Factors causing rubber aging
Factors of rubber aging
Oxygen
A) Oxygen: Oxygen reacts with rubber molecules in a free radical chain reaction, causing molecular chains to break or over-crosslink, resulting in changes in rubber properties. Oxidation is one of the important causes of rubber aging.
Ozone
B) Ozone: Ozone is much more chemically active than oxygen and more destructive. It also causes molecular chains to break, but the effect of ozone on rubber varies depending on whether the rubber is deformed or not. When acting on deformed rubber (mainly unsaturated rubber), cracks appear in the direction of stress, which is the so-called "ozone cracking"; when acting on deformed rubber, only an oxide film is formed on the surface without cracking.
Heat
C) Heat: Increasing the temperature can cause thermal cracking or thermal crosslinking of rubber. But the basic role of heat is activation. Increasing the oxygen diffusion rate and activating the oxidation reaction, thereby accelerating the oxidation reaction rate of rubber, is a common aging phenomenon - thermal oxygen aging.
Light
D) Light: The shorter the light wave, the greater the energy. The ultraviolet rays with higher energy are the ones that damage rubber. In addition to directly causing the breakage and cross-linking of rubber molecular chains, ultraviolet rays can also generate free radicals due to the absorption of light energy, which triggers and accelerates the oxidation chain reaction process. The ultraviolet rays play a role of heating. Another feature of light action (different from heat action) is that it mainly occurs on the rubber surface. For samples with high rubber content, mesh cracks will appear on both sides, which is the so-called "light outer layer cracking".
Mechanical stress
E) Mechanical stress: Under the repeated action of mechanical stress, the rubber molecular chain will be broken to generate free radicals, triggering an oxidation chain reaction and forming a mechanochemical process. Mechanical break molecular chain and mechanical activation oxidation process. Which one is dominant depends on the conditions. In addition, under the action of stress, ozone cracking is easily caused.
Moisture
F) Moisture: The effect of moisture has two aspects: rubber is easily damaged when it is exposed to humid air or soaked in water. This is because the water-soluble substances and hydrophilic groups in the rubber are extracted, dissolved, hydrolyzed or absorbed by water. Especially under the alternating action of water immersion and atmospheric exposure, the destruction of rubber will be accelerated. But in some cases, water does not damage rubber, and even has the effect of delaying aging.
Oil
G) If rubber products are in contact with oil media for a long time during use, the oil can penetrate into the rubber and cause it to swell, resulting in a decrease in the strength and other mechanical properties of the rubber. The reason why oil can cause rubber to swell is that after the oil penetrates into the rubber, molecules diffuse mutually, causing the network structure of the vulcanized rubber to change.
Other factors
H) Other factors that affect rubber include chemical media, variable valence metal ions, high-energy radiation, electricity and biology.
Oxygen
A) Oxygen: Oxygen reacts with rubber molecules in a free radical chain reaction, causing molecular chains to break or over-crosslink, resulting in changes in rubber properties. Oxidation is one of the important causes of rubber aging.
Ozone
B) Ozone: Ozone is much more chemically active than oxygen and more destructive. It also causes molecular chains to break, but the effect of ozone on rubber varies depending on whether the rubber is deformed or not. When acting on deformed rubber (mainly unsaturated rubber), cracks appear in the direction of stress, which is the so-called "ozone cracking"; when acting on deformed rubber, only an oxide film is formed on the surface without cracking.
Heat
C) Heat: Increasing the temperature can cause thermal cracking or thermal crosslinking of rubber. But the basic role of heat is activation. Increasing the oxygen diffusion rate and activating the oxidation reaction, thereby accelerating the oxidation reaction rate of rubber, is a common aging phenomenon - thermal oxygen aging.
Light
D) Light: The shorter the light wave, the greater the energy. The ultraviolet rays with higher energy are the ones that damage rubber. In addition to directly causing the breakage and cross-linking of rubber molecular chains, ultraviolet rays can also generate free radicals due to the absorption of light energy, which triggers and accelerates the oxidation chain reaction process. The ultraviolet rays play a role of heating. Another feature of light action (different from heat action) is that it mainly occurs on the rubber surface. For samples with high rubber content, mesh cracks will appear on both sides, which is the so-called "light outer layer cracking".
Mechanical stress
E) Mechanical stress: Under the repeated action of mechanical stress, the rubber molecular chain will be broken to generate free radicals, triggering an oxidation chain reaction and forming a mechanochemical process. Mechanical break molecular chain and mechanical activation oxidation process. Which one is dominant depends on the conditions. In addition, under the action of stress, ozone cracking is easily caused.
Moisture
F) Moisture: The effect of moisture has two aspects: rubber is easily damaged when it is exposed to humid air or soaked in water. This is because the water-soluble substances and hydrophilic groups in the rubber are extracted, dissolved, hydrolyzed or absorbed by water. Especially under the alternating action of water immersion and atmospheric exposure, the destruction of rubber will be accelerated. But in some cases, water does not damage rubber, and even has the effect of delaying aging.
Oil
G) If rubber products are in contact with oil media for a long time during use, the oil can penetrate into the rubber and cause it to swell, resulting in a decrease in the strength and other mechanical properties of the rubber. The reason why oil can cause rubber to swell is that after the oil penetrates into the rubber, molecules diffuse mutually, causing the network structure of the vulcanized rubber to change.
Other factors
H) Other factors that affect rubber include chemical media, variable valence metal ions, high-energy radiation, electricity and biology.