Relaxation Behavior of Natural Rubber Composites Through Recovery Measurement after Tension and Compression Set

Relaxation behavior of natural rubber (NR) composites in term of the recovery after tension and compression set had been successfully studied. The effect of crosslink density, either physical or chemical, on the recovery percentage was evaluated. Filler carbon black N-330 and sulfur crosslinking agent were varied for this purpose. N-330 loading ranging from 30, 35, 40 and 45 phr with baseline of 2 phr sulfur. Meanwhile, sulfur loading ranging from 1, 2, 3 and 4 phr with the baseline of 30 phr N-330. Tension set was performed on constant elongation with 25, 50 and 100% strain. The measurements were performed at 100°C for 72 h. While compression set was carried out in constant deflection 25% of initial thickness, carried out both at room temperature and 100°C for 72 h. The results findings showed that the tension set was independent to crosslink densities, but greatly depended on the strain level. Low strain level provided higher recovery percentage. The filler increment markedly increased the compression set, but sulfur tended to improve it. Compression set was higher at elevated temperature since the deterioration not only generated by physical process but also by chemical oxidative thermal process.