The Effect of Specimen Thickness on Rate of Artificial Aging

Abstract

Abstract From time to time the question of the effect of thickness on the rate of deterioration of rubber samples subjected to accelerated aging tests, particularly the oxygen-bomb test, is raised. Apparently little experimental work has been done, and no satisfactory answer has yet been given. According to the well-known laws of mass action, the rate of deterioration should slow up with increasing thickness of rubber, and one might expect thin articles to deteriorate further, in a given bomb-aging period, than similar articles of heavier gage. Nevertheless, it is tacitly assumed that variations in thickness have practically no effect—and for small variations this assumption is reasonable considering the oxygen concentration used; or possibly no assumption is made, and the aging tests are just performed mechanically without regard for theoretical considerations and possibilities. The fact that the oxygen-bomb is used largely for comparing the aging quality of similar articles, usually of comparable gage, has doubtless tended to keep the question of the influence of thickness dormant. Again, in the testing of laboratory compounds, most laboratories have standardized on a uniform thickness of cured slabs (0.075″), so that the question of thickness in this type of work does not come into the picture. Occasionally, however, it may be desirable to compare the bomb-aging behavior of articles of quite different types, and when in such cases there is a large difference in thickness, the validity of the comparison may be called in question.