Comparison of Glass Transitions by DSC
Purpose
To compare the glass transitions of several different amorphous or semicrystalline unvulcanized elastomers.
Sample
Various unvulcanized rubbers.
- Silicone rubber
- NR: natural rubber
- EPDM: amorphous ethylene-propylene-diene rubber (EPG 3440)
- CR: chloroprene rubber
- NBR: acrylonitrile-butadiene rubber
- E-SBR: styrene-butadiene rubber (emulsion polymerized)
- L-SBR: styrene-butadiene rubber (polymerized in solution)
Conditions
Measuring cell: DSC822ewith liquid nitrogen or IntraCooler cooling option
Pan: Aluminum standard 40 µl, pierced lid
Sample preparation: Pieces of rubber of approx. 10 mg.
DSC measurement: The samples were cooled at 5 K/min from room temperature to below the glass transition and then measured. To prevent crystallization, the silicone rubber was placed directly in the cold measuring cell (at 140 °C). Different temperature ranges Heating rate: 10 K/min
Atmosphere: Nitrogen
Evaluation
The ASTM method was used to evaluate the glass transition temperature, Tg, and the step height, Δcp, from the DSC curves. The results are summarized in the following table.
Conclusions
The glass transitions of the polymers are very different. The information can be used to identify the type of rubber.
Comments
Different types of rubber (even with the same polymeric constituents) can differ due to their different molecular structure (e.g. sequence lengths or side chain distribution), their supermolecular structure (e.g. crystallinity) and the presence of plasticizers, polymerization residues, etc. These factors can all influence the glass transition.
Comparison of Glass Transitions by DSC | Thermal Analysis Handbook No.HB431 | Application published in METTLER TOLEDO TA Application Handbook Elastomers, Volume 2