Ozone aging of rubber
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Release time:
Aug 11,2021
Ozone is also a very important reason for the aging and deterioration of rubber in the atmosphere. Ozone aging is first in the surface layer, especially at the stress concentration or at the interface between the particles and the rubber. Usually, a thin film is formed, and then the thin film cracks. Especially when used under dynamic conditions, the thin film is more likely to crack and expose fresh surface, making ozone aging develop in depth until it is completely destroyed.
One. Characteristics of Ozone Aging
Ozone aging of rubber is a surface reaction.
2. Ozone cracking of rubber requires a certain stress or strain, and the surface of unstretched rubber after ozone aging forms a hard and brittle film similar to spray frost. Under the action of stress or strain, ozone cracking occurs in the film.
3. The crack direction of ozone cracking is perpendicular to the direction of force.
II. Factors Affecting Ozone Aging of Rubber
1The impact of the type of rubber:
（1) Double bond content:The higher the content of double bond, the worse the resistance to ozone aging;
（2) Characteristics of substituents on carbon atoms of double bond:The electron-withdrawing substituent reduces the reactivity of the double bond and reduces the ozone reactivity; the electron-donating substituent increases the electron cloud density, improves the reactivity of the double bond and improves the ozone reactivity. For example, the ozone aging resistance of CR, BR and NR is CR>BR>NR.
2Effects of Ozone Concentration
The higher the concentration of ozone, the worse the resistance to ozone aging;
Under the same ozone concentration, the rubber structure is different, and the ozone aging characteristics are different. For example, NR produces cracks in a short time, but the growth rate of cracks is slow; SBR, BR, and NBR require a long time to produce cracks, but the growth rate of cracks is fast.
3. Effect of stress and strain:
Ozone attack the surface of the rubber, aging on the surface, the surface of the formation of ozonous oxide film, ozonous oxide film is relatively hard, brittle, can prevent the ozone to the internal penetration, but under dynamic conditions, the aging film is easy to rupture, ozone and rubber reaction, and finally make the rubber fracture.
The number of cracks produced by low elongation is small, the crack growth rate is fast, and the crack is deep; the number of cracks produced by high elongation is large, the crack growth rate is slow, and the crack is shallow.
4The effect of temperature
As the temperature rises, the ozone aging speed is accelerated.
Three. Ozone aging protection
1. Physical Protection Method:
The third scenario is most commonly used. To prevent the aging of rubber ozone wax is divided into paraffin wax and microcrystalline wax.
Paraffin: composed of straight chain alkanes, low molecular weight, high crystallinity, the formation of large crystals, melting point range of 38~74 ℃.
Microcrystalline wax: Residue of high molecular weight petroleum, consisting mainly of branched or isoparaffins, formed in small, irregular crystals, melting point 57-100 ℃.
Wax is a relatively brittle material, in the dynamic case, the wax film is prone to dynamic rupture, so in the dynamic case should use wax and anti-ozone agent and other methods.
2Chemical Protection Method
Chemical anti-ozonants are added to the rubber, and chemical anti-aging agents can be used under dynamic and static conditions. The dosage of anti-ozone agent is generally 1.5 to 3.0 parts, almost all of which are nitrogen-containing compounds. Commonly used are p-phenylenediamines.
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