Deterioration by Heating in Air
It is necessary to determine how rubber specimens deteriorate upon heating to learn what volatile materials could be released in the process. The volatile materials given off upon heating, such as antioxidants, could migrate into other rubber compounds and subsequently influence the degradation rate of those compounds. One of the ways that rubber compounds suffer from deterioration is via heated air, and therefore compounds are tested for this effect.
One of the concerns of a product design engineer is the expected life of a component. Properties of vulcanized rubber change during service, so elastomers and rubber products must resist the deterioration of physical properties over time caused by oxidative and thermal aging.
Testing (ASTM D865-99)
The apparatus for the heat aging tests consist of borosilicate glass test tubes, that are 38 mm (1.52 in.) in diameter and 300 mm (12 in.) in length, that are heated uniformly in a suitable equipment such as an oil or water bath or metal block.
Samples for testing and comparison are taken from materials that completed vulcanization at least 24 hours previously.
Results of the heat aging test for each aging period are expressed as a percent change in each physical property (tensile strength, ultimate elongation, tensile stress), and are calculated as follows:
P = (A – O)/O X 100
- P = change in property, %
- O = original value
- A = value after aging
Using the above formula, results are reported as the percent change where attention is made to include repeatability and reproducibility. These inclusions are important when results on various types of specimens are listed along with results from other testing laboratories.