Plastic materials are quickly gaining credibility in the fastener industry and for good reasons. Plastic fasteners are strong yet flexible, durable, cost-effective, and they fail to rust, which is a big plus.

PEEK, also known as polyetheretherketone, is one type of plastic that offers high-performance engineering and versatility. This material has an extremely stable chemical structure that’s rare to find in other plastics, making it ideal for use in fasteners in several applications and industries.

For example, PEEK is often used in components for the automobiles, aerospace, marine, nuclear, oil and gas, and in the electronics sectors. It’s also considered an advanced biomaterial and medical implants are made from it. As a result, it’s increasingly used in spinal fusion devices and for reinforcing rods. Additionally, PEEK fasteners are used in the food and beverage industry for food and feed drying.

Clearly, this material is versatile and reliable, even in demanding applications. Aside from fasteners, parts such as bearings, pumps, pistons, compressor plate valves, cable insulation, and others use PEEK.

Key features
PEEK is a semi-crystalline, high-temperature resistant thermoplastic. The processing conditions used to mold it can influence its crystallinity and mechanical properties.

Its Young’s modulus (this is the mechanical property that measures the stiffness of a solid material) is 3.6 GPa and its tensile strength is 90 to 100 Mpa. PEEK has a resistance to hydrolysis so it’s unable to absorb water. This makes it highly tolerant to thermal degradation and attacks by organic and aqueous environments.

A few other features are that it’s susceptible to halogens and strong Bronsted and Lewis acids, as well as some halogenated compounds and aliphatic hydrocarbons at high temperatures. (Lewis acid accepts a pair of electrons while a Bronsted acid accepts pairs of electrons at an acidic hydrogen.) PEEK is soluble in concentrated sulfuric acid at room temperature.

The material also has superior creep resistance, serving as a high-strength alternative to fluoropolymers.

Environmental considerations
PEEK has a glass transition temperature of 143° C (289° F) and melts at 343° C (662° F). Some grades have a continuous operating temperature of up to 250° C (482° F).

Aside from being resistant to organic and aqueous environments, it’s also highly resistant to thermal degradation. PEEK has a UL flammability rating of V-0 and exhibits low smoke and toxic-gas emissions. The plastic resists radiation and a wide range of solvents. It can withstand boiling water and the super-heated steam used with autoclave and sterilization equipment at temperatures higher than 250° C (482° F).

Grades
The unfilled grade offers the highest elongation and toughness of all the grades of PEEK. It is available in light brown or tan and black. Reinforcing fibers are often added to plastic resins to increase the tensile strength and flexural modulus of the composite.

• PEEK 30% glass-filled includes glass fibers as an additive. This grade is ideal for structural applications that require improved strength, stiffness, or stability at temperatures of about 300° F (150° C). This grade dramatically lowers the material’s expansion rate and increases its flexural modulus. Glass-filled PEEK is light brown or tan.
• PEEK 30% carbon-filled uses carbon fibers as an additive. The carbon fibers enhance the compressive strength and stiffness of the material and dramatically lowers its expansion rate. This plastic material grade offers optimum wear resistance and excellent load-carrying capability. PEEK 30% carbon-filled provides three-and-a-half times higher thermal conductivity than the unfilled grade. Therefore, it dissipates heat from the bearing service faster. PEEK 30% carbon filled is black.
• PEEK (Bearing Grade, Ketron HPV) is a grade that’s reinforced with graphite, PTFE and carbon fibers. This grade offers the lowest coefficient of friction and the best machinability of all the PEEK grades. The bearing grade, Ketron HPV sports an excellent combination of low friction and wear, high limiting PV, low mating part wear, and easy machining. This grade is black or dark gray.

Thanks to several of PEEK’s properties, the plastic can serve as an alternative to steel, aluminum, and brass fasteners. A summary of its benefits include resistance to high temperatures, chemicals, hydrolysis (exposure to steam or high-pressure water), and fire. PEEK fasteners can also withstand forces (such as stretching and pulling) and abrasion, making them ideal for nearly every industry.

~ This article was compiled by Barbara Gerard, CEO of Craftech Industries, Inc.