Thermal-Oxidative Resistance of Elastomers

DIN 53508 [241] describes two types of artificial aging on elastomers heat exposure at increased temperature and exposure to oxygen at 21 bar. 

Aging tests for elastomers are performed preferably at70°C or 100°C In air according to DIN 53508. After exposure for a certain period of time (1 day, 7 days, 14 days or more), the aged test specimen is tested for service-relevant properties elasticity, hardness, tensile strength, elongation at break, and other materials parameters. The increase or decrease in a material property compared to the value prior to heat 

Tests for elastomer resistance to air have to be considerably accelerated in the laboratory by exposure to pure oxygen (pressure test, 21 bar, 70°C) or in the ozone test chamber (standard pressure, 50-200 ppm ozone, 25°C, s. Section 2.2.8). While oxygen influence is rated as a percentage loss of properties, comparable to heat aging tests in air, ozone influence is evaluated according to crack formation in the rubber transverse to the tensile or bending direction (evaluation levels 0 to 3) [229]. 

The measurement of stress relaxation at various temperatures allows for precise evaluation of elastomer aging behavior and offers detailed insight into the mechanisms of elastomer aging [229]. Multiple loads act on almost all elastomers seals and molded rubber technical parts [242]  

The experimental determination of the two latter influences on the elastic properties of a vulcanized elastomeric material is performed effectively with the aid of stress relaxation tests [242]. Relaxation effects depend on temperature and loading time. Here, a distinction must be made between physical and chemical relaxation [242]. 

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