Effect of Divalent Metal Ions on Curing Characteristics and Dynamic Mechanical Properties of Natural Rubber

The study examined the effects of three different divalent metal ions (Ca2+, Cu2+ and Fe2+) upon the curing characteristics and dynamic mechanical properties of vulcanised natural rubber with respect to scorch and cure times, cure rate index, storage modulus (E') and damping peaks (tan delta(max)). The metal ions were added to natural rubber latex solutions at three concentrations of 20, 100 and 500 ppm, respectively. It was found that scorch and cure times increased with increasing metal ion concentration, with a decrease in cure rate index. Longer scorch and cure times were observed in the case of Cu2+, also with a lower cure rate index. Storage modulus values decreased with increasing metal ion concentration, with the exception of Ca2+, which produced the highest E' value. The damping peaks of filled natural rubber decreased with increasing metal ion concentration. The smallest ion (Cu2+) also led to a decrease in the damping peak. The T-g of the natural rubber was unaffected by either concentration or type of metal ion.