Oxidative-Induction Time (OIT) and Oxidative-Onset Temperature (OOT)

Oxidative Induction Time (isothermal OIT) is a relative measure of the resistance of a (stabilized) material to oxidative decomposition, determined by calorimetric measurement of the time interval to the beginning of the exothermal oxidation of the material, which is exposed to an oxygen or air atmosphere under atmospheric pressure at a fixed temperature.

Oxidative-Induction Temperature (dynamic OIT) or Oxidative-Onset Temperature (OOT) is a relative measure of the resistance of a (stabilized) material to oxidative decomposition, determined by calorimetric measurement of the temperature at the beginning of the exothermal oxidation of the material, which is exposed to an oxygen or air atmosphere under atmospheric pressure at a fixed heating rate.

The oxidative-induction time can be determined by means of DSC measurements. To achieve this, the sample body and a reference substance are heated at a constant rate in an inert gas atmosphere (nitrogen flow). When the defined temperature is reached, the atmosphere is replaced by an oxygen or air atmosphere with the same flow rate. The sample is then held at a constant temperature until the oxidative reaction is indicated by the exothermal deviation of the DSC heat flow curve. The isothermal OIT is the time interval between the start of the oxygen or air flow and the beginning of the oxidation reaction. The method is described in numerous technical standards such as DIN EN ISO 11357-6.

Figure 1: OIT measurement on PE-HD (isothermal OIT)Figure 1: OIT measurement on PE-HD (isothermal OIT)

The oxidative-induction temperature (dynamic OIT) is also determined by means of DSC. Here, the specimen and a reference substance are heated in a dynamic oxygen or air atmosphere at a constant rate until the oxidation temperature is revealed via an exothermal deviation in the DSC heat flow curve. The dynamic OIT is the temperature at which the oxidation reaction begins. Because of the dynamic temperature control, the beginning of oxidation is often indicated by a sharp increase in the DSC heat flow curve in the exothermal direction during the DSC measurement.

Figure 2: Dynamic OIT measurement (oxidative-induction temperature) on PE-HDFigure 2: Dynamic OIT measurement (oxidative-induction temperature) on PE-HD

Related Methods

DSC