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Itaconic acid has been employed as a special facilitator to construct divalent metal ion based ionic crosslinking framework in the acrylonitrile butadiene rubber matrix. Readily accessible double bonds in itaconic acid could directly react with the elastomer to form effective covalent bonds. On the other hand, presence of easily dissociable protons in itaconic acid enables them to form ionic bonds that leads to an increase in crosslinking density of the vulcanizates. The synergistic effect of covalent crosslinking induced by peroxide and ionic crosslinking induced by metal carboxylate could effectively enhance the overall mechanical and dynamic mechanical properties of the rubber composites. In this study, three metal oxides, that is, zinc oxide, magnesium oxide, and calcium oxide, have been selected for this purpose. Tensile strength of nitrile rubber composites depends on the strength of ionic crosslinks, which in turn is influenced by the size of the alkaline earth metals, such as Mg, Ca, etc., and stoichiometric quantity of itaconic acid, which is at par in the formulation of this study. The novelty of this study is that the introduction of a dicarboxylic acid in combination with metal oxides enhances the crosslink density and tensile strength of nitrile rubber composites which could result from the metal organic framework.

Functionalization of non-polar ethylene propylene diene monomer (EPDM) rubber by melt grafting of maleic anhydride (MA) and in situ incorporation of sol–gel derived silica in the MA grafted EPDM has been done to prepare EPDM/silica composites to use dual benefits of both the approaches, which results in adequate rubber–filler compatibility, good filler dispersion, and enhanced composite properties. Controlled growth of silica up to 25 parts per hundred rubber (phr) is carried out with the solution sol–gel process using tetraethoxysilane (TEOS) as a silica precursor. Mechanical and dynamical properties of the composites are found to improve consistently as silica content increases. Furthermore, treatment of maleic anhydride grafted EPDM by γ-aminopropyltrimethoxysilane (γ-APS) results in remarkable improvement in composite properties even at the same silica content. This is attributed to the generation of uniformly dispersed spherically shaped nanosilica throughout the rubber matrix as observed in a transmission electron microscopic (TEM) study. This contributes to enhanced crosslinking density and improved rubber–filler interaction. In fact, the reinforcement effect brought by in situ silica relative to unmodified in situ silica/EPDM composites is found to be much higher than that reported in recent work on EPDM/in situ silica composites even with higher silica loading. The mechanical, rheological, and dynamic mechanical behaviors of all the composites are evaluated and compared in detail.