Polyaryletherketone (PAEK) is a family of semi-crystalline thermoplastics with high-temperature stability and high mechanical strength. Plastics that fall within this family include:

• Polyetherketone (PEK)
• Polyetheretherketone (PEEK)
• Polyetherketoneketone (PEKK)
• Polyetheretherketoneketone (PEEKK)
• And the wonderfully named polyetherketoneetherketoneketone (PEKEKK)

The first significant commercialisation in this field was PEEK. Victrex of Lancashire, England, introduced PEEK resins commercially in 1981, when it was a unit of ICI Chemicals. The company went private in a management buyout in 1993. ICI also manufactured other high temperature thermoplastics under the Victrex trade name, notably polyethersulphone (PES).

The German plastics giant BASF AG exited the race to gain market share with PEK resins, ending its attempt to break into the market for polyketones, and stopping production and marketing of polyetheretherketoneketone (PEKEKK) resins. This left Victrex as the sole supplier of PEK resins in the world.

But growth rates for PEEK, increasingly used because of its high mechanical strength and chemical resistance in automotive, electronics, aircraft and medical applications, are around 10 percent. As a result, other suppliers have entered the market. Suppliers of PEEK now include Victrex (UK), Solvay Speciality Polymers (Belgium and US), Panjin Zhongrun High Performance Polymers (China) and Jida Evonik High Performance Polymers (China).

Recent developments

Reflecting this high demand for high-heat engineering thermoplastics, in 2015, Solvay announced that it would invest more than $85 million in expansions at its Specialty Polymers site in Augusta, Georgia and at a site already under construction in Panoli, India. Solvay's global PEEK capacity is now more than 2,500 metric tons with a new plant in Augusta, Georgia.

At the same time, Victrex also announced a return to double-digit growth and a £1.3 million grant from the UK government’s Regional Growth Fund to build a Polymer Innovation Center in a major new R&D facility in northern England.

These announcements were particularly timely because of the shortages of SABIC’s Ultem polyetherimide (PEI) high-heat resin, triggered in part by failure of capacity to keep up with demand.

PAEKs can be produced in two ways: the nucleophilic route and the electrophilic route. The nucleophilic route has the formation of ether linkages in the polymerization step. The electrophilic route has the formation of carbonyl bridges during the polymerization step.

They can be processed using all of the typical thermoplastic processes, such as injection molding, extrusion, compression molding, and transfer molding.

Due to excellent resistance to hydrolysis, the materials are being used in medical devices because they do not break down when sterilized. For example, PEKEKK is used to make surgical implants, such as artificial hips.

PEEK melts at a relatively high temperature (343°C), compared to most other thermoplastics. The San Francisco company Fictiv demonstrated for the first time the possibility of processing granular PEEK into filament form and 3D printing parts from the filament material using fused deposition modeling (FDM).

In January 2016 the German start-up Indmatec presented a PEEK filament for producing medical devices up to class IIa. With this new filament, it is possible to use the fused filament fabrication (FFF) method for different medical applications, including dentures.

PEEK is not traditionally a shape memory polymer; however, recent advances in processing have allowed shape memory behavior in PEEK with mechanical activation. This technology has expanded to applications in orthopedic surgery.

China approval for PEEK

Solvay has announced that Zeniva PEEK, one of the four products comprising its family of Solviva Biomaterials offered for use in implantable devices for spine, orthopedics, cardiovascular and dental applications, has successfully passed the biocompatibility testing at the China Food and Drug Administration’s Tianjin Medical Device Quality Supervision and Inspection Center. The inspection center at Tianjin is recognized as the most influential testing agency in the field of orthopedics in China.

Solvay’s family of Solviva Biomaterials has been commercially available in China since 2013. In addition to Zeniva, the product line features Veriva polyphenylsulfone (PPSU), which combines toughness with transparency and excellent biocompatibility; Proniva self-reinforced polyphenylene; and Eviva polysulfone (PSU), a transparent, biocompatible polymer that offers high strength and toughness.

All can be sterilized using all conventional methods including gamma radiation, ethylene oxide, and steam. These sterilizable products are available in grades for injection molding or extrusion, as well as stock shapes for machined components.

The test took over a year to complete and during this lengthy process, properties of Zeniva PEEK such as sensitization, intra-cutaneous toxicity, acute systemic toxicity, sub-chronic toxicity, genotoxicity and bone implant compatibility tests were examined to ensure biological safety in the human body.

PEEK medical devices

Zeniva PEEK boasts a modulus very close to that of cortical bone, plus excellent fatigue resistance and toughness. In addition, it offers advantages over metals, such as reduction of stress shielding, no heavy metal allergy or ion erosion, and has radiolucent properties which allow x-ray and CT scanning procedures without interference.

At the EUROSPINE 2016 exhibition, Solvay announced that its medical grade KetaSpire PEEK and AvaSpire PAEK polymers have enabled medical device pioneer, Shanghai Reach Medical Instrument Company, to develop a lighter, more ergonomic and highly cost-effective kit of reusable instruments for spinal surgeries.

“For decades, metal was the material of choice for medical instruments because conventional plastics could not deliver metal’s combination of high modulus, strong chemical resistance and compatibility with stringent sterilization methods,” said Xiaomin Huang, General Manager of Shanghai Reach. “Today, Solvay’s broad range of specialty polymers is changing that reality – not only by offering metal-like performance, but by also enabling the fabrication of more complex and integrated parts through cost-effective injection molding.”

Shanghai Reach’s innovative kit includes six reusable instruments: one rod bender, two pairs of distraction and compression pliers, and three awls. For the rod bender, the medical device-maker specified KetaSpire KT-880 CF 30 PEEK, a 30 percent carbon fiber-reinforced resin that delivers the high strength and stiffness necessary to bend implantable 5.5-6.0 mm titanium rods. For the pliers and awls, Shanghai Reach chose AvaSpire® AV 651 GF 50 PAEK, a 50 percent glass fiber-reinforced resin offering a cost-effective balance of strength, stiffness and dimensional stability.

Typically, these parts would be made from stainless steel. But Shanghai Reach’s goal was to reduce instrument weight by up to 70 percent for improved ergonomics, yet not compromise on mechanical properties or sterilizability.

Elsewhere, Instratek, a developer of medical devices for extremity surgery, has chosen Solvay’s biocompatible Zeniva PEEK resin to fabricate the radiolucent implant component of its innovative ToeTac Hammertoe Fixation System for the operative repair of hammertoe deformities.