DMA Measurements of Silicone Elastomer - METTLER TOLEDO

DMA Measurements of Silicone Elastomer

Purpose

To measure the mechanical behavior of an incompletely vulcanized silicone elastomer by DMA over a wide temperature range. 

 

Sample

Incompletely vulcanized, filled silicone elastomer 

 

Conditions

Measuring cellDMA/SDTA861ewith shear sample holder

Sample preparation: Cylinders of 5 mm diameter were punched out of a 0.7 mm thick film and mounted in the shear sample holder with 10% predeformation.

DMA measurement: The measurement was performed at 1 Hz and a heating rate of 2 K/min in the temperature range –150 °C to 250 °C. Maximum force amplitude 10 N, maximum displacement amplitude 5 µm, offset control zero.

 

Interpretation

The sample was mounted in the DMA sample holder and cooled from room temperature to 150 °C at 10 K/min before the measurement. The material is then in a semicrystalline state. The glass transition is visible as a step at –120 °C in the G' curve and as peaks in the G" and tan g curves. Melting at –45 °C causes the storage modulus, G', to decrease by about 2.5 decades. Afterward the material exhibits rubbery elastic behavior. The storage modulus is about 0.5 MPa and remains practically constant to about 80 °C. The modulus then increases to about 0.7 MPa as a result of post-vulcanization. This part of the curve is shown on an expanded linear scale in the upper right part of the diagram. During vulcanization the sample becomes more elastic. At the same time tan g decreases stepwise. Lines have been drawn in the diagram so that the changes during vulcanization can be more clearly seen. The loss modulus is always less than the storage modulus. This is due to the silicon dioxide present as filler. Both effects - the vulcanization and the filler – lower the damping and therefore the value of G".

 

Conclusions

Post-vulcanization can be measured with great sensitivity by DMA. It is a very good method to detect post-cross-linking processes even if the reaction takes place over a wide temperature range, e.g. of 100 K. Besides these changes, DMA can also measure the glass transition and melting process. 

 

DMA Measurements of Silicone Elastomer Thermal Analysis Application No. HB442 | Application published in METTLER TOLEDO TA Application Handbook Elastomers, Volume 2