In our continuing series of blog posts on extreme polymers, we are going to talk about the third most heat resistant polymer on the market today: PEEK.
Introduction
PEEK, which stands for polyether ether ketone, is a heat resistant, robust, high performance thermoplastic used in a variety of applications and industries. It can be found in industries like oil and gas, biomedical, pharmaceutical, food and dairy, automotive, nuclear, semiconductor, and aerospace and can be used for everything from bearings and seals to biomedical implant devices even in the most aggressive environments.
General Properties
PEEK is known for durability, dimensional stability, strength, and toughness. It is abrasion resistant and offers excellent resistance to aggressive chemicals, besides its outstanding thermal properties across a wide temperature range. PEEK also works very well in high PV applications and has a relatively low coefficient of friction.
It is very well adapted for use in some of the harshest environments today, including constant exposure to steam and hot water with continuous operating temperature is 480°F. It exhibits low smoke/toxic gas emission when exposed to open flame and carries a V-0 flammability rating. PEEK also has good thermal conductivity to aid in heat dissipation and very good radiation resistance.
PEEK is also resistant to hydrolysis and can withstand both superheated steam and boiling water. In addition to its other properties, it offers very low moisture absorption. Its chemical resistivity is comparable to PPS but it can handle much higher temperatures.
PEEK is very flexible when it comes to processing and manufacturing. It lends itself to injection molding, compression molding, extrusion, and machining. Note that bearing grade PEEK is ideal for machining.
Note that bearing grade PEEK is ideal for machining.
The main weakness of PEEK is its susceptibility to certain concentrated acids.
Grades of PEEK
PEEK is typically available in virgin, glass-reinforced, and carbon-reinforced grades. Glass-filled PEEK has added stiffness and strength and works well at temperatures over 300°F. The addition of glass also increases its stability by reducing expansion.
Carbon-filled peek has improved compressive strength and stiffness with a much lower rate of expansion compared to virgin PEEK. It also allows heat to be dissipated much more quickly because of its high thermal conductivity.
Bearing grade peek (tradename Ketron HPV) combines carbon, graphite, and PTFE to provide extremely low friction (lower than any other grade of PEEK), excellent wear and fatigue properties, and a high PV limit.
There is also a special high temperature grade of PEEK that has a melting point of 705°F and retains its strength at temperatures up to 54°F than virgin PEEK. It also offers very good toughness, chemical resistivity, and strength and shares PEEKs low smoke emission and flammability ratings.
Conclusion
When looking for a thermoplastic that offers excellent heat resistance at reasonable cost, take a look at some of the available grades of PEEK. PEEK combines outstanding thermal performance with good strength, wear, and chemical resistance.
Interested in learning more about the benefits of PEEK for polymer seals, bearings and parts? You may enjoy these articles:
- Polymer Sacrifice: Carbon Fiber Reinforced PEEK as a Wear Component Material
- 5 Top Reasons PEEK is a Popular Choice for Seals
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