Abstract
The conservation of polymer-based cultural heritage is a major concern for collecting institutions internationally. Collections include a range of different polymers, each with its own degradation processes and preservation needs, however, they are frequently unidentified in collection catalogues. Fourier transform infrared (FTIR) spectroscopy is a useful analytical tool for identifying polymers, which is vital for determining storage, exhibition, loan and treatment conditions. Attenuated Total Reflection (ATR), and External Reflection (ER) are proven effective FTIR sampling techniques for polymer identification and are beginning to appear in conservation labs. This paper evaluates and optimises the application of these two FTIR techniques to three-dimensional plastic objects in the museum context. Elements of the FTIR measurement process are investigated for 15 common polymers found in museum collections using both authentic reference sheets, and case study objects to model for surface characteristics. Including: use of the ATR and ER modules, the difference between clamping and manually holding objects in contact with the ATR crystal, use of the Kramers–Kronig Transformation, signal-to-noise ratios for increasing number of co-added scans, resultant time taken to collect each measurement, associated professional, health and safety considerations, and the use and availability of reference materials for polymer identify verification. Utilising this information, a flowchart for applying FTIR spectroscopy to three-dimensional historic plastic objects during museum collection surveys is proposed to guide the conservation profession.
Highlights
Cultural heritage institutions have significant and growing collections of polymer-based objects which they have a responsibility to preserve for present and future generations
The signal-to-noise ratio (SNR) values produced by the External Reflection (ER) module (Fig. 2b) reflect the much higher signal as compared to Attenuated Total Reflection (ATR) measurements, for glossy materials (ABS, HDPE), which are highly reflective resulting in a large signal
This paper investigated a number of aspects of the Fourier transform infrared (FTIR) instrument measurement process for identifying polymers in three-dimensional objects during museum collection surveys by conservators
Summary
Cultural heritage institutions have significant and growing collections of polymer-based objects which they have a responsibility to preserve for present and future generations. The majority of literature concerning the identification of polymers in cultural heritage collections is focused on the use of Fourier transform infrared (FTIR) spectroscopy as an accessible, fast and non-invasive technique [1,2,3,4,5] Additional techniques such as Raman spectroscopy [5, 6], near infrared spectroscopy [5, 7], gas chromatography–mass spectrometry (GC–MS) [5, 8], nuclear magnetic resonance spectroscopy [9], and volatile organic compound (VOC) analysis [10,11,12] are utilised. Student’s undertaking postgraduate studies in conservation are trained in use of FTIR spectroscopy, which has becomes widespread in conservation, and is likely to increase further as an area of expertise in the profession
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