Reasons for Rubber Aging
Rubber products in the long-term storage and use process, due to thermal, oxygen, ozone, variable value metal antioxidant ion mechanical stress, light, high-energy radiation, as well as other chemical substances and fungi erosion, will gradually stick, harden, brittle or crack. This phenomenon of physical and mechanical properties decreasing with time and elasticity decreasing is called rubber aging.
The main factors affecting rubber aging are:
1. Oxygen: Oxygen reacts with rubber molecules in free radical chain reaction, and molecular chains are broken or over-crosslinked, resulting in changes in rubber properties. Oxidation is one of the important causes of rubber aging.
2. Ozone: The chemical activity of ozone is much higher than that of oxygen, which is more destructive. It also breaks the molecular chain, but the effect of ozone on rubber varies with rubber deformation or not. When rubber is used for deformation (mainly unsaturated rubber), cracks occur in the direction of stress action, which is called "ozone cracking". When rubber is used for deformation, only oxide film is formed on the surface without cracking.
3. Heat: Increasing temperature can cause thermal cracking or crosslinking of rubber. But the basic function of heat is activation. Increasing oxygen diffusion rate and activating oxidation reaction speed up rubber oxidation reaction, which is a common aging phenomenon - thermal oxygen aging.
4. Mechanical stress: Under the repeated action of mechanical stress, the rubber molecular chain will be broken to form free crown, which will trigger the oxidation chain reaction and form a mechanochemical process. Mechanically fractured molecular chains and mechanically activated oxidation processes. Which one is dominant depends on its conditions. In addition, ozone cracking is easily caused by stress.
5. Moisture: The function of water has two aspects: rubber is easy to be destroyed when it is wet in the air or immersed in water for a long time. This is due to the water-soluble substances and hydrophilic groups in rubber are dissolved, hydrolyzed or absorbed by water extraction. Especially under the alternate action of water immersion and air exposure, the damage of rubber will be accelerated. But in some cases, moisture has no destructive effect on rubber, and even has the effect of delaying aging.
6. Oil: If contacted with oil medium for a long time during use, oil can penetrate into rubber and cause swelling, resulting in the decrease of strength and other mechanical properties of rubber. Oil can make rubber swell, because the oil infiltrated into rubber, resulting in molecular diffusion, so that the network structure of vulcanizate changes.
7. Other factors affecting rubber include chemical medium, variable valence metal ions, high energy radiation, electricity and biology
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