Comparison of DSC and DMA Measurements of Polyurethane - METTLER TOLEDO

Comparison of DSC and DMA Measurements of Polyurethane

Purpose

Polyurethane elastomers consist of macromolecules containing hard and soft segments. The purpose of the experiment was to compare the results of DMA measurements.

 

Sample

Technical polyurethane elastomer

 

Conditions

Measuring cell: DSC822e with liquid nitrogen cooling option

Pan: Aluminum 40 µl, pierced lid

Sample preparation: Piece of elastomer, 22.12 mg.

DSC measurement: Heating from 100 °C to 80 °C at 2 K/min

Atmosphere: Nitrogen, 50 ml/min

 

Evaluation

In the DSC curve, the glass transition is clearly visible at –32 °C. The value of the step Δcp, is 0.36 J/gK, which is somewhat less than that of amorphous material (0.47 J/gK). This indicates that the sample is semicrystalline. The maximum of the melting peak is at 45 °C. With DMA, the glass transition is observed as a frequency-dependent step in the curve of the storage modulus, G'. The beginning of the step coincides with the onset of the glass transition step in the DSC curve (38 °C). The storage modulus changes by about 2 decades over a relatively broad temperature range of about 60 K. The loss factor, tan g, exhibits a broad frequency-dependent peak in this region with a shoulder between –10 °C and 0 °C. This shoulder indicates that, in this material, there is a phase separation between the hard and soft segments, which have different glass transitions. The crystallites melt at 40 °C. This endothermic process is observed in the storage modulus curve as a step whose position is independent of frequency. In the tan g curve, a small peak can be seen on melting whose temperature maximum is also frequency independent. 

 

Conclusions

Both the glass transition and the melting process of the polymer can be seen in the DMA measurement. Compared with DSC, it is in some cases possible to obtain additional information on the fine structure of the glass transition. This fine structure is linked to the phase behavior and morphology of the material. The double peak in the tan g curve is an indication of the fine structure associated with the glass transition.

 

Comparison of DSC and DMA Measurements of Polyurethane | Thermal Analysis Handbook No.HB437 | Application published in METTLER TOLEDO TA Application Handbook Elastomers, Volume 2