Accelerated thermal ageing studies on nitrile rubber O-rings

yPoly(acrylonitrile-butadiene) rubber (NBR) O-rings have been aged in air whilst under 12.5% compression at temperatures up to 110 degreesC. The compression set properties together with oxygen uptake of the O-rings under the applied load conditions were measured and results analysed using time-temperature superposition and Arrhenius kinetics. The compression set results suggest a single degradation process with an activation energy of 81.03 kJmol(-1). This compares well with the activation energy of 74.3 kJmol(-1) obtained from oxygen consumption. Results from solvent swell and oxygen uptake tests show that the main influence on ageing of the rubber is oxidative cross-linking, leading to the material becoming hard and brittle. The approach presented here predicts that the rubber will reach full compression set by 40 (+54/-7) years based on 95% confidence bands. Crown Copyright (C) 2003 Published by Elsevier Science Ltd. All rights reserved.