PE, Melting Curve and Thermal History

Sample

PE-HD film

Conditions

Measuring Cell: DSC821^e with air cooling

Pan: Aluminum standard 40 ul, lid is hermetically sealed

Sample preparation: Disk of 2.33 mg punched out of film

DSC measurement: Pretreatment: annealing for 60 min at 129°C followed by cooling to 40°C at 5 K/min

Heating from 40° to 180°C at 5 K/min (see curve of PE-HD with thermal history eliminated)

Atmosphere: Static Air

Evaluation

The melting gap can be evaluated as an onset, or the melting behavior can be characterized by the conversion curve. However, the most important information it reveals is the temperature at which annealing was performed.

Interpretation

Crystallite segregation occurs during annealing at 129°C or lower cannot of course be formed during this process. As the sample is cooled, small crystallites with lower melting points form again, but a gap at 129°C (called the melting gap) appears in the second heating run of the sample. On complete melting, any thermal history is eliminated.

Conclusions

The shape of the DSC melting curve depends on the thermal history of the sample. The melting gap is often used to check that the processing temperature was correct, e.g. the annealing of PE high voltage cables. Complete melting eliminates any thermal history and is a prerequisite for the comparison of different raw materials.

^{PE, Melting Curve and Thermal History | Thermal Analysis Application No.HB205 | Application published in METTLER TOLEDO TA Application Handbook Thermoplastics}