Effects of imidazolium ionic liquid on cure characteristics, electrical conductivity and other related properties of epoxidized natural rubber vulcanizates

Epoxidized natural rubber (ENR) was compounded with imidazolium ionic liquid and the resulting curing characteristics, electrical conductivity, and thermomechanical and dynamic mechanical properties were characterized. It was found that addition of the ionic liquid (IL) (1-ethyl-3-mehylimidazolium chloride) below 5 phr significantly increased the vulcanization rate, decreasing scorch and cure times. However, at higher loadings the IL had the reverse effects on cure time and cure rate index. In addition, electrical conductivity of these ENR vulcanizates abruptly increased from 10−8 S m−1 (without IL) to 10−6 S m−1 (with 3 phr of IL). Also, the DC conductivity gradually increased with the content of IL. Furthermore, the tensile strength and elongation at break of the ENR vulcanizates decreased with IL content, due to plasticizing effects retarding the strain-induced crystallization of ENR molecules. The crosslink density was quantified by thermal scanning stress relaxation (TSSR) and by using the Mooney-Rivlin equation. The crosslink density estimates from the two techniques had similar trends. That is, increasing trend of the crosslink density was observed with increasing IL contents up to 5 phr, with decreasing trend thereafter. Therefore, the ENR vulcanizates with IL have potential as conductive rubber materials in some electronic appliance applications.