Comparison of DSC and DMA Measurements - METTLER TOLEDO

Comparison of DSC and DMA Measurements

Purpose

To compare DSC and DMA measurements by demonstrating the dependence of the shear modulus on the thermal events

 

Sample

Unfilled silicone oil 

 

Conditions

Measuring cell: DMA/SDTA861e and DSC822e

Pan: For DSC measurements, aluminum pan, 40 µl.

Sample preparation: The two gaps in the shear sample holder for liquids were set to 0.3 mm and filled with sample. The diameter was 11 mm. The sample holder was then installed in the clamping assembly that had been cooled to –140 °C. The sample weight for DSC measurements was 22.4 mg.

DSC measurement: Heating from –140 °C at 10 K/min.

DMA measurement: Heating from –140 °C at 2 K/min with a frequency of 1 Hz. Maximum force amplitude 5 N; min with a frequency of 1 Hz. Maximum force amplitude 5 N; maximum displacement amplitude 10 µm; offset control zero


 

Interpretation

The upper diagram shows the DSC heat flow curve. The characteristic features of the different thermal events such as the glass transition (about –125 °C), crystallization (between –110 °C and 85 °C) and melting (between –60 °C and –30 °C) can be clearly seen. The lower diagram shows the storage part of the shear modulus in semilogarithmic presentation. During the glass transition the modulus decreases by about 3.5 decades. The glass transition appears broader in the DMA curve. During crystallization the material becomes partially crystalline. This leads to an increase in the stiffness and in the modulus. On melting the semicrystalline polymer is transformed into a relatively low-viscosity liquid. The modulus decreases by about 4.5 decades. 

 

Evaluation

The temperature ranges of melting and crystallization measured by the two techniques were compared by overlaying the DSC curve and the first derivative of the logarithm of the modulus with respect to temperature. The curves are shown in the following diagram. The black curve is the heat flow, and the red curve the derivative of the modulus.


The peaks at about –100 °C correspond to crystallization. This peak is shifted to higher temperature in the DSC curve. This is a result of the different cooling rates used before the measurement and the different heating rates. On melting, the two signals agree very well. The high temperature sides of the melting peaks are practically coincident. 

 

Conclusions

A comparison of the DSC and DMA curves shows the typical behavior of the mechanical modulus during different thermal events (decrease at the glass transition and melting, and increase at crystallization). The excellent agreement of the DSC curve and the curve of the first derivative of log G' at the end of the melting range demonstrates the accuracy of the temperature measurement in the DMA.

 

Comparison of DSC and DMA Measurements | Thermal Analysis Handbook No. HB417 | Application published in METTLER TOLEDO TA Application Handbook Elastomers, Volume 1