PEK (Polyetherketone) Overview
PEK is part of the polyetherketone group of semicrystalline polymers that also includes PEEK and PAEK. Compared to the latter two materials, PEK offers higher performance levels in several areas including strength retention at higher temperatures, and a higher degree of wear resistance in dynamic load applications.
PEK resin is produced by Victrex® PLC. under their brand Victrex HT and available in two viscosities, high flow G-22 and low flow G-45.
Like all polyetherketone polymers, PEK HT exhibits excellent long-term resistance to a wide range of aggressive chemicals. However, PEEK resists the widest spectrum of chemicals because of its unique ether-to-ketone ratio in its polymer structure.
PEK Performance Profile
A major attribute of PEK HT compared to traditional PEEK is its higher temperature resistance. The higher thermal capability it provides applications in use is evident in its 320°F (160°C) glass transition temperature, a step up in performance compared to typical unreinforced PEEK-based polymers.
A high-performance semicrystalline thermoplastic, PEK HT provides more resistance to creep and deformation under load than traditional unreinforced PEEK. It also retains its higher tensile strength and flexural modulus at 54°F (30°C) beyond the limits of standard PEEK.
PEK HT’s greater strength retention and load bearing capabilities at higher temperatures combined with its inherent resistance to many chemicals position it as an upgrade to traditional PEEK for a variety of applications. Although the creep modulus of PEK HT and PEEK are comparable at room temperature, at a temperature level of 150°C (302°F), PEK HT polymer’s creep modulus is more than two times that of traditional unreinforced PEEK. As a result, in actual applications PEK HT can support higher loads at higher temperature levels without exhibiting permanent deformation.
Fatigue resistance is another attribute of PEK HT that ranks higher on properties charts than PEEK. This is a consequence of the semicrystalline molecular structure of the PEK polymer. It is also a benefit for applications where fatigue resistance at high stress levels is a key requirement.
With up to three times more wear resistance than traditional PEEK, PEK HT also provides longer service life for moving parts and components under dynamic load. Thrust washer tests conducted in Victrex’ facilities under a variety of PV conditions demonstrated that PEK HT showed as little as 33% of the wear exhibited by the supplier’s standard Victrex 450G PEEK grade. PEK HT also showed a consistently lower specific wear rate than the traditional unreinforced PEEK grade under all other bearing and wear test conditions.
Its hydrolysis resistance makes PEK HT a good option for components in food processing equipment that require frequent and thorough cleaning with high pressure steam. This same attribute supports its use in medical applications that require autoclave sterilization. Other notable properties include inherently low flammability and smoke emission, an asset in aerospace components.
Typical PEK Applications
Structural strength retention at high temperatures, electrical and thermal properties and chemical and wear resistance position PEK as a high-performance material for severe service components in a wide array of applications.
In downhole equipment used in the oil and gas industry, potential applications include back up seal rings, valve seats, seals, and electrical insulators. PEK also can be used for connectors in electrical submersible pumps (ESPs) that operate in high temperature – high pressure (HTHP) downhole environments. Its strength and stiffness retention at high temperatures also prevents distortion from hydrostatic pressure in thin-walled bulkhead seals.
Resistance to high-pressure steam and hot sanitization chemicals along with FDA compliance are other advantages PEK brings to components in food and pharmaceutical production equipment. Its wear resistance also extends the service life and replacement cycles for moving parts and dynamic load bearing components. PEK also features electrical and thermal insulation properties that make it suitable for heat exchanger components and electrical applications such as those in subsea exploration equipment.
PEK Resins and Stock Shapes
Victrex HT G45 and HT G22 are the most common HT PEK resin grades. HT G22 is a high flow resin used widely for injection molding. Drake Plastics extrudes stock shapes from Victrex HT G45 PEK. The higher viscosity of G45 allows large cross sections to be produced during melt processing and the higher molecular weight of this grade offers improved toughness and strength. Extruded HT PEK rod and plate made from unreinforced G45 resin are available from Drake’s inventory. Specialty grades Drake produces on request include glass and carbon fiber reinforced HT G45 GL30 and HT G45 CA30, and PEKEKK, a polyketone related to PEK and supplied under the Victrex® STTM polymer tradename.
PEK stock shapes are also offered by Greene, Tweed & Co. under their Arlon® 2000 brand.