Abstract
A novel experimental methodology is developed for the characterization of the vulcanization and foaming processes of an ethylene propylene diene (EPDM) cellular rubber and for establishing the relationship of its physical and mechanical property evolution with vulcanization and foaming process temperature. To establish this relationship, the vulcanization and foaming reaction kinetics and their coupling have been determined, as well as important parameters in the behaviour of the material, such as conductivity, specific heat capacity and coefficients of expansion and foaming. This aforementioned strategy allows the setting of a material model that can be implemented into finite-element (FE) codes to reproduce the material changes during the vulcanization and foaming processes. The material model developed reproduces with enough accuracy the coupling of chemical kinetics of vulcanization and foaming reactions. The results provided by the numerical material model fit a similar trend, and values with an accuracy of 90–99% to those observed in the experiments conducted for the determination of the cellular rubber expansion in function of the temperature. Moreover, the cellular rubber expansion values agree with the structural analysis of vulcanized and foamed samples at different isothermal temperatures and with the proportional loss of mechanical properties in the function of the vulcanization and foaming degree.
Highlights
A novel experimental methodology is developed for the characterization of the vulcanization and foaming processes of an ethylene propylene diene (EPDM) cellular rubber and for establishing the relationship of its physical and mechanical property evolution with vulcanization and foaming process temperature
A large number of rubber-based foams are commercially available attending to their chemical structure: based on polyurethane (PU), ethylene vinyl acetate (EVA) copolymer, natural rubber (NR), styrene-butadiene rubber (SBR), chloroprene (CR), alkyl acrylate copolymer (ACM), ethylene propylene diene (EPDM) terpolymer and acrylonitrile butadiene rubber (NBR), silicon rubber and so on [2–4]
The exothermic enthalpy related to the vulcanization is obtained from the area enclosed between the first and the second heating step of the Differential Scanning Calorimetry (DSC) thermogram represented in function of time instead of temperature
Summary
Due to the excellent properties of EPDM elastomers, such as good weatherresistance, high resistance to acid, alkali, oxygen and ozone, insulation properties, high tear, impact and abrasion resistance and high and low temperature performance [2,3,6], they have been increasingly used as cellular material since the beginning of the 1990s. For these reasons, EPDM rubbers are especially used for the automotive industry for hoses, wipers, bumpers, gaskets, pipe insulation, door seals and weather-stripping [2,6,7]. The average molecular weight of EPDM lays between 30,000 and 150,000 g/mol, depending on the polymerization and the ethylene/propylene/diene ratio
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