A first approach into the characterisation of historical plastic objects by in situ diffuse reflection infrared Fourier transform (DRIFT) spectroscopy

This research explores the potential of a portable instrumentation of diffuse reflection infrared Fourier transform (DRIFT) spectroscopy for the in situ characterisation of plastics cultural objects. As sampling has been increasingly questioned in the conservation field, the development of portable devices has been sought. Among them, infrared (IR) spectroscopy in reflection mode has been gaining a powerful position in conservation research. Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) has been widely used for plastics, yet the strong contact required by the technique can make it inappropriate for flexible and/or fragile historic objects. Therefore, in this study, the potential of in situ DRIFT spectroscopy is assessed on both references and historical objects made of the same polymers – polyethylene (PE), polypropylene (PP) and polystyrene (PS). Plastic samples showing different characteristics such as refractive and absorption indexes and topography are also included. These different polymers and surface qualities are discussed as factors influencing the final spectra. In situ DRIFT proved to be very versatile as it could be applied in a variety of plastics and objects' shapes, does not require sampling nor an intimate contact as ATR. Moreover, specific bands and spectral profiles were identified as DRIFT markers of the polymers under study. The acquisition conditions for the in situ analysis were optimized and a pilot spectral database using different IR modes (transmission, ATR and DR) was created. Important information was collected, which allowed the polymer identification of the majority of the historical objects produced between the 1940s and 1980s, from a Portuguese private collection.