Study on the Stress-Induced Crystallization and the Constitutive Equation of Ethylene-Propylene Diene

Abstract

The composition and sequence structure of a serial of ethylene-propylene diene (EPDM) were analyzed according to the 13C-NMR analysis. The stress-induced crystallization was occurred in EPDM 3080 which the segment chains of methylene were long enough. The mechanical properties of stress-induced crystallization of EPDM 3080 were increased rapidly when the extension ratio reached about 4.5. With the observation by the synchrotron two-dimensional wide angle X-ray diffraction, it confirmed that the increasing stress just begin at the extension ratio of 4.5, which can be attributed to the stress-induced crystallization. Based on the rubberlike network model with crosslinking, entanglement and stress-induced crystallization interaction points, the constitutive equation can be derived according to rubber statistical distribution function and the free energies of deformation. The modified constitutive equation was compared with the stress-strain experimental data. It showed that the deduced stress-induced crystallization constitutive equation of EPDM rubber was in good agreement with the experimental results, which offered a theoretical base for the prediction of the stress-induced crystallization rubber materials.