PVDF
Polyvinylidene fluoride selection by resin grade, supplied form, exposure and fabrication process.
Tags: materials, polymers, fluoropolymers
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Identity and grade selection
Ensinger's TECAFLON PVDF natural gives a longitudinal coefficient of 16 × 10⁻⁵/K over 23–60°C. An assumed 100 mm free length heated uniformly across that interval expands 0.592 mm. Evaluate restraint and differential expansion before assigning a fit clearance. Ensinger TECAFLON PVDF stock-shape table
PVDF is polyvinylidene fluoride, a semi-crystalline thermoplastic fluoropolymer. Ensinger supplies TECAFLON PVDF natural as an unreinforced stock-shape material; its fact sheet marked 20-EN-10|25 describes rods, plates and tubes. Those product claims concern machinable stock, rather than every PVDF resin, coating or piping assembly. Ensinger: TECAFLON PVDF fact sheet
The purchase description should preserve the manufacturer, complete grade, homopolymer or copolymer identity, additives, color and supplied form. Arkema, for example, identifies Kynar 740 as a fluorinated homopolymer pellet for applications including tube and plaque extrusion, compression molding and transfer molding; it separately identifies Kynar 741 as a powder form. A resin's product documentation cannot automatically establish the performance of a machined, welded or coated component. Arkema: Kynar 740 technical datasheet
Stock-shape data and dimensional change
Ensinger's TECAFLON PVDF natural datasheet is dated 24 June 2024, version AF. It lists density of 1.78 g/cm³ and longitudinal thermal-expansion coefficients under DIN EN ISO 11359-1/-2:
| Temperature interval | Listed CLTE |
|---|---|
| 23–60 °C | 16 × 10⁻⁵ K⁻¹ |
| 23–100 °C | 18 × 10⁻⁵ K⁻¹ |
Its disclaimer identifies guideline values rather than guaranteed specification limits, generally obtained from extruded and machined reference specimens, typically 40–60 mm diameter rods. Dimensions and orientation can affect properties. Ensinger: stock-shape datasheet
For a precision valve seat, spacer or pump component, define the temperature at dimensional acceptance and the allowable operating deformation. Keep thermal expansion, molding shrinkage and permanent distortion as separate quantities.
Chemical resistance and exposure boundaries
Arkema explains that chemical resistance depends on concentration, time, temperature, pressure, cycling, abrasion and mechanical stress. Combined chemical exposure and load can produce stress cracking even when an unstressed material appears resistant. Its guidance also distinguishes PVDF homopolymers from flexible copolymers. A favorable family-level chart entry is therefore a screening result, not approval for an unspecified grade and duty. Arkema: chemical-resistance guidance
The same guidance warns that permeability and adhesion influence coating performance, so a coating may not behave exactly like melt-processed resin. Do not transfer bulk-resin compatibility to a thin coating, welded liner or multilayer construction without examining the whole system. Arkema: coating applicability
For qualification, identify the actual fluid mixture, impurities, cleaning chemicals, concentration, exposure duration and maximum excursions. Assess mass or dimensional change, retained mechanical performance and leakage or permeation as appropriate. A part may remain visually intact while failing a purity or containment requirement.
Temperature and pressure belong to the system
A supplier's stock-shape temperature rating is not a pressure rating. GF Piping Systems' Industrial Piping Systems, 08/2024, section 2.2.7, provides a concrete example: its PVDF pressure-temperature diagrams use a 25-year service-life basis and stated design factors. They apply to water or water-like media without a chemical-resistance reduction factor, with separate treatment for chemical applications. Valves and special fittings can have different limits because of construction and sealing materials. GF: design and installation, PVDF diagrams
GF explicitly limits these diagrams to liquid applications and recommends a strength check for changing operating conditions. Select the applicable curve, pipe dimensions, joints and component ratings together; neither a nominal pipe pressure class nor the highest temperature shown in a chart is a universal PVDF operating envelope. GF: PVDF chart conditions
For a new assembly, document continuous conditions separately from cleaning, startup, shutdown and fault excursions. Confirm which component and exposure determines the limit.
Processing and joining
Arkema's molding guidance explains that crystallinity makes shrinkage and void control important, especially in thick sections. Its Kynar 740 shrinkage table lists 2.8–3.5% in flow and 1.9–3.0% across flow, measured after 24 hours at ambient conditions, and states that actual shrinkage depends on part size and geometry. These are process-characterization ranges, not machining allowances or finished-part tolerances. Arkema: processing guidelines
Obtain the exact grade's tooling, melt-processing and venting recommendations. Verify internal soundness as well as external dimensions where a thick molded or machined section will contain pressure or carry load. Do not replace a molding recommendation with a stock-shape service temperature.
Fusion joining is also process-specific. Arkema lists heat-contact and hot-gas methods, among others, and labels its butt-welding table as recommended starting points for Kynar 740 on a Wegener machine. The table differentiates thickness, temperature, pressures and heating/cooling stages. That scope matters: it is not a universal recipe for every PVDF pipe, fitting, sheet or welding machine. Arkema: welding guidelines
Use the system supplier's qualified procedure, compatible joining materials and inspection requirements. Retain joint preparation, equipment settings, operator qualification and acceptance results where the application requires them. A satisfactory-looking bead alone cannot establish joint strength or leak integrity.
Purchasing, handling and validation
A useful material and component record includes:
- Complete grade, form, color/additives and approved substitution requirements.
- Property-source revision, specimen geometry, direction and test conditions.
- Manufacturing history, joints, supports and inspection requirements.
- Mechanical load, pressure, temperature and chemical exposures, including cycles.
- Cleanliness, extractables or regulatory requirements for the exact intended use.
- Finished-part acceptance tests and limits, including aging where relevant.
Request current safety and processing information for the exact resin or stock product before heating, machining or joining it. Keep raw-material certification separate from component and system qualification; a high-purity description does not define an extractables limit, cleaning method or medical approval.
The Ensinger documents above provide a dated version or printed document code, and the cited GF section carries an 08/2024 footer. The accessible Kynar 740 sheet carries an HPP footer dated 23 October 2026. Arkema’s cited web guidance does not establish a clear revision date; search-engine publication dates are not technical revisions. Verify the required edition at procurement.