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Several things that form rubber aging O-rings

Update:14-12-2019
Summary:

(A) Oxygen: Oxygen undergoes free radical chain reactio […]

(A) Oxygen: Oxygen undergoes free radical chain reaction with rubber molecules in the rubber O-ring, and the molecular chain is cracked or excessively cross-linked, resulting in a change in the function of the rubber O-ring. Oxidation is one of the important reasons for the aging of rubber O-rings.
(B) Ozone: The chemical activity of ozone is much higher than that of oxygen, and it is more damaging. It also causes the molecular chain to crack, but the effect of ozone on rubber varies with the deformation of the rubber. When used as deformed rubber (mainly unsaturated rubber), cracks appearing in the direction of stress, so-called "ozone cracking"; when acting on deformed rubber, only an oxide film is formed on the surface without cracking.
(C) Heat: Advancing temperature can cause thermal cracking or thermal crosslinking of rubber O-rings. But the hot substrate is still activation. Advancing the rate of oxygen dissipation and activation of the oxidation reaction, and then accelerating the rate of rubber oxidation reaction, this is a common aging phenomenon-thermal oxygen aging.
(D) Light: The shorter the light wave, the greater the energy. What damages the rubber O-ring is the high-energy ultraviolet rays. In addition to ultraviolet light, which can directly cause the cracking and cross-linking of rubber molecular chains, the rubber absorbs light energy to generate free radicals, which triggers and accelerates the oxidation chain reaction process. Outside light plays a heating role. Another feature of light effect (unlike heat effect) is that it mainly grows on the surface of oak. For samples with a high gel content, reticular cracks will appear on both sides, which is called "light outer layer cracking".

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