Why do we need to conduct ozone aging tests?

I. Definition of Ozone Aging

Ozone aging is a technique designed to evaluate the aging resistance of ozone-sensitive materials such as rubber and certain plastics. By simulating environmental conditions, this method accelerates the ozone-induced degradation process of rubber to assess its durability. Ozone primarily resides in the Earth's ozone layer, located within the stratosphere (approximately 20 kilometers above sea level). However, trace amounts of ozone also exist in the surface atmosphere, originating from natural electrical discharges (e.g., lightning) and photochemical reactions—such as the formation of ozone from nitrogen oxides (NOx) in vehicle exhaust under UV irradiation. Due to the susceptibility of many rubber and plastic materials to ozone, even low concentrations can induce cracking. To mitigate this issue, ozone aging tests are critical for material evaluation and improvement.

II. Ozone Aging Test Procedure

Under static tensile strain conditions, specimens are exposed to a sealed test chamber with controlled ozone concentration, temperature, and humidity. The onset of cracking is periodically inspected. The following evaluation methods can be adopted based on selected ozone concentrations and test temperatures:

• a) After a specified test duration, inspect the specimen for any signs of cracking. If required, assess the severity of cracking.
• b) Determine the shortest time to crack initiation under a predefined tensile strain.
• c) Measure the critical strain at a specified exposure duration.

III. Mechanism of Ozone Corrosion

Ozone's oxidative properties cause the rupture of unsaturated organic molecules. Ozone molecules react with double bonds in organic compounds, forming ozonides. Spontaneous fragmentation of ozonides yields a carboxyl compound and a zwitterion (an unstable molecule with acidic and basic groups), which further decomposes into acids and aldehydes. Additionally, ozone is inherently unstable and readily dissociates into oxygen and reactive oxygen atoms. These atoms aggressively react with organic materials, causing degradation.