Materials and applications are in a state of constant movement: metals replacing plastic, plastics replacing wood, ceramics replacing plastics, etc. Materials ‘bandits’ are hijacking properties that are more commonly found in other materials families and using them in products.
At the top of the polymers family tree, with properties beyond conventional engineering polymers, exists the group of ultra polymers. This group encompasses materials that are fairly uncommon in design, such as sulphones, polyamide-imides and polyetheretherketones (more commonly known as PEEK). These plastics, which have properties that go beyond most physical and mechanical characteristics of plastics, occupy a top tier of performance engineering, with features that allow them to infiltrate applications that traditionally belong to other materials such as metals.
There aren’t many applications where you would actually see this material and admire its properties. Regarded as a high performance polymer, PEEK has a long list of properties that make it suitable for a range of demanding, high-end engineering applications. These properties are characterized by high stiffness and chemical resistance that, unlike for most other plastics, are maintained at high temperatures. As a result of these properties, PEEK demonstrates its superior nature by being used to replace aluminium and other metals in various industries.
Image: Carbon nanotube enhanced PEEK, Solvay plastics
Key features
•Versatile processing
•Retains its properties up to 300ºC (572ºF)
•Excellent wear and fatigue resistance
•Excellent chemical resistance
•Radiation resistant
•Recyclable
Sources
Widely available from multiple global suppliers.
Cost
High cost: £64 ($100) per kg.
Sustainability issues
PEEK is one of the purest and most stable polymers, so does not contain additives that might be released during heating in the moulding process. This also makes it suitable for implantation in the body in the medical industry.
Production
Although there are other plastics with high-performance traits, the benefit of PEEK is that it can be formed using conventional moulding machinery. It offers advantages over conventional low-temperature metals such as zinc and aluminium or magnesium die-casting, which have higher material costs and shorter mould lifespans. Recent introductions by Victrex, a leading manufacturer of PEEK, are PEEK coatings and PEEK film. In film form, the material (available in thicknesses ranging from 6-750 microns) is used in anything from speaker diaphragms to microphone spacer film for mobile phones, which need to withstand high temperatures during the manufacturing process. As a coating it is applied to a range of metal substrates to increase chemical resistance.
Its high cost means that applications tend to be limited to engineering components, which require high performance structural and mechanical properties: typical examples are bearings, bushings, coatings, protective tubing and electrical connectors. It is also used in the medical industry because it can be continually sterilized and is biocompatible. A new application being explored is using PEEK as a metal replacement for gears in automotive gearboxes as a way to reduce engine noise. As a film it is also used for acoustic insulation in aircraft interiors. In the food industry it is used in aseptic packaging, which needs to have operating temperatures high enough to kill bacteria. However, for a more visible consumer application, PEEK has been used as the inner pot for rice cookers, which had traditionally been made from aluminium and were susceptible to corrosion.
Derivatives
PEEK is also available in glass or carbon-filled grades and Swiss-based Sefar have produced PEEK-based fabrics.
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–Easy to process –Robust and hardwearing –Biocompatible –Widely available –Radiation resistant –Recyclable |
–High cost limits its application to high performance engineering components |