PEEK, Plastic of Last Resort

A bold statement but heard time after time when someone tries to provide a simple description of PEEK.

Polyetherether ketone began its rise in the early 1980’s as an alternative to Torlon (Polyamide imide) and Polyimides. Where PEEK couldn’t compete with its competitors is in the very highest temperature applications, PEEKs relative ease of molding, its amazing chemical resistance, and impact strength give it significant advantages. One of the initial failures with Torlon (and other polyimides) was moisture absorption, and release of that moisture in a catastrophic manner when heated over 250F too quickly.

PEEK can handle that with ease. Torlon is still used in the highest temperature/load applications especially with thinner walls, which let’s moisture escape quickly. Because of its very high cost of $40 to $80/pound, PEEK will always be used when nothing else works. A lot of molders don’t entertain processing PEEK for two reasons. First, every pound counts. A molding opportunity can become a nightmare if housekeeping, processing, and quality are substandard. Second, oil heat (or steam) heating for hot molds (350F) is required to achieve full crystallinity. This maximum crystallinity can be seen with a light grey/brown appearance versus the amorphous brown color. Achieving full crystallinity with colder molds can be achieved with post molding heat treatment with the risk of warpage taking place. Running scrap is painful. Peek replaces nylon when it has to go into high temperature applications requiring impact strength and chemical resistance for example. An early high-volume application was valve plates in gas compressors. In many ways PEEK is very similar to 6/6 Nylon in the way it processes, warps, and sinks. It has increased shrinkage with increased wall thicknesses.

It replaces brass when machining becomes expensive and molding is possible. It has replaced brass distributor gears in high performance race engines because of improved wear resistance, capable of multiple 500-mile races where brass barely makes one race at full performance.

There is nothing like PEEK for use in high temperature steam, better than even stainless steel.

Typical applications today are in medical applications in titanium replacement bone and joint areas. Nuclear parts are in applications due to radiation resistance. Aerospace/military components are used due to low smoke generation and inherent lack of flammability, and extraordinary impact resistance. Automotive applications get used where metal replacement is cost effective. Chemical processing and oil field equipment usages are where high temperature and chemical resistance are fundamental. Oven applications see PEEK choices where non-lubricated wear parts are needed.

3D printing of PEEK is getting a lot of attention but is restricted to costly printers with 350C capabilities. 3D filaments are available but are costly, sometimes over $500 per pound, and are not UL certified. As time goes on, pricing of printers and filaments are sure to become more reasonable. Speaking of UL, it is rated at 240C relative temperature index(RTI).

Filled PEEK exists in many forms: glass fiber, carbon fiber, graphite filler are a few. In the filled forms, PEEK becomes a more capable friction and wear option. Natural high temperature capability means higher loads and speeds are possible, especially with the carbon fiber option improving heat dissipation.

Per Flem
Nearly 45 years of PEEK experience