When an elastomer is cooled below its glass transition temperature (Tg), it loses its elasticity and
becomes brittle. For elastomer O-rings, that are used for sealing purpose, Tg thus corresponds to a lower limit of use. Problems arise when they are used in high pressures systems, as their Tg may be
shifted to higher temperatures. The HP-MicroDSC technique is the most suited to investigate the Tg dependence vs. pressure as it allows purely isobaric temperature scanning experiments.
Three 360mg samples of the same elastomer O-ring were heated between -40°C and 20°C at a rate of 1K/min under nitrogen pressures of 1, 100, and 400bar.
RESULTS AND CONCLUSIONS
Glass transition temperature (Tg) can be determined at each pressure thanks to the heat capacity
change of the elastomer. It is noticed that Tg increases with pressure, with a shift of about 10°C
between 1 bar and 400 bar. As a first approach, the evolution of Tg is described by a linear equation on the tested pressure range with a R2 value of 1. More tests at different pressures would of course be required to confirm this trend.