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Quantitative confirmation of diffusion-limited oxidation theories
Exposure of polymers to air during aging (radiation, thermal, UV) often results in inhomogeneously oxidized samples, a complication which impacts attempts both to understand the oxidation process and to extrapolate accelerated exposures to long-term conditions. The most important such complication involves diffusion-limited oxidation which can occur if the rate of oxygen consumption in a material is greater than the rate at which oxygen can be resupplied by diffusion processes from the surrounding air atmosphere. Thus, in order to confidently extrapolate accelerated simulations to long-term, air-aging conditions, one must be able to monitor and quantitatively understand diffusion-limited oxidation effects. Experimental techniques for monitoring diffusion-limited oxidation profiles have recently been reviewed. By comparing experimental profiles with theoretically derived profiles, the theories can be verified and then confidently used to predict the importance of diffusion effects prior to the initiation of aging tests. This paper summarizes what we believe is the first quantitative experimental confirmation of diffusion-limited oxidation theories.