Enhanced elastomer toughness and fracture properties imparted by chemically reactive flat nanoparticles

A remarkable enhancement in the mechanical and fracture properties of elastomers, imparted by flat predominantly 2-dimensional nanoparticles, is reported. Elastomers of hydrogenated nitrile butadiene rubber (HNBR), incorporating surface-functionalized montmorillonite clay, nanographite, carbon fiber, or carbon black, were thermally crosslinked in the presence of a bismaleimide coagent using a peroxide free-radical generator. Clay platelets, side-functionalized with octadecyl amine and edge-functionalized with reactive amino groups, were used to achieve good dispersion in the elastomer matrix. The clay-filled elastomer exhibited multiple glass transitions in their dynamic mechanical analysis (DMA) and approx. 6 times higher tear resistance, 4× higher rubbery plateau modulus, 2× higher modulus of toughness, and 2× higher crack initiation resistance than an elastomer containing equivalent carbon black concentration. Nanographite also resulted in property enhancement, albeit to a lower extent than nanoclay. Flat fillers are evidently able to arrest crack growth better than fillers with spherical or elongated shapes. DMA loss tangent data, and dissipated energy fraction calculated from the cyclic tensile test data, show that the flat fillers are better able to release strain energy in the form of viscous dissipation, rather than use it for increasing the crack surface area. SEM images of fractured surfaces are reported and discussed. •Comparison of flat and fibrous fillers with carbon black for reinforcement of HNBR.•Increased stiffness, ductility, and toughness imparted by 2-D graphite and clay nanoparticles.•500% improvement in tear resistance because of surface-functionalized clay nanoparticles.•Polymer-particle and particle-particle co-network formation by maleimide-amine reaction.•Higher strain energy release due to interfacial dissipation improves fracture resistance.