The mechanical properties of a polyurethane (PUR) film were investigated using DMA in the tension mode. Besides α- and β-relaxation, a further process was found above the glass transition. Additional DSC measurements and DMA multi-frequency scans help to explain the effects observed in the first and second heating runs.
This article shows how the DMA 1 can be used to measure a relatively soft PUR sample in the tension mode. Besides the glass transition and secondary relaxation, other effects were also found. These were interpreted as crystallization and melting using DSC measurements. This was confirmed by performing DMA multi- frequency scans in the tension mode. In contrast to relaxation processes, no frequency dependence is expected for crystallization and melting.
Tension measurements
The tension measurements were performed using a PUR film measuring about 10 mm x 5 mm x 0.6 mm. The first and second heating runs were measured from –150 °C to +150 °C at a heating rate of 3 K/min and a frequency of 10 Hz in the Auto-Tension mode. The displacement amplitude was 20 μm and the pretension force 1 N.
The multi-frequency scans in the frequency range 1 to 20 Hz were measured at a heating rate of 1 K/min.
DSC measurements
The DSC measurements were performed using a DSC 1 with a liquid nitrogen cooling system in the temperature range –150 °C to +150 °C at a heating rate of 20 K/min. The sample mass was about 15 mg.
Results and discussion
Figure 1 shows the results of the first and second heating runs performed in the tension mode at a frequency of 10 Hz.
In the temperature range –85 °C to –35 °C, the storage modulus, E', falls by about 2 decades. This step is due to the glass transition (α-relaxation) and appears as a peak in the loss factor tan delta curve...
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Summary
DMA is a powerful technique for characterizing material properties and provides information about relaxation processes in materials. The sample exhibited different relaxation effects, cold crystallization and melting.
The effects were investigated with respect to their frequency dependence. DSC measurements were used to confirm the results obtained from the DMA 1. Crystallization and melting are frequency-independent processes and can be distinguished from frequency-dependent relaxation processes.
Measurement of a Polyurethane Film in Tension using the DMA 1 | Thermal Analysis Application No. UC363 | Application published in METTLER TOLEDO Thermal Analysis UserCom 36