HYDROLYTIC STABILITY OF URETHAN ELASTOMERS
ARMY WEAPONS COMMAND ROCK ISLAND IL RESEARCH DEVELOPMENT AND ENGINEERING DIRECTORATE
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The resistance to hydrolysis of millable, castable, and injection moldable urethan elastomers was determined. Conditions most frequently used were exposure over water at 158 deg F. and at or near room temperature. Polyesters were shown to suffer much more rapid deterioration under both conditions than polyethers. Attack at 158 deg F. appears to involve a simple hydrolysis of the main chain ester groups resulting in reversion. Attack at or near room temperature is more complex, involving both a rapid typically two to three weeks hydrolytic cracking of stressed or unstressed specimens and a gradual reversion over a period of many months. The latter attack especially the early cracking seems to be of microbiological origin. Hydrolytic decomposition can be retarded by additives such as diisocyanates, carbodiimides, and fungicides. However, these agents frequently lead to lower original properties. Also, those giving protection at 158 deg F. often cause accelerated deterioration at or near room temperature while those providing protection at the lower temperatures lead to accelerated deterioration at 158 deg F. Results of outdoor and shelf aging at Rock Island, Illinois and Panama indicate a general correlation with accelerated tests.
- Elastomers and Rubber