A series of thermoplastic vulcanizates of polypropylene (PP)/nitrile butadiene rubber (NBR) (50/50) have been prepared by melt-mixing method, using phenolic resin/SnCl 2 as the curing system and maleic anhydridefunctionalized PP (PP-g-MA) and carboxylated NBR (NBRE-RCOOH) as the compatibilizing system. Triethylenetetramine was also employed to promote the reaction between the functionalized polymers. The effects of curing agent and compatibilizer on the mechanical and morphological properties have been studied. A novel technique based on positron annihilation lifetime spectroscopy has been used to measure the free volume parameters of these systems. The positron results showed minimum free volume size and free volume fraction at 5.0% of the curing agent suggesting some crosslinking in the rubber phase. The reduction in free volume holes at 2.5% of the compatibilizer is interpreted as improvement in the interfacial adhesion between the components of the blend. The observed variation of free volume fraction is opposite to the tensile strength and exhibits the correlation that, lesser the free volume more is the tensile strength at 2.5% of the compatibilizer in the blend.

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The reactive compatibilization of ethylene‐propylene‐diene (EPDM)‐based dissimilar elastomer blends has been investigated in terms of mechanical properties and swelling degree. The use of mercapto‐functionalized copolymers resulted in an improvement of mechanical properties of natural rubber‐EPDM blends. The mercapto‐groups are able to react with the carbon‐carbon double bonds of the high diene rubber, resulting in a good interaction between phases. These interactions were confirmed by the amount of insoluble material obtained in non‐vulcanized blends. From dynamic mechanical properties and swelling degree, one can suggest a covulcanization process in these blends cured with sulfur‐based system. Blends composed by nitrile rubber with EPDM displayed good results in terms of mechanical properties when mercapto‐functionalized EVA was employed instead of functionalized EPDM, probably because of the higher polarity of the former associated to its lower viscosity. Additionally, an improvement on mechanical properties was also achieved by using EPDM functionalized with mercapto or anhydride groups in combination with nitrile rubber functionalized with epoxy or oxazoline groups.

Summary: The reactive compatibilization of ethylene‐propylene‐diene (EPDM)/nitrile rubber (NBR) blends was performed using mercapto‐modified copolymers (mercapto‐modified EPDM, EPDMSH, and mercapto‐modified ethylene‐vinyl acetate copolymer, EVASH) in combination with oxazoline‐functionalized NBR (NBR‐ox). The best mechanical performance was achieved with the two EVASH‐based compatibilizing systems, especially the one containing the co‐reactive copolymers because of the reactivity of the oxazoline group. The presence of insoluble material in non‐vulcanized blends suggested the reactive compatibilization. The morphologies of these blends were examined through scanning electron microscopy (SEM). Blends compatibilized with the EVASH‐based systems showed finer morphologies than the non‐compatibilized blend or those compatibilized with the EPDMSH‐based systems. In non‐vulcanized NBR/EPDM (70:30 wt.‐%) blends, the presence of the co‐reactive EVASH/NBR‐ox system changes the morphology from a cocontinuous structure towards a droplet‐matrix morphology, and also results in a significant broadening of the damping curve related to the NBR transition, observed from DMTA analysis. The effect of the compatibilization on aging resistance has also been evaluated.SEM micrograph of a non‐vulcanized NBR/EPDM blend compatibilized with a NBR‐ox/EVASH co‐reactive copolymer.magnified imageSEM micrograph of a non‐vulcanized NBR/EPDM blend compatibilized with a NBR‐ox/EVASH co‐reactive copolymer.

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