Isothermal DSC Measurements of Oxidation Stability

Purpose

To compare the oxidation stability of two materials.

Sample

Two commercially available elastomers based on NR stabilized to different extents against oxidation. Sample 1 has good oxidation stability, and Sample 2 poor oxidation stability.

Conditions

Measuring cell: DSC822^e with air cooling and gas box

Pan: Aluminum 40 ul, without lid

Sample preparation: Mass approx. 7.5 mg 

DSC measurement:  Heating from 40 °C to 165 °C at 10 K/min and 5 min isothermal at 165 °C under nitrogen (50 ml/min). The purge gas was then switched to air (50 ml/min) and the sample measured at 165 °C for 180 min.  

Atmosphere: Nitrogen then air, automatically switched 

Evaluation

The diagram shows the section of the isothermal measurement curves in the air atmosphere. Both curves show relatively flat exothermic reaction curves. The peak maximum of sample 1 is 99 min and that of sample 2 is 62 min. The oxidation reaction takes place more rapidly with sample 2 than with sample 1. This confirms that sample 1 has better oxidation stability than sample 2. 

To save time, the measurements can be performed at higher temperatures. The peak maxima then occur after shorter time intervals, but the difference between samples cannot be measured so accurately. 

Conclusions

The oxidation stability of elastomers can be compared by means of isothermal measurements under air. If the oxidation stability of a sample is poor, the maximum of the reaction peak is shifted to shorter times compared with a sample that has good oxidation stability. Dynamic DSC measurements do not show significant differences. 

_{Isothermal DSC Measurements of Oxidation Stability | Thermal Analysis Application No. HB 492 | Application published in METTLER TOLEDO TA Application Handbook Elastomers Volume 2}