Ozone cracking

Ozone cracking in natural rubber

As ozone cracking the formation of characteristic cracks included in various elastomers and rubbers referred to by ozone produced. In the past, the problem was particularly widespread with tires , but now rarely occurs there due to preventive measures. In contrast, cracking is problematic in many other areas, including those that are critical to safety, such as fuel lines and rubber seals. A relatively low concentration of the gas is sufficient to initiate the formation of ozone cracks. Ozone in the air attacks double bonds in rubber, with natural rubber , polybutadiene , styrene-butadiene rubber and nitrile rubber being the most sensitive to decomposition.

The reaction between double bonds and ozone is called ozonolysis , when a molecule of the gas reacts with the double bond:

The problem can be prevented by adding antiozonants to the rubber before vulcanization . Ozone cracks were commonly found in car tire sidewalls but are rarely seen today thanks to the use of these additives . A common and inexpensive antiozonant is a wax that exudes on the surface and forms a protective layer, but other specialty chemicals are also widely used.

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  Macro photograph of ozone cracking in diaphragm seal of nitrile -butadiene rubber (NBR)

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  ESEM recording of ozone cracks in diaphragm seals made of NBR, which are formed at sharp corners

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  ESEM close-up of the ozone crack in NBR diaphragm seal

literature

• Richter / Blobner: Ozone cracks in elastomeric seals and components - a common but avoidable cause of failure , 2017.
• Lewis, Peter Rhys, Reynolds, K., Gagg, C .: Forensic Materials Engineering: Case studies , CRC Press (2004), ISBN 978-0-8493-1182-6 .
• Lewis, Peter Rhys: Forensic Polymer Engineering: Why polymer products fail in service , 2nd edition, Woodhead / Elsevier (2016), ISBN 978-0-08-100728-0 (e-book) or ISBN 978-0-08- 101055-6 (hardcover).
• YS Zuev: The Protection of Rubbers against Ozone Cracking. In: Rubber Chemistry and Technology. 28, 1955, p. 788, doi: 10.5254 / 1.3542839 .

Web links

Commons : Ozone Cracking  - Collection of Pictures, Videos and Audio Files

Individual evidence

1. ^ Robert W. Layer, Robert P. Lattimer: Protection of Rubber against Ozone. In: Rubber Chemistry and Technology . 63, 1990, p. 426, doi: 10.5254 / 1.3538264 .