerations. Therefore, reference objects were prepared by Natmus in the form of a doll (Polly) for simultaneous exposures in different environmental conditions. The doll comprised of 11 different plastics representative of types typically found in modern museum collections. The 16 identical dolls realized were exposed in different places, not only in normal exhibit conditions, but also in some selected extreme conditions to ascertain possible acceleration of the deterioration process. In most cases the environmental parameters were also measured. The dolls were periodically evaluated by visual inspection and in selected cases by instrumental analyses. Exposures were interrupted after 18 -20 months to suit Poparts time scale. Instrumental analysis included non- invasive techniques, such as colorimetry and UV-VIS-NIR spectroscopy, which allowed the monitoring of the conservation state during the period of display without altering the dolls themselves, but additional micro-invasive and invasive analyses (FT-IR, Chemiluminescence, Thermogravimetry) were made at the end of the exposure period to obtain more information about the deterioration mechanisms. Reference dolls were stored in dark or closed boxes for the entire exposure period to avoid external interferences.
In order to standardise the visual evaluation of the dolls by different operators, a reference scale was adopted based on four degrees of alteration:
0 = no visible change
1 = just noticeable change
2 = evident change
3 = very strong change
Despite its simplicity, this evaluation method could be also used to monitor possible alterations of actual works of art with time. In fact, if the monitoring is done periodically, this simple action is a useful tool to establish the health of the artefact and to alert conservators to take proper decisions and to prevent further damage. Although visual evaluation is a very rough method to assess the damage, because it strongly depends on the sensitivity of the observer and cannot be considered an objective indication of the extent of the damage, it remains one of the most used methods to assess the conservation state of three dimensional artworks and it was considered favourably for use in this context. Actually, the introduction of a reference evaluation scale turned out to be effective in reducing the degree of arbitrariness. In spite of the fact that a change could be considered by one person as insignificant and rated as 0, while another could rate the same change as1, all the results of the experimentations were consistent.
The most degradation was seen in the right and left feet, which comprised polyurethane ether and polyurethane ester foams, respectively. The second most frequently changed material was polyamide (nylon 6), which was reported to be yellowed in several cases. The other polymers were visually unaltered. Some colour changes, which were measured at IFAC-CNR by non-invasive reflectance spectroscopy (FORS), were not due to alteration of plastic material, but only to the pigment/dye added to the plastics. Of course, this aspect that does not imply instability of the plastic material is important when it is considered in the context of an actual work of art, which is constituted by a complexity of materials (different plastics, pigments and dyes, other organic/inorganic compounds) and for which colour is an intrinsic and essential factor of the artefact.
Chemiluminescence measurements done at PISAS showed alterations also in PS and PET besides PUR ester and ether foam, while FT-IR spectra recorded at RCE indicated an increase of crystallinity in PA, PET, PS and PAN.

In conclusion the experimental campaign carried out with Polly dolls can be viewed as a pilot study aimed at tackling the practical issues related to the monitoring of real three dimensional plastic artworks and the surrounding environment.
The overall exposure period (one year and half) was sufficient to observe initial changes in the more susceptible polymers, such as polyurethane ethers and esters, and polyamide, with detectable chromatic changes and surface effects. Conversely the other polymers were shown to be stable in the same conditions over this time period.

The experimentation was also an occasion for testing and comparing different approaches for the assessment of degradation on real objects, from the easiest method based on visual evaluation to the non-invasive techniques, such as the colorimetric analysis and the micro-analytical and analytical techniques commonly used in laboratories (FT-IR, chemiluminescence).
Last but not least, the educational and communication benefits of an object like Polly facilitated the dissemination of the Popart Project to the public, and increased the awareness of issues associated with plastics in museum collections.

*Third objective : Assessement of plastic degradation

Plastics in museums artefacts suffer from the extensive degradation which brings about devaluation of artefacts collections. The successful strategy of the further artefact preservation and/or conservation is related with the right identification of the plastics which is realised by means of suitable non-destructive method (FTIR) or by analysis of microsamples (up to 1 mg). As no information about the character and amount of additives in artefact is available and the position of the material on the trajectory of its life is uncertain, the reliable methodology based on nonisothermal chemiluminescence, thermogravimetry and differential scanning calorimetry has been worked out in the Popart project for testing the remaining service life of artificially and naturally aged polymers. It was verified on 100 various polymers which were aged within 0 2.5 years under different conditions (temperature, humidity, light) and nonisothermal curves of e.g. chemiluminescence from 40 to 250 oC were compared with the original sample. It has been shown that the shift of nonisothermal runs to lower temperatures for the aged plastics indicates that the material is still within the acceptable service life. Provided that the shift to higher temperature is observed the plastics approaches to its failure. At this stage no obvious signs of mechanical failure are still observable. This is related to the formation (shift to lower temperatures) and subsequent consumption (shift to higher temperatures) of the reactive sites of degradation due to the ageing.

-Cellulose nitrate degradation

New findings concerning the cellulose nitrate decomposition were presented that may help in the subsequent conservation of these highly vulnerable materials. It was shown how nitration destabilizes the original cellulose. The effect of oxygen on the degradation of nitrocellulose is not almost visible on thermogravimetry experimental runs while that for pure cellulose it is significant. This may be explained by the intervention of oxygen into the initiation reaction of oxidation via the carbon atom 6 of glucopyranosyl unit of the cellulose while in the case of nitrocellulose the initiation occurs independently via the scission of bonds O-NO2. Oxygen affects the oxidation in the subsequent stages of the reaction. The loss of volatiles is also much sharper for nitrocellulose than for cellulose. At high temperatures there remains a certain amount of char residue which under nitrogen looses the weight slowly. In oxygen an acceleration of the char residue oxidation may be observed above 420 oC. From the non-isothermal thermogravimetry runs of the set of nitrocellulose samples in nitrogen at the rate of heating 10 oCmin-1 worth of noticing is that with the progress of the sample ageing at 130 o C in air the temperature of the inflexion point shifts to higher values being 197.7 oC for reference sample and 207.7 oC for the most aged sample. This corresponds with the gradual loss of nitro groups from nitrocellulose due to ageing. At the same time the percentage of the char residue which remains after thermogravimetry experiment at 550 o C slowly increases.
Activation energy estimated when using the model proposed in the project for the release of volatiles decreases with the progress of nitrocellulose ageing being 260 kJmol-1 for the reference and 130 kJmol-1 for the sample aged 16 days in air at 130 oC. At the same time, the rate constants k1 calculated from Arrhenius parameters for 130 oC increase while those for 200 oC decrease with the extent of nitrocellulose ageing. This fact should be considered when treating different nitrocellulose samples of the different storing history.
The rate constants of the first order determined for 130 and 200 oC correlate with the percentage of the char residue determined from non-isothermal TG runs; those at 130 oC with an increasing percentage of the char residue increase. Although the extrapolation of rate constant to 130 oC from non-isothermal TG is affected by the faster auto-accelerating decomposition process occurring above 190 oC, the increasing tendency of the rate constants indicate that there may occur the effect of the forming char on the autocatalysis of decomposition of nitrocellulose. Until now the autocatalysis in decomposition of nitrocellulose was ascribed to the effect of nitric acid.
With the extent of nitrocellulose ageing there occurs also the shift of the maximum of DSC exotherm to higher temperatures while the peak height is reduced. Provided that the surface below DSC exotherm is proportional to the concentration of unreacted nitro groups and the kinetics of nitrocellulose decay during its ageing at 130 oC is approximated by the first order scheme we see that the rate constant of nitrocellulose degradation is somewhat lower than that found by extrapolation from chemiluminescence measurement. However, the difference is not as large.
When comparing DSC and chemiluminescence records in oxygen we see another peak appearing in the latter case which is likely to correspond with the oxidation of char residue. In nitrogen experiments this peak was not observed. We may also see that in the presence of nitrogen the chemiluminescence signal that is lower than that in oxygen, is also important.
There are no doubts that the initial step in degradation of nitrocellulose is the splitting of O-NO2 bonds of the secondary nitrate group joined to carbon atoms 2 or 3 of the glucopyranosyl ring. These bonds have the dissociation energy 167 kJmole-1 while those at the primary position of carbon atom 6 have dissociation energy about 330 kJmole-1. The sequence of beta-scissions opens the glucopyranosyl ring, the free radicals formed split out another molecule of NO2 and finally there appear aldehydes, which are prone to oxidation due to direct reaction with oxygen or in its absence with NO2. The transfer reaction to CH2 bonds on carbon atoms 6 may induce the splitting off the formaldehyde. Nitric acid which is formed from NO2 due to the presence of air humidity will contribute to the cation induced cleavage of glycosidic bonds C-O-C linking glucopyranosyl units and the molar mass of nitrocellulose is reduced. At the same time, after decarbonylation of aldehydic groups the sequential moieties in the nitrocellulose macromolecules may be formed which form the possible skeleton of the char formed.

-PUR degradation

Three structures of polyurethanes were examined namely polyether urethane having toluene (TDI) and diphenyl methane diisocyanate (MDI) moieties (Sample 1 and 3) and polyester urethane (sample 2) with toluene diisocyanate units.
These polyurethanes foams were supplied by RAJA company, France. The foams were subjected to light ageing under daylight 1000 Wm-2, 25°C/50% relative humidity or thermal ageing under dry (90°C, <10% RH) or humid (90°C, 50% RH) conditions.
It was found that the thermal oxidation of polyester based polyurethanes starts in polyisocyanate segments, probably on methylene units adjacent to NH groups. This was confirmed by experiments of chemiluminescence in oxygen of either polyisocyanate or polyol in comparison to polyurethane prepared from the two components. The increase of the light emission from polyisocyanate precedes that from polyester polyol. Polyester urethane storage during 18 months was found to lead to a considerable change of the chemiluminescence vs. temperature pattern. The sample became less thermally stable in oxygen and the intensity of the light emission was also lower. At the same time, the molar mass distribution of the polyol did not change.
The contact with tap water of a polyurethane film cast on glass caused a reduction of the themooxidative stability of polyurethane. This was attributed to the combined effect of hydrolysis and ions present in the water.
The simple and fast differentiation between polyether and polyester urethanes realized through the thermooxidation experiment performed on chemiluminescence device may be demonstrated as follows: Polyether urethanes due to the ether structures CH2-O- and much easier oxidation perform considerably higher light intensity at final stages than polyether urethane. However, the degradation of the latter starts earlier. We have shown that the development of the chemiluminescence follows after the release of the nitrogen containing moieties and is linked with the oxidation of the crosslinked structures in the polymer.
Polyester urethane in oxygen undergoes the extensive crosslinking which is accompanied by carbonization of the superficial layes and sudden release of volatiles at elevated temperature.
The mutual links of the outputs of respective methods (thermogravimetry, DSC, chemiluminescence) were presented. DSC endotherms in nitrogen represent the records of the active decomposition of both polyurethanes into volatiles and confirm the essential differences in polyether and polyester urethanes degradation.
Also non-isothermal thermogravimetry records of original polyurethane samples 1 and 2 and those aged by light shows on significant differences not only between non-aged samples but also between aged samples. While original polyurethane foams give in nitrogen two waves of the formation of volatiles which were ascribed to the decomposition of polyisocyanate (the first) and polyol or/polyester (the second) moieties, aged polyether samples give only one wave of the decay of the mass. The aged polyether samples are already scrumbled. Polyester urethanes start to loose volatiles from polyisocyanate moieties at lower temperatures but the mass loss from polyester part is shifted to higher temperature when compared with polyether urethanes. Typically much more carbon residue remains on the pan for aged samples which shows on the additional crosslinking in polyol or polyester part of polyurethane provoked by ageing.
Also chemiluminescence temperature records in oxygen are significantly changed by polyurethane ageing.
From the set of rate constants on degradation in oxygen (CL) and in nitrogen (TG) which were determined for 100, 200 and 250 oC we may see that pre-ageing of polyurethanes leads to the increase of the respective rate constants which is very pronounced in the case of polyether urethane and less significant in the case of polyester urethane.
While the investigation of the changes of the solid matrix of PURs is the subject of numerous papers only a few studies are devoted to the formation of volatile organic compounds (VOC) emitted by polyurethanes during their degradation. Low molar mass compounds, either degradation products or manufacturing residual products are emitted from the polyurethane matrix and a relationship between the environmental factors (humidity, temperature and daylight) and the volatile fraction formed and the bulk polymer composition has been established. From this viewpoint the samples of polyether urethanes and polyester urethane original and artificially aged were examined by using solid phase microextraction coupled with gas chromatography/mass spectrometry (SPME-GCMS) and pyrolysis-gas chromatography/mass spectrometry (Py-GCMS).
In addition to this, four naturally aged foams collected from various daily life objects were examined as well. Sample S1 was taken from a suitcase and visually seemed to be in poor state of conservation. Sample S2 was part of a conditioning box and appears to be in a good state of conservation. Sample S3 was taken from a much degraded chair stuffing. Sample S4 was collected from the back of a chair not exposed to light and also seemed to be in very good state of conservation. Samples S1 and S3 were yellow and showed a total loss of integrity and a pronounced degradation resulting in powdering.
Morphological changes were followed based on visual examinations (binocular); naturally aged foams were preliminary characterized using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Infrared data were also collected from newly made foams after artificial ageing.
Similarly as from chemiluminescence, DSC and thermogravimetry data from all artificially and naturally aged samples, visual observations and Py-GCMS data and in agreement with the literature it follows that PUR esters are more sensitive to humid conditions due to hydrolysis, and less sensitive to light ageing while PUR ether degrade primarily by photo-oxidation and have higher resistance to hydrolysis.
It is interesting to note that artificial and natural ageing PUR esters and PUR ethers were providing similar analytical results and thus, it seems relevant to use such accelerated ageing to simulate natural degradation processes. The results are exemplified on commercial PUR esters and samples S1 and S2.

After 8 weeks of ageing in humid condition, commercial PUR esters, besides the important loss of mechanical properties and darkening, give white crystals of adipic acid (AA) which appear inside the pores and on the surface of the foam. Adipic acid crystals were also observed in naturally aged foam S1. Such crystals have been also detected and identified from one PURs museum artifacts. The Py-GCMS analysis permits to identify potential chemical markers of the PUR ester degradation. In the unaged commercial sample S2, we identified the compounds such as carbon dioxide, adipic ketone (K), diethylene glycol (DEG), 2,4- and 2,6-toluene diisocyanate isomers (TDI) and some adipate derivatives (A), which chemical structures have not been identified. The adipic ketone (C5H8O, MW 84) can originate from the adipic acid raw material. The DEG (C4H10O3, MW 106), a low molecular weight polyol is used in the polyurethane synthesis either as chain extenders or component of the polyester polyol synthesis. During the artificial ageing, the chromatographic fingerprints become simple and the isocyanate moiety was modified. After 4 weeks of ageing, in addition to the relative increase of diethylene glycol, the occurrence of toluene amino isocyanate isomers (TAI) and 2,4- and 2,6-toluene diamine isomers (TDA) may be noted. TAI may undergo hydrolysis to TDI and 2,4- and 2,6- toluene diamines are being formed. After 8 weeks of ageing, adipic acid appeared.
Two Py-GCMS fingerprints of S1 and S2 foams which were in different states of degradation. helped us in their identification; they are from poly(diethylene glycol adipate) polyurethanes. Phthalate derivatives (i.e. phthalic acid diisobutyl ester) could originate from plasticizers introduced during the manufacturing process. Sample S1 gave a relatively high amount of diethylene glycol (DEG), 2,4- and 2,6-toluene diamines (TDA) and of adipic acid (AA). Pyrogram of the foam S2 which was in a relatively good state showed a lower amount of diethylene glycol (DEG), presence of toluene amino isocyanate isomers (TAI) and no adipic acid. These results were coherent with those obtained from artificial ageing.
Chromatograms of the SPME extracts from the commercial polyurethane ester foam artificially aged in humid conditions did not indicate the obvious changes within the VOCs composition except for the presence of diethylene glycol (DEG). Chromatograms of the SPME extracts from naturally aged PUR ester foams were very similar but, the presence of diethylene glycol in different relative amount was noted.

-VOCs emitted from commercially available plastics

More than 200 different VOCs were detected and identified from the set of the thirteen plastics samples as well-resolved chromatographic fingerprints. Two categories of VOCs were distinguished: the non-specific and the specific ones. Non-specific VOCs are either compounds detected from most plastics and as such are considered as ubiquitous, or compounds detected only once. The specific VOCs are typical for a given polymer nature and are mainly monomer residues remained in the polymer matrix from the synthesis.
Non-specific VOC were divided in two categories namely additives and other compounds. Additives are antioxidants and plasticizers. They were: 2,4-di-tert-butylphenol, 2,5-di-tert-pentylbenzoquinone and bisphenol A. Glycerol diacetate and benzoate 2-ethylhexyl were also identified. Four plasticizers were detected predominantly. Among them, the 2,2,4-trimethyl-1,3-pentanediol diisobutyrate is largely used plasticizer in the manufacture of flexible plastic and especially for soft surface products. The release of phthalates from artifacts into the atmosphere occurs via their migrations through polymeric materials to the surface followed by their evaporations. Among the other compounds category, five linear acids (n-C1 and n-C6 to n-C9) which are more or less ubiquitous acids were also detected. They have various chemical origins and can not be thus considered as specific compounds. 2-ethyl 1- hexanol was also identified. It is assumed that it is a degradation product of di(2-ethylhexyl) phthalate (DEHP), the largest phthalate ester used as a general purpose plasticizer. 2-ethyl 1-hexanol has been detected in plastic emissions and mainly from polyvinyl chloride-based materials. For polystyrene based plastics styrene monomer is present in the chromatograms of the two polymers. Traces of three oligomers of styrene namely 1,3-diphenylpropane and (trans/cis) isomers of 1,2-diphenylcyclobutane were also detected from polystyrene. These dimers are formed through side reaction during processing of polystyrene. The lack of such dimers in the emission of the acrylonitrile-butadiene-styrene sample can be easily explained by the lower initial abundance of polystyrene in this copolymer. Ethylbenzene is the second and third most abundant specific compound emitted by polystyrene and acrylobutrile-butadiene-styrene, respectively. Methylstyrene can also be traced as specific VOC of styrenic polymers. The presence of benzaldehyde, phenol and acetophenone may be due to oxidized fragments of styrenic polymers. It should be underlined that the specific volatile markers like styrene and ethylbenzene allow distinguishing styrenic family from the other tested families, although it does not allow going further in the polymer identification.
For the polyolefins (low density polyethylene, polypropylene and polybutylene), the most abundant compounds released were linear and branched alkanes. Finding this range of alkanes as well as the predominance of tetradecane and pentadecane is most probably due to their high affinity with the coating of the fibre. Volatile traces from polyolefins are typically series of linear and branched alkanes, which, however, do not allow discriminating between the three tested polymers but allow distinguishing polyolefins from the other plastics.
Some specific and volatile monomers were also detected on the SPME extracts of acrylic, polyamide and polyphenylene oxide samples. They are methylmethacrylate and ethylacrylate for acrylics, caprolactame for polyamide 6, and isomers of dimethylbenzoquinone and phenol for polyphenylene oxide. These compounds are marker monomers and their occurrence permit to identify unambiguously the nature of their polymeric matrix.
The chromatogram of the SPME extract of polyether- and polyester-based polyurethane samples revealed the presence of glycol derivatives and diethylene glycol which can be considered as volatile markers for polyurethanes. As expected camphor can be considered as a marker for celluloid used as a plasticizer.

*Fourth objective : Conservation treatment, cleaning strategies

-Evaluation of cleaning practice, Production of fact sheets on How to clean

An extensive literature search concerning cleaning procedures and examination methods for commercial and cultural plastics was carried out. This formed the basis for development of the research strategy. Six model plastics which represented those most in need of cleaning in POPART partners collections were selected and sourced, namely polymethyl methacrylate (PMMA), plasticized PVC (PVC), cellulose acetate (CA), high density polyethylene (HDPE), high impact polystyrene (HIPS) and polystyrene foam (XPS). Model plastics were as pure as possible without colouring agents or fillers because such additives complicate examination of cleaning on the polymer itself. Polymers were the components of plastics which were the focus area for POPART.

To ensure that all materials were tested on an equal basis, one institution, Natmus, carried out mechanical cleaning on all six model plastics. All partners involved in WP4 developed and agreed cleaning protocols for conducting mechanical cleaning which were also applied to aqueous, solvent and chemical cleaning techniques. The protocols defined how many mechanical rubs of a cloth, sponge or brush and their direction should be used when evaluating cleaning. WP4 partners also developed examination protocols to evaluate the effects of cleaning quantitatively. All studies of conservation cleaning of plastics prior to POPART used qualitative measurements alone such as visual and microscopic examination. These are important but subjective and therefore poorly repeatable. Changes in gloss, percentage of area scratched and change in surface energy determined from contact angle of water on surfaces were used to calculate a quantitative cleaning vector.

Mechanical cleaning has long been perceived as the least damaging technique to remove soiling from plastics. The results obtained from POPART suggest that the risks of introducing scratches or residues by mechanical cleaning are measurable. Some plastics were clearly more sensitive to mechanical damage than others. From the model plastics evaluated, HIPS was the most sensitive followed by HDPE, PVC, PMMA and CA. Scratches could not be measured on XPS due to its inhomogeneous surfaces. Plasticised PVC scratched easily, but appeared to repair itself because plasticiser migrated to surfaces and filled scratches.

Photo micrographs revealed that although all 22 cleaning materials evaluated in POPART scratched test plastics, some scratches were sufficiently shallow to be invisible to the naked eye. Duzzit and Scotch Brite sponges as well as all paper based products caused more scratching of surfaces than brushes and cloths. Some cleaning materials, notably Akapad yellow and white sponges, compressed air, latex and synthetic rubber sponges and goat hair brushes left residues on surfaces. These residues were only visible on glass-clear, transparent test plastics such as PMMA. HDPE and HIPS surfaces both had matte and roughened appearances after cleaning with dry-ice. XPS was completely destroyed by the treatment. No visible changes were present on PMMA and PVC.

Of the cleaning methods evaluated, only canned air, natural and synthetic feather duster left surfaces unchanged. Natural and synthetic feather duster, microfiber-, spectacle - and cotton cloths, cotton bud, sable hair brush and leather chamois showed good results when applied to clean model plastics.

Most mechanical cleaning materials induced static electricity after cleaning, causing immediate attraction of dust. It was also noticed that generally when adding an aqueous cleaning agent to a cleaning material, the area scratched was reduced. This implied that cleaning agents also functioned as lubricants. A similar effect was exhibited by white spirit and isopropanol.
Based on cleaning vectors, Judith Hofenk de Graaff detergent, distilled water and Dehypon LS45 were the least damaging cleaning agents for all model plastics evaluated. None of the aqueous cleaning agents caused visible changes when used in combination with the least damaging cleaning materials. Sable hair brush, synthetic feather duster and yellow Akapad sponge were unsuitable for applying aqueous cleaning agents. Polyvinyl acetate sponge swelled in contact with solvents and was only suitable for aqueous cleaning processes.

Based on cleaning vectors, white spirit was the least damaging solvent. Acetone and Surfynol 61 were the most damaging for all model plastics and cannot be recommended for cleaning plastics. Surfynol 61 dissolved polyvinyl acetate sponge and left a milky residue on surfaces, which was particularly apparent on clear PMMA surfaces. Surfynol 61 left residues on surfaces on evaporating and acetone evaporated too rapidly to lubricate cleaning materials thereby increasing scratching of surfaces.

Supercritical carbon dioxide induced discolouration and mechanical damage to the model plastics, particularly to XPS, CA and PMMA and should not be used for conservation cleaning of plastics.
The many cleaning vectors obtained for model plastics, each of which comprises quantitative changes in gloss, contact angle and percentage of area scratched by cleaning for a particular plastic, were combined with qualitative visual assessments and after cleaning and summarised as a set of flow charts for cleaning CA, HDPE, HIPS, PMMA and PVC. They are intended to assist conservators optimize the removal of soil while minimising the risk of damaging the plastic types researched in the project. Flow charts are based on the results obtained both from cleaning model plastics and on applying those results to real museum objects or study pieces by POPART partners.
The experimental approach and findings from cleaning model plastics and real or study objects have been documented in the book, Preservation of Plastic Artefacts in Museum Collections, edited by Bertrand Lavedrine, Alban Fournier and Graham Martin, published by Editions du Comité des travaux historiques et scientifiques, 2012, ISBN: 978-2-7355-0770-2. In addition, the results were presented and two practical workshops conducted for conservators at the POPART International conference in Paris in March 2012.

-Thin coating and consolidation

Literature research has been conducted to get insight in failure mechanisms for polyurethane-ester (PUR-ES) materials which comprise foam artworks and furniture insulation, cushioning, heat and sound insulation and paints. The main cause of degradation of such materials is moisture and light. From this point of view the coating functionality is determined; i.e. the coating should diminish the impact of (UV) light exposure to the object.
Furthermore the coating matrix should adhere well to the object. Early in the project it became evident that it was not feasible to develop a coating which was reversible and would therefore comply with conservation ethical requirements. Because of the good adherence, it is impossible to undo the coating of the object without damaging it.

An important part of the research was to develop the coating recipe such that it can be easily applied to the art object. Therefore the viscosity of the coating before applying it should not be too high. Furthermore the coating should be curable without destroying the PUR-ES polymer sample. The final coating recipe can be applied using spray method followed by drying for 24 hours.

The selected coatings for the experiments were Bemiguard MC, PRS, PRH and X09.46 (commercial names). These were dispersed in water and/or organic solvents in varying concentrations. The organic coating was tested with many different additives that possess the properties of light absorbance and stabilization of radicals that are produced during the degradation mechanism of the PUR-ES. The selected additives were X10-149, X10-150, X10-151 and X10-152 (commercial names) consisting of stabilizers and cross-linkers.

The combinations of 4 different base coatings with varying concentrations dispersed with varying concentrations in water or ethanol together with 4 additives in different concentrations resulted in an extensive experimental matrix. All coating recipes were synthesized and tested on PUR-ES samples. Tested properties are thickness, adhesion, colouration, penetration depth and degradation resistance. Samples were examined using spectroscopy, electron and visible microscopy.

The coating recipe that shows best performance is 4% BTZ (X10-149) and 4% HALS (X10-150) added to the Bemiguard MC dispersion diluted with 7 parts of water (12.5%). From experiments and accelerated aging it can be concluded that the optimized coating can significantly increase the lifetime of PUR-ES samples by protection against photo degradation. Therefore the feasibility for the use of this coating for preservation of real PUR-ES art objects is demonstrated.

In the last stage of the project the coating was applied to a real art object (collaboration with Reboot project, Rotterdam, The Netherlands). Although this art object was made of polyester and is placed outside instead of PUR-ES inside the museum first tests showed that the coating is suitable. Although the project ends, the status of the art work and the coating will be monitored throughout the next years.

Polyurethane (PUR) foams have also been chosen to test consolidation treatments. PUR foams deteriorate rapidly within 20-30 years under ambient conditions. The main degradation symptoms are discolouration, yellowing, loss of flexibility, brittleness and crumbling, which occur under the influence of moisture, heat and light. Consequently, conservators of modern and contemporary art museums have often to deal with PUR foam artefacts that exhibit severe loss of mechanical properties and, concerning PUR ester foams, no effective solutions exist preventing this material from crumbling. The large number of studies concerning degradation and conservation strategies regarding PUR foam artworks reflects the importance of research in this area and this brought to the choice of PUR foam for coating and consolidation tests.

A PUR dispersion in water (Impranil DLV) applied by spray or nebuliser has already been successfully used for the stabilisation of PUR ether foam. However, for PUR ester foams, no convenient consolidation treatment exists at the moment. For this reason this work focused on PUR ester foams. PUR ester foams are very sensitive to humid environments. Hydrolysis of the polyol ester part is the main cause of degradation. It leads to lower molecular weight PUR chains and low molecular weight degradation products, and induces a large change in the mechanical properties of the material that became fragile. The PUR ester foam cell walls became brittle and can easily collapse under stress. Consolidation coatings have been tested with the aim to prevent this cell wall collapsing.

Two consolidants, the 3-aminopropylmethyldiethoxysilane (AMDES) and the N-(2-Aminoethyl)-3-aminopropylmethyldimethoxysilane (DIAMINO), of the family of aminoalkylalkoxysilanes (AAAS) have been applied by immersion in hexamethyldisiloxane (HMDS) solvent solutions. Application by immersion was chosen according to the need of obtaining uniform reproducible samples. Nevertheless, the low viscosity of the solutions allows applications by nebulization or spray as well. The treatments have been tested on unaged and artificially degraded samples (degraded samples, representative of naturally aged foams, have been prepared according to the study on PUR foam degradation presented in WP3).

To assess the effects of the treatments, visual examination, color change, low vacuum scanning electron microscopy (LV-SEM), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and mechanical compression test have been performed.

Mechanical compression test shows that, after treatment of PUR ester foams with AAAS, a reinforcement effect is obtained on both unaged and artificially aged samples. On artificially aged samples, DIAMINO treatment at a concentration of 2.5% vol/vol in HMDS solvent turned out to be the most effective. It is able to reinforce the degraded PUR ester foam structure and to restore its original elasticity. ATR-FTIR and SEM imaging show that AAAS polymerize on the cell wall surfaces and partially diffuse into the foam branches. It was then demonstrated that this reinforcement effect is a consequence of the formation of an interpenetrate polymer network between the PUR macromolecules and the poly-AAAS.

Beyond its reinforcement effect, the polymeric network formed after treatment has two significant characteristics. Firstly, he CIELab coordinates measurements proved that it weakly affects the visual aspect of the object since it does not change significantly its original color, secondly it does not fill the void of the open cells preserving the natural structure of the foam.

The long term effect of the consolidation treatment has been tested by artificial aging. The treated samples have been subjected to artificial aging at 50°C and 70%RH for 15 days. Reference samples have been subjected to the same artificial aging. The results show that, when the treatment is applied on new PUR ester foams, there is no difference between treated and untreated samples after artificial aging. This means that no preventive effect of the treatment on the degradation of the PUR ester foam has been highlighted in these particular conditions of artificial aging, probably because the exposure time was not sufficient. But when the treatment is applied on degraded PUR ester foam, after artificial aging, a further straightening of the sample mechanical properties occurs, while the reference degraded samples continue to degrade and became weaker.

Since the interactions between the PUR and the AAAS based treatment are not very clear at the moment, the treatment was not applied on real artwork. Further studies to better understand the chemistry behind this consolidation and the stability of these polymers to aging are required.

Potential Impact:
Cultural heritage is recognised as an economical factor, the cost of decay of cultural heritage and the risk associated to some material in collection may be high. It is generally estimated that plastics, developed at great numbers since the 20th centurys interbellum, will not survive that long. This means that fewer generations will have access to lasting plastic art for study, contemplation and enjoyment. On the other hand will it normally be easier to reveal a contemporary objects technological secrets because of better documentation and easier access to artists working methods, ideas and intentions. A first more or less world encompassing recognition of the problems involved with museum objects made wholly or in part of plastics was through the conference Saving the twentieth century held in Ottawa, Canada in 1991. This was followed later by Modern Art, who cares in Amsterdam, The Netherlands in 1997, Mortality Immortality? The Legacy of Modern Art in Los Angeles, USA in 1998 and, for example much more recent, Plastics Looking at the future and learning from the Past in London, UK in 2007. A growing professional interest in the care of plastics was clearly reflected in the creation of an ICOM-CC working group dedicated to modern materials in 1996, its name change to Modern Materials and Contemporary Art in 2002, and its growing membership from 60 at inception to over 200 at the 16th triennial conference in Lisbon, Portugal in 2011 and tentatively to over 300 as one of the aims put forward in the 2011-2014 programme of that ICOM-CC working group. When consulting the ICCROM library resources for papers on plastics in the sense relevant to the subject of Popart, then these steadily grow from 7 in the quinquennium 1986-1990, over 12, 13 and 16 to 19 in the quinquennium 2006-2010. Clearly, the apparent growth in intellectual resources over two decades only, to improve the study and conservation of plastics in art, reflects the growing concerns regarding the limited longevity of plastics and the growing awareness regarding the need for appropriate conservation measures. On the other hand do needs not always result in conservation action. Often, prioritization comes into play and with respect to plastic art, some peculiar reflections deserve attention. So may it be questionned why the value of modern art doesnt seem to follow the more traditional relationship with the age of art. We must also reflect on the emotional relationship between apparent damage as a sign of age and value, as well as on the difference between perceived surface damage and patina. Another element pertaining to conservation of modern art is the copyright of artists that extends at least 50 years beyond their death. Both, damage, value and copyright may influence the way by which damage is measured through scientific analysis, more specifically through the application of invasive or non invasive techniques. Any selection of those will not only have an influence on the extent of observable damage, but also on the detail of information gathered and necessary to explain damage and to suggest conservation measures.
Legal issues were discussed in a 2011 ICOM-CC paper authored by Marina Pugliese (member of the POPART project advisory committee). Their importance is emphasized further by the tentative programming of a joint meeting of the Modern Materials and Contemporary Art and the Legal Issues in Conservation working groups of ICOM-CC. This project and the book provided describes in great detail the multifaceted issues related to the study, condition analysis and conservation of plastic artefacts. This more than 300 pages book should be considered a further milestone publication aiming at better informed care of plastic artefacts. It will contribute to total eradication of the plastics denial syndrome, diagnosed and eloquently formulated by Brenda Keneghan in 1996. The Popart project has stated very clearly that regular examinations and surveys, multi-approach scientific analysis and raising public awareness must be at the basis of motivated and justified conservation of plastic museum objects. Of course, a statement of this kind should not be considered breaking news, but the way these ideas are given a solid basis to work with in order to reach the final objective, that is informed conservation, is to be called exemplary. The consortium provided an extensive collection of reference materials, both plastics as such and objects. This collection was used, not only to perform matchings with unknowns, but also to compare the potential, the usefulness, the pros and cons of relevant and innovative analytical techniques for the characterization and degradation assessment of plastics. The information given in the analytical techniques summarizing table stretches beyond pure science by also including estimations of expertise required and cost. Although condition survey results will depend on the age of the collection, on the types and frequences of individual plastics and on conservation conditions, it is obvious from surveys carried out in several museums in France, the UK and The Netherlands that from 15 to 35 % of what I would then call an average plastic material based collection is in a poor to unacceptable condition. However, some 75 % would require cleaning. The Popart project has clearly shown that an essential and thought- simple action such as cleaning must be considered with utmost care with respect to materials, solvents and deliberately chosen active chemicals. One of the prevailing factors leading to uncertainties in evaluating the causes of plastic deterioration are, besides their composition, the conservation history and different present-day conservation conditions of museum objects. The creation of, whats in a name, Polly, aimed at following plastic degradation processes in known environments in real time on the medium term. Moreover, both the physical appearance of the doll and the information displayed together with her in some museums must have triggered awareness of the visitors for the vulnerability of often tough and robust appearing contemporary art. Observing, measuring and archiving damage must inevitably lead to discussions on conservation. Attempts to slow down the degradation of plastic objects are mainly restricted to environmental control, including temperature, relative humidity, electromagnetic radiation and gaseous pollutants, although synergistic actions have just started and have already led to interesting observations. However, already nowadays and certainly in years to come, more remedial actions will be required to prolong the lifetime of those objects. Such actions are still scarce. The production of detailed flowcharts for cleaning five major plastics must be considered prominent breaking points within this scarcity. Observations and justified actions for the conservations of plastic artefacts will be considerably improved and systematized thanks to the survey form, developed by the Popart consortium. Preserving plastic objects of art and culture for future generations requires optimized merging of preventive and remedial conservation measures, and may involve restoration in some cases. The Popart project has responded to research needs for the investigation and conservation of plastic artefacts. Yet, much more will have to be done. Hopefully, the collaborations and sharings of knowledge renewed or developed within Popart will continue and extend in the future. There will be a continued need indeed to refine analytical methods for the characterization of the material and of its ageing and degradation; to study conservation processes; to document artists working methods; and to generalize condition surveys. At the 8th European Commission Conference on Sustaining Europes Cultural Heritage, held in Ljubljana, Slovenia, 2008, a questionnaire was organised to help clarifying to what extent EC project deliverables have had a significant impact on activities and procedures executed by stakeholders in the multifaceted field of the conservation of cultural heritage. One of the prominent results of this questionnaire was that both conservation scientists and conservators considered education and other long-term training projects one of the most useful instruments in cultural heritage research. Hopefully major national and international professional organisations will join forces for supporting the introduction of newly gained knowledge and expertise in professional training programmes, regarding understanding the composition, condition and remedial conservation steps of plastic art; and that these forces may find appropriate support within the EC Horizon 2020 actions as Popart 2 for instance!

The Popart project reached an international audience far beyond European borders. It contributed to establish an interdisciplinary approach involving scientists, conservators, curators and the developed methodologies has been broadly disseminated and used beyond the EU. The three-day international conference held in Paris in March 2012 showed that the project and its results were followed at a world level and Popart helped to increase the awareness for plastic conservation. A 325 pages book in full color was printed and disseminated during the conference. Besides this general conference, the project was also disseminated through 7 articles published in the popular press, 24 presentations during symposiums, 2 exhibitions, 2 interviews, 2 TV clips, 10 workshops, 12 posters, 12 publications, 2 thesis, 1 website (http://popart.mnhn.fr/)

List of Websites:
POPART public website and intranet:
http://popart.mnhn.fr/

POPART public results website (final dissemination website): POPART Highlights
http://popart-highlights.mnhn.fr

Final Report Summary - POPART (Strategy for the preservation of plastic artefacts in museum collections)

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