Effect of the stretching on the network structure of carbon black filled EPDM rubbers.

Abstract : The present work proposes an approach to identify the network structural evolution of EPDM rubbers induced by loading. An experimental device based on two camera pair systems has been developed in order to accurately measure the volume change of rubber samples during stretching. Results show that the loading is associated with an increase of volume change (∆V/V0) up to 2% and should be related to cavitation/decohesion at the interface between fillers and the rubbery matrix. Post mortem analysis of the microstructure, combining swelling and thermoporosimetry experiments, were then carried out. A good agreement has been found between the volume change and the microstructural evolution: as compared to virgin samples (not submitted to loading), the effective network density estimated from swelling measurements of tested materials (ν) is decreased of 7% and thermoporosimetry shows that damage during stretching is accompanied by an average increase of the chains length. These changes are significantly increased for samples stretched up to the rupture (λ=8). Indeed, in that case, the effective network density is decreased of more than 20%.