Ozone is one of the important factors that lead to the aging of rubber products in the atmosphere. Ozone is more active than oxygen, so it is much more serious to the rubber, especially the unsaturated rubber.
Atmospheric ozone (O3) is absorbed by oxygen molecules in the sun´s ultraviolet light after ultraviolet light, the decomposition of the
The harm caused by different near the place of 5x10 re oxygen atoms and oxygen molecules into. From the earth´s surface 20? 30 km high air there is a layer of concentration is about the ozone layer ´with the air of vertical flow, ozone is brought to the earth´s surface, the ozone concentration from the upper to the ground gradually reduced. In addition, in the UV centralized place, discharge and motor, in particular, is to produce electric spark will produce ozone. Usually atmospheric ozone concentration is 0? 5X10-8.´ ozone concentration of different, different seasons, ozone concentrations are also different. Although the ground in the vicinity of the ozone concentration is very low, but the rubber is can not be ignored.
Unsaturated rubber easy appearance of ozone and ozonation, and different thermal aging, one is the surface layer of ozonation of rubber products only in contact with ozone, the ozone oxidation process is the process of rubber from the outside to the inside; two with ozone reaction to generate a layer of silver white dura (about lOnm thick in the static condition), this film can prevent the ozone deep contact with rubber, but in dynamic strain conditions or in the static state when the rubber tensile elongation or tensile stress exceeds its critical elongation or critical stress, this film will produce crack and make contact with the rubber surface ozone is new. Continue ozonization and crack growth, and crack due to the base of the stress concentration, so it is easier to crack and the formation of cracks. The crack deepens in the direction perpendicular to the direction of stress, usually in small strain (5%) only A small amount of cracks, the crack direction is clear, when the rubber multi direction stress is very difficult to distinguish the direction of the crack.
One, rubber smelly oxidation reaction mechanism
The reaction mechanism of ozone and unsaturated rubber can be explained in the light of the formula.
When ozone contact with rubber products, ozone, and active double bond occurred addition reaction, generate molozonide, molozonide is very unstable, quickly decompose and generate carbonyl materialized II and zwitterionic (3). In most cases amphoteric ion and carbonyl compounds will re knot synthesis of ISO ozonide, amphoteric ion can also polymerized peroxides or high peroxide, also when there is activity of methanol solvent, amphoteric ion can react with generation methoxy hydroperoxide (7).
Ozone and unsaturated rubber reaction activation energy is very low, very easy, double bonds in the reaction until the rubber consumption is completed so far. At this time in the surface of the rubber generation a layer of silver white loses its elasticity film, as long as there is no external forces to make the film cracking, rubber will no longer continue to ozone. If have ozonation rubber tensile or the dynamic deformation, generated ozone oxidation film will appear cracks, revealing new rubber surface can react with ozone, which allows for crack continues to grow.
Saturated rubber because of not containing double bonds, although it can react but slow reaction with ozone, not easy to crack.
There have been many people of unsaturated rubber production and growth of ozone cracking done research. These researchers according to experimental data, are presented and the mechanism of cracking growth. For example, some people think that the crack, because under stress because of ozone decomposition of molecular chain rupture produced. Tend to separate more than re combined tendency results. And the movement of crack growth and the concentration of ozone and rubber chain, when the ozone concentration, the greater the chain movement, crack growth more quickly. Some people think of ozone cracking production and growth of rubber and ozonation the formation of oxide layer and smelly raw rubber surface layer
Of things different. For example, Murray finds rubber of the ozonation process is common occurrence of physical and chemical processes. When the rubber is contacted with ozone, surface of the double bond quickly react with ozone, majority of the generated ozonide, originally soft rubber chain quickly turn into containing many ozonide ring of stiff chain. When the stress applied on rubber, stress the rubber chain stretching out and make more double bonds and ozone exposure, the rubber chains containing more ozonide ring, become more brittle, brittle surface in stress or dynamic should force is prone to cracking.