The rheological properties of gum and carbon black compounds of an ethylene-propylene terpolymer elastomer at 20, 30, 40, and 50 vol.% carbon loadings have been investigated over a very wide range of stresses and shear rates. This was accomplished using (1) a constant shear stress creep instrument, (2) a rotational rheometer and (3) a capillary extrusion rheometer at higher shear rates. The stresses used in the studies included magnitudes leading to shear flow and stresses below the yield value, where rubber compounds exhibit only finite deformation. Much attention was given to measurements of creep and strain recovery at low stresses. The magnitudes of yield stresses obtained from these low stress and recovery experiments are significantly lower than those obtained using standard extrapolation to zero shear rate of higher stresses from rotational and capillary instruments.
