are mixed for one minute then the ram is raised and a sweep performed the ram is lowered and mixing continued until the batch reaches an internal temperature of 104 u00b0 c materials for the examples were mixed in a farrel br1600 internal mixer with a volume of 1 6 liters the curing properties were determined on a model odr 2000 oscillating disc rheometer the dynamic properties were determined at 60 u00b0 c and 10 hz over a strain range of 0 2 to 14 single strain amplitude using a model rpa 2000 rubber process analyzer standard astm test methods were used for measurement of mooney viscosity d3346 90 odr cure characteristics d2084 92 stress strain d412 92 and shore a hardness d2240 91 the advantages and the important features of the present invention will be more apparent from the following examples this example demonstrates the use of azodicarbonamide in reducing hysteresis and the benefit of mixing it with rubber and carbon black in a separate mixing step a comparison of compounds b and d demonstrates that the greatest reduction in hysteresis is obtained when the azo compound is added along with the carbon black and that adding the carbon in a separate step after the incorporation of the azo compound not.