Ozone is a highly reactive gas composed of three oxygen atoms (O₃). It exists in the Earth's atmosphere, both in the stratosphere, where it forms a protective layer against harmful ultraviolet radiation, and at ground - level, where it is considered a pollutant. As a supplier of NBR (Nitrile Butadiene Rubber) seals, understanding the impact of ozone on NBR seals is crucial for providing high - quality products and ensuring customer satisfaction.
Chemical Reaction between Ozone and NBR
NBR is a synthetic rubber copolymer made from acrylonitrile and butadiene. The double bonds in the butadiene part of the NBR structure are vulnerable to attack by ozone. When ozone comes into contact with NBR, it reacts with these double bonds through a process called ozonolysis.
The reaction mechanism involves the initial formation of a cyclic intermediate called a molozonide, which is highly unstable. This molozonide quickly decomposes into a carbonyl compound and a zwitterion. The zwitterion then reacts further to form a secondary ozonide. These chemical reactions lead to the breaking of the polymer chains in the NBR, which has significant consequences for the physical and mechanical properties of the seals.
Physical and Mechanical Property Changes
Cracking
One of the most visible impacts of ozone on NBR seals is the formation of cracks. Ozone - induced cracks typically start on the surface of the seal and propagate inward. The cracks are often perpendicular to the direction of stress on the seal. In static applications, where the seal is not subject to significant movement, ozone can cause surface cracks over time. In dynamic applications, where the seal is constantly flexing, the cracking process is accelerated. These cracks can compromise the integrity of the seal, allowing fluids or gases to leak through. For example, in pneumatic systems, a cracked NBR seal can lead to loss of pressure, reduced efficiency, and potential system failure.
Hardening and Brittleness
As the polymer chains in NBR are broken down by ozone, the rubber becomes harder and more brittle. This change in hardness affects the seal's ability to conform to the mating surfaces. A hardened NBR seal may not be able to maintain a proper seal under pressure, leading to leakage. In addition, the brittleness makes the seal more prone to breaking during installation or operation. For instance, in automotive engines, where NBR seals are used in various components such as oil seals and gaskets, hardening and brittleness can cause premature failure of the seals, resulting in oil leaks and potential engine damage.
Reduction in Tensile Strength and Elongation
Ozone exposure also reduces the tensile strength and elongation at break of NBR seals. Tensile strength is the maximum stress that a material can withstand before breaking, while elongation at break is the percentage increase in length of the material before it fractures. As ozone attacks the NBR, the polymer chains are weakened, leading to a decrease in both tensile strength and elongation. This means that the seal is less able to withstand mechanical forces without breaking. In industrial applications, such as hydraulic systems, a reduction in tensile strength and elongation can cause the seal to rupture under high - pressure conditions, leading to system downtime and costly repairs.
Factors Affecting the Impact of Ozone on NBR Seals
Ozone Concentration
The higher the ozone concentration in the environment, the more severe the impact on NBR seals. In industrial areas with high levels of air pollution, where ozone concentrations can be several times higher than in clean air, NBR seals are at a greater risk of ozone - induced damage. For example, in chemical plants or near busy roads with heavy traffic, the increased ozone levels can accelerate the degradation of NBR seals.
Temperature
Temperature also plays an important role in the ozone - NBR interaction. Higher temperatures generally increase the rate of chemical reactions, including the ozonolysis of NBR. At elevated temperatures, the polymer chains in NBR are more mobile, which makes them more susceptible to attack by ozone. On the other hand, very low temperatures can make the NBR more brittle, and the combination of low - temperature brittleness and ozone exposure can further reduce the seal's performance.
Stress
The level of stress on the NBR seal affects the development of ozone cracks. Seals that are under constant tension or compression are more likely to develop cracks than those in a stress - free state. The stress can cause the polymer chains in the NBR to align in a certain direction, making them more vulnerable to ozone attack along the direction of alignment.
Mitigation Strategies
Ozone - Resistant Formulations
To improve the ozone resistance of NBR seals, manufacturers can use special formulations. One approach is to add antioxidants and antiozonants to the NBR compound. These additives react with ozone before it can react with the polymer chains, thereby protecting the rubber. Antiozonants such as para - phenylenediamines are commonly used in NBR compounds to provide long - term ozone protection.
Coating and Encapsulation
Another strategy is to apply a protective coating or encapsulation to the NBR seal. The coating can act as a barrier between the NBR and the ozone, preventing direct contact. For example, a thin layer of fluoropolymer coating can be applied to the surface of the NBR seal. This coating not only provides ozone resistance but also offers other benefits such as improved chemical resistance and reduced friction.
Applications and Considerations
Pneumatic Systems
In pneumatic systems, NBR seals are widely used to prevent the leakage of compressed air. However, due to the presence of ozone in the environment, especially in industrial settings, the seals are at risk of ozone - induced damage. When selecting NBR seals for pneumatic applications, it is important to consider the ozone concentration in the operating environment. For long - term performance, Long - life Pneumatic Cylinder Nbr Seal Ring Gasket with ozone - resistant formulations should be used.
Automotive Industry
In the automotive industry, NBR seals are used in various components such as engine seals, transmission seals, and fuel system seals. Ozone can affect the performance of these seals, leading to oil leaks, fuel leaks, and reduced engine efficiency. Automobile manufacturers need to ensure that the NBR seals used in their vehicles are ozone - resistant, especially in regions with high ozone levels. Long - life Waterproof Wearproof Viton Epdm Oil Seal Ring can be a good option for automotive applications where ozone resistance is required.
Industrial Machinery
Industrial machinery often operates in environments where ozone is present, either due to air pollution or as a by - product of certain manufacturing processes. NBR seals in industrial machinery need to be able to withstand ozone exposure to ensure reliable operation. For applications such as hydraulic pumps and valves, Long - life Waterproof Washer Shaft Oil Seal Ring with ozone - resistant properties can be used to prevent leakage and extend the service life of the machinery.
Conclusion
As a supplier of NBR seals, it is essential to understand the impact of ozone on these seals. Ozone can cause significant changes in the physical and mechanical properties of NBR, including cracking, hardening, and reduction in strength. However, through the use of ozone - resistant formulations, coatings, and proper selection of seals for specific applications, the negative effects of ozone can be mitigated.
If you are in need of high - quality NBR seals that can withstand ozone exposure, please feel free to contact us for more information and to discuss your specific requirements. We are committed to providing the best sealing solutions for your applications.
References
- Morton, M. (1973). Rubber Technology. Van Nostrand Reinhold.
- ASTM D1149 - 10. Standard Test Method for Rubber Deterioration - Cracking in an Ozone - Containing Atmosphere.
- Brydson, J. A. (1999). Plastics Materials. Butterworth - Heinemann.