Temperature-Dependent DMA Measurements of Filled Elastomer Blend - METTLER TOLEDO

Temperature-Dependent DMA Measurements of Filled Elastomer Blend

Purpose

Filled elastomer blends are measured with DMA in order to assess the influence of the composition on the modulus and damping.  

 

Sample

Two filled elastomers based on different polymer blends are measured.  


DSC measurements on these materials have already been presented in Section 4.5.3. Glass transition of incompatible polymer blends.  

 

Conditions

Measuring cell: DMA/SDTA861e with shear sample holder 

Sample preparation: Cylinders of 5-mm diameter were punched out from a 0.9mm thick film and mounted in the shear sample holder with 10% predeformation. 

DMA measurement: The NBR/CR blend was measured with a frequency series of 1, 10, 100 and 1000 Hz. The NR/SBR blend was measured with single frequencies of 1 Hz and 100 Hz. The heating rate was 2 K/min. An amplitude-dependent measurement was performed before the measurement in order to determine the limits of the linear range of the sample (see Section 4.3.5). The maximum displacement amplitude was then set to 3 μm. The maximum force amplitude was set to 10 N.  


Interpretation

Analogous to the unfilled NR/SBR blend in Section 4.5.5.Temperature-dependent DMA measurements of an unfilled SBR/NR elastomer, two glass transitions can also be seen with the NBR/CR elastomer. The first at –50 °C to –30 °C has a height of about 0.5 decades. This is due to the chloroprene. The glass transition measured at about 0 °C with a step in the storage modulus slightly less than 2 decades is that of the NBR. Due to the filler, the storage modulus in the rubbery plateau is larger than with unfilled materials. The damping is however less. This is confirmed by the smaller peaks in the tan G curves and the smaller values of the loss modulus, G".

With the NR/SBR elastomer, both glass transitions are clearly observed in the DSC measurement curve although the intensity of the SBR step is relatively small due to its low concentration (about 7%). From the glass transition temperature, which is below 40 °C, it can be deduced that it is an emulsion polymerized SBR (see Section 4.5.3. Glass transition of incompatible polymer blends). In the DMA heating experiments, the glass transition of the SBR can only be detected as a small shoulder in the tan g peak at low frequency (1 Hz). If a higher measurement frequency is used, the glass transition of the NR broadens so that the weak effect of the SBR glass transition can no longer be seen.

 

Conclusions

Temperature-dependent DMA measurements can provide information on the mechanical properties, structure and composition even of filled materials. For good quality measurements it is, however, essential to measure the sample within its linear range. This makes the use of low displacement amplitudes necessary. The maximum amplitude can be determined beforehand in a trial experiment. If the displacement amplitude is set too large, the Payne effect influences the measurement, which leads to misinterpretation of the results.

 

Temperature-Dependent DMA Measurements of Filled Elastomer Blend | Thermal Analysis Application No. HB 478 | Application published in METTLER TOLEDO TA Application Handbook Elastomers Volume 2