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SPECIALTY PLASTICSPolyetherether ketone (PEEK)

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S

C

O

O O

Polyaryletheretherketone

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Characteristics:

Crystalline thermoplastic

Chemically resistant

Operates in a wide pH range (from 60% sulphuric acid to 40% sodium hydroxide) & at high temperatures

Additional chemical resistance includes the organic solvents, aqueous reagent, and long term performance in superheated water at 260oC.

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Characteristics:

• Heat distortion temperature of glass filled grade 315oC. Retains mechanical properties close to its melting temperature of 343°C. Continuous service possible at 240oC

• High mechanical properties

• Very low smoke emission. Low flammability value of UL 94 V-0 at 1.45 mm. Limiting oxygen index of 35% at 3.2 mm. Self extinguishing characteristics

• Unparalleled wear and friction resistance in special tribological grades

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Available Grades– Regular, – Glass-fibre filled– carbon-fibre filled grades,

In critical in-engine parts, the polymer withstands high temperatures and the tribological interaction of dry and lubricated material contacts.

In aircraft exterior parts, the polymer provides excellent resistance to rain erosion, while for aircraft interior components, its inherent flame retardancy and low smoke and toxic gas emission reduce the hazard to passengers and crew in the event of a fire.

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AdditivesThe most important additives for PEEK are

glass fiber and carbon fiber reinforcements.

As an example non-filled PEEK has an HDT of 140oC at 1.81 MPa, this value increases markedly for C-fiber reinforced PEEK, reaching a maximum at 315oC. PEK is superior with HDTs of 186oC and 360oC for non-filled and glass-fiber filled material respectively.

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Thermal Properties

• PEEK shows a drop in properties such as modulus and strength as temperature increases.

• PEEK is suitable for use, albeit for short periods, at temperatures in excess of 300 oC

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Thermal Properties

• Good retention of modulus is shown up to the glass-transition temperature of 143 oC. Beyond this the modulus drops sharply, but some rigidity is maintained up to the melting point of 334 oC.

• In the case of the glass –reinforced grades, the level of rigidity is significant as evidenced as a heat-distortion temperature of 300 oC, with a fiber reinforcement level of 30%.

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Electrical Properties• The combination of thermal

stability and good dimensional stability at elevated temperatures, good melt process ability and good electrical properties over a wide range of temperature favor the use of PEEK in electrical and electronics engineering.

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Resistance to Chemicals

• PEEK is resistant to most chemicals.

• Only concentrated sulfuric acid decomposes the product.

• Nitric acid and some halogenated hydrocarbons degrade PEEK.

• PEEK does not hydrolyze in water even at 280°C (18 bar).

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Resistance to Stress Cracking

– Very resistant to stress cracking.

– Hairline cracks occur only in acetone.

– High mechanical stresses may shorten service life.

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Weathering Resistance

PEEK is affected by the UV component in sunlight. Pigmentation or lacquering of molded material is thus recommended for extreme weathering conditions. Colorants and carbon black are suitable.

Resistance to High Energy Radiation

PEEK shows superior radiation resistance. It withstands a -radiation dosage of 107 J kg-1. GF reinforced grades exhibit even higher resistance.

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Flammability

– Even without the addition of flame retardants, PEEK is of low flammability.

– PEEK 450 G is classified as V-O (2 mm thick) to UL94.

– The oxygen index is 35% and thus higher than that of polysulfone and polyimide but lower than that of polyamide-imide and PPS.

– Smoke development is the lowest of all thermoplastics.

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Processing• PEEK is processed by injection molding.

• It must be pre dried at 150 °C for at least 3hours.

• The melt temperature is 350 to 380 °C for unreinforced material and 370 to 400 °C for reinforced material. Recommended mold temperatures are 150 to 180°C.

• Shrinkage is 1 % and 0.1 to 1.4% for the unreinforced and fiber reinforced materials, respectively.

• Peeled film up to 20 mm can be produced from injection molded semi-finished products. These can be used in place of biaxially oriented films.

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Surface FinishingPEK and PEEK moldings can be lacquered and vacuum metallized.

JoiningWelding Molded PEK and PEEK can be joined by ultrasonic and friction welding. The high melting temperature (334°C) and high contact pressure must be taken into account.

Bonding The surfaces to be joined must be clean, dry and free from grease. The strength of the join can be improved by roughening, flame treatment or etching with chrome sulfuric acid. Suitable adhesives are epoxide resins, cyanoacrylate, anaerobic and silicone adhesives. EP resins result in the greatest strength.

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Typical Applications

Automotive, aircraft and electrical industry in the form of injection moldings, cable sheathing, monofilaments and film.

Metal parts are coated electrostatically or by fluidized bed. Trials are being undertaken in hip joint replacement.

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Typical Applications

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PEEKTypical Applications

SEALS AND GASKETS

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Typical ApplicationsAPC (aromatic polymer composite) from ICI, a combination of PEEK as matrix and C-fibers as reinforcement is supplied as tape (3mm to 500mm wide) and sheet which can be used in high performance applications. The excellent mechanical properties are achieved by special pretreatment of the C-fibers.Claimed advantages are:- 30% lighter than aluminum,- more easily processed than EP resins,-higher impact strength than unreinforced PEEK and no propagation of cracks, - high shear & fatigue strength,- low water absorption and high resistance to solvents,- scrap can be recycled,- can be thermoformed, cold rolled and wound.

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Trade Names

Arotone (Du Pont de Nemours, US)

Doctalex (Mitsubishi Chemical Ind., lP)

Kadel (Amoco Performance Products, US)

Mindel (Amoco Performance Products, US)

PEEK (ICI, UK)

Santolite (Monsanto Co., US)

Staber (ICI, UK)

Ultrapek (BASF, DE)

Zyex (ICI, UK)

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Further Reading

1. BRYDSON J.A, Plastics Material, Butterworth Heinemann, oxford, New Delhi (2005)

2. DOMININGHAUS H., Plastics for Engineering, Hanser publishers, Munich, New York (1998)

3. CHARLESS A . HARPER, Modern Plastics Hand Book McGraw –Hill, New York (1999)

4. MARGOLIS J. M., Engineering Thermoplastics, Marcel-Dekker, New York (1985)

TABLE: Guide values of properties of PEEK

PropertiesUnits PEEK PEEK (Glass Filled)

Density g/cm3 1.32 1.44

Water absorption (23°C, 24h) % 0.5 0.06Mechanical

Yield stress N/mm2 1.2

Elongation at yield % 4.9

Tensile strength N/mm2 92 208Elongation at break % 50 1.3Tensile modulus of elasticity N/mm2 3650 13000Impact strength (Izod) J/m No break 749Notched impact strength J/m 83 85Notched impact strength kJ/m2 82 5.4Rockwell hardness scale M 99 M 107

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TABLE: Guide values of properties of PEEK

PropertiesUnits PEEK PEEK (Glass Filled)

Thermal

Service temperature in air without mechanical loading

short-term °C 300 300

long-term °C 250 250

Glass transition temperature °C 143 143HDT, ISO Method A °C 140 315Coefficient of linear expansion between 0 & 50 °C mm/mm/°C 47x10-6 15x10-6

Thermal conductivity W/mK 0.25 0.92ElectricalVolume resistivity cm 5x10-16 1.4x1015

Dielectric constant 3.2

Dissipation factor, tan d 50 Hz 0.003

Dielectric strength kV/mm 190/cm

Fire performance to UL 94 class V-0 V-0

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