1 MOIST HEAT AND STEAM TESTS

Judging by the lack of standard test methods, there is not generally great concern over the long term effects of moist heat, although the importance of conditioning at a known humidity for such tests as electrical properties is generally appreciated. However, there are circumstances where the ageing effect of high humidity may be important; Soden and Wake ^[1] found a near doubling of the rate of deterioration of natural rubber by increasing the humidity to 100% in a 70 C air ageing test, and polymers containing hydrolysable bonds (e.g. polyurethanes) can be especially liable to breakdown under humid conditions.

If the effects of humidity are of interest, then tests along the same lines as the heat ageing tests would be used but both temperature and humidity would be controlled. A simple standard method is given in ASTM D3137 ^[2] for determining the effect of moisture on tensile strength, it being recommended that a similar dry heat ageing test be conducted so that the effect of humidity can be isolated. The test pieces are suspended above water in a loosely capped container in an oven...