Rubber aging is one of the main reasons for seal failure. So, what is rubber aging and what factors can lead to rubber aging
Aging phenomenon
During the processing, storage, and use of rubber and its products, due to the combined effects of internal and external factors, the physical, chemical, and mechanical properties of rubber gradually deteriorate, and eventually lose their use value. This change is called rubber aging.
The symptoms include cracking, tackiness, hardening, softening, pulverization, discoloration, and mold formation.
Aging factors
A) Oxygen: Oxygen in rubber undergoes a radical chain reaction with rubber molecules, resulting in molecular chain breakage or excessive cross-linking, resulting in changes in rubber properties. Oxidation is one of the important reasons for rubber aging.
B) Ozone: Ozone has a much higher chemical activity and is more destructive than oxygen. 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 used as rubber for deformation (mainly unsaturated rubber), cracks appear in the direction of stress action, known as "ozone cracking"; When applied to deformed rubber, only an 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 can 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. The damaging effect on rubber is the high-energy ultraviolet rays. In addition to directly causing the breakage and cross-linking of rubber molecular chains, ultraviolet radiation can also absorb light energy and produce free radicals, triggering and accelerating the oxidation chain reaction process. External light plays a heating role. Another characteristic of light action (unlike heat action) is that it mainly grows on the surface of oak. A sample with a high adhesive content may exhibit network cracks on both sides, known as "light outer layer cracks.".
E) Mechanical stress: Under the repeated action of mechanical stress, rubber molecular chains will be broken to form free radicals, triggering oxidation chain reactions and forming a mechanochemical process. Mechanical fracture of molecular chains and mechanically activated 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 is twofold: When rubber is exposed to rain in humid air or soaked in water, it is prone to damage, which is caused by factors such as water soluble substances and hydrophilic groups in rubber being extracted and dissolved, hydrolyzed, or absorbed by water. Especially under the alternating action of water immersion and atmospheric exposure, rubber damage will be accelerated. However, in some cases, water does not damage the rubber, and even has the effect of delaying aging.
G) Oil: If contacted with oil media for a long time during use, oil can penetrate into the rubber and cause swelling, resulting in reduced strength and other mechanical properties of the rubber. The reason why oil can cause rubber to swell is that after oil penetrates into the rubber, molecules diffuse with each other, resulting in changes in the network structure of vulcanizates.
H) Other factors affecting rubber include chemical media, variable valence metal ions, high-energy radiation, electricity, and biology.