Nanocomposite formation in hydrogenated nitrile rubber (HNBR)/organo-montmorillonite as a function of the intercalant type

Hydrogenated acrylonitrile butadiene rubber (HNBR) was melt compounded with montmorillonite (MMT) and organophilic modified MMTs prior to sulfur curing. In contrast to the micro-composite formation resulting from the compounding of the HNBR and pristine MMT, the modified MMTs (i.e.,octadecylamine: MMT-ODA, octadecyltrimethyl-amine: MMT-ODTMA, methyltallow-bis(2-hydroxyethyl) quaternary ammonium: MMT-MTH intercalants) produced nanocomposites. It was found that the organoclay with primary amine intercalant (cf. MMT-ODA) gave confined structures along with the exfoliate/intercalated structures. This was traced to its reactivity with the curatives. By contrast, the organoclays containing less reactive quaternary ammonium compounds (cf. MMT-ODTMA, MMT-MTH) were exfoliated and intercalated based on X-ray diffraction (XRD) and transmission electronmicroscopy (TEM) results. The hydroxyl functional groups of the MMT-MTH supported the clay dispersion. The better adhesion between MMT-MTH and HNBR was explained by hydrogen bonding between the hydroxyl groups of the intercalant and the acrylonitrile group of the HNBR matrix. This HNBR/MMT-MTH nanocomposite showed the best mechanical properties as verified by tensile mechanical tests and dynamic mechanical thermal analysis (DMTA). The high tensile strength along with the high elongation at break for the rubber nanocomposites were attributed to the ability of the 'clay network' to dissipate the input energy upon uniaxial loading.