Comparison of DSC Measurements of Vulcanization Reaction

Purpose

To show how the vulcanization behavior of two elastomers differs using DSC measurements. 

Sample

Unvulcanized NBR with 50% polymer content 

Unvulcanized silicone rubber without any fillers  

Conditions

Measuring Cell: DSC822^e with IntraCooler cooling option

Pan: Aluminum 40 µl, with pierced lid

Sample preparation: Cubes were cut from the starting material immediately before the measurement. With NBR rubber the sample weight was 27.4 mg, and with silicone rubber 46.8 mg. The large difference is due to the greater density of silicone rubber

DSC measurement: Silicone rubber from -65°C to 290°C at 10 K/min; NBR from -60°C to 220°C at 10 K/min

Atmosphere: Nitrogen 50 ml/min

Interpretation

The DSC curve of NBR shows the glass transition at 30 °C and indications of melting at approx. 50 °C and 95 °C. The exothermic vulcanization reaction then takes place with a peak maximum at 153.6 °C. Silicone rubber has a glass transition below 70 °C. The curve shows a sharp melting peak at 40 °C. The vulcanization reaction gives an exothermic peak with a peak maximum at 179.7 °C.

Conclusion

The vulcanization reaction of silicone rubber takes place at a higher temperature than that of NBR. This means that the material must be processed at higher temperatures or must be annealed after prevulcanization. The specific enthalpies of reaction depend on the filler content, the cross-linking system and the cross-linker content. Compared with other thermal events, the enthalpies of reaction of the vulcanization reactions are relatively low. 

_{Comparison of DSC Measurements of Vulcanization Reaction | Thermal Analysis Handbook No.HB 407 | Application published in METTLER TOLEDO TA Application Handbook Elastomers, Volume 1}