Spectroscopic methods (Room A.2.19)

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FTIR spectroscopy is also a very common method for analysing plastics, as it enables the molecular groups (monomers) that make up the polymers to be identified. Medium infrared light is shone through the plastic and a spectrum is generated. From this, the type of plastic, mixtures, additives or modifications can be identified. It is also possible to analyse unknown polymer materials. If comparative samples are available, it is often possible to recognise subtle chemical differences.
With an additional device, the IR microscope, very small areas in the component can be analysed (less than 0.1 mm), so that impurities and inclusions can be identified separately from the surroundings.
Another additional method (ATR, Attenuated Total Reflection) allows the analysis of thin layers on the surface (thickness in the µm range), which would otherwise be below the detection limit (with transmission) or would mix with the bulk material in the spectrum.
Coupling with the TGA is also possible.

UV/VIS spectroscopy analyses the permeability of plastics to visible and UV light. This allows additives, especially UV protective agents, to be detected and identified.

A chamber for visual sampling (standard illuminants D65 and A) and two spectrophotometers are available for the reproducible determination of the colour of plastic components. The latter measure the remission R (λ) of the surface in the visible and near UV range using diffuse illumination (Ulbricht sphere or integrating sphere) and use this to calculate the colour, quantitative colour differences (Δ E) or metamerism, e.g. in the L•a•b space. These measurements can also be carried out with the gloss components excluded.