PFAS

Definition: What Are PFAS, and Why Are They “Persistent”?

PFAS stands for per- and polyfluoroalkyl substances. The term does not refer to a single chemical but to a very large class of synthetic organic fluorine compounds. PFAS are substances that contain at least one fully fluorinated carbon atom — for example as a –CF₃ group or as a –CF₂– unit in a chain. This structure matters for classification in technology and regulation because it ties to a chemical core feature, not to individual trade names.

The term “persistent” describes that many PFAS are only very slowly broken down in the environment. The reason lies in the strong C–F bond and the overall high chemical stability of strongly fluorinated structures. This stability is often technically desirable (resistance to media, temperature, and aging) but, in environmental contexts, leads to substances persisting over long periods of time and, depending on the substance, also migrating or accumulating. In the discussion, it is also relevant that PFAS can include both low-molecular substances (small molecules) and polymers (high-molecular materials). These groups differ in properties, exposure paths, and assessment, but they are sometimes considered together under a common umbrella term in regulation.

Why PFAS Were Long the Standard in Sealing Technology

In sealing technology, the combination of medium, temperature, pressure, type of motion (static/dynamic), and required service life frequently decides. Fluorinated materials became the standard in many applications because they could cover several of these requirements simultaneously and well. Typical features are high media resistance against aggressive or strongly additivated fluids, a broad temperature window, and good aging stability (for example against oxidation).

For dynamic sealing points in particular, friction and stick-slip are also relevant. Stick-slip describes jerky sliding due to alternating static and sliding friction, which can cause problems in control loops, positioning tasks, or at low speeds. As a result, fluorinated polymers and coatings can contribute, depending on the system, to low friction and more stable sliding behavior here. In addition, wetting and permeation play a role: some media diffuse through materials or change their surface behavior, which affects tightness and long-term stability. The sum of these effects leads in many cases to long service lives but makes substitution demanding.

Which PFAS-Related Material Families Are Typically Affected

PFAS relevance arises in sealing technology mainly where fluorinated polymers or auxiliary substances are used. Typical categories are:

Which of these categories is actually affected depends on the specific sealing system. In hydraulics and pneumatics, fluorinated materials frequently appear where high temperature, aggressive additive packages, low leakage, and reproducible friction behavior come together.

Why PFAS Are Being Regulated

Regulatory pressure arises mainly from the combination of persistence and potential environmental and health risks that are particularly intensively discussed for certain well-studied low-molecular PFAS. In the EU, PFAS is moreover the subject of dynamic REACH processes, and internationally further requirements exist — for example for selected PFAS in drinking water or extensive reporting obligations in individual jurisdictions. For technical decision-makers, the individual detail is less decisive than the direction: the material corridor is narrowing, and the requirements for documentation, verification, and risk assessment are rising.