Recovery Behaviors of NR, SBR and BR Vulcanizates from Circular Deformation

Recovery behaviors of unfilled NR, BR, and SBR vulcanizates after aging with a circular deformation were compared to prevent the influence of reinforcing agent. Samples were aged at room temperature, 50, 70, and 90 degrees C for 10 days. Recovery increased by increasing the measurement time. Instantaneous recoveries less than 1.0 sec were obtained using the recovery variations with the measurement time. For aging at room temperature, difference in the recoveries of the rubber samples was not significant because the aging time was too short. However, for accelerated thermal aging at 50, 70, and 90 degrees C, difference in the recoveries of the rubber samples was significant. Degree of recovery of BR specimen was higher than those of the others, while that of SBR was lowest. However, for accelerated thermal aging at 90 degrees C, recovery of the NR sample was higher than that of the BR one. The initial recovery decreased by increasing the aging temperature and the decrement of SBR was larger than the others. The experimental results were explained with the resilience properties of rubbers and the crosslink density changes by thermal aging.