AbstractPolyethylene films and sheets were oxidized in oxygen, air, or aqueous nitric acid at temperatures up to 100°C., and the decay of physical properties was measured by mechanical testing. In some instances, weight change and volume of oxygen absorbed were reliable indexes of the physical degradation as measured by a particular property such as ultimate stress or ultimate elongation, but they were unreliable in comparing the degradation of different types of polyethylene. Although the more crystalline polyethylenes absorbed less oxygen than branched polyethylenes, the former degraded more rapidly in air at 100°C. In degradation by air or oxygen, exposure time affected the ultimate elongation more than it did ultimate tensile strength. In nitric acid the reverse was true. The yield elongation and the yield stress were virtually unaffected by any of the degradation methods unless the exposure was very long. A preferential oxidation of the noncrystalline regions is proposed to account for this result. The appropriateness of any tensile property as a measure of degradation is concluded to depend on the intended use of the plasti
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