Polyketone High-Performance Thermoplastic Polymer
Aliphatic Polyketone (PK) is a high-performance thermoplastic polymer with a melting point of 220°C. This is the result of polar ketone groups in the polymer backbone creating a strong attraction between polymer chains. Polyketone (PK) meets the demands of a wide range of applications and has been enjoying somewhat of a renaissance thanks to its environmental credentials relative to other polymers. This is due to comonomer CO (carbon monoxide) in the structure of the polyketone. An industrial “waste” gas which can contribute to global warming, it bonds with a polymer to form a highly favourable monomer.
Polyketone has several properties which no other polymer has in this combination. Freshly injection-moulded polyketone has the greatest yield strain (over 20 %) compared to all other semi-crystalline polymers, virtually independently of moisture. This tremendous elasticity gives many components made of PK a high degree of safety in the design phase.
The outstanding characteristics of PK:
• excellent resilience
• reduced moisture absorbtion
• good tribological properties
• good resistance to chemicals
• good hydrolysis resistance
• shorter cycle times
Injection molding process
Polyketone tends to thermo-oxidative degradation and / or crosslinking reactions under excessive thermal stress. This can be recognized by an increase in viscosity and / or the appearance of dark spots in natural colored compounds. During the injection molding process, a residence time of 10 minutes should not be exceeded.
AKRO-PLASTIC succeeded in developing a product series, which is characterized by a larger process window during processing. As you can see from the graph, the injection pressure of the currently available AKROTEK® PK-VM GF 30 black(4896) increases continuously with the increase of the dwell time in the injection molding unit and has reached a pressure maximum at a dwell time of 10 min. The optimized variant with improved stabilization, AKROTEK® PK-VM GF 30 black (8655), exhibits an almost constant injection pressure over a wide dwell time range.
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AKROTEK® PK-VM GF 30 FR orange (8537) is a Polyketone with 30% glass-fibers and flame retardant free of halogens similar to RAL 2003. This grade meets the highest requirements for flammability such as UL94 V0 at 0,8 and electrical properties such as CTI of 600 V. This grade is optimized to the requirements of larger processing windows. Engineered for injection moulding this material can also be 3D-printed using pellet extrusion in large scale additive manufacturing. Read more about the flame retardent here.
Freshly injection-moulded polyketone has the greatest yield strain (over 20 %) compared with all other semi-crystalline polymers, virtually independently of moisture. This tremendous elasticity gives many components made of AKROTEK® PK a high degree of safety in the design phase.
AKROTEK® PK is particularly well suited for designs which must exhibit constant mechanics even under changing climatic conditions.
Polyketone has an inherently low moisture absorption. Tests according to ISO 1110 show that all tested AKROTEK® PK compounds reach their equilibrium moisture after just 2 to 3 days, compared with polyamide 6.6 compounds, which require over 20 days.
Moisture absorption vs. Exposure time 500 h at 70 °C and 62 % rel. humidity following ISO 1110.
The measured dynamic friction coefficient and specific wear rate show outstanding values with even the standard AKROTEK® PK grades. Our TM (tribologically modified) grades can significantly reduce both wear and the dynamic glide coefficient.
Universal Tribometer Set-Up
Pin-Plate Principle: We have tested the tribological properties of various AKROTEK® PK grades using a universal tribometer according to the “pin-plate principle”. With this method, a sample taken from a tension test bar is pressed against an oscillating steel plate (100Cr6).
The Least Wear
It may not be possible for design reasons to avoid pairings of similar friction surfaces, AKROTEK® PK shows the least wear of all polymers tested. When different materials are used, a combination with PA is good, and a combination with POM is the best pairing by far.
By means of common welding processes, individual components can be joined together and show a high weld seam strength, even when these weld seams are under load. For example, the weld strength of a component made of polyketone that is in contact with water/glycol is much stronger than that of a component made of polyamide. This is because it is not naturally resistant to water/glycol.
Infrared welding is a contact-free welding method in which the components are warmed with an infrared radiator and then welded under joining pressure. In the infrared welding method, AKROTEK® PK-HM demonstrates welding seam resistances of over 90 % of the initial stability. This extremely high figure enables welded designs with virtually no mechanical weakness in the seam area. The strength of AKROTEK® PK-HM GF 30 is almost at the same level as dry AKROMID® B3 GF 30. Thus nearly 90% of the polymer strength is achieved with glass fibre reinforced polyketone.
Typical Infrared Welding parameters are:
- Cooling-time: 40 seconds
- Warm-up distance: 18,5 mm
- Warm-up time: 20-30 seconds
- Power: 700W – short wave
- Joining pressure: 2-5 N/mm²
Resistance to Media
Plastic components that come into contact with water/glycol mixtures require special compounds. Here, good chemical resistance and low water absorption are the be-all and end-all. The PA 6.6 GF 30 HR established on the market is reaching its limits here, especially in the area of thermal management for the e-mobility sector.
Polyketone compounds inherently exhibit very low moisture absorption, which means that the components show very good dimensional stability in humid environments. The excellent hydrolysis resistance to water / glycol is one of the major strengths of AKROTEK® PK.
When ageing according to the VW standard (TL 52682 over 1000h/135°C), only a very small decrease of the material strength is visible compared to PA 6.6 GF 30 HSRL (see figure). This provides a significant advantage in the design of the component geometry. Thin component wall thicknesses with constant pressure ratios in the component can thus be realized without any problems.
Resistance to Media
Further information on the media resistance of AKROTEK® PK can be found on the right link.
The minimal loss of tensile strength in the samples exposed to ethanol, methanol or mixtures of the two materials results from the plasticising effect of alcohol. The tensile strength can be restored by drying the samples before testing.
Resistance to Media
The chemical resistance of AKROTEK® PK is one of the materials’ biggest strengths. It resists corrosion due to weak acids, which typically corrode longchain polyamides such as PA 12 and PA 6.6. Only light surface discolorations can be observed after 30-day conditioning in 10 % hydrochloric acid, 30 % sulphuric acid or battery acid. The elongation at break remains virtually at the starting level, however.
Trouble Shooting Guide
When injection molding aliphatic polyketone (PK), various errors can occur that affect the quality of the parts produced. Here are some common polyketone injection molding problems and how to improve them.
AKROTEK® PK is an absolutely versatile material. The most important markets for AKROTEK® PK are the automotive, furniture and food industry and mechanical engineering. Have a look at the polyketone with universal qualifications and its applications.
Disclaimer: All specifications and information given on this website are based on our current knowledge and experience. A legally binding promise of certain characteristics or suitability for a concrete individual case cannot be derived from this information. The information supplied here is not intended to release processors and users from the responsibility of carrying out their own tests and inspections in each concrete individual case. AKROMID®, AKROLEN®, AKROLOY®, AKROTEK®, ICX®, PRECITE® and DIA(hr)LOG® are registered trademarks of AKRO-PLASTIC GmbH.