Introduction
Ozone (O₃), a highly reactive allotrope of oxygen, is a strong oxidizing agent that readily attacks double bonds, unsaturated polymers, and many organic materials. Its impact on elastomers varies greatly depending on the molecular structure and chemical stability of the material. Two commonly used materials in high-performance sealing and insulation applications—Teflon (polytetrafluoroethylene, PTFE) and Viton (fluoroelastomer, typically a copolymer of vinylidene fluoride and hexafluoropropylene)—exhibit markedly different behaviors when exposed to ozone.
Ozone and Teflon (PTFE)
Teflon’s exceptional chemical inertness arises from its fully fluorinated carbon backbone (–CF₂–CF₂–). The strong C–F bond (≈485 kJ/mol) and the shielding effect of fluorine atoms make PTFE extremely resistant to attack by oxidizing species, including ozone. When ozone contacts Teflon under ambient conditions, no observable reaction occurs: the gas cannot insert into or break the C–F bonds, nor can it abstract fluorine atoms due to the high bond dissociation energy and lack of available reactive sites.
Only under extreme conditions—such as elevated temperatures (>300 °C) or high-energy plasma containing atomic oxygen—can ozone or oxygen species initiate degradation. In such cases, chain scission may occur at C–C bonds rather than C–F bonds, leading to formation of small perfluorinated fragments (e.g., CF₄, COF₂). However, these reactions are not characteristic of normal environmental exposure. Therefore, PTFE is considered immune to ozone cracking, and its mechanical and dielectric properties remain unchanged even after prolonged exposure.
Ozone and Viton (Fluoroelastomer)
In contrast, Viton, while also a fluorinated polymer, contains a partially fluorinated backbone and may include small amounts of unsaturation depending on the specific grade. Ozone reacts primarily with carbon–carbon double bonds through the ozonolysis mechanism:
- O₃ adds across a C=C bond forming a molozonide intermediate.
- The unstable molozonide rearranges to form ozonide and eventually cleaves, producing carbonyl compounds and peroxides.
- The resulting chain scission reduces molecular weight and elasticity, leading to surface cracks oriented perpendicular to tensile stress.
Modern Viton formulations minimize unsaturation, but trace double bonds at chain ends or in curing sites can still undergo ozonolysis, causing gradual embrittlement and surface degradation. As a result, although Viton exhibits better ozone resistance than traditional hydrocarbon rubbers, it is not completely inert.
Comparative Summary
| Property | Teflon (PTFE) | Viton (Fluoroelastomer) |
| Chemical structure | Fully fluorinated, no C=C bonds | Partially fluorinated, may contain C=C or cure-site unsaturation |
| Primary ozone reaction | None under normal conditions | Ozonolysis at double bonds |
| Result of exposure | No effect on physical properties | Surface cracking, chain scission, loss of elasticity |
| Temperature for degradation | >300 °C | May degrade at ambient temperature over time |
Conclusion
Ozone exerts negligible chemical or physical effects on Teflon due to its fully fluorinated, saturated molecular structure. In contrast, Viton is moderately resistant but still susceptible to ozone attack at residual unsaturated sites. For applications where long-term ozone exposure is expected—such as in corona discharge environments or outdoor sealing systems—PTFE remains the material of choice, while Viton requires protective additives or controlled conditions to ensure longevity.