Construction In Space Two Cones

Introduction

Currently, at that place are few options for in situ not-subversive monitoring of the stability of modern polymeric materials within heritage collections. Past research has focused on exploiting the information contained in volatile organic compounds (VOCs) emitted from an object to empathise decay mechanisms or identify the polymer composition (Lattuati-Derieux et al. 2013; Hakkarainen, Albertsson, and Karlsson 1997). The central shortcoming of many previous studies utilising VOC capture is that often they use destructive analysis, elevated temperatures, artificially aged samples or combinations of these during analysis. While these studies take given us a wealth of data regarding disuse profiles and key VOCs emitted from specific polymers, they often lack real-world applicability.

Previous work past Curran et al. (2016) has shown that it is possible to capture relevant VOC data from three-dimensional polymer objects at room temperature using solid phase microextraction gas chromatography/mass spectrometry (SPME-GC-MS). All the same, this required pre-concentration of VOCs within Tedlar sealable numberless, which introduces risks to the object from poor treatment during bagging, and severely limits the size of objects which can exist studied. The novelty of the method described here lies in using SPME to undertake a systematic and repeated not-destructive and non-invasive monitoring programme of multiple points-of-interest (POI) around a naturally aged three-dimensional polymer object within its normal storage surround.

The central questions this enquiry aimed to answer were –

Can key VOC markers for polymer composition or decay be efficiently and confidently detected using SPME-GC-MS in a museum storage environment?
Tin can differences between the intensity of central VOC markers be detected from different POIs around the object?
Tin can insights into object material condition be detected using SPME-GC-MS?
What is the potential impact for conservation exercise and VOC monitoring?

Materials and methods

Two experimental campaigns were carried out on the constructivist sculpture Construction in Space 'Two Cones' (Tate T02143, 1936, this replica 1968) by the artist Naum Gabo. The work is available for study because information technology is deemed too deteriorated for display, and currently suffers, among other bug, from warping, crazing, and crystal growth (Figure 1(b)). Every bit such an authorised replica is being used instead for display (Lawson and Cane 2016). The sculpture is principally synthetic from cellulose acetate (CA) and is currently loosely packed within a polymer storage crate lined with activated charcoal cloth wrapped around Plastazote foam, a Plastazote base, covered past fabric to prevent dust accumulation, but not enclosed. During each campaign, POIs around the object (see Figure 1(a,b) for locations) were examined by placing an exposed 50/xxx μm DVB/CAR/PDMS SPME fibre at each POI. A 5th SPME fibre was placed within the room housing the object to measure the background VOCs present. The two experimental campaigns differed in the length of time the SPME fibre was exposed to the object. One entrada was exposed to the object for 24 hours, the other for 7 days. Three replicate measurements were fabricated during each campaign, on dissimilar dates. Tiptop areas were normalised to the peak area of ethylbenzene from a MISA Group 17 Not-Halogen Organic Mix (Sigma Aldrich 48133 Supelco) standard.

Figure i. (a) Shows the POIs where the four fibres were placed around the object. (b) Shows a close-up of the location of fibre two and the status of the polymer surrounding it. Photos: Marking Kearney. Artwork © Nina and Graham Williams, DACS and Tate 2018.

Results

The results accept shown that an exposure fourth dimension of 24 hours is adequate for the capture of VOCs relating to polymer limerick and disuse markers (). VOCs such as acetic acid and phenol, which relate to decay mechanisms, and the plasticisers diethyl phthalate and dimethyl phthalate, were constitute at each of the POIs examined, though the concentration levels varied at each location.

Tabular array 1. Normalised peak surface area results from 24-hr exposure.

Another pregnant result was the apparent differences between POI associated with areas of disuse and those POI slightly further abroad. At both exposure times, the concentration of the four key VOCs, mentioned above, was significantly higher shut to an area with visible signs of decay every bit opposed to the fibres placed inside the storage crate but slightly away from the object – giving two singled-out sets of results from the four fibres places effectually the object.

Possibly the nigh significant insight was the articulate difference between the two areas of decay examined, suggesting different decay mechanisms present on a single object. The surface area where fibre two was placed had a significantly higher ratio of phenol to acetic acrid than where fibre four was placed (Effigy 2). This characteristic was present for both 24 hours and 7 days exposure times, though the ratio was less at 7 days (). Despite this difference in ratio, the overall concentration of acerb acid was higher at fibre four than at fibre 2. Visually, the area centred around fibre two appeared to be more heavily rust-covered and contained more crystal growth on the polymer surface than fibre four, which had virtually no crystal growth. FTIR analysis was performed on a crystal which had formed on the SPME fibre housing, still, definitive identification was not possible. Results suggested some form of phenyl phosphate plasticiser (tri- or diphenyl phosphate could not be distinguished). These results are also backed up by previous analysis on the object (Townsend, Angelova, and Ormsby 2016) which did show the presence of triphenyl phosphate (TPP). The high levels of phenol could be explained past the work by Shinagawa, Murayama, and Sakaino (1992) who proposed that the decay of TPP, via hydrolysis, led to diphenyl phosphate and phenol. Our results are also in keeping with those of Tsang et al. (2009) who noticed that CA plasticised with TPP appeared to decay at a faster rate than CA without. Our results, therefore, heavily propose that we are detecting 2 distinct decay mechanisms from the ii different areas. The higher levels of acetic acrid seen at fibre four are generated by the deacetylation of CA, while hydrolysis of TPP leads to higher levels of phenol.

Figure 2. Ratios of phenol to acetic acid for the ii exposures. Not the consistent high levels of phenol recorded past fibre two (in black) compared to fibre 4 (in grayness). This suggests that there is something boosted driving the emission of phenol in the surface area covered by fibre ii.

Taken together, these results suggest that SPME is an efficient methodology for monitoring polymer object decay. Our inquiry besides provides evidence that monitoring of VOCs emitted from polymer objects either needs to exist targeted at specific POIs close to the object, or else generally, with the understanding that VOC 'hot spots' may be missed.

Our work highlights the capabilities of SPME-GC-MS to detect potential differences in decay mechanisms from a single object. Our piece of work also adds further evidence to the theory that CA plasticisers with TPP decay at a faster rate than other forms of the material.

In that location is also a potential impact for collection care, equally our enquiry suggests that electric current storage practices, such equally open up storage and charcoal inhibitors for highly decayed polymer objects are insufficient for eliminating VOC build-upwardly in certain areas. Our research points towards the demand for better control of the ventilation of troublesome polymer objects kept at room temperature – this would probable take the form of an invasive procedure such as a continuous air period over the object or periodic flushing of the atmosphere around the object.