PK Polyketone: Low Permeability, High Chemical Resistance for Harsh Environments

PK Polyketone is a high-performance engineering thermoplastic gaining recognition for its unique combination of low permeability, high chemical resistance, and robust mechanical performance in harsh environments. While not as widely known as commodity plastics, Polyketone offers a compelling solution for demanding applications across automotive, oil and gas, and industrial processing sectors where resistance to aggressive chemicals, minimal substance transmission, and durability under mechanical stress are paramount.

Understanding PK's properties is increasingly relevant for engineers specifying hose and tubing materials in fuel, chemical, and fluid transfer systems — as the clamping requirements for PK components directly influence clamp material and design selection. Where PK hoses or fittings are used, corrosion-resistant hose clamps in W4 or W5 stainless steel are the appropriate specification to match PK's chemical resistance at the connection point.

Composition and Structure

Polyketone (PK) is a linear, semi-crystalline thermoplastic polymer formed by the copolymerisation of carbon monoxide with alpha-olefins — typically ethylene and/or propylene. The perfectly alternating structure of carbon monoxide and olefin units in the polymer backbone gives rise to its distinctive properties. Two main grades exist:

• Copolymer (CO/ethylene): Higher crystallinity — improved barrier properties and chemical resistance; higher melting point.
• Terpolymer (CO/ethylene/propylene): Enhanced toughness and impact resistance at the cost of slightly reduced barrier performance — broader temperature and processing window.

This unique chemical architecture is the foundation for PK's resistance to chemical attack and its barrier properties — properties that distinguish it from PA66 and PA12 in the most chemically aggressive applications.

Low Permeability: An Excellent Barrier

One of PK's standout properties is its low permeability to gases and liquids. Substances have difficulty passing through the material, making it an excellent barrier — particularly valuable where containment, prevention of leakage, or protection from external elements is required.

Low permeability applications include:

• Fuel Systems: Components in automotive fuel handling where preventing fuel permeation is critical for efficiency and environmental compliance — a primary driver of PK adoption in European automotive OEM fuel line and connector applications.
• Chemical Storage and Transport: Liners, containers, and pipes for safely storing and transporting chemicals — minimising evaporation or leakage. When hoses connect to PK fittings, W4 stainless worm drive clamps maintain the chemical integrity of the connection point.
• High-Barrier Packaging: Films and containers for sensitive goods where preventing oxygen or moisture ingress — or volatile compound egress — is necessary to maintain product quality.
• Hoses and Tubing: Conveying gases or liquids where low diffusion through the hose wall is required.

High Chemical Resistance

PK exhibits high chemical resistance to a broad spectrum of aggressive substances. Its chemical structure — particularly the presence of ketone groups and the carbon-carbon backbone — provides inherent resistance to attack from many chemicals that degrade other polymers, including some that attack PA66.

PK demonstrates excellent resistance to:

• Hydrocarbons: Wide range of aliphatic and aromatic hydrocarbons, fuels, oils, and greases — superior to PA66 in continuous fuel immersion.
• Solvents: Many organic solvents that cause swelling or dissolution in other engineering plastics.
• Salt solutions: Resistant to many salt concentrations including marine brines.
• Dilute acids and bases: Good resistance to weak acids and alkalis — verify against specific chemistry, concentration, and temperature for each application.

Important limitation: strong inorganic acids and strong alkalis — especially at elevated temperatures — can degrade PK. Always verify chemical compatibility against specific fluid chemistry before specifying PK for highly aggressive media.

Where PK components operate in chemically aggressive environments and require metal clamps, specify W5 (316SS) clamps — matching the chemical resistance of the PK substrate at the connection point prevents the clamp becoming the weakest element of the assembly.

Durability in Harsh Environments

The combination of low permeability and high chemical resistance, coupled with strong mechanical properties, makes PK highly durable in harsh operating conditions:

• High Toughness and Impact Resistance: Withstands sudden shocks and impacts without fracturing — important for components in offshore and industrial environments subject to mechanical shock.
• Excellent Wear and Abrasion Resistance: Performs well in applications involving friction and material contact — extending component lifespan in abrasive environments.
• Good Fatigue Resistance: Resists failure under repeated stress cycles — relevant for hose and fitting components subject to pressure pulsation or vibration.
• Hydrolysis Resistance: Good stability in the presence of water and humid environments — an advantage over some other engineering plastics in aqueous applications and wet industrial environments.
• Moderate Temperature Performance: Maintains good mechanical properties across a useful temperature range for industrial and automotive applications — though not a high-temperature specialist material like PEEK.

Key Applications for PK Polyketone

• Automotive Fuel Systems: Fuel lines, connectors, pump components, and chemical reservoirs — PK's low permeability and fuel resistance make it a growing material of choice for European automotive OEM fuel system applications where traditional PA12 or PA11 may underperform.
• Oil and Gas: Seals, valve components, and downhole equipment where resistance to crude oil, natural gas, and corrosive fluids is essential — particularly where barrier performance and chemical resistance combine as requirements.
• Industrial Processing: Pumps, valves, filters, and chemical handling equipment in chemical plants and water treatment facilities with continuous exposure to aggressive chemicals.
• Pipes and Fittings: Demanding fluid transfer applications where chemical resistance and low permeability are required simultaneously — applications where PA6 or PP would be insufficient.
• Electrical and Electronics: Components in chemically exposed environments where moisture and chemical resistance are needed alongside good electrical insulation.
• Marine and Offshore: Components in saltwater-exposed equipment benefiting from PK's combined chemical and hydrolysis resistance.

Clamping PK Components: What to Specify

When hoses are connected to PK fittings or PK pipe systems require securing, clamp selection should match PK's chemical resistance profile:

• For fuel and hydrocarbon environments: Mikalor ASFA-S W4 or Jubilee W4 (304SS) provide the chemical resistance and mechanical strength required for fuel line connections.
• For marine, offshore, or high-chloride chemical environments: Upgrade to Mikalor Supra W5 or Mikalor ASFA-S W5 (316SS) — matching PK's chloride resistance with equivalent clamp specification.
• For non-metallic requirements: Where metal clamps are unsuitable, HCL's Herbie Clip and Ezyclamp PA66 polymer clamps provide fully corrosion-free clamping — confirm PA66 compatibility against the specific chemical environment.

Conclusion

PK Polyketone is a high-performance engineering plastic offering a compelling combination of low permeability and high chemical resistance — making it a durable material choice for harsh applications across automotive fuel systems, oil and gas, offshore, and industrial chemical processing. Its resistance to hydrocarbons, solvents, and aqueous environments positions it as a step above PA66 and PA12 in the most chemically demanding fluid handling applications. When specifying clamps for PK pipe and fitting systems, match the clamp material grade to the chemical environment: W4 for general chemical and fuel applications, W5 for marine and high-chloride environments. Browse HCL's range of Mikalor, Jubilee, and polymer hose clamps, or contact our technical team for clamp selection advice for PK and chemically resistant hose applications.