Structure And Molding Processing Of Polyether Ether Ketone PEEK

Polyether ether ketone (PEEK) is a semi-crystalline, linear aromatic polymer compounds developed by the British Imperial Chemical Industries (ICI) in 1978, by the ether bond, aryl ring, carbonyl alternately connected to form a thermoplastic ultra-high-performance special engineering plastics. the molecular structure of the main chain of the PEEK contains a large number of benzene rings, its own C-O bond is relatively soft, the two benzene ring larger bit resistance. The C-O bond is relatively soft, and the two benzene rings have large site resistance to effectively protect the C-O bond from being destroyed, and the oxygen atom and carbonyl group will form a p-π conjugation effect with the benzene ring. These structural features give PEEK the following excellent performance.

Properties of PEEK

Polyether ether ketone (PEEK) belongs to the aromatic crystalline thermoplastic polymer materials, its glass transition temperature of 143 ℃, melting point of 334 ℃, with high mechanical strength, high temperature, impact resistance, flame retardant, acid and alkali resistance, hydrolysis resistance, abrasion resistance, fatigue resistance, resistance to irradiation and excellent electrical properties, radioactivity is the best of all plastics, oxygen index is high, the combustion of the smoke is small and non-toxic. In most cases, it can be enough to replace metal, alloy, ceramic and other materials.

1.Mechanical properties

PEEK creep and fatigue resistance is excellent. Glass fiber reinforced and carbon fiber reinforced PEEK and unreinforced grade compared to the strength and modulus is higher, the temperature is higher than the glass transition temperature, the strength and modulus of the decline is more pronounced. PEEK in crystalline polymers in the melting point and the glass transition temperature is very high, in 200'C or more, but still be able to maintain a high strength and modulus. In addition, PEEK has a low coefficient of friction and wear over a wide range of temperatures and can withstand the repeated action of higher loads.

Table 1-1 Properties of Typical Grades of Victrex PEEK

2.Heat-resistant performance

PEEK has excellent heat resistance. Long-term use temperature up to 240 ℃. Thermogravimetric measurement of PEEK thermal weight loss curve shows that 400 ℃ weight loss of 0%; 500 ℃ for 2.5%; 600 ℃ mass loss increased to 59%.

Unreinforced PEEK and glass fiber or carbon fiber reinforced PEEK, after 1000h heat aging, tensile strength are not reduced. PEEK coated wire heat aging resistance is shown in Table 1-2, usually it is at 220 ℃ service life of more than 6000h.

This characteristic makes it the material of choice for thermoforming, oilfield development, and aerospace and other high-temperature operating environments.

Table 1-2 Aging resistance of PEEK-coated wires

3. Hot water resistance

Resistance to hot water and steam is one of the most important features of PEEK. In 80 ℃ hot water immersion 800h, its tensile strength and elongation at break basically unchanged. 200 ℃ steam, its tensile strength and appearance did not change significantly, so can be used in steam for a long time. Among all engineering plastics, PEEK has the highest steam resistance.

4. Electrical properties

The volume resistivity of PEEK resin reaches 1016Ω.cm, and the dielectric loss angle tangent is small at high frequencies. In high temperature, high pressure and high humidity and other harsh environments can still maintain good electrical insulation.

5. Chemical resistance

PEEK in addition to concentrated sulfuric acid, almost any chemical; at higher temperatures, it can still maintain good chemical stability. Compared with polycarbonate, modified polyphenylene ether and polysulfone, the chemical resistance of PEEK under stress is extremely excellent (Table 1-3).

Table 1-3 Chemical Resistance of PEEK and Other Engineering Plastics under Stress

However, stress cracking often occurs when PEEK is immersed in some chemicals (e.g., acetone, etc.) when its crystallinity is not high. In this regard, it can be annealed (e.g., at 200 degrees Celsius treatment) to improve its crystallinity and resistance to stress cracking.

6. Flame retardant

PEEK has a self-extinguishing, without the addition of flame retardant 0.8 ~ 1.6 mm thick PEEK flame retardant up to UL94V ~ O level. The amount of smoke under forced combustion is also very small, and does not contain toxic gases.

7. Radiation resistance

PEEK has strong radiation resistance. Its resistance to Y-ray in the whole engineering plastics is the best. PEEK absorbs a dose of (1.0 ~ 1.2) × 107Gy of Y-rays after the beginning of the brittle; (0.l ~ 12) × 106Gy of β-rays have no effect on it.

8. Self-lubrication

PEEK has a very high self-lubricating properties, suitable for strict requirements of low coefficient of friction and friction wear-resistant applications. Especially with carbon fiber, graphite, PTFE modified PEEK wear resistance is very superior.

9. Biocompatibility

PEEK is non-toxic, safe and non-allergic, physiologically compatible. Implant-grade PEEK in foreign independent testing organizations in strict accordance with the requirements of ISO10993, conducted a complete biocompatibility test. The results show that the implantable grade PEEK has excellent biocompatibility and has no side effects.

Molding process of PEEK

1. Molding characteristics

PEEK melt viscosity above 380'C becomes less dependent on temperature, but more dependent on shear stress and shear rate. In other words, it is effective to increase the pressure in order to obtain high melt fluidity during molding.

2. Injection molding

PEEK melting point is high, compared with general engineering plastics, melt viscosity is also larger, so the molding temperature is also higher, the barrel temperature is generally controlled at 350 ~ 400 ℃. Before molding, the material generally need to be pre-dried, pre-drying conditions for 150 ℃, 3h.

PEEK is a crystalline polymer, only in the molding to make it fully crystallized, in order to get products with excellent performance. When the mold temperature of 150 ~ 160 ℃, PEEK injection products are opaque and high degree of crystallinity, but the surface layer may be transparent and low crystallinity; while the mold temperature of 180 'C, you can get a high degree of crystallinity products. If the molding process can not be used higher mold temperature, the product should be post-treatment to improve its crystallinity. Post-treatment conditions are generally 200 ℃, 1 h or 300 ℃, 2 min. PEEK injection molding can be used ordinary injection molding equipment. But in the molding of large, thin-walled or complex shape of the product, it should be used in high aspect ratio and short compression section of the screw. Table 2-1 lists the PEEK injection molding process conditions.

3.Extrusion molding

PEEK can be prepared by extrusion molding of film, monofilament, rod, pipe and coated wire and other products.PEEK unstretched film crystallinity is low, after stretching and heat treatment of PEEK film, melting point and mechanical strength have significantly improved, in PET film and Polyimide film Kapton between, belongs to the C level Insulation Materials.PEEK film transparent, Japan Sumitomo Chemical Industries, Inc. PEEK film transparent, Sumitomo Chemical Industries, Japan, PEEK film, light transmission rate of 85% or so. Table 2-2 lists the properties of PEEK film.

Table 2-3 lists the process conditions for PEEK extrusion molding. It should be noted that when large parts with diameters greater than 6.3 cm are prepared, the inner layers and surfaces crack due to the large internal stresses generated by the difference in crystallization rates. This can be improved by high temperature annealing (300°C, several hours).

4. Laminate molding and electrostatic coating

PEEK as the matrix resin, and glass fiber or carbon fiber, or a mixture of the two composite, through the laminated molding can produce excellent performance of composite laminate materials, it is below 300 ℃, bending elasticity modulus retention rate is high (Table 2-4).

70% unidirectional carbon fiber reinforced PEEK will show higher strength and toughness, tensile strength at 23 ℃ up to 1540MPa, tensile modulus of elasticity of up to 130GPa. At present there is no organic solvent can completely dissolve PEEK, so it can not be coated with solution, but can be used in the formation of electrostatic coating of powder to get electrical insulation, corrosion resistance, heat resistance and water resistance of excellent PEEK powder coated metal. PEEK powder coated metal products.

5. Secondary processing

PEEK can be machined, ultrasonic welding, plating, sputtering and other methods for secondary processing. Also available epoxy resin, polyurethane, silicone and other adhesives for bonding. In order to improve the bonding strength, the surface of the parts can be used for pretreatment with acid.