Effect of Phthalic Anhydride on Thermo-Mechanical Properties of Ionic Elastomer Based on Carboxylated Nitrile Rubber

The effect of phthalic anhydride (PhA) on the rheometric, viscoelastic, and mechanical properties and processability of an ionic elastomer based on carboxylated nitrile rubber (XNBR) cured with zinc oxide have been investigated. It has been found that the presence of this crystalline additive strongly affects the material properties and the ionic association. The rheometric results revealed new characteristics of rheographs with faster curing rates and a point of maximum torque values upon the addition of PhA. The values of elastic torque as well as loss torque depend on PhA loading and the maximum value have been found at the loading of 2.5 parts per hundred parts of rubber (phr). Dynamic mechanical thermal analysis also revealed that the viscoelastic properties, the storage modulus (E′) and the tan δ transition temperature are highly affected by the incorporation of PhA. Although the main chain glass transition temperature is unaffected by the addition of PhA, the high temperature transition temperature, due to ionic cluster formation, did shift to a higher temperature. The optimum valus of E′ and tan δ were at loading of 2.5 phr. The stress at break and elongation at break did not change significantly, whereas sharp rises in 300% modulus and hardness values were found at 2.5 phr loading of PhA. The plasticity results of 2.5 phr PhA loaded sample showed better proccssability characteristics with low scorch as compared to pure XNBR-ZnO vulcanizate.