Influence of crosslinker and water on cyclic properties of carboxylated nitrile butadiene rubber (XNBR)

This study evaluates the effect of network structure (ionic versus covalent crosslinks) on the mechanical behavior of carboxylated nitrile butadiene rubber (XNBR) under cyclic loading. Additionally, the influence of water on the mechanical properties of the XNBR networks is assessed. Reversible and dissipated energies of cyclic tests (with constant maximum strain in each cycle) and step cycle tests (with increasing maximum strain in each cycle) of non-swollen and swollen samples are determined as a function of the used crosslinking system. Energies obtained from step cycle tests are compared to total absorbed energies obtained from monotonic tensile tests. The results show a good correlation between network structure and cyclic behavior. Ionic rearrangement processes are found to be more pronounced in samples with higher ionic crosslinker content. The introduction of covalent crosslinks imparts spatial restriction to ionic rearrangement and improves the cyclic performance of XNBR films upon water exposure.