Infrared Spectroscopy (IR Analysis)

Polymer determination and substance detection

Significance and Test Method

Infrared spectroscopy, in short IR spectroscopy, is a simple and fast method to determine the polymer and the ingredients of an elastomer compound. The irradiation of material samples with electromagnetic waves in the infrared range makes it possible to detect resonance vibrations of various organic molecules.

Particularly for elastomers, this enables to identify their functional groups, which allows for a relatively reliable polymer determination.

However, IR spectroscopy is not a trace analysis. The detection limit is 2 to 5%, but in exceptional cases it can be much more sensitive.

Nowadays, mainly Fourier transform infrared spectrometers (FTIR) are used. These offer some decisive advantages over the formerly used dispersive spectrometers. For example, the measurement times are relatively short and the signals obtained are strong.

Types of Sample Preparation and Analysis

Since most elastomers are black and therefore not translucent nor permeable to infrared light, this requires special sample preparation techniques. Pyrolysis FTIR analyses the condensed vapour of a thermally decomposed elastomer sample, which is transparent to infrared light.

Attenuated total reflectance (ATR) is a sampling method in which light is shone on a sample to obtain information about its structure and composition. It enables the analysis of solid and liquid material samples.

Also extracts of elastomers are analysed. Hot extraction separates many components of the formulation from the rubber, making them easier to dissolve and to identify using IR spectroscopy.

Significance of IR Spectroscopy for Application Technology

FTIR analysis is a frequently used analytical method in elastomer technology. Within the framework of quality assurance, it allows polymers to be determined quickly and easily with a manageable amount of effort. After all, every formulation has a typical ATR band spectrum (medium resolution) as well as a typical spectrum of the extracts (high resolution). These are used to prove the sampling status of a formula with regard to the substances it contains. Combined with other analytical techniques, IR spectroscopy with its special forms is a proven tool for damage analysis.

For IR spectroscopy, a material sample is exposed to electromagnetic waves in the infrared range. The absorption of this radiation excites certain organic molecular bonds in the material to resonate. These resonance oscillations are displayed as bands of an IR spectrum in a chart and identified by reference spectra.

In the DICHT! special edition O-Ring Prüflabor Richter you will find a comprehensive overview of common tests and analysis methods in elastomer technology. Discover the collected knowledge about elastomer testing in this issue.