PHOTODEGRADATION OF THYLENE-CO-PROPENE-CO-(5-ETHYLIDENE-2-NORBORNENE)] RUBBERS .2. PHYSICAL AND DYNAMIC-MECHANICAL BEHAVIOR UNDER ACCELERATED CONDITIONS

The physical and dynamic-mechanical behaviour during the photo-oxidati on under accelerated conditons of three (ethylene-co-propene-co-5-ethy lidene-2-norbornene) (EPDM) rubbers with different contents of 5-ethyl idene-2-norbornene(b)) (ENB) are reported. These results show the depe ndence of the glass transition temperature both on the ENB content and on the photo-oxidation time in accordance with network formation in t he rubber matrix under accelerated conditions. The tensile experiments also show an increase of the elastic modulus as function both of ENB content and of photo-oxidation time. The Murayama and Mooney-Rivlin eq uations are applied to estimate the average molecular weight between t wo crosslinking nodes occurring in the rubber matrix during photo-oxid ation with tensile and dynamic-mechanical experiments, respectively. S ome correlations of physical and dynamic-mechanical changes with the p roposed mechanism of photo-oxidation, due to the formation and reactiv ity of unsaturated groups, show that the crosslinking processes prevai l over chain scissions.