DMA Measurements of a Chloroprene Elastomer - METTLER TOLEDO

DMA Measurements of a Chloroprene Elastomer

Purpose

To show the effect of the vulcanization reaction on the mechanical behavior of elastomers using technical chloroprene elastomer as an example. 

 

Sample

Unvulcanized chloroprene elastomer

 

Conditions

Measuring cell: DMA/SDTA861e with shear sample holder

Sample preparation: Cubes with a square surface area of 10 mm by 10 mm and 3.6 mm thick were mounted in the shear sample holder with 10% predeformation.

DMA measurement: The measurement was performed in the multifrequency mode between 1 Hz and 10 Hz at a heating rate of 2 K/min. Maximum force amplitude 3 N, maximum displacement amplitude 10 Pm, offset control zero. The sample was measured up to 220 °C. Afterward the sample was cooled and measured again under the same conditions without removing it from the sample holder (2nd run). 

 

Interpretation

For reasons of clarity, only the measurements at 1 Hz and 10 Hz are shown. The glass transition is observed at about –40 °C in the measurement curves of the unvulcanized material (1st run). It is shifted to higher temperatures at higher frequencies. A small step in the storage modulus can be seen at about 40 °C. In contrast to the glass transition, the temperature position of this step is practically independent of the frequency. Although the crystallinity of the polymer is relatively low, the step is due to the melting of the crystallites. This melting process is also the reason for the step in the tan G curve at 40 °C. In the liquid phase, tan g is larger at low frequencies than at higher frequencies; the step height is therefore also larger at lower frequencies. In the temperature range 110 °C to 190 °C, the material vulcanizes. As a result of this, it can be seen that tan g becomes smaller and the storage modulus larger.

Immediately after this measurement, the sample was cooled to –90 °C and measured again (2nd run). The DMA curves show that the glass transition is shifted slightly to higher temperatures. This material is completely amorphous (see Section 4.1.3. Measurements of the crystallization and melting of chloroprene rubber (CR)) and does not therefore exhibit melting. The storage modulus remains practically constant over the entire temperature range from 0 °C to 210 °C. 

 

Conclusions

DMA can easily detect vulcanization and measure its effect on the mechanical properties of the material. In particular, the different behavior shown by the mechanical properties allows information to be obtained on processes and reactions occurring in the sample. Simultaneous measurements at different frequencies is very useful for this purpose. 

 

DMA Measurements of a Chloroprene Elastomer | Thermal Analysis Application No. HB443 | Application published in METTLER TOLEDO TA Application Handbook Elastomers, Volume 2.