The curing of rubbers leads to a limited range of properties that is not sufficient to open all the doors of the industrial applications.
The plasticization of rubbers has been used since the beginning of the natural rubber industrialisation to:
* Ease processing
* Increase the loading
* Soften the vulcanizates
* Improve low-temperature behaviour…
Starting from natural products such as pine-tar, vegetable oils and so on, the plasticizers were more and more sophisticated. Now, there are two main types:
* The petroleum oils especially for hydrocarbon rubbers such as SBR
* The esters especially for the polar rubbers such as NBR.
The response depends on the chemical nature of the rubber. Oils are preferably used in non-polar rubbers because of the better compatibility. The table 1 displays some examples of solubility parameters of rubbers and plasticizers (oils and esters).
The benefits of the plasticization can be suppressed if the plasticizers disappear during the service life by:
* Volatilization, the more so as the temperature rises