Poly aryl ether ketone (PAEK) and Polyether ether Ketone composite material for aerospace applications:

Excerpt:

Poly aryl ether ketone is (PAEK) is a family of semi-crystalline thermoplastics with high-temperature stability and high mechanical strength, PAEK has a continuous operating temperature of 250 °C (482 °F) and under short-term loads can function up to 350 °C (662 °F). PEEK is a semicrystalline thermoplastic with excellent mechanical and chemical resistance properties that are retained to high temperatures. Because of its robustness, PEEK is used to fabricate items used in demanding applications, Using PAEK and PEEK a thermoplastics composites were prepared by hybrid moulding technic called ovrmolding. Overmolding is a process where a single part is created using two or more different materials in combination. One can mold PEEK over PEEK, but it doesn’t fuse together. Fusion of the matrices requires a substrate with a lower melt temperature than the overmold. PAEK based thermoplastics composite are the solution of choice for applications that demand the performance of PEEK combined with increased mechanical properties.

Poly aryl ether ketone is (PAEK) is a family of semi-crystalline thermoplastics with high-temperature stability and high mechanical strength. PAEK is condensation product of 1,1-bis(hydroxy phenyl)-1-(phenoxy)-1-(pheny) methane and 4,4’-Difluoro benzophenone in presence of potassium carbonate in sulfonal as solvent at 200 degree C.Fig.1

Fig1

PAEK has a continuous operating temperature of 250 °C (482 °F) and under short-term loads can function up to 350 °C (662 °F). When burned, it has the least toxic and corrosive fumes. It also has a low heat output when burned, so it qualifies for use in interior aviation applications. It also has good overall chemical resistance. In addition, PAEK materials show very good impact strength at low temperatures, high mechanical fatigue strength, a very low tendency to creep as well as good sliding and wear properties. Due to their unusual characteristics, poly aryl ether ketones are used for particularly demanding applications.

Poly ether ether ketone (PEEK)

PEEK polymers are obtained by step-growth polymerization by the dialkylation of bisphenolate salts. Typical is the reaction of 4,4'-difluorobenzophenone with the disodium salt of hydroquinone, which is generated in situ by deprotonation with sodium carbonate. The reaction is conducted around 300 °C in polar aprotic solvents - such as diphenyl sulphone.

PEEK is a semicrystalline thermoplastic with excellent mechanical and chemical resistance properties that are retained to high temperatures. The processing conditions used to mold PEEK can influence the crystallinity, and hence the mechanical properties. Because of its robustness, PEEK is used to fabricate items used in demanding applications, including bearings, piston parts, pumps, HPLC columns, compressor plate valves, and cable insulation. It is one of the few plastics compatible with ultra-high vacuum applications.

Fig 2

In the composites industry, use of polyetheretherketone (PEEK) has recently experienced an uptick in thermos stamped aircraft fuselage clips and brackets made from pre-consolidated blanks with woven and/or unidirectional reinforcements. But those who use and those who make the blanks recognize their limitations. Compression-formed laminates did not offer the design flexibility and manufacturing efficiency being sought by aircraft designers. PAEK in combinations with PEEK can overcome these limitations also one can obtained a combine properties chemical resistance and moldability of thermoplastics with the high performance and light weight of composites.

Using PAEK and PEEK a thermoplastics composites were prepared by hybrid moulding technic called ovrmolding. Overmolding is a process where a single part is created using two or more different materials in combination. Typically the first material, sometimes referred to as the substrate, is partially or fully covered by subsequent materials (overmold materials) during the manufacturing process. The substrate could really be anything; a machined metal part, a molded plastic part, or even an existing product like threaded inserts, screws, or electrical connectors. It is the first piece in what will eventually become a single continuous part composed of chemically bonded and often mechanically interlocked materials of separate types. Overmold materials (typically plastic) start off in pellet form. These pellets are mixed with additives like colorants, foaming agents, and other fillers. They’re then heated to their melting point and injected into the mold tooling as a liquid. There are some limitations on what materials are suitable for overmolding. If you are overmolding a metal part with plastic, you can really use any plastic. If you are overmolding a plastic part with another plastic (or a rubber or TPE), then there can be compatibility issues. The material manufacturer typically publishes a compatibility chart for overmolding.

One can mold PEEK over PEEK, but it doesn’t fuse together. Fusion of the matrices requires a substrate with a lower melt temperature than the overmold. To consolidate two parts one requires fusing of two materials. So, one needed a low-temperature processing PAEK that has PEEK properties as the same time they have compatibility. Therefore, a composite of PAEK and PEEK is desirable one. For PEEK that uses a lower temperature continuously-reinforced (PAEK) composite as a substrate, overmolded with short fiber-reinforced PEEK, to produce a high-performance thermoplastic composites having very good chemicals, mechanical , thermal and moladability properties. This gives the efficient processing and performance advantages of PAEK thermoplastic composites. A loaded bracket that is as much as 60% lighter than comparable metal components is obtained by this technique (Fig.3). The new joint venture company TxV Aero Composites, created by Victrex and Tri-Mack Plastics Manufacturing Corporation are the manufacture of such composite commercially. With an estimated 35,000 new aircraft to be launched in the next 20 years, the aerospace industry is embracing thermoplastic composites as a cost-effective solution to support this growth.

Fig.3

PAEK based thermoplastics composite are the solution of choice for applications that demand the performance of PEEK combined with increased mechanical properties. The results are a material that offers comparable performance with metals and additional benefits.

• Fatigue resistance and strength comparable to metals, but a metal alternative is needed.

• High strength and stiffness to weight ratio.

• Improved damage tolerance compared with thermoset composites.

• Tailored mechanical properties, including localised reinforcement, within the component.

• Up to 60% lighter than metals and metal alloys.

• Up to five times higher specific strength than metals and alloys.

• Part manufacturing cycle times measured in minutes compared to the hours it could take for a thermoset or metal equivalent.

Because of all above performance properties these are widely used in Aerospace brackets, clips, clamps and fasteners and Structural components and systems in the aircraft