Aging and Service Life of Natural Rubber in Air and Seawater

As a part of the U.S. Navy development of a rubber disk to serve as the torpedo launcher on Virginia-class submarines, an aging study has been conducted for sulfur-cured deproteinized natural rubber, subjecting the compound to accelerated aging in air and seawater. The fatigue life correlated with the failure strain, so that latter could be used to quantify the rate and extent of degradation. A master curve of failure strain as a function of log(exposure time) was constructed by superposing different temperature curves. The shift factors followed the Arrhenius equation, with activation energies of 90 ± 4 and 63 ± 3 kJ/mol for air and seawater, respectively. The difference is due to the different oxygen concentration in the two environments.