Effects of Jatropha Oil on Degradation of Fluoroelastomer and Silicone Rubber Automotive Seals

Flouroelastomers and silicone rubbers are commonly employed in static and dynamic seals for automotive applications. In order to prevent premature failures and leakages caused by swelling and/or changes in their mechanical properties, materials for seals are selected according to their compatibility with the environment and fluids involved in the engine operation. Thus, in particular, the use of new fuels and additives in automotive engines requires the assessment of compatibility with common sealing elastomers to prevent failures. Currently, Jatropha oil is being used as a renewable source of fuel in diesel engines for electricity production, transport or agricultural mechanization in various countries. It is used either as biodiesel or as straight vegetable oil (SVO) since it has good heating power and provide exhaust gas with almost no sulfur or aromatic polycyclic compounds. However, the compatibility of elastomers with this SVO has not been investigated yet. Therefore, in this work, the physical degradation of silicone rubber (VMQ) and fluoroelastomer/Viton® (FKM) in contact with three fuels, namely, straight Jatropha oil (SJO), diesel, and a blend 80 wt%-diesel 20 wt% SJO was studied via static immersion tests (670 h at 24°C) according to the ASTM-D471 method. Changes in mass, volume, tensile and tear resistance and hardness were assessed according to the standard method. Since viscoelasticity is also an important property for the sealing performance of elastomers, the changes in creep compliance were determined by creep tests. In addition, the changes of surface morphology and topography were evaluated by scanning electron microscopy (SEM) and optical profilometry, respectively, in order to evidence pitting or cracking caused by degradation. Overall, according to the standard method, low degradation was found for both elastomers immersed in SJO, VMQ being the less degraded. However, a loss of resilience was observed for both materials in the different fluids, which may be relevant in certain applications.