NONLINEAR VISCOELASTICITY OF NONCRYSTALLINE EPDM RUBBER NETWORKS

An experimental study has been carried out to specify the nonlinear viscoelastic behavior of noncrystalline peroxide-cured terpolymers of ethylene, propylene, and a diene monomer (EPDM) networks covering a range in elongation ratios between one and seven. Stress-strain curves, measured at constant rates of elongation at 300, 345, and 390 K, are analyzed. Time and strain effects are shown to be separable. The results are compared with the strain measures of two phenomenological theories, namely with the Mooney-Rivlin equation and a constitutive equation which contains the nonlinear n measure of strain, and with the predictions of the molecular theory of elasticity of polymer networks developed by Flory.