FTIR Spectroscopy
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FTIR spectroscopy
Fundamentals of FTIR spectroscopy
FTIR spectroscopy (often just called IR spectroscopy) is one of the most important methods for the identification and structure elucidation of plastics. It belongs to the methods of molecular spectroscopy. Infrared light in the wavelength range from 2.5 to 25 μm causes the molecules of the plastic to vibrate forcibly. Part of the emitted radiation is absorbed by the molecules, the remaining part of the radiation passes through the examined plastic unhindered.
The absorption bands appearing in the IR spectra are assigned to the vibrations of individual atomic groups (functional groups). Qualitative and quantitative analysis using IR spectroscopy is based on the wavelength-dependent interaction between IR radiation and molecules. Based on this interaction, absorption spectra with characteristic bands are generated.
Possible applications of FTIR spectroscopy
FTIR spectroscopy is thus used for material identification, the detection of atypical foreign substances on or in plastics and the detection of ageing and degradation processes. However, certain bond types, tacticity and crystallinity can also be determined; plasticisers and additives can be detected in the spectra too.
The evaluation of the recorded IR spectra is carried out using already known comparison or sample spectra of known reference materials, which are available in extensive "infrared libraries" in books or in commercially available software. In plastics testing, especially plastics diagnostics and failure analysis, FTIR spectroscopy is a proven tool to determine possible deviations of the plastic of a damaged part from regularly used (required) plastic types (reference materials).
See also
References
- DIN 53742 (1971-09): Testing of Plastics – Determination of the Vinyl Acetate Content of Copolymers of Vinyl Chloride and Vinyl Acetate – Infrared Spectrographic Method (withdrawn)
- Trempler, J.: Infrared Spectroscopy. In: Grellmann, W., Seidler, S. (Eds.): Polymer Testing. Carl Hanser Munich (2022) 3. Edition, pp. 325–327 (ISBN 978-1-56990-806-8; E-Book ISBN: 878-1-56990-807-5; see AMK-Library under A 22)
- Hellerich, W., Harsch, G., Baur, E.: Werkstoff-Führer Kunststoffe. Carl Hanser Verlag, München Wien (2010) 10. Auflage (ISBN 978-3-446-42436-4; see AMK-Library under G 37)