The factors causing rubber aging are as follows
Free radical chain reaction occurs with rubber molecules in rubber, and the molecular chain breaks or over crosslinks, resulting in the change of rubber properties. Oxidation is one of the important reasons for rubber aging.
The chemical active oxygen of ozone is much higher and more destructive. It also breaks the molecular chain, but the effect of ozone on rubber is different with rubber deformation or not. When the rubber is used for deformation (mainly unsaturated rubber), there are cracks in the direction of stress action, which is called "ozone cracking"; When applied to the deformed rubber, only oxide film is formed on the surface of the rubber without cracking.
The increase of temperature can cause the thermal cracking or thermal crosslinking of rubber. But the basic function of heat is activation. Increasing oxygen diffusion rate and activating oxidation reaction can accelerate rubber oxidation reaction rate, which is a common aging phenomenon thermal oxygen aging.
The function of water has two aspects: rubber is easy to be damaged when it is soaked in water or wet air. This is because the water-soluble substances and water-soluble aggregates in rubber are extracted and dissolved by water. It is caused by hydrolysis or absorption. Especially under the alternate action of water immersion and atmospheric exposure, the damage of rubber will be accelerated. However, in some cases, moisture does not damage the rubber, and even has the effect of delaying aging. The factors affecting rubber include chemical medium, variable valence metal ions, high energy radiation, electricity and biology.