The effect of nano-zinc oxide on the mechanical properties of the cured ethylene-propylene-diene monomer rubber with a semi-efficient vulcanisation system

Abstract

The present investigation is dedicated to the impact of replacing conventional zinc oxide (ZnO) with nano-zinc oxide (nZnO) in ethylene-propylene-diene monomer (EPDM) rubber compounds. Multiple rubber compounds were prepared utilising conventional and nano-zinc oxides, followed by vulcanisation employing a semi-efficient vulcanisation system (SEV). Results indicate that nZnO promotes a more uniform dispersion within the rubber matrix compared to ZnO. Moreover, the incorporation of nZnO enhances the vulcanisation process, yielding a notable 27% increase in crosslink density. Nevertheless, the mechanical properties of the cured rubber, encompassing tear strength, hardness, tensile strength and elongation at break, remained either unaffected or exhibited slight deterioration. This observed discrepancy is ascribed to the inherent tendency of nZnO particles to self-aggregate, thereby disrupting the homogeneous distribution of the activator within the rubber matrix and fostering the formation of localised crosslink networks around the nano-particles. To overcome this challenge, the study proposes potential strategies, including nano-particle surface modification, optimisation of mixing parameters, and integration of compatibilisers, aiming to enhance the interaction between nZnO and rubber chains, mitigate agglomeration and facilitate a more even dispersion. The study suggests the potential of nZnO in augmenting the crosslinking efficiency of rubber compounds while emphasising the imperative need to address nano-particle agglomeration to optimise overall mechanical properties.