The factors causing rubber aging are:
A) Oxygen, oxygen reacts with rubber molecules in rubber to form free radical chain reactions, causing molecular chains to break or over-crosslink, causing changes in rubber properties. Oxidation is one of the important reasons for rubber aging.
B) Ozone, the chemically active oxygen of ozone is much higher 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 generated on the surface without cracking.
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.
D) Light: The shorter the light wave, the greater the energy. The higher energy ultraviolet rays 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. Samples with high rubber content will have network cracks on both sides, which is the so-called "light outer layer crack".
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 rupture of molecular chains and mechanical activation of oxidation processes. Which one is dominant depends on the conditions. In addition, under the action of stress, ozone cracking is easily caused.
F) Moisture: The role of moisture has two aspects: rubber is easily damaged when it is exposed to rain in humid air or soaked in water. This is because the water-soluble substances and water clumps in the rubber are extracted and dissolved by water. Hydrolysis or absorption and other reasons. Especially under the alternating action of water immersion and atmospheric exposure, the destruction of rubber will be accelerated. But in some cases, moisture does not damage rubber and even delays aging.
G) Other factors that affect rubber include chemical media, variable valence metal ions, high-energy radiation, electricity and biology, etc.