Vulcanization of carboxylated nitrile rubber (XNBR) by a mixed zinc peroxide-sulphur system

Vulcanization of carboxylated nitrile rubber (XNBR) with a mixed system bas ed on zinc peroxide and sulphur accelerators produces materials with favour able mechanical properties because of the formation of ionic aggregates whi ch give the vulcanized compounds a certain rigidity. These properties are d rastically reduced by the effect of saturated ammonia vapour which plastici zes the ionic aggregates. This plasticization, however, is reversible and t he aggregates can be regenerated by addition of a solvent, which results in recovery and even improvement of the original properties such as stress at constant deformation, tensile strength, crosslinking density and storage m odulus. The temperatures of the two transitions observed in the relaxation spectra, the glass transition of the polymer and the ionic transition corresponding to ionic aggregates, are displaced to higher values when ionic structures are regenerated. (C) 2000 Society of Chemical Industry.