by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

The Basics of PVDF

Kynar PVDF (property of Arkema) is a high purity polymer that combines extreme-temperature performance, easy manufacturability, and durability in some of the harshest environments. 

What is PVDF?

PVDF (polyvinylidene difluoride or polyvinyl fluoride) is a fluorinated thermoplastic resin that is classified as a specialty polymer whose brand names include Kynar (Arkema), KF (Kureha), and Solef or Hylar (Solvay). This engineering polymer can often be found in environments that involve high purity, hot acid, extremely high temperatures, and/or radiation. 

Where is PVDF Used?

PVDF is used extensively in a wide range of industries. Semiconductor manufacturing makes use of PVDF’s ultra-pure status and its ability to perform in harsh environments that may involve extreme temperatures and aggressive chemicals. Electronics and electricity applications depend on PVDF’s outstanding low smoke emission and fire-resistant properties along with electrical properties for use as wiring insulation.

PVDF’s ability to handle radiation makes it an excellent choice for nuclear waste handling, and its high-temperature performance and chemical compatibility lends itself readily to the oil and gas industry. Because PVDF has excellent high-temperature performance, high purity, and low permeability, excellent strength, and chemical compatibility, it is used extensively in chemical processing.

Purity and FDA approval have made it a popular choice in food and beverage packaging and processing as well as pharmaceutical processing. It is often used in connection with water and wastewater management for similar reasons. PVDF is also used extensively in the medical market and healthcare industry where it is used as a biomaterial for medical textiles, such as hernia meshes, as well as for medical sutures.

The transportation and energy market has begun using PVDF as a binder for cathodes and anodes in HEV/EVs (Hybrid Electric Vehicle/Electric Vehicle). Its chemical compatibility and anti-corrosion properties make it useful as a barrier liner for fuel lines and tanker trailer lines. Aviation also makes ample use of PVDF for wiring harnesses and general coatings

How is PVDF Used?

PVDF is commonly used for several specific types of applications across industries:

  • Pump assemblies
  • Heat exchangers
  • Tanks and vessels
  • Nozzles
  • Sensors and actuators
  • Fittings, pipes, tubing, and valves
  • Membranes, including microfiltration membranes
  • Filters and filter housings
  • Liners and films
  • Cable jacketing and harnessing
  • Biocompatible materials

Key Properties of PVDF

As alluded to in previous sections, PVDF possesses several features of interest to engineers:

  • Extremely high purity with low permeability
  • FDA compliant and non-toxic
  • Excellent heat resistance and thermal stability 
  • Good mechanical properties
  • Resistant to a wide range of aggressive chemicals
  • Resistant to UV exposure, ozone oxidation reactions, and radiation
  • Resistant to the growth of microorganisms
  • Excellent burn characteristics 
  • Good manufacturability
  • One of the lowest melting points of commercial fluoropolymers
  • Excellent electrical properties
  • Excellent abrasion resistance
  • Low density (1.78 gm/cm3)
  • Recyclable

In addition, PVDF offers excellent abrasion resistance, is lightweight, and can be recycled. Also, note that there are additives available for PVDF to enhance its properties and its melt processability.

Purity and FDA Compliance

In addition to being an extremely high purity polymer, PVDF is both FDA compliant and non-toxic while exhibiting very low gas and liquid permeability.

Heat Resistant and Thermal Stability

One of the outstanding features of PVDF lies in its excellent performance, chemical stability, and dimensional stability in high-temperature environments with a service temperature rating of up to 300 F.

Mechanical Properties

Among the outstanding mechanical properties possessed by PVDF are good deflection, tension, compression, and torsion when compared to other fluorinated polymers. In addition, its low rate of water absorption (0.4%) means that it will remain dimensionally stable (not swell) when in a moisture-rich environment. In addition, PVDF has excellent impact strength.

Chemical Compatibility

PVDF is known for its excellent chemical compatibility that includes weak and strong acids (including mineral and organic); alcohols; aromatic and aliphatic solvents; weak bases; hydrocarbons; halogenated compounds; ionic and salt solutions; and oxidants. Its primary weaknesses are caustics, esters, strong bases, and ketones. 

Microorganism Growth

The surface of PVDF is highly resistant to the growth of microorganisms, including bacteria, fungi, and mold. It is also resistant to weathering, grime, and even graffiti (which is why it is often used in the architectural industry).

Burn Characteristics

PVDF has excellent flame and smoke properties, including UL 94 V-0 rating indicating it is both non-flammable and self-extinguishing along, or more specifically “Burning stops within 10 seconds on a vertical specimen; drips of particles allowed as long as they are not inflamed.” In addition, certain grades of PVDF also possess an excellent flame spread/smoke developed rating of 25/50 (when tested in accordance with ASTM E 84).

Manufacturability

PVDF is also highly manufacturable and melt-processable, lending itself to precision machining, rotomolding, compression molding, injection molding, and extrusion as well as subsequent welding and fabrication. Its ability to be used in molding is primarily due to its low melting point of 352 F, compared to PTFE at 621 F or FEP at 517 F.

Electrical Properties

In addition to electrochemical stability, PVDF also possesses a very high dielectric constant (280 volts per meter) and a high piezoelectric constant. In fact, it possesses both piezoelectric and pyroelectric properties.

Conclusion

One of the polymers we work with here at Advanced EMC is PVDF Kynar made by Arkema. If you are interested in Kynar, have questions about its usage and processing, or need a quote, feel free to contact us and we will have one of our experts respond right away.

by Sara McCaslin, PhD Sara McCaslin, PhD No Comments

Injection Molding of Fluoropolymers: What You Need to Know

Injection Molded Parts

Fluoropolymers are used in multiple industries, including aerospace, transportation, chemical and petrochemical processing, pharmaceutical, medical, telecommunications, and electronics where they are used for seals, gaskets, bushings, bearings, hoses, tubing, wiring, and even fiber optic cladding. There are multiple ways to manufacture parts and components made from fluoropolymers, and injection molding is one of them.

What Are Fluoropolymers?

Fluoropolymers, as the name no doubt implies, are polymers that are based on bonding between fluorine and carbon. The first fluoropolymer was PTFE (polytetrafluoroethylene), which is perhaps better known by its trade name Teflon. Other common fluoropolymers include ETFE (ethylene tetrafluoroethylene), PFA (perfluoroalkoxy alkane), PVDF (polyvinylidene fluoride), PVF (perfluoralkoxy), FEP (fluorinated ethylene propylene), and ECTFE (ethylene chlorotrifluoroethylene).

They are popular materials because of their properties that include resistance to high temperatures, chemical attacks, and electrical current. They are also low friction, non-toxic, exhibit minimal aging and leaching of chemicals, and non-stick. In addition, many fluoropolymers are biocompatible, making them ideal for medical applications.

Injection Molding Process

Injection molding is a manufacturing method for thermoplastic materials where the plastics are heated almost to their melting point and then fed into aluminum or steel molds at extremely high pressures using a powerful screw mechanism. There are several benefits to injection molding:

  • Can handle high-volume production
  • Labor costs are relatively low
  • Products highly accurate parts that can meet tight tolerances
  • Consistent results
  • Supports fairly complex designs with fine details
  • Produces an excellent surface finish
  • In many instances, the scrap can be recycled

The major cost involved in injection molding is the tooling: to achieve good results, the molds must be high-quality and well designed. However, molds can be configured to make multiple parts at one time with minimal post-processing.

Note that injection molding can be used to manufacture otherwise challenging components, including thin-walled parts. The feasible envelope for parts can typically range from 0.01 in³ to 80 ft³ (depending on the fabricators’ capabilities) and can achieve tight tolerances and smooth surfaces.

Injection Molding Fluoropolymers

While fluoropolymers can be challenging to injection mold, the process is not impossible for most materials. Some of the best fluoropolymers for injection molding include PFA and FEP, which are both melt-processable. Additional consideration may have to be given to the tooling for molding fluoropolymers, including a hot runner system to keep the polymer flowing easily as it moves through the mold. 

PTFE, however, is challenging to injection mold because even when heated above its melting point because it simply will not flow like other thermoplastic polymers. It does soften, but not enough to make injection molding possible. Fortunately, there are several other options when it comes to manufacturing with PTFE, including machining, compression molding, cold extrusion, and isostatic pressing.   

Conclusion

Fluoropolymers are widely used in many different industries and applications. If you are looking for an effective way to reliably manufacture components using a fluoropolymer, injection molding may be an excellent option.

Want to learn more? Contact us today!