Factors of rubber aging

A) Oxygen: oxygen has a free radical chain reaction with rubber molecules in rubber, and the molecular chains are broken or over crosslinked, causing changes in rubber properties. Oxidation is one of the important reasons for rubber aging.

B) Ozone: the chemical activity of ozone is much higher and more destructive than oxygen. It also breaks the molecular chain, but the effect of ozone on rubber varies with whether the rubber is deformed or not. When it is used as rubber for deformation (mainly unsaturated rubber), cracks appear in the direction of stress action, that is, the so-called "ozone cracking"; When acting on deformed rubber, only oxide film is formed on the surface without cracking.

C) Heat: increasing the temperature can cause thermal cracking or thermal crosslinking of rubber. But the basic function of heat is activation. Increasing the oxygen diffusion rate and activating the oxidation reaction, so as to accelerate the oxidation reaction rate of rubber, which is a common aging phenomenon - thermal oxygen aging.

D) Light: the shorter the light wave, the greater the energy. What destroys silicone rubber sundries is ultraviolet light with high energy. In addition to the direct breaking and crosslinking of rubber molecular chain caused by ultraviolet light, rubber produces free radicals due to the absorption of light energy, which initiates and accelerates the oxidation chain reaction process. The external light plays the role of heating. Another feature of light action (different from heat action) is that it mainly grows on the surface of rubber. The sample with high glue content will have network cracks on both sides, that is, the so-called "smooth outer layer crack".

E) Mechanical stress: under the repeated action of mechanical stress, the molecular chain of rubber will be broken to form free Tsuen, which will cause oxidation chain reaction and form a mechanochemical process. Mechanical breaking of molecular chains and mechanical activation of oxidation processes. Which one has the advantage depends on its conditions. In addition, it is easy to cause ozone cracking under stress.

F) Moisture: the role of moisture has two aspects: silicone rubber miscellaneous parts are easy to be damaged when exposed to rain or soaked in water in humid air, which is caused by water-soluble substances and hydrophilic groups in rubber being extracted, dissolved, hydrolyzed or absorbed by water. Especially under the alternating action of water immersion and atmospheric exposure, it will accelerate the destruction of rubber. However, in some cases, moisture does not damage the rubber, and even has the effect of delaying aging.

G) Silicone rubber miscellaneous products: in the process of use, if it is in long-term contact with oil medium, oil can penetrate into the rubber to cause swelling, resulting in the reduction of the strength and other mechanical properties of the rubber. The reason why oil can make rubber swell is that after oil penetrates into rubber, molecules diffuse each other, which changes the network structure of vulcanizate.

H) Other factors: chemical media, variable valence metal ions, high-energy radiation, electricity, biology and so on.