Natural rubber (NR) from Hevea brasiliensis is known to have highly unsaturated backbone, and it also shows low oil and organic solvent resistance due to nonpolarity [1]. Owing to the presence of the polarity of the fluorine atoms in fluoro elastomer (FKM), NR/FKM blends should be resistant to ozone, oil, heat, and nonpolar chemicals. As the matter of fat, based on chemical structure, the NR/ FKM blend becomes incompatible due to the difference in polarity. The resulting blend exhibits poor mechanical properties due to the poor adhesion between the phases [2].
There are a lot publications that have discussed rubber blends based on the addition of a third homopolymer or graft or block copolymer that binds with the two phases and the introduction of bonds between the homopolymer phases [3-8]. According to Karnika de Silva and Lewwan [3] the addition of graft copolymer of NR reduced phase sizes attained in NR/NBR blends over a wide range of acrylonitrile content of NBR. K. Prakashan and coworker [4] studied compatibility problems in polypropylene (PP)/poly(dimethylsiloxane) (PDMS) elastomer blend. Maleic anhydride grafted polypropylene (PP-g-MAH) was reported to act a compatibilizer for these blends.
Epoxidized natural rubber (ENR) contains polyiso- prene as main chain and epoxidize group as side group which should be reacted to NR and FKM molecules, re- spectively (Figure 1). Then, ENR was interested to be used as a third component for NR/FKM blend. Not only ENR but also polyisoprene-graft-maleic acid mono- methyl ester (PI-ME) was interested to be used as a third component for these blend. PI-ME also contains polyiso- prene as main chain and maleic acid monomethyl ester as a grafting group. The grafting group of PI-ME contains carbonyl group which should react to the FKM molecule. According to M. Abdul Kader and A. K. Bhowmick [8] reported that blend of acrylate rubber and FKM was mis- cibility due to interaction between C=O group of acrylate rubber and –CF3 group of FKM in the blend.
In this study, the cure characteristics, morphology,mechanical properties, as well as automotive fuel resistances of 70/30 NR/FKM blends with and without a third component, ENR or PI-ME, were investigated. The selected automotive fuels were B5-biodiesel, diesel, gasoline and gasohol. amounts of all chemicals except Luperox® 101-XL 45 and SR533 were added to the masticated rubber. The mixture was then blended with FKM and further mixed. Lastly SR533 and Luperox® 101-XL 45 were added. To vulcanize the blends, they were compression molded using a hydraulic hot press at 180°C [2], under a pressure of 15 MPa according to their respective cure times, as determined by oscillating disk rheometer (ODR GT- 707052). ODR gives digitals outputs of curing character- istics such as scorch time, cure times and torque value.