Comparison of Two Fluoroelastomers by DSC - METTLER TOLEDO

Comparison of Two Fluoroelastomers by DSC

Purpose

TGA was used to compare two fluoroelastomers in Section 4.4.1. TGA of fluoroelastomers (FPM). The same samples will now be compared by DSC.

 

Sample

Two fluoroelastomers

The TGA measurements yielded the following compositions:

 

Conditions

Measuring cell: DSC822e with liquid nitrogen cooling option

Pan: Aluminum 40 µl, pierced lid

Sample preparation: Cubes of about 20 mg cut from the starting material

Measurement: Heating from 140 °C to 120 °C at 10 K/min. 

Atmosphere: Nitrogen, 50 ml/min 

Interpretation

The glass transition is the only relevant thermal event observed in the DSC curves. The glass transition temperatures are –14.6 °C and –17.4 °C respectively, i.e. the glass transition of sample 2 is some 3 K lower than that of sample 1. This could be due to differences in the polymer used or to different degrees of vulcanization. 

The step heights at the glass transition, Δcp, are slightly different - 0.156 J/gK for sample 1 and 0.160 J/gK for sample 2. If the composition of the samples is taken into account, the step height at the glass transition for the pure polymers, Δcp,100% , can be calculated using the equation: 

where wpis the proportion of the polymer in the sample. This gives values of 0.217 J/gK (sample 1) and 0.216 J/gK (sample 2) for the pure polymers. These two values are practically identical. It shows that the comparison of the step height at the glass transition is consistent with the TGA content determination. The small change in the heat capacity at the glass transition can be accounted for by the higher molecular mass of fluorine compared with hydrogen. 

 

Conclusions

For fluoroelastomers, the content determined by DSC using the step height at the glass transition is also consistent with the results obtained by TGA. This could be useful because relatively large amounts of carbon black are formed during pyrolysis in the TGA. It might be difficult to distinguish this carbon black from the carbon black present as filler. The analysis of the glass transition by DSC takes only the polymer part into account. The step height at the glass transition of 0.22 J/gK is relatively small. The glass transition temperature is –15 °C

 

Comparison of Two Fluoroelastomers by DSC | Thermal Analysis Handbook No.HB464 | Application published in METTLER TOLEDO TA Application Handbook Elastomers, Volume 2