Parylene vs. PTFE (Teflon) Coating

Whether you’re manufacturing electronics or medical equipment, the coating you use can make all the difference. Parylene and PTFE (Teflon) are versatile coatings used in many of today’s medical, industrial and commercial industries. Both are used to enhance strength, function, and increase the life cycles of everyday products. To better understand and compare the two coatings, it pays to take a look back at their history as well as the ways they’re used today. Let’s dive in.

The Discovery of Parylene

Parylene, or poly paraxyxylene, was discovered by British chemist Michael Szwarc in 1947 as he was conducting experiments on chemical bonds between carbon and benzene rings. Szwarc produced the polymer through the thermal decomposition of p-xylene at a temperature of 700-900 degrees Celsius. He confirmed the product as para-xylylene by reacting the vapors with iodine. Szwarc’s observations inspired further research by DuPont, Kellogg, and Polaroid.

William F. Gorham at Union Carbide found a more efficient route to produce the polymer in a way that reduced the gaseous by-products. In February of 1965, the new polymeric coating system was given the title of Parylene. Union Carbide continued to produce 20 types of Parylene, but only three were deemed commercially viable.

Features and Uses of Parylene

Today, Parylene is used in virtually every global industry and is considered to be the ultimate coating for the protection of devices, components, and surfaces in electronics, aerospace, medical device and other engineering-driven industries. Parylene’s ultra-thin lightweight film provides pinhole-free protection against the effects of fluids and solvents. For an in-depth look at how it works, you can download VSi Parylene’s Complete Guide to Parylene Coatings.
With its bio-compatible composition, parylene is widely used in the medical sector. Typical products coated with Parylene include coronary stents, probes, needles, catheters, hearing aids, and medicine bottles.

Other benefits are as follows:

• PFAS-free lubricious coating alternative to PTFE
• High stability since it is inert and insoluble in most solvent systems within its temperature range.
• Extremely high dielectric strength of 7 kV/mil.
• Acts as a dry film lubricant, eliminating the need for liquid release agents.
• Provides protection from moisture, corrosive bodily fluids, chemicals, gases, temperature, and fungus.
• Sterilization has little impact on Parylene’s physical properties.
• Parylene is optically clear to allow markings under parylene to be seen.

Other popular uses of Parylene coating include:

• Military and defense parts
• Semiconductor products
• LEDs
• Corrosion protection for metallic surfaces.
• Microwave electronics.
• Wires and cables

PTFE’s Accidental Discovery

Polytetrafluoroethylene (PTFE) was discovered by accident in 1938 when Dr. Roy J. Plunkett produced the substance with a sample of frozen, compressed tetrafluoroethylene (TFE). Thinking that the canister of TFE was malfunctioning, Dr. Plunkett cut it in half where he discovered a white flake, a polymer, had developed inside.

Dr. Plunkett ran further tests on the substance and found it was impossible to polymerize. It was also one of the most slippery substances ever encountered. PTFE was also discovered to be non-corrosive, chemically stable, and have a high melting point.

Further research was allocated to chemists at DuPont’s Central Research Department and was registered in 1945 under the Teflon trademark. The Chemours Company, a spin-off from DuPont, produces a family of Teflon fluoropolymers for various uses.

Benefits and Uses of PTFE

PTFE’s melting point is around 327 degrees Celsius and is almost totally chemically inert, highly insoluble in most solvents and chemicals, and has high flexural strength even at low temperatures. PTFE’s unique properties offer several other benefits, including the following:

• Excellent thermal and electrical insulation properties
• Low coefficient of friction
• FDA approved
• Chemical and high-heat resistant
• UL94-CO flame rating

While widely recognized as a non-stick coating for pots and pans, the coating’s chemical inertness and temperature resistance makes it ideal for use in industrial settings with harsh environments. As a liquid, PTFE’s lubricating properties make it an excellent choice to reduce friction and component wear in machines with sliding parts, gears, slide-plates, and other moving components. PTFE is used in the following industries:

• Oil and gas refineries and pipelines depend on Teflon’s high chemical and thermal resistance to chemicals
• Aerospace and aircraft industries use PTFE fluoropolymers for their resistance to hydraulic fluids and solvents, as well as for operation over extreme temperature ranges
• PTFE fluoropolymers are used in semiconductor manufacturing to increase corrosion resistance and prevent leaching
• Medical packaging and chemical processing rely on PTFE films for chemical and weather resistance

Comparing Parylene vs. PTFE

When it comes to solving engineering challenges both Parylene and PTFE offer valuable benefits. Though PTFE has a lower coefficient of friction compared to Parylene, in many cases, the specific requirements of the application can make Parylene a better choice. Areas of comparison are outlined below.

1. PFAS-free alternative: PFAS (Per- and Polyfluoroalkyl Substances) are a group of synthetic chemicals commonly found in PTFE coatings, including PFOA (perfluorooctanoic acid) and PFOS (perfluorooctanesulfonic acid). These chemicals have raised environmental and health concerns due to their persistence in the environment and potential adverse effects on human health.Parylene, on the other hand, does not contain any PFAS, PFOA, solvent, and hex chrome compounds while offering similar desirable properties to PTFE coatings, such as low friction, excellent moisture barrier, and dielectric properties. Parylene is also REACH and RoHS compliant.
2. Particulate: PTFE, which is a relatively hard coating, can chip and flake under certain conditions. The removal of PFOA (C8) from all PTFE used in Medical Device applications has further increased adhesion challenges. Reports of poor adhesion and delamination on stainless steel guide wires and other mandrel-type products have led to voluntary recalls. In contrast, Parylene, being a softer polymer, such as R80, provides higher yield and reusability in low friction applications. It does not chip or flake like PTFE, making it a better choice where particulate risks exist.
3. Complex typographies: Parylene’s unique vapor deposition process allows for a conformal ultra-thin coating. For lubricity in mandrels, the typical Parylene coating thickness is around 4µm, and as low as 0.15µm for elastomers. On the other hand, PTFE is typically applied by spray or dip and can be prone to pooling, bridging, and edge effects. Consequently, Parylene is a superior solution where dimensional tolerance is tight and for parts with complex topography.
4. Mechanical wear: Both PTFE and Parylene can exhibit good adhesion on mandrels, but since PTFE is a harder coating, it might seem like a better option. However, the wear characteristics depend on the application and operator use. Comparative performance testing is crucial to making a long-term choice for a specific application. While Parylene provides higher yield in low friction applications, it tends to wear in high friction scenarios.
5. Sterilization methods: Parylene’s properties remain largely unaffected by any sterilization method. On the other hand, PTFE is unsuitable for Gamma sterilization and does not perform well with autoclaving. When Gamma sterilization is used, ETFE becomes a better choice for catheter lumens. In such cases, a Parylene-coated introducer mandrel complements ETFE for release-ability, as PTFE does not release from ETFE effectively.
6. Manufacturing and coating process: PTFE manufacturing involves toxic byproducts, such as hydrofluoric acid, carbon dioxide, hydrogen chloride, and other toxic substances released at high temperatures. Additionally, PTFE curing at high temperatures makes it unsuitable for heat-sensitive substrates like Nitinol. In contrast, Parylene is a green chemistry solution. It is chemically inert, non-toxic, and produces no leachable ingredients, residues, or toxic byproducts. Parylene can be applied at room temperature, making it the natural choice for heat-sensitive components and substrates.
7. Cost: PTFE pre-coated spool wire has a lower upfront cost, which tends to influence the decision for stainless steel single-use mandrels. However, for longer bare wires, non-rounds, and shaped parts, this cost difference diminishes. In many cases, where there is potential for reuse, Parylene yields better results, reducing the overall unit cost.

Key Takeaways

It’s true that PTFE and Parylene coatings are used in a variety of settings to protect products from heat, moisture, and chemical damage, and both can prolong the lifespan of components while adding only minimal weight. However, when comparing Parylene vs. PTFE side-by-side, Parylene often comes out on top as the better and safer choice, providing substantial benefits for a wide variety of uses and industries. It especially shines in medical settings, as it protects both patients and providers from potential chemical contamination. Plus, its unique properties make it the ideal coating for electronics manufacturers around the globe.

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