Some rubber contains unsaturated groups, due to the activity of these groups, sulfur can be used for vulcanization, on the other hand, it is precisely because of the presence of these unsaturated active groups, which makes rubber easy to react with oxygen, ozone and other active substances to break the rubber chain, crosslinking and so on. Even after destruction, diolefin rubber such as natural rubber, styrene butadiene rubber, butadiene rubber, isoamyl rubber, butadiene rubber and neoprene rubber still contain unsaturated groups and are affected by the above factors. The higher the temperature, the stronger the effect of these factors. These phenomena are particularly serious when the rubber is over-sulfur, at which time the free double bond in the rubber can also react with free sulfur to harden the vulcanized rubber, the so-called "post-vulcanization". In synthetic rubber, the material also hardens and becomes brittle due to further polymerization and intramolecular cross-linking (cyclization). Moisture, especially at high temperatures, can break rubber (such as polyurethane rubber) that can be hydrolyzed. In addition, rubber products often appear in the use of the surface cracking, white, physical and mechanical properties decline, these phenomena are collectively referred to as "aging".
Rubber aging is not a simple process, but a general term for the decline in the performance of rubber and its products. The main factors leading to aging are thermal oxidation, oxidation with mechanical stress (flexion cracking), ozonation with mechanical stress (ozone cracking), oxidation with light and ultraviolet light (fine cracking effect), oxidation with heavy metal participation (accelerated aging of rubber poisons), hydrolysis of hot water, steam and water (hydrolytic aging), and simple heat Effects (thermal decomposition, post-vulcanization, cyclization, vulcanization reduction) and mold corrosion.
In order to make durable rubber products, it is necessary to add some substances that can inhibit the above various aging phenomena in the rubber material, which is generally called "antioxidant". In fact, natural rubber, depending on its manufacturing method, always contains more or less organic substances that can inhibit oxidation (these substances are partly consumed in the vulcanization process). However, it can not meet the requirements of modern technology for the aging properties of rubber products, so it is still necessary to add antioxidants when manufacturing rubber products. Although most synthetic rubber has added some antioxidant as a stabilizer in the manufacturing process, a certain amount of antioxidant needs to be added in the application, especially to protect against ozone and flexor cracking.
