Effects of two nano-ZnO processing technologies on the properties of rubber

Two different technologies (direct mixing and three-roll milling) were applied to facilitate the dispersion of nano-ZnO in a nitrile rubber (NBR) composite. The vulcanization, mechanical, friction, and wear characteristics of the two resulting rubbers were studied. Wear surfaces were measured and analyzed via 3D scanning, scanning electron microscopy, and X-ray photoelectron spectroscopy. Results showed that the three-roll milling rubber had faster vulcanization rate, delayed optimum cure time, and better tensile strength (4.1% higher) and tear strength (6% higher). The hardness, tensile elongation and compression deformation were also improved in the three-roll milling NBR composite (this greatly enhanced its comprehensive mechanical properties). The wear resistance performance of the three-roll milling NBR composite experienced a significant improvement too (the wear loss in the three-roll milling NBR composite was 14% of that in the direct mixing NBR composite). Three-roll milling produced a better dispersion of the ZnO nanoparticles in the rubber matrix facilitating the vulcanization, crosslinking and hardening of the rubber matrix. Moreover, the formation of a covalent bond between ZnO and S further enhanced mechanical properties, friction reduction, and anti-wear capacity.