PE, Characterization by Crystallinity

Sample

PE-LD and PE-LLD as pellets, PE-HD as a film

Conditions

Measuring Cell: DSC821^e with air cooling

Pan: Aluminum standard 40 ul, lid hermetically sealed

Sample preparation: PE-LD: Disk of 9.796 mg cut from pellet

                                     PE-LLD: Disk of 8.128 mg cut from pellet

                                     PE-HD: Disk of 10.314 mg punched from film

DSC measurement: Heating from 30 to 180°C at 10 K/min

Atmosphere: Static air

Evaluation

Note: A straight baseline has been used for integration. Since the normalized value is used, it is important that the sample weight is accurate. 

Interpretation

The area under the peak corresponds to the heat of fusion of the sample. It is proportional to amount of crystallites present in the sample. The degree of crystallinity is determined by comparing the measured heat of fusion with the theoretical heat of fusion of 100% crystalline polyethylene of 293 J/g (see table on page 25).

Conclusion

The DSC crystallinity indicates the percentage of the material that is crystalline versus amorphous. The degree of crystallinity depends on how regular the structure of the molecule is (no branches or short branches in regular distance) and on the thermal history. Since hardness and strength increase with increasing crystallinity, the DSC result correlates with the mechanical properties.

^{PE,  Characterization by Crystallinity | Thermal Analysis Application No. HB201 | Application published in METTLER TOLEDO TA Application Handbook Thermoplastics}