Source Year: 2000

Reversion of NR if crosslinked with sulphur shows reversion in two ways. One is chain scission as a consequence of increase oxygen concentration at higher service temperatures, the other is a scission of the sulphur crosslinks due to aminic accelerator decomposition products. The very different nature of the two kind of reversion limits the service temperature and service life of engine mounts manufactured with NR. A solution could be the usage of polymers with resistance to oxygen because of a saturated polymer backbone and peroxide crosslinking. Both ways have been attempted in engine mount manufacturing, but unsuccessfully as the properties of such rubbers are not sufficient. The polymers or type of crosslinking shows poor dynamic fatigue to failure. To use NR engine mounts at higher service temperatures, both reversion mechanisms must be prevented. While reversion resistance due to crosslinking systems are investigated, fatigue failure of barrier to oxygen uptake during ageing is observed. A flexible layer which will not allow the permeation of oxygen is developed. This barrier is applied as a coating in a two-step process. It shows the similar physical static and dynamic properties as the substrate made from NR. Under test conditions simulating service, less of a decrease of dynamic properties is reported.