Morphology and mechanical and rheological studies of zinc oxide/silicone rubber nanocomposites

Zinc oxide (ZnO) nanoparticles were synthesised by the co-precipitation method and the nanocrystals were found in the range 30-50 nm in size. Silicone rubber (SiR) nanocomposite samples were prepared using different concentrations (1, 3, 5, and 7 wt%) of zinc oxide (ZnO) nanoparticles through mechanical mixing and hot press moulding. The surface morphology of prepared silicone elastomer nanocomposites was studied using a scanning electron microscope (SEM) to investigate the smooth dispersion of ZnO nanoparticles inside the matrix and at higher concentration (7 wt%) agglomerates were formed. With increasing ZnO concentration, the mechanical properties of silicone rubber nanocomposite exhibited an increase in tensile strength, modulus, and decrease in elongation at break, which can be attributed to good distribution and reinforcing activity of nanoparticle in the elastomer matrix. At higher concentration (7 wt%), the rate of increase of mechanical properties was nominal due to the agglomeration of nanoparticles. The effect of ZnO nanoparticle concentration on the rheological properties of silicone rubber nanocomposites such as loss modulus, storage modulus, and complex viscosity was studied as a function of temperature and at different frequency 1, 10, and 100 Hz. The effect of ZnO nanoparticle concentration on the rheological properties showed an increase in loss modulus, storage modulus, and complex viscosity due to increase in volume fraction of nanofiller and reinforcement. The loss factor of silicone elastomer nanocomposites decreased with ZnO concentration which can be attributed towards better polymer-nanoparticle interactions. The addition of ZnO nanoparticles up to 5 wt% concentration level provided better rheological properties beyond which the rate of increase was marginal. Based on the results of morphology, mechanical and rheological properties of silicone rubber nanocomposites, 5 wt% ZnO nanoparticles may be considered as the percolation limit.