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The connection between rubber deterioration and ozone

The first design considerations when working with rubber engineers should take into account the effect of ozone. This question must be asked - how much exposure should there be rubber and what is the life expectancy of the rubber product?
What can be done with ozone on rubber? Common effects include cracking along exposed, stretched, or stressed faces - this is sometimes referred to as dry rot.
Ozone can be found everywhere. Even "normal" air can have up to 0.01 ppm of ozone. The added electrical equipment or lighting can be increased at the ppm level.
Different rubber polymers have greater or less resistance to ozone - less saturated rubber polymers, for example, will experience greater ozone effects. Unsaturation is a polymer structure of double and triple chemical bonds, which becomes free radicals that are easily generated by ozone and breaks the amount of bonds.
The resistance of the material will determine which applications should be used such as car door seals and weather strips. These are usually made of EPDM, which is very stable in ozone and will last for a long time.
On a small road, it is used in oil or fuel-related applications. Even seals need some ozone resistance to prevent deterioration and storage after production.
Fortunately there are a number of different standard test methods that can help to classify when exposed to ozone, such as the behavior of ASTM D1171 specific rubber. Specifically, ASTM D1171's standard test method for rubber deterioration - surface ozone cracks outdoors or indoors (triangular specimens). The advantage of this method is that it can be tested against a predetermined level, producing a pass/fail status. This method can also be used to track the growth rate of cracks in the material and see how quickly it deteriorates.
This article is a room-based method. Apple Rubber utilizes a mast/trapezium 700-10 LTA ozone lab. This is just a sealed chamber with an additional ozone generator adjusted by ozone meters. This test uses a triangular shape from the desired material, which has a 0.075 inch triangular base with a 0.75 inch baseband 0.5 inch radius molded sample. The total length of the specimen is 10 inches long. These pieces are subsequently set in the strain position by fixing them with the wires and cycling them over two inches of mandrel.
Install specimens before testing
The test preparation allows the specimens to be mounted for 70-72 hours to move them to the ozone chamber for another 70-72 hours at room temperature in a lab environment at 40°C without ozone occurring. The pretreatment allows the wax to bloom to the surface, which protects the rubber if rubber-like part.
Specimen Room Exposure to Ozone
The standard test exposure then proceeds at an ozone concentration of 50±5 PPHM for 72 hours. After this period, the samples were taken out and given on a one-by-one basis. ) According to a magnification of 2 times, and b) the amount of cracking). It compares the numbers given in the description. It is also very common specimens that were marked at 24 hours and 48 hours were removed and given those time periods ratings, and the following are three examples of these materials after the 72-hour period. The material is an ethylene-propylene (EPDM) rubber, silicone, and HNBR material. These materials tend to do very well, and there are 0 good evaluation times when compared to ozone degradation specifications.
From the top: EPDM rubber, silicone rubber, hydrogenated nitrile rubber and rubber The final test piece is a nitrile, which is not very resistant to ozone, which can grow through the strained portion of the sample. There will be three comparative evaluations of this sample, which is the worst grade for this specification. One can quickly understand that even though nitrile (nitrile) rubber is readily available, it may not be the best choice.
As an example, the design we usually see is a failed medical device. In the initial test, some of the parts may work well. On-site testing, however, may fail because the seal is exposed to ozone, which can lead to a certain degree of degradation and lead to failure. Sometimes, design engineers can even see the behavior of this process, even if they just want medical devices to sit on their desks for a long time.
Nitrile rubber (nitrile rubber) rubber
Sometimes, with the known ozone very wear-resistant materials (such as ethylene propylene), some product developments can also choose to increase the exposure time followed by the second half of the test method. In this case, the exposure time in the ozone chamber was increased to six weeks to pull out a sample that was checked for signs of cracking every two weeks.
Another long-term exposure application is conducted by the Underwriters Laboratories (UL). This application uses a test method called UL 157 listed atmospheric ozone and produced ozone compounds. The mounted specimens were subjected to 90-110 MPa, 70-hour partial pressure of ozone and 40±2°C (104±3.6°F), used to cover atmospheric ozone applications at a temperature of 10,000 and ozone partial pressure - 15000 MilliPascal for 70 hours and 40±2°C (104±3.6°F) for the temperature of the application covering the generated ozone. There are two compounds in apple rubber, 14SL7ML and 35SL5ML, that is UL's end-use list. These two compounds are silicone polymers.
The last method used by some developers for this test method is the outdoor exposure, not the controlled room. In this way, the parts are mounted so that they are exposed facing south at an angle of 45° from the ground. The advantage of this method is that real-time exposure weathering can be done.
However, the same real-time exposure can also be a disadvantage. It is not always part of a workable design, and when it is seen it starts to deteriorate, using weather/ozone resistant materials especially when the waiting time is extended for this time.
When the rubber polymer is attacked by ozone, a mix of waxes and angiozondiants (chemicals added to the formulation of the polymer skeleton that clears the free radicals produced by them before attacking them) is used to protect the rubber. The wax blooms to the surface and protects the rubber by slowing the penetration of ozone. This is common when buying new tires - consumers can see wax on the surface of new tires. This is also why people who buy new bike or motorcycle tires should ride slowly, remove the wax and create the correct road friction before using it normally.
EPDM rubber, silicone, hydrogenated nitrile rubber, neoprene, fluoroelastomer, and fluorosilicone rubber must have greater ozone resistance. Nitrile (NBR), natural rubber, and SBR are more susceptible to ozone attack. The design should always consider whether the rubber part will be exposed to ozone - even in storage. After how long, once exposed, what part do you want to last? Will there be a motor or equipment close to the rubber? These are the key design issues first considered before the rubber needs to be selected.

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