Effects of blend composition and mixing method on mechanical and morphological properties of zinc dimethacrylate-reinforced acrylonitrile-butadiene copolymer nanocomposites

Two kinds of rubber composites were prepared by melt mixing of acrylonitrile-butadiene rubber (NBR) with zinc dimethacrylate (ZMA). In one system ZMA was added in the form of powder; and, in another system, the ZMA was prepared by in-situ reaction of ZnO and methacrylic acid (MA) during melt mixing. Both systems showed similar tensile strength, however the elongation at break, tear strength, and fatigue resistance were higher for the in-situ prepared system. The composite prepared by direct addition of ZMA powder showed a corresponding peak for ZMA particles in the wide angle x-ray diffraction (WAXD) spectra, indicating the existence of two phases, while there was no such peak for the in-situ prepared blend. The comparison of cross-link densities of these two blends showed a higher proportion of total cross-link density (calculated from covalent and ionic cross-linking) for the blend prepared from the direct addition method. The morphology of torn surfaces based on field-emission scanning electron microscopy (FE-SEM), showed a different nature of fracture behavior in these blends. The mean particle size and distribution of ZMA in NBR matrix as measured by atomic force microscopy (AFM) and small angle x-ray scattering (SAXS) indicated the formation of nanostructured domains of ZMA of particle size in the range of 10-40 nm with more uniform distribution in the in-situ blends.