ADSC Measurements of the Glass Transition of Elastomers

Purpose

The experiment demonstrates the use of ADSC to achieve a better separation of the individual glass transitions.

Sample

Vulcanized elastomer based on an NR/SBR blend (DSC measurements of this sample are presented in Section 4.5.3. Glass transition of incompatible polymer blends)

Composition:

Conditions

Measuring cell: DSC821^e with liquid nitrogen cooling option 

Pan: Aluminum standard 40 µl, pierced lid

Sample preparation: Piece of elastomer of approx 20 mg.  

DSC measurement: The sample was cooled from 120 °C to –80 °C at 5 K/min and then measured from 80 °C to –10 °C. 

Underlying heating rate: 2 K/min.

Temperature amplitude: 0.5 K 

Period: 90 s  

Atmosphere: Nitrogen, 50 ml/min 

Interpretation

The diagram displays the complex heat capacity for the glass transition region of the NR/SBR blend. In the conventional DSC measurement curve (Section 4.5.3. Glass transition of incompatible polymer blends ), a peak occurred at the glass transition of the NR that was due to enthalpy relaxation. This made it difficult to evaluate the smaller glass transition of the SBR that followed. The peak could, for example, be interpreted as an exothermic effect. In contrast, the ADSC curve shows two distinct glass transitions.

The evaluation of the glass transitions of the two polymer phases is easier with ADSC than with conventional DSC. The interpretation is unambiguous. The measured step heights gave an NR/SBR ratio of 3.6:1. The actual ratio according to the formulation was 3.5.

Conclusions

ADSC measurements can improve the separation of different processes compared with conventional DSC. This is particularly the case for the measurement of the glass transition of incompatible polymer blends. The accuracy of the evaluation is significantly improved.  

_{ADSC Measurements of the Glass Transition of Elastomers | Thermal Analysis Application No. HB 473 | Application published in METTLER TOLEDO TA Application Handbook Elastomers Volume 2}