The crosslinking of carboxylated nitrile rubber (XNBR) with magnesium oxide (MgO) leads to an ionic elastomer with thermoplastic nature and better physical properties than the ones obtained with other metallic oxides. The crosslinking reaction leads to the formation of a metallic salt as unique product, as it could be seen on the ATR analysis of the samples, prepared at different reaction times. The mechanical properties of the material increase with the amount of crosslinking agent and segregation of an ionic microphase takes place. The presence of this microphase is demonstrated by a relaxation at high temperatures. The apparent activation energy of this relaxation is smaller than the activation energy of the glass transition of the elastomer, the former being more dependent on the amount of metallic oxide than is the latter.
ABSTRACT:The properties of carboxylated nitrile rubber crosslinked through ionic crosslinks with calcium oxide (CaO) have been studied at two reaction temperatures (100 and 150°C). These properties increase with the CaO content to reach an optimum level, after which they tend to drop again as the level of CaO increases further. The changes in the properties are directly proportional to the amount of carboxylate formed. At any CaO content, a rise in the temperature and the corresponding reduction in the reaction time have a favorable effect on the properties.
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