Characterization of PTFE by DMA and DSC - METTLER TOLEDO

Characterization of PTFE by DMA and DSC

Sample

Polytetrafluroethylene, PTFE: a) white rod, 2.16-mm thick; b) film 0.2-mm thick
The purpose of the experiment was to investigate the transitions of PTFE in the temperature range from -120 °C to the melting temperature using both dynamic mechanical analysis (DMA) and differential scanning calorimetry, DSC. 

 

Conditions

Measuring cells: DMA/SDTA861e and DSC822e

Sample preparation: DMA shear deformation: two disks, 2.16-mm thick of 6-mm diameter, were cut from the rod.
                                     DMA tensile deformation: a 6.65-mm wide strip was cut from the film and clamped in the sample holder to provide an active measurement length of 10.41 mm.

DMA measurements: The shear measurement was performed at 1 and 10 Hz from -140 °c to 300 °C at a heating rate of 2 K/min. Maximum force amplitude 8 N; maximum displacement amplitude 10 µm; offset control zero

DSC measurement: 25.33 mg of the PTFE (sample b) in a 40 µl aluminum pan were heated from -150 to 400 °C at 10 K/min.

Atmosphere: DMA. static air; DSC nitrogen, 50 ml/min.


 

Interpretation

The DMA/SDTA861e tensile measurement shows three main steps in the Young's modulus (E') curve and three main peaks in the corresponding tan δ curve. The transition peaks at room temperature and the melting peak can be clearly seen in the DSC curve. 

The transitions can be identified as follows according to McCrum et. al (see reference at the end of the text);

 

Conclusions

Using the DMA/SDTA861e in the shear mode, the modulus G', and tan δ can be measured over a wide stiffness range. Transitions in PFTE can be easily characterized, even at low temperatures. Either shear or tensile deformation can be used; both give the same results. The DMA measurements show transitions not observed by DSC. DMA has the advantage that the influence of frequency on the transitions can be studied.

 

Reference

N.G.McCrum, B.E Read, G. Williams, Anelastic and Dielectric Effects in Polymeric Solids, Dover Publications Inc., New York (1991) pages 450-460.

 

Characterization of PTFE by DMA and DSC | Thermal Analysis Handbook No.HB244 | Application published in METTLER TOLEDO TA Application Handbook Thermoplastics