Mechanochemically induced grafting of maleic anhydride/zinc diacrylate onto butadiene rubber and its application in rubber-to-metal bonding

Mechanochemical grafting of MAH and ZDA enables the functionalization of BR. • Co-grafting of MAH and ZDA enhances the grafting degree of MAH. • The peptizing agent promotes chain scission and enhances the grafting degree of MAH. • The application of graft-modified BR enables robust rubber-to-metal bonding. The adhesion between metal and rubber plays a crucial role in modern industrial applications, particularly in the fabrication of high-performance composite structures. This study investigates rubber-to-metal bonding via a mechanochemical grafting strategy, where butadiene rubber (BR) was functionalized with maleic anhydride (MAH) and zinc diacrylate (ZDA). The intense shear forces generated within an internal mixer induce the formation of free radicals on BR, thereby facilitating the co-graft of MAH and ZDA. The addition of 2,2′-dibenzamidodiphenyl disulfide (DBD) promoted chain scission and enhanced the grafting degree. The graft-functionalized BR was incorporated into the rubber compound and co-vulcanized with γ-aminopropyltriethoxysilane (KH550)-modified steel substrates, thereby achieving strong rubber-to-metal bonding. It was confirmed that MAH and ZDA were successfully grafted onto the molecular chains of BR. At a loading of 1.0 phr for both MAH and ZDA, the BR-1.0 MZ-0.5 D sample exhibited a grafting degree of 0.74% and a grafting efficiency of 68.24%, representing 284.6% and 264.3% of the DBD-free control. When the loadings of MAH and ZDA were 1.5 phr with the addition of DBD, the 90° peel strength reached a maximum value of 10.2 kN/m, exhibiting cohesive failure. Therefore, mechanochemical grafting effectively enhances rubber-to-metal adhesion, and DBD markedly improves grafting degree.