February 5. 2020 - [caption id="attachment_27030" align="alignleft" width="300"] Fig. 1: PRI of raw NR and NR with varying amounts of copper compounds (in logarithmic coordinates).[/caption] Oxygen in the air is responsible for the thermooxidation of rubber and is catalysed by “rubber poisons”, mainly by copper and manganese compounds. In this study, a variety of copper compounds were used such as copper stearate, copper oxide and copper sulphate. They were mixed with rubber. The thermooxidation of the rubber was evaluated using the traditional plasticity retention index (PRI) and the alternative Mooney retention index (MRI). The vulcanization behaviour of the mixtures contaminated by copper compounds was studied using a rubber process analyzer (RPA). Mechanical properties like tear strength and elongation at break were also tested.