Rubber after a long time, some will become sticky soft, some will harden hair brittle. In daily life, we can often see some with the old tire side to produce Gougou cracks, professionally known as cracking. In this case, the original elasticity and strength of rubber decreased significantly, these phenomena are called aging.
Aging is the result of the change of rubber structure under the influence of various external factors, the most common is the thermal oxygen aging caused by heat and oxygen.
Rubber can degrade when heated to a certain temperature. Natural rubber, for example, starts to decompose low-molecular-weight substances at over 200 degrees Celsius. The thermal stability of rubber depends largely on its chemical composition and structure, and the thermal stability of silicone rubber and fluorine rubber is better than that of general rubbers. In general rubber, the thermal stability of BR is the best, and SBR is the second.
With the participation of oxygen, all kinds of rubber aging results are different. Natural rubber and isoprene rubber, as well as butyl rubber in the process of thermal oxygen aging is mainly the formation of macromolecular chain fracture, soft and sticky, and styrene-butadiene rubber, BR, NBR and EPDM in the process of thermal oxygen aging is mainly broken chain products intertwined, destroying the elastic structure of rubber, so it hardens brittle.
The bane of rubber's thermal aging lies in its unsaturated bonds. Natural rubber and some general synthetic rubber each 1000 carbon atom contains 150 to 250 double bonds, these parts are most likely to chemical reaction, so their thermal oxygen aging performance is not good, especially natural rubber. The structure tends to saturated silicone rubber, fluorine rubber, butyl rubber, ethylene propylene rubber, polyurethane rubber, acrylate rubber, etc. belong to heat-resistant aging elastomer.
Although the aging of rubber may not be completely avoided, but can be postponed, the most convenient and effective measure is to add anti-aging agent. Antioxidant can capture rubber thermal oxygen aging process produced by active substances, so as to protect the role of rubber. Anti-aging agent of a wide range of more commonly used amines and phenols two series, adding a general amount of rubber weight of 1% to 1.5%.