DECOMPOSITION TEST (LÜTOLF DYNAMIC)
[VDI 2263, Part 1]
2 g of the test substance and 2 g of graphite powder, as reference, are heated with constant rate (as a rule 2,5 °C/min).
The temperature difference between the sample and the reference (DT-signal) is recorded and plotted against the reference temperature.
The lowest temperature, at which the DT signal deviates from the baseline in positive direction is defined as the begin (onset) of the first exothermic reaction.
This value can be used to determine safe drying temperatures in contact dryers (e.g. vacuum dryers).
Depending on the dryer type the recommended maximum drying temperature is about 100-150 °C below the onset of the first exothermic reaction in this test.
Very often these values are too conservative (because they result from a simple screening test).
For a more precise evaluation of safe drying temperatures, additional tests, e.g. isoperibolic tests in a dewar flask, are recommended.
If the DT signal shows a very narrow peak, i.e. if DT increases faster than 5 °C/min at a heating rate of 2,5 °C/min, the decomposition is defined as "spontaneous".
From the DT-curve, the maximum DT-value (dTmax) and the temperature, at which the peak of the DT-signal occurs Tpeak are derived.
If dTmax>10% (TPeak in °C), a special test for "spontaneous decomposition" should then be carried out.