PVDF (Polyvinylidene Fluoride)

Definition and Classification

PVDF (polyvinylidene fluoride) is a fluoropolymer based on the monomer vinylidene fluoride. It belongs to the thermoplastics — that is, plastics that become soft when heated and can be processed in that state. In sealing technology, this classification is important because, as a result, PVDF is used rather for dimensionally stable sealing parts than for elastic seals such as O-rings, which are typically made of elastomers.

From a materials science point of view, PVDF is semi-crystalline. This means the material contains ordered crystalline and disordered amorphous regions. From this structure, the typical property profile follows: PVDF combines high chemical resistance with comparatively good strength and stiffness for a fluoroplastic. In media-contacting components in fluid technology, it is therefore frequently chosen where aggressive media occur and dimensional stability is still required — for example in valves or linings.

Typical baseline values (guideline values, depending on grade and test conditions) are:

Why “Semi-Crystalline” Matters in Practice

Semi-crystallinity influences how PVDF behaves under pressure, temperature, and medium. The crystalline regions contribute to stiffness and to a certain barrier effect — that is, to lower substance permeability (permeation) than with some other plastics. The amorphous regions influence toughness and deformation behavior.

For sealing functions, this becomes specifically relevant when a sealing part has to maintain its geometry under contact pressure and, at the same time, mass transport through the material has to be limited — for example with gas- or solvent-containing media.

Properties: Temperature, Mechanics, and Permeation (Seal-Oriented)

PVDF is often described in data sheets with a continuous-use temperature range around $\sim 150\text{ °C}$. For sealing technology, however, what is decisive is what acts simultaneously: temperature, pressure, contact pressure, and motion. Under high mechanical stress, the tendency to deform rises, and with increasing temperature, creep increases. Creep means that a plastic slowly deforms plastically under sustained load, even when the load remains constant.

Compared with PTFE, PVDF is frequently stronger and stiffer and, in many applications, less prone to creep. This can be helpful with seat seals or sealing and back-up rings, because contact forces are better maintained. At the same time, PVDF remains a thermoplastic, so that with an unfavorable combination of high temperature and high surface pressure, a settling deformation can still lead to failure.

Another selection criterion is permeation. Permeation describes how strongly media molecules diffuse through a material. In practice, this affects emissions, odor, pressure loss, or media migration. PVDF can offer a more favorable barrier in many cases than some standard plastics, but the assessment must always be made on a media- and temperature-specific basis.

What “Up to 150 °C” Means in Sealing Operation

The value is a guideline for continuous operation under defined conditions. In sealing operation, frictional heat is often added — for example at moving sealing points or in valve seats with frequent switching cycles. At the same time, pressure raises the contact pressure, and thereby the likelihood of creep rises. Therefore, the permissible temperature is in practice frequently limited by the specific load case.

Under strong overheating, fluoropolymers can decompose and release decomposition products that are problematic from a health perspective. From an operational safety point of view, a temperature and load match with a safety margin is therefore sensible — particularly with dynamic applications.

Chemical Resistance: Typical Media and Known Limits

PVDF is considered very resistant to many inorganic acids, salt solutions, and many hydrocarbons. It is therefore frequently chosen when components are permanently in contact with media and corrosion or extraction with metals — or swelling with other plastics — would be critical.

Limits are mainly discussed in practice where very reactive or strongly interacting media are present. These include strongly basic media (high pH), amines, and certain strongly polar solvents — particularly at elevated temperature. In such cases, swelling can occur — that is, media uptake with dimensional change — or chemical attack. Under mechanical stress, the risk of stress cracking additionally rises — that is, crack formation through the interplay of stress and chemical action.

For material selection, this means: it is rarely the medium alone that decides, but the combination of chemistry, temperature, and mechanical loading. With critical media, media-specific testing or a reliable compatibility approval is customary.

Use in Sealing Technology and Material Comparison (PVDF vs. PTFE), Including Risks/Compliance

In sealing technology, PVDF is used primarily where a sealing function has to be combined with dimensional stability. It is well suited for components that act as sealing partners or sealing carriers and at the same time must be chemically robust. For classic elastic sealing elements (O-rings), by contrast, PVDF is rarely chosen, because elastomers with defined recovery force are customary here.

Important misuse risks arise from the load profile: too high a temperature with simultaneously high surface pressure can amplify creep. Critical media can promote swelling or stress cracking. Thermal overload is also relevant from an occupational safety and plant perspective.

From a regulatory point of view, purity and conformity requirements can be important depending on the application field — for example FDA or USP Class VI references in pharma and life-science applications. In addition, PVDF is discussed in many contexts as part of the PFAS substance group. Whether and how this is relevant for a specific application depends on internal approvals, customer requirements, and the regulation in force at the time.

Typical PVDF Sealing and Valve Components

• Valve seat seals and seat rings (soft seats, sealing and back-up rings)
• Linings in fittings or pipe components
• Media-contacting valve and fluid technology components with a sealing function in a composite

Brief Comparison: PVDF vs. PTFE for Sealing Tasks

In practice, the decision is made via the specific sealing case: medium, temperature, pressure, geometry, motion, and permissible leakage act together. In case of uncertainty, application-specific material testing or specialized consultation is sensible.