Polyketone (POK) is a rare case where an engineering polymer does not try to be «slightly better nylon», but occupies a niche of its own. Wherever aggressive chemistry, intensive friction and impact risk meet in a single component, the list of viable materials narrows sharply. That intersection is exactly where polyketone is at home.
- POK is an aliphatic thermoplastic built from regularly alternating carbon monoxide (CO) and olefin units; the all-carbon backbone with carbonyl groups delivers chemical resistance, wear resistance and impact toughness at the same time.
- The melting point of Exablend® POK grades is 220 °C by DSC, and the glass transition temperature is 15 °C.
- The processing window is narrow: melt at 235–250 °C, mold around 80 °C; overheating triggers degradation.
- POK is not «universally better»: POM is stiffer and more dimensionally stable, while polyamides are cheaper and offer a broader range of reinforced grades.
This is an overview of the material class. If you already know what polyketone is and are deciding whether to move a specific part to POK, the practical angle is covered in our design guide «POK instead of POM and polyamide». The underlying chemistry and research base are covered in our review of polyketone research.
What polyketone is
Polyketone (POK; designated PK under ISO 1043-1) is an aliphatic thermoplastic polymer whose main chain consists of alternating carbon monoxide (CO) and olefin units. Commercial grades are mostly terpolymers: CO, ethylene and a small fraction of propylene.
It has a feature no other engineering thermoplastic shares: the polyketone main chain is built entirely from carbon atoms, with carbonyl groups (C=O) regularly embedded in it. A polyamide chain contains amide bonds, and those bonds are the ones vulnerable to hydrolysis. Polyketone has no such weak point in its backbone — hence its signature combination: chemical inertness, abrasion resistance and impact toughness at once.
Chemistry and structure
Picture a thread in which two units strictly alternate: one derived from a molecule of CO gas, the other from an olefin molecule. The result is a perfectly regular alternating copolymer:
This regularity produces high crystallinity, and with it stiffness and chemical resistance. The catch is that the pure CO-ethylene copolymer, according to published data, melts at around 257 °C — uncomfortably close to its thermal degradation temperature, which makes it hard to process.
The solution is elegant: a little propylene is added to the chain. Methyl branches disrupt the perfect crystal packing and lower the melting point to a workable 220 °C without destroying the remaining advantages. It is like tossing a handful of irregular bricks into an even course: the wall ends up slightly lower, but it can actually be built. This is why almost all modern commercial polyketones are CO/ethylene/propylene terpolymers.
Carbonyl groups are polar, so strong dipole-dipole interactions act between adjacent chains. Hence the resistance to hydrocarbons and fuels: non-polar gasoline simply has nothing to grip in such a structure.
What this structure delivers
Three class-level advantages of polyketone do not always fit into a table, so they are worth stating separately.
- Impact toughness. Polyketone will bend rather than crack — it takes an impact where polyacetal (POM) has already turned brittle.
- Wear resistance. According to base-resin producers, the abrasion resistance of polyketone exceeds POM by a wide margin (some sources quote an order of 10× and above). The actual advantage should be confirmed by testing on the specific friction pair.
- Hydrolytic stability. There is no amide bond in the backbone, so hot water and steam do not cleave the chain the way they do in an unprotected aliphatic polyamide.
Exablend® POK grades: data sheet values
In the Material Wizard portfolio, polyketone is offered under the Exablend® brand as mineral-, glass- and carbon fiber-reinforced grades. Below is a summary from the technical data sheets; all values were measured on dry-as-molded specimens.
| Grade | Reinforcement | Density, g/cm³ | Tensile strength, MPa | Tensile modulus, MPa | Impact strength | HDT, °C |
|---|---|---|---|---|---|---|
| Exablend® POK MF25 S | 25 % mineral | 1.40 | 55 | 2500 | 5 kJ/m² (Izod, notched) | 190 (0.45 MPa) |
| Exablend® POK GF30 S | 30 % glass fiber | 1.47 | 150 | 10 000 | 13 kJ/m² (Izod, notched) | 200 (1.8 MPa) |
| Exablend® POK GF50 S | 50 % glass fiber | 1.65 | 195 | 17 000 | 14 kJ/m² (Izod, notched) | 205 (1.8 MPa) |
| Exablend® POK CF20 S TRM | 20 % carbon fiber | 1.30 | 155 | 12 700 | 40 kJ/m² (Charpy, unnotched) | 213 (1.8 MPa) |
Methods: ISO 1183-1 (density), ISO 527-1/-2 (tensile), ISO 180/1A and ISO 179-1/1eU (impact), ISO 75-1/-2 (HDT), ISO 11357 (DSC). The melting point of all four grades is 220 °C.
Exablend® POK CF20 S TRM deserves a separate note: a surface resistivity of about 10³ Ω (IEC 62631-3-2) places the grade in the conductive range, while a moisture absorption of 0.4 % (23 °C, 50 % RH, ISO 62) keeps dimensions stable. That combination is sought for housings and fuel-system components where static charge must be dissipated.
Exablend® POK polyketone — the Material Wizard rangeMineral-, glass- and carbon fiber-reinforced grades · high wear and chemical resistance · grade selection for your partAvailable with delivery across Ukraine →Injection molding
Polyketone is harder to process than polyamide, yet entirely manageable. The window is narrow, and it is discipline in temperature control that separates a stable production run from scrap.
- Drying. The material is supplied pre-dried in moisture-proof bags, but once exposed to air the pellets rapidly pick up moisture. Take the drying schedule from the TDS of the specific grade.
- Melt temperature. 235–250 °C (up to 255 °C for Exablend® POK GF50 S). Overheating starts degradation, so the barrel profile is controlled and melt residence time is kept short.
- Mold temperature. Around 80 °C (typical range 60–90 °C) — for full crystallization and dimensional stability of the part.
- Pressure and speed. Molding pressure of 80–130 MPa, medium to high injection speed.
- Regrind. Up to 25 % may be returned without significant loss of properties, depending on processing conditions.
A shop already running technical thermoplastics can realistically master polyketone. But it should not be molded on improvisation: the narrow temperature window does not forgive a careless profile.
Polyketone next to POM and polyamide
POK is most often considered as a candidate to replace polyacetal or polyamide, so it helps to see the strengths and weaknesses side by side.
- Contact with fuels, glycols and cleaning solutions
- Friction pairs running without abundant lubrication
- Humid environments combined with impact loading
- Maximum stiffness and precision tolerances without chemical exposure — POM is often the more rational choice
- A broad range of reinforced grades at a lower price — polyamides
- Sustained load at high temperature — that is polyphthalamide territory
| Property | POK | POM | PA6 | PA66 |
|---|---|---|---|---|
| Chemical resistance (fuels, glycols) | very high | moderate | moderate to low | moderate |
| Wear resistance | very high | high | moderate | moderate |
| Impact toughness | very high | moderate | high (conditioned) | moderate |
| Water absorption | low to moderate | very low | high | moderate |
| Melting point, °C | 220 | 165–175 | 220 | 260 |
| Dimensional stability in humid environments | high | very high | low | moderate |
The honest conclusion: polyketone is not «universally better». POM is stiffer and absorbs even less water, so for precision, dimensionally stable parts it often remains the rational choice. Polyamides are cheaper and offer a broader range of reinforced grades; we covered the basic chemistry of that class in «What is polyamide 6». Polyketone starts to win when three requirements converge in a single component: aggressive chemistry, intensive friction and impact risk.
Designation and standards
Under ISO 1043-1, aliphatic polyketone is designated PK. As with other thermoplastics, a filler index is appended to the base code: PK-GF30 denotes polyketone with 30 % glass fiber, PK-CF denotes carbon fiber reinforcement. Mechanical performance is assessed to ISO 527 (tensile) and ISO 178 (flexural), impact strength to ISO 179 (Charpy) or ISO 180 (Izod), heat resistance to ISO 75 (HDT), and flammability to UL 94.
Where polyketone is used
- Fuel and fluid systems. Connectors, tubing, pump housings — anything in contact with gasoline, diesel or antifreeze. Here POK wins on chemical resistance where polyamide gradually degrades.
- Water meters and water treatment systems. Impellers, housings, fittings. Low dimensional change preserves metrological accuracy; potable water clearance is confirmed by the grade certificate.
- Gears, bushings and plain bearings. High wear resistance makes polyketone attractive for unlubricated friction pairs.
- Conveyor rollers and wheels. A combination of wear resistance, a low friction coefficient and impact toughness.
- Pipes and fittings. Chemical resistance plus impact toughness — for pressure applications and aggressive media.
- Barrier films and packaging. High barrier performance against oxygen and hydrocarbons.
- Conductive and antistatic parts. Carbon fiber-reinforced grades such as Exablend® POK CF20 S TRM — housings and functional elements where static charge must be dissipated.
A little history
Polyketone is produced by the catalytic copolymerization of carbon monoxide with olefins over palladium catalysts — a relatively young route that became industrially viable at the end of the 20th century. In the 1990s Shell brought the Carilon grade to market; the material looked promising but did not achieve broad commercial success at the time, and production was discontinued. Polyketone found its second wind in the 2010s, when the South Korean group Hyosung launched industrial production under the POKETONE brand. Today polyketone is a niche but steadily available engineering thermoplastic, not a laboratory curiosity.
Five expert questions before choosing polyketone
When is polyketone better than POM?
When the part operates in contact with fuels, glycols or other aggressive chemistry and is simultaneously exposed to impact. POM is stiffer and absorbs less water, but polyketone is markedly more resistant chemically and to impact. If maximum stiffness and precision dimensional stability are needed without chemical exposure, POM often remains the more rational option.
How does polyketone differ from polyamide in a humid environment?
Aliphatic polyamides absorb water readily, so the part changes dimensions and mechanical behavior; the amide bond is also vulnerable to hydrolysis. Polyketone absorbs markedly less water and is more stable in humid environments, although it yields to polyacetal here. For components in permanent contact with water this is often the decisive argument.
Is polyketone difficult to injection mold?
Harder than polyamide, but manageable. The temperature window is narrow: polyketone melts at 220 °C, and the melt is held within 235–250 °C. An accurate temperature profile, a mold temperature of around 80 °C and control of melt residence time in the barrel are critical. Pellets are dried before molding according to the grade TDS.
Can polyketone replace metal in friction pairs?
In a number of assemblies, yes. Thanks to its wear resistance and low friction coefficient, polyketone is used in gears, bushings and plain bearings, where it reduces noise and removes the need for lubrication. But the absolute stiffness of the polymer is lower than that of metal, so the part is normally redesigned for the polymer rather than copied from the metal drawing.
Is polyketone suitable for potable water contact?
Specific grades with the appropriate certification are suitable. Polyketone itself is non-toxic, which is what led to its adoption in water meters and water treatment systems, but for a formal application rely on the certificate of the selected grade rather than on the general material description.
Sources
- POKETONE — polyketone properties and chemistry, Hyosung Chemical
- POKETONE — technical overview, Mitsui Plastics
- Poketone (Polyketone PK), K.D. Feddersen
- Technical data sheets of Exablend® POK MF25 S, GF30 S, GF50 S and CF20 S TRM grades (Material Wizard).