Measurement of Swelling Behavior

Purpose

The swelling behavior of elastomers in different solvents is often of interest their intended application and analysis. TMA measurements can be used to obtain useful information in this regard. The purpose of the experiment was to measure the swelling behavior of different technical elastomers in toluene.

Samples

MQ methyl-silicone rubber

EPDM ethylene-propylene-diene terpolymer

NBR acrylonitrile-butadiene rubber

FPM fluororubber  

Conditions

Measuring cell: TMA/SDTA840

Measurement of the swelling behavior requires a special vessel with a lid. The plane parallel sample is put into the vessel and covered with a quartz glass plate. The lid is then placed on the vessel. The lid is necessary to prevent evaporation of the solvent. There is a hole in the lid to allow the probe to enter. The probe measures the change in thickness of the sample on swelling.

Probe: Ball-point probe (quartz glass); dia

Sample preparation: A parallel plate approx. 1 mm thick cut from the starting material. The sample was placed in the glass vessel for swelling measurements and covered with a thin quartz glass disk. The glass vessel was closed with the lid. It is important to ensure that the sample does not touch the sides of the glass vessel when it swells. 

TMA measurement: The sample was allowed to equilibrate for 2 min. Afterward the furnace was opened briefly and the glass vessel filled with solvent using a syringe. Isothermal measurements at 25 °C; Force: 0.1 N

The TMA curves display the relative change in thickness as a function of time.  

Interpretation

The swelling of the elastomer samples is measured as a function of time. FPM swells by only about 2% in toluene. The material is clearly very resistant to toluene. It can for example be used as a sealing ring in this solvent. The situation is very different with the other elastomers. In particular the silicone rubber O-ring swells by over 35%.

Conclusions

TMA can be used to measure the swelling behavior of elastomers. This allows elastomers and sealing rings to be selected individually for particular applications.

^{Measurement of Swelling Behavior | Thermal Analysis Application No. HB490 | Application published in METTLER TOLEDO TA Application Handbook Elastomers Volume 2}