Effect of zinc oxide nanoparticles on isothermal cure kinetics, morphology and mechanical properties of EPDM rubber

The morphology, cure behavior and mechanical properties of various ethylene-propylene-diene-monomer (EPDM) rubber containing zinc oxide nanoparticles (nZnO), were investigated comparing to those of EPDM with conventional zinc oxide (cZnO). The X-ray diffraction (XRD) analyses revealed that nZnO had lower grain sizes with respect to cZnO. The field-emission scanning electron microscopy (FESEM) studies showed that unlike the conventional system, the formation of large size ZnO agglomerates was discouraged for nZnO filled systems. The rheological characterization showed that replacing cZnO with lower content of nZnO in the recipes resulted in lower cure time and higher crosslinking density which further supported by Fourier transform infrared spectroscopy (FTIR) and swelling tests. The cure kinetic analysis showed that the activation energy of curing reaction was remarkably reduced upon the decrease of ZnO particle sizes. Therefore, we could interestingly show the improvement in cure characteristics particularly associated with the superior mechanical properties of nZnO-activated EDPM systems.

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► nZnO structure had strongly textured crystals with lower grain size over cZnO.
► Replacing cZnO by nZnO resulted in lower cure time and higher crosslink density.
► The activation energy remarkably reduced upon the decrease of ZnO particle sizes.