Unveiling the composition of historical plastics through non-invasive reflection FT-IR spectroscopy in the extended near- and mid-Infrared spectral range

The inspection of the enlarged spectral range allowed the detection of fundamental, combination and overtone bands which provided reliable identification and semi-quantitative characterization of different polystyrene-based co-polymers. Furthermore the variation of the plastic optical properties across the explored spectral range allowed us to sample the plastic materials to different depths in the mid- and near-IR regions, so as to probe the chemistry at the surface and in the plastic bulk, respectively, in a non-invasive manner. This proved particularly useful to observe spectral markers of surface degradation occurring in historical ABS-based polymers. (C) 2021 Elsevier B.V. All rights reserved.

The present research exploits the strengths of external reflection FT-IR spectroscopy to non-invasively study heritage plastic objects through inspection, for the first time, of the wide spectral range including the near-and mid-IR (12500-350 cm(-1)). Unlike most of previous works on historical plastic objects, reflection-mode spectra were not corrected for the unfamiliar surface reflection profiles to the more recognizable absorption-like band shapes. This avoided data misinterpretation due to ill-suited Kramers Kronig correction when volume reflection is also present or when highly absorbing IR compounds generate Reststrahlen bands.