In this study combined effect of nano clay and carbon black on the curing process and physico- mechanical properties of SBR/BR and NR/BR blends was investigated. Mixing method in this study was melt blending and sulfur curing system is used. Dispersion state of nano clay and carbon black was studied by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) analysis. Comparison of XRD results showed that the portion of intercalated structure in SBR/BR blends is more than NR/BR. Thus the percentage of exfoliated nano clay in NR/BR blends is greater than SBR/BR blends. The presence of carbon black in the SBR/BR nano composites was increased the gap among clay platelets and intercalated structure becomes more stable. In contrast the presence of carbon black was not affect on gap among clay platelets and dispersion state of nano clay in NR/BR nano composites. The results were in good agreement with SEM observations. Curing curves showed that by increasing the amount of nano clay, the scorch time and the optimum cure time are reduced. Also as a result of increasing in nano clay amount, the difference between maximum and minimum torque decreased. This could be the indicator of reduction in cross linked density of blends. Physical and mechanical properties (tensile strength, heat buildup, tear strength, fatigue resistance, abrasion resistance) and friction factor at different concentrations of carbon black and nano clay. The results showed that at the same total filler loadings, by replacing 6 parts of carbon black with nano clay (4 wt%) in blends compositions, tensile strength, elongation at break, fatigue resistance and tear strength are increased and friction factors (static and dynamic) decreased in comparison with blends that have only carbon black in their composition. But by increasing the amount of nano clay from 6 to 9 parts (4 to 6 wt %) physico- mechanical properties of blends reduced. This is probably as a result of nano clay agglomeration. Therefore 6 parts of nano clay is the optimum concentration for reaching to the favorite physical and mechanical properties.
