PE, oxidation stability
Sample
Lupolen GM5040 T12 (stabilized PE-HD film)
Conditions
Measuring Cell: DSC821e with air cooling and gas controller
Pan: Aluminum standard 40 ul without lid, 40 ul copper pan without lid, for comparison
Sample preparation: Disk punched out of film
DSC measurement: According EN 728 (European standard):
Under nitrogen, 50 cm3/min
3 min isothermal at 30°C, then heating to 200°C at 20 K/min, 2 min isothermal at 200°C
Under oxygen, 50 cm3/min (automatically switched by the gas controller);
Isothermically at 200°C starts the actual measurement. Since only the onset of oxidation is required, the actual measurement.
Since only the onset of oxidation is required, the actual measurement time can be reduced using the Conditional Experiment Termination Software option.
Atmosphere: Nitrogen and oxygen, respectively, automatically switched by the gas controller
Evaluation
The oxidation induction time (OIT) in the aluminum pan is 15.9, in the copper pan 9.5 min. The melting curve could also be evaluated.
Interpretation
The time after switching to oxygen to the onset of oxidation (intersection of baseline with the tangent) is called the induction period or Oxidation Induction Time, OIT. A long OIT indicates good stability and vice versa. Contact with copper or copper alloys catalyzes the oxidation reaction. Polyolefins that will be exposed to copper require special additives that neutralize this catalytic effect. The efficiency of such additives is determined by carrying out the experiment with the sample in a copper pan. Good <<copper stability>> results in an OIT of at least half the value obtained in the aluminum pan. Without such addictives, the OIT is about 10 times shorter in a copper pan.
Note: Polyolefines give distinct induction periods. Other polymers are best tested by exposure to oxygen on heating at relatively low rates, preferably 5 K/min, until distinct exothermal oxidation is visible.
Conclusion
The determination of the oxidative stability by DSC is fast and easy. It is especially recommended for the quality assurance of long-life goods such as electrical cables and water pipes. Each batch of the raw material should be measured. In addition, the polymer can be identified from the fusion peak obtained.
PE, Oxidation Stability | Thermal Analysis Application No. HB 209 | Application published in METTLER TOLEDO TA Application Handbook Thermoplastics