Full definition
The progressive and irreversible degradation of elastomer physical properties over time due to environmental exposure. Primary aging mechanisms: thermal oxidation (heat + oxygen break polymer chains and cross-links, causing hardening and cracking), ozone attack (surface cracking perpendicular to stress direction, especially in NR and SBR — concentration as low as 25 ppb causes damage), UV photodegradation (breaks polymer bonds, causes surface chalking and cracking), and chemical attack (solvents, acids, bases causing swelling, softening, or embrittlement). Evaluated by accelerated aging tests: ASTM D573 (air oven aging — measures changes in hardness, tensile, and elongation after 70-168 hours at elevated temperature), ASTM D1149 (ozone resistance), ASTM D750 (rubber deterioration by cut growth). Aging resistance ranking (best to worst): EPDM and silicone (excellent ozone/UV), neoprene (good ozone), NBR (moderate), NR and SBR (poor — require antioxidant/antiozonant protection). Per ISO 188 for heat aging methodology.