Irradiation effects on the relaxation behaviour of EPDM elastomers

Abstract

γ‐irradiation of ethylene–propylene diene monomer (EPDM) elastomers under oxidant atmosphere was carried out in order to change their mechanical and dielectric behaviour. Three different formulations of EPDM (70 wt% ethylene, 28 wt% propylene; diene monomer: 2 wt% norbornene) were studied: a non‐crosslinked EPDM terpolymer, a crosslinked EPDM and a crosslinked EPDM stabilized with an antioxidant. Dielectric and mechanical relaxation show a β‐sub‐glass relaxation at about −120 °C (1 Hz) and an α‐relaxation at −15 °C (1 Hz) associated with the glass transition but influenced by the effects of irradiation. The local mobility associated with the β‐relaxation is only weakly influenced by γ‐irradiation up to 450 kGy. The α‐process is shifted to higher temperatures as a result of crosslinking and changes in the semicrystalline structure. The amplitude of the dielectric α‐process increases as a result of the formation of oxidized species during irradiation under oxygen. In contrast, the mechanical α‐relaxation amplitude decreases as a result of physical and chemical cross‐linking. It was shown that the main factors that determine the crosslinking/chain scission balance are (1) the presence of oxygen together with the irradiation dose, (2) the dose rate and (3) the initial crosslink density of the EPDM material. As a result, the individual contribution of crosslinking and crystallization, and therefore the understanding and prediction of the properties after γ‐irradiation can only be deduced after comparison of the polymer behaviour below and above its melting temperature. Copyright © 2004 Society of Chemical Industry

Degradation of EPDM and FPM elastomers irradiated at very high dose rates in mixed gamma and neutron fields

“…For EPDM, the T g shift and peak reduction is much weaker than for FPM. The increment in T g (less than 5°C) is comparable with that reported by Celette et al for EPDM samples irradiated with beta rays under inert conditions (4°C at 0.50 MGy). A broad secondary transition is present above T g .…”

“…Ethylene‐propylene copolymers with ethylene contents higher than about 60–70 mol% like the one here investigated are semicrystalline. The secondary transition above T g has been ascribed to the motion of the segments at the interface with lamellas . Thus the evolution of the loss factor traces with the irradiation time shown in Fig.…”

Degradation of EPDM seal used for water supplying system

“…In the last two decades, the degradation of EPDM has been investigated in terms of a variety of methods: for instance, thermal aging [10], thermal oxidation aging [11], photo aging [12,13], radiation-induced oxidation aging [14], g-irradiation [15,16] and so forth. Some functional groups such as carbonecarbon double bonds, carbonyl groups and ester groups were found to occur after degradation of EPDM [15].…”

Evolution of EPDM networks aged by gamma irradiation – Consequences on the mechanical properties

“…This mechanism artificially induces an accelerated evolution of the mechanical properties material. Indeed, chain scissions occur, counterbalanced by a cross-linking mechanism which depends on the initial cross-linking of the material, which, in turn, leads to modifications of the macroscopic mechanical properties [3,4,5,6,7]. The consequence of such ageing, at temperatures higher than the melting temperature of the EPDM crystallites, is a decrease in the material stiffness.…”