What chemical modifications can improve the oil resistance of natural rubber?

Several chemical modifications can improve the oil resistance of natural rubber. Natural rubber, being primarily polyisoprene, is susceptible to swelling and degradation in the presence of oils and non-polar solvents. Epoxidation is one effective method. By introducing epoxide groups along the rubber chain, the polarity of the rubber increases, making it less compatible with non-polar oils. This reduces the swelling of the rubber in oil. Another method is hydrogenation. Hydrogenation involves reducing the number of double bonds in the polyisoprene chain. This makes the rubber more saturated and less reactive, thereby improving its resistance to oxidation and degradation by oils. Halogenation, such as chlorination or bromination, can also enhance oil resistance. The introduction of halogen atoms increases the polarity and reduces the solubility of the rubber in non-polar solvents. Grafting is another approach where polar monomers, such as acrylonitrile or methyl methacrylate, are grafted onto the rubber backbone. This creates a copolymer with improved polarity and oil resistance. Blending natural rubber with more oil-resistant synthetic rubbers, such as nitrile rubber (NBR), is a common technique to improve overall oil resistance. The resulting blend exhibits a combination of the properties of both rubbers. For example, epoxidized natural rubber (ENR) is used in seals and gaskets where oil resistance is important.