PEEK is a workhorse – perhaps the closest to a perfect material that is utilized in a wide range of industries and in a variety of applications. It is known for its impressive durability in punishing environments. Glass and carbon reinforced grades are among the strongest of all thermoplastics at room temperature and unfilled grades are highly resistant to some of the most chemically aggressive environments including high-pressure steam.
First introduced by Victrex PLC, then ICI (Imperial Chemical Industries) in the early 1980s it has been gaining use for nearly 40 years. Others including Solvay entered PEEK resin production in the early 2000s after Victrex PLC’s patent rights expired so today end users and specifiers have no shortage of PEEK resin grades from which to choose. Name recognition still favors the Victrex brands but others led by Solvay’s Ketaspire PEEK are gaining both volume and market share each year. Today Solvay is the only US-based producer of PEEK resin.
PEEK is short for polyether ether ketone, which doesn’t make sense to many other than those with a strong chemistry background. Put simply, it refers to the chemical structure of the polymer although most polymer scientists identify PEEK as being part of the broader family of ketone polymers called polyarylether ketones (PAEKs). This PAEK family covers a number of different compositions with different ratios of ether groups to ketone groups, the most common of which is PEEK. Regardless of the specific chemistry it is the polyketone chemical structure that makes PEEK so formidable in so many environments. What is it about PEEK that makes it a natural fit for so many engineering applications?
More On Why Peek
- Excellent thermal properties – Unfilled PEEK offers high strength and excellent resistance to high temperatures, and will not melt until it reaches about 650 degrees Fahrenheit. It is useful at temperatures up to nearly 500 degrees Fahrenheit long term and far higher short term, which is well beyond what most polymers are capable of. PEEK’s glass transition temperature or softening temperatures is close to 300 degrees Fahrenheit. This inherent characteristic can be compensated for through reinforcements and chemistry modifications.
- Formidable chemical resistance – Unfilled PEEK offers broad chemical resistance that approaches that of PTFE but with far greater strength, which is why it is a favorite choice for chemical processing and oil and gas companies. Some of the chemicals it can withstand include most acids (the only exceptions are hydrofluoric and hydrobromic), acetone, all alcohols, ammonia, benzene, chlorine, ethylene oxide, formaldehyde, gasoline and most fuels, glycerin, hydrogen peroxide, hydrogen sulfide, methane, MEK, methylene chloride, ozone, pentane, sodium carbonate, sodium hydroxide and Toluene. And that’s just a fraction of the substances PEEK is resistant to. This broad resistance is a primary reason why PEEK is so ubiquitous, as it can be adapted for nearly any application.
- Superior wear resistance – Few polymers can match PEEK in terms of well-rounded wear resistance. Of course, “wear” is a general term, and requires further explanation.
Abrasive wear refers to cutting action caused by the countersurface’s irregularities. Fatigue wear refers to material deformation resulting from repeated pressure and stress. Friction is the resisting force against motion, and though it isn’t “wear,” it is problematic nonetheless. PEEK’s properties provide resistance to abrasive and fatigue wear, and it is a naturally low friction material. PEEK that is alloyed with PTFE graphite and carbon fiber provides low wear rates at high pressure-velocity conditions in even abrasive environments. Unfilled PEEK provides superior fatigue resistance and good wear resistance as well, provided the maximum stress and velocity are low. Twenty percent (20%) PTFE filled PEEK (FE20) offers a lower coefficient of friction and improved wear rates over unfilled PEEK
- Great processability – PEEK’s ease of processing has contributed to its wide acceptance in high volume commercial applications. PEEK components are injection molding in high volume tooling equipped with hot runner systems, machined from both extruded and injection molded stock shapes and even stamped and machined from thin strip stock or film. Machining high performance thermoplastics can be a challenge because the availability of the needed shape is often limited meaning the manufacturing cost increases due to unnecessary machining swarf and the time to create it. PEEK’s high molecular weight and melt stability enables it to be extruded into large cross sections such as rods greater than 200mm, plate up to 4” and tubes with 2” thick walls. There are more than 50 different sizes of PEEK rod and plate stocked and ready for immediate shipment. Additionally PEEK is one of the few high performance thermoplastics that can tolerate the kind of extensive machining needed to produce components with complex geometries one of reasons why it is found in so many diverse applications.
- Biocompatibility – The medical industry is always in search of materials that can be utilized in the human body. Many polymers are rejected by the body’s immune system, resulting in serious, even life-threatening complications. And even when the material is accepted, it may wear down due to abrasive wear and intense friction, causing pieces of the material to splinter off and interfere with biological function. PEEK’s high strength and modulus that approximates human bone already been used in many procedures, including spinal implants and skull reconstruction. PEEK is inert and biocompatible and is considered a leading candidate for surfaces and parts that direct contact bio fluids whether during chemical analysis or surgical procedures.
Machining or Injection Molding… You choose how to make it
Because PEEK can either be injection molded or machined into components, some insight into both processes bears mentioning. To be clear upfront, neither process is clearly superior in all instances. Process selection is something project engineers will need to study closely, and something that should be discussed with component suppliers.
During injection molding, the PEEK is injection molded into a custom cavity that is part of a complex tool generally costing more than $10,000. This is the most efficient and fastest route to making parts provided the tooling investment is justified. Machining, on the other hand, uses stock shapes and machine shops that mirror the route most metal parts are produced. A bar of PEEK rod can generally be machined into bushings or bearings often within a few days for hundreds of dollars meaning speed and flexibility are unmatched. The properties of extruded shapes offer the highest stiffness and greatest toughness and in general the most reliable performance.
Machining PEEK is the preferred option in most high precision applications. This includes when production runs involve lower volumes (especially runs under 5,000 parts), when larger components need to be produced and when toughness and impact strength are major priorities. In short, machining works best when the components need to offer excellent mechanical and wear properties.
Again, there is no clear winner between the two processes but there are situations where one offers a major advantage. Injection molding PEEK is the better choice when producing complex parts (usually more than 10,000 during a single run), as injection molding eliminates machining time and waste resulting in the lowest possible unit costs. Injection molding is also the appropriate choice when machining presents difficult to overcome geometric challenges.
Where PEEK is Used?
Unfilled PEEK dominates the volume of PEEK consumed worldwide. Its durability, availability and processability make PEEK the material of choice when high strength and inertness especially at elevated temperature a fit in many industries. New uses are being devised for the polymer all the time. Some of the polymer’s prominent uses include:
- Semiconductors and electronics – PEEK’s ability to retain its strength at high temperatures, its purity as well as its ability to withstand harsh chemicals makes it a natural fit for semiconductor and electronics manufacturing. PEEK can be machined into wafer handling tools and hardware, which is especially useful during chemical washing. Unfilled PEEK is also critical during chip production, particularly during chemical mechanical planarization and etching. One of the largest volume applications for PEEK film is in cellular phones
- Oil and Gas – In the oil and gas industry, unfilled PEEK and glass-filled PEEK are typically processed into seals and electrical connectors, where they serves as insulators and isolators as well as reinforcements for softer seal materials. PEEK is a strong choice for oil and gas applications as it is highly resistant to steam and the kinds of chemicals encountered in aggressive downhole environments. PEEK valve seats and seals down stream help manage the flow of petrochemical gases and liquids without risk of chemical degradation
- Aerospace – PEEK is utilized in both commercial and military aircraft, and in both settings, only reliable, durable materials are utilized. In the aerospace industry, it is PEEK’s low smoke generation and excellent thermal resistance that prove valuable as unfilled PEEK is so resistant to heat and fire that it self-extinguishes. These properties make it a good fit for aerospace electronics, which tend to be highly stressed, and thermal isolators, which must handle both high heat and very cold conditions. Carbon fiber reinforced PEEK grades like 450CA30 and KT820CF30 provide the maximum strength and stiffness without the high density of glass reinforced PEEK grades.
- Medical – Unfilled PEEK’s biocompatibility has already been addressed, and it is this property that has unfilled PEEK acting as implants, including spinal and dental implants. Even carbon fiber reinforced PEEK remains inert and stable for long periods of time, to the point where implants outlive patients. PEEK’s inertness and stability mean it can withstand repeated autoclaving allowing it to function in reusable medical instruments. Also valuable is PEEK’s radiolucency. In other words, PEEK remains invisible to radio imaging, which includes CT and MRI scanning, as well as X-ray imaging. This radiolucency is especially important for studying tissue growth processes, as the implant will not screen surrounding tissues from view.
- Food and packaging – Unfilled PEEK comes in food-grade varieties, so it can be integrated into appliances and surfaces that come in contact with food. Standard applications include filling nozzles, mixing paddles, bearings, bushings and valve components especially those involved in citrus fruit processing and hot filling machines. Valve bodies have migrated from acetal to unfilled PEEK as process temperatures have increased. Additionally, unfilled PEEK is impervious to all clean in place (CIP) solutions.
The above is only scratching the surface for PEEK applications. As companies reach for greater and greater “in use” cost-effectiveness, they often turn to PEEK to get there. PEEK is the most available and versatile high performance polymers on the market today.
What types of PEEK are available?
Unfilled PEEK offers unmatched chemical Inertness, FDA compliance and strength up to 300°F. Its superior machinability and cleanliness make it ideal among all ketone based polymers for tightly toleranced complex machined parts or injection molded parts such gears, ferrules and life science and medical parts. See more on KT820NT Comprehensive Overview
Carbon Fiber Reinforced PEEK offers the highest strength and stiffness among the PEEK grades. It is 7% lighter than glass reinforced grades despite containing more reinforcement per unit volume. It is an excellent choice for highly load machined or molded parts. See more on 450CA30 or KT820CF30 Comprehensive Overviews.
Glass Fiber Reinforced PEEK offers the higher strength and stiffness than unfilled PEEK grades but with excellent electrical and thermal insulation characteristics. It is an excellent choice for highly load machined or molded parts including back up seals and electrical connector bodies. See More on KT820GF30 Comprehensive Overview
Bearing Grade PEEK offers the lowest wear rates among the PEEK grades for demanding wear applications. The most common grades contain a combination of graphite, PTFE and carbon fiber with the most common ration being 10-10-10 blend. This combination promotes low friction and higher conductivity enabling for higher PVs and lower wear rates. See 450FC30 or KT820SL30 or 450FE20 Filled Peek Comprehensive Overviews
High-Temperature PEEK or PEK is a slightly different chemistry and is based on polyether ketone PEK rather than PEEK. PEK and PEKEKK offer higher softening temperatures than traditional PEEK chemistries. The improvement enables PEK based materials such as HT to retain strength and stiffness at 50°F higher temperatures expanding the potential for PEEK in downhole electrical connectors. See PEEK HT Comprehensive Overview