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Thermal or oxidative stability

If organic substances or plastics are exposed to heat, light and above all atmospheric oxygen for a long time, a so-called aging process takes place. On the one hand, this is a slow oxidation of individual components, on the other hand, some molecules are not stable in the long term and disintegrate after an unknown time.

In order to investigate the thermal stability of such compounds, the OIT test is often used, where OIT stands for “Oxidation Induction Time”. In this test, the sample to be examined is brought under inert atmosphere to a temperature below the melting point.

Then you change the atmosphere to oxygen or air and measure the calorimetric signal. After a time, oxidation will start, which normally manifests itself as an exothermic reaction, and the sample temperature will thereby increase slightly.

From this small increase you can read off the corresponding reaction time and this gives the OIT time. Also, a statement about the reaction rate and decomposition rate of the onset of oxidation can be made by DSC, if one evaluates the data with the associated software.