Polymer materials in industrial components: properties and applications of PTFE, PEEK, POM

1. Introduction

The industrial landscape of Ukraine, which constantly strives to increase the efficiency and continuity of production cycles, critically depends on the reliability and durability of its production components. In conditions where traditional metal parts are often exposed to aggressive chemical environments, extreme temperatures or excessive wear, advanced polymer materials become indispensable solutions. Polytetrafluoroethylene (PTFE), Polyetheretherketone (PEEK) and Polyoxymethylene (POM) represent a class of high-performance plastics that are fundamentally changing operational paradigms in sectors from chemical processing to precision engineering. This article provides an in-depth technical guide to the properties, applications, selection criteria and best operating practices for these key polymers, highlighting their role in increasing equipment reliability and extending service life in challenging industrial environments, in full compliance with national and international standards such as DSTU, EN and ISO.

2. Fundamental principles

Polymers are macromolecules consisting of repeating structural units (monomers). Their unique properties are determined by their chemical structure, molecular weight, and chain organization.

2.1. Polytetrafluoroethylene (PTFE)

PTFE is a fluoropolymer consisting of repeating units of tetrafluoroethylene (-CF₂-CF₂-)n. Its exceptional chemical inertness is due to the high energy of the C-F bond and the dense shielding of the carbon chain by fluorine atoms, which makes it resistant to most chemical reagents. Symmetrical structure and strong intermolecular forces ensure high melting point and mechanical stability. The low coefficient of friction is due to the low surface energy and slippage of the chains.

2.2. Polyetheretherketone (PEEK)

PEEK is a semi-crystalline thermoplastic belonging to the polyketone family. Its structure is characterized by the presence of ether (-O-) and ketone (-CO-) bonds, which alternate with phenyl groups (aromatic rings). These aromatic rings provide rigidity and high thermal stability, while the ether linkages provide some flexibility that contributes to high fatigue strength. The crystalline structure of PEEK ensures its high strength, rigidity and exceptional chemical resistance even at elevated temperatures.

2.3. Polyoxymethylene (POM)

POM, also known as polyacetal, is a highly crystalline thermoplastic composed of repeating units of formaldehyde (-CH₂-O-)n. Its highly regular structure allows the formation of dense crystalline regions, which gives it high hardness, stiffness and strength. The presence of oxygen atoms in the chain contributes to good antifriction properties and wear resistance. Homopolymers (POM-H) and copolymers (POM-C) are distinguished, where copolymers have slightly lower crystallinity, but better thermal stability and resistance to hydrolysis.

3. Technical characteristics and standards

Choosing a polymer for industrial use requires careful analysis of its technical characteristics and compliance with industry standards.

3.1. Polytetrafluoroethylene (PTFE)

• Working temperature: from -200 °C to +260 °C (short-term up to +300 °C).
• Friction coefficient: 0.04-0.10 (one of the lowest).
• Chemical resistance: Exceptional to most acids, alkalis, solvents, with the exception of molten alkali metals and elemental fluorine.
• Dielectric strength: up to 180 kV/mm (according to IEC 60243-1).
• Water absorption: <0.01% (according to ISO 62).
• Certification: Often meets FDA 21 CFR 177.1550 for food contact. CE and UkrSEPRO certification confirms compliance with European and Ukrainian safety standards.
• Standards: ISO 13000 (PTFE semi-finished products), ASTM D4894/D4895 (PTFE powders).

3.2. Polyetheretherketone (PEEK)

• Operating temperature: from -60 °C to +260 °C (long-term operation), glass transition temperature +143 °C, melting temperature +343 °C.
• Tensile strength: 90–100 MPa (according to ISO 527).
• Modulus of elasticity: 3.7–4.5 GPa.
• Abrasion resistance: High, especially in filled versions (for example, with carbon fiber).
• Chemical resistance: High to most chemicals, hot water and steam, hydrolysis, except concentrated sulfuric acid.
• Fire resistance: UL 94 V-0 (natural).
• Biocompatibility: Meets ISO 10993 and ASTM F2026 for medical implants.
• Certification: CE, UkrSEPRO, as well as FDA for medical and food applications.
• Standards: ISO 23153 (PEEK classification), ISO 527 (tensile strength), ISO 178 (flexural strength).

3.3. Polyoxymethylene (POM)

• Working temperature: from -40 °C to +100 °C (briefly up to +140 °C), melting point 165–178 °C.
• Tensile strength: 60–90 MPa (according to ISO 527).
• Modulus of elasticity: 2.5–3.5 GPa.
• Coefficient of friction: 0.25-0.35 (with low slip resistance).
• Hardness: 80–85 according to Shore D.
• Chemical resistance: Good for organic solvents, fuels, lubricants, alkalis. Sensitive to strong acids and oxidizing agents.
• Water absorption: 0.2% (according to ISO 62), which ensures high dimensional stability.
• Certification: Many brands of POM have FDA and EU 10/2011 food contact approvals. CE and UkrSEPRO certification.
• Standards: ISO 9988 (POM classification), ASTM D6778 (POM classification), ASTM D1894 (coefficient of friction).

4. Guide to the selection and calculation of sizes

Correct selection of the polymer material and accurate calculation of component dimensions are critical to ensure reliability and durability. Below are the factors and criteria for making engineering decisions.

4.1. Selection criteria

When choosing between PTFE, PEEK and POM, the following key parameters should be considered:

• Temperature regime: High temperatures (above +100 °C) definitely indicate PEEK or PTFE. POM is suitable for moderate temperatures up to +100 °C.
• Chemical environment: For the most aggressive environments (acids, alkalis, solvents) PTFE is unsurpassed. PEEK also exhibits high chemical resistance. POM is resistant to many organic substances, but sensitive to strong acids.
• Mechanical loads: For high mechanical loads, wear resistance and fatigue strength, PEEK is the leader. POM provides good stiffness and strength under moderate loads. PTFE has lower mechanical properties, but excellent anti-friction properties.
• Abrasion and Friction: PTFE (with or without fillers) and POM are excellent for friction and wear conditions. PEEK (especially with fillers) also exhibits exceptional wear resistance.
• Dimensional Accuracy: POM is characterized by low water absorption and high dimensional stability, making it ideal for precision parts. PEEK also has high stability.
• Cost: PTFE and POM are generally more economical options compared to PEEK, which is a premium polymer for extreme conditions.

4.2. Calculation of dimensions (example for sliding sleeves)

When calculating lubrication-free polymer bushings, it is important to consider heat generation and allowable pressure-velocity (PV factor).

Formula for calculating the maximum working pressure:
P_max = (PV_limit) / V
Where:

• P_max is the maximum allowable pressure (MPa)
• PV_limit is the limiting PV factor of the material (MPa·m/s)
• V is the sliding speed (m/s)

Example of PV factors:

• PTFE (unfilled): 0.2–0.5 MPa·m/s
• PTFE (with fillers, e.g. fiberglass, bronze): 1.0–5.0 MPa·m/s
• POM: 0.1–0.3 MPa·m/s
• PEEK (unfilled): 0.5–1.0 MPa·m/s
• PEEK (with fillers, for example, carbon fiber): 3.0–10.0 MPa·m/s

Calculation of thermal expansion:
ΔL = L₀ * α * ΔT
Where:

• ΔL is the change in length (mm)
• L₀ — initial length (mm)
• α is the coefficient of linear thermal expansion (mm/(mm·°C))
• ΔT — temperature change (°C)

Typical coefficients of thermal expansion (α × 10⁻⁵, °C⁻¹):

• PTFE: 8–10
• PEEK: 4–6
• POM: 10–14

This allows engineers to account for mounting clearances and minimize thermal stresses.

5. Recommendations for installation and commissioning

Even the most advanced polymer component will not reach its design life without proper installation and compliance with operational standards.

• Cleanliness: Installation must be carried out in a clean environment. Polymer surfaces are sensitive to abrasive particles that can lead to premature wear.
• Tolerances and clearances: Always consider thermal expansion coefficients. For polymer bushings and seals, it is necessary to provide sufficient gaps to compensate for thermal expansion, especially when operating in a wide temperature range. Excessive compression may cause creep or warping.
• Conjugation surface: For optimal operation and minimization of wear of polymer components (especially seals and sliding bearings), the surface quality of the metal parts that come into contact with them is critically important. The recommended surface roughness (Ra) is 0.4-0.8 µm for PTFE and POM, and 0.2-0.4 µm for PEEK.
• Tightening: Avoid excessive tightening of fasteners when installing polymer parts. This can cause internal stresses, material creep and subsequent deformation or failure. Use the recommended tightening torques.
• Compatibility: Before commissioning, check the chemical compatibility of the polymer with all working media (liquids, gases, lubricants) and cleaners.
• Initial Run: When first running equipment with new polymer components (especially bearings and seals), it is recommended to gradually increase the load and speed, allowing the material to adjust. This reduces the likelihood of initial wear.

6. Types of failures and root cause analysis

Understanding the typical failure modes of polymer components allows engineers to effectively diagnose and prevent reoccurrences, increasing the MTBF (mean time between failure) of the equipment.

6.1. Typical types of failures

• Creep: Deformation of material under constant load for a long time, especially at elevated temperatures. It manifests itself as a gradual decrease in the thickness of the seal or a change in the geometry of the bearing sleeve.
  • Visual signs: Constant deformation, "squeezing out" of the material from under the load.
  • Reason: Exceeding the permissible load, long-term effect of high temperature, wrong choice of material for a specific load.
• Thermal degradation: Destruction of the polymer chain due to exceeding the maximum operating temperature.
  • Visual signs: Color change (darkening, charring), brittleness, appearance of cracks, loss of shape, smoke, characteristic smell.
  • Reason: Overheating, insufficient heat dissipation.
• Chemical degradation: Destruction of material as a result of exposure to incompatible chemical reagents.
  • Visual signs: Swelling, softening, cracking, discoloration, loss of mechanical properties (breaks easily).
  • Reason: Contact with aggressive acids, alkalis, solvents for which the material is not intended.
• Abrasive wear: The removal of surface material by friction against hard particles or an uneven mating surface.
  • Visual signs: Furrows, scratches, matte surface, reduction in thickness, loss of tightness.
  • Reason: Insufficient cleanliness of the working environment, contamination, incorrect surface roughness of the metal part.
• Fatigue failure: Cracking or breaking of a material under the action of cyclic loads.
  • Visual signs: Cracks spreading from stress concentration points, subsequent complete destruction.
  • Reason: Constant vibrations, cyclic pressures, insufficient material strength for dynamic conditions.

6.2. Root cause analysis

To effectively eliminate the problem, it is necessary to conduct a systematic analysis:

1. Data collection: Record operating conditions (temperature, pressure, environment, load, duration), type of failure, visual signs.
2. Component Inspection: Detailed visual inspection, possibly using a microscope.
3. Comparison with the new component: Detect changes in size, color, texture.
4. Analysis of conditions: Were the recommended operating parameters (temperature, pressure, chemical exposure) violated?
5. Documentation: Check drawings, material specifications, installation instructions.
6. Laboratory tests: In complex cases, analyzes such as infrared spectroscopy (FTIR) to detect chemical degradation or scanning electron microscopy (SEM) to analyze the wear surface may be required.

7. Predictive maintenance and condition monitoring

Implementing predictive maintenance strategies for polymer components allows you to predict potential failures and plan interventions before critical situations occur, significantly reducing downtime and operating costs.

• Visual inspection: Regular visual inspection is the basic method. Check for visible signs of wear, deformation, discoloration, cracks or "squeezing" of the material. Particular attention should be paid to seals and moving elements.
• Thermography: Using thermal imagers to monitor the temperature of polymer bearings, bushings and seals. An abnormal increase in temperature may indicate increased friction, overload, or the beginning of destruction. For example, exceeding the operating temperature of PEEK by 20 °C can reduce its service life several times.
• Vibration analysis: For polymer bearings or dampers, a change in the vibration spectrum can indicate material deterioration, increased clearances, or wear. This method allows you to detect problems at an early stage.
• Acoustic monitoring: A change in noise from working polymer parts can be an indicator of wear.
• Monitoring of the working environment: Regular analysis of the chemical composition of liquids or gases in contact with the polymer allows you to identify potentially aggressive impurities that can cause degradation.
• Dimensional measurements: Periodic measurements of key dimensions of polymer seals, bushings or guides. Deformation or dimensional changes may indicate material creep or excessive wear. Tolerances for precision POM parts can be ±0.02mm.
• Temporary Maintenance (TBM): Scheduled replacement intervals can be established for certain polymer components based on MTBF statistics. For example, some PTFE seals in aggressive environments can have an MTBF of 8,000 to 12,000 hours, while PEEK bearings in mild environments can have an MTBF of over 50,000 hours.

8. Comparison matrix

For a visual comparison of the key characteristics of PTFE, PEEK and POM, which are decisive when choosing a material for specific industrial tasks, the following table is presented.

9. Conclusion

The choice between PTFE, PEEK and POM is a strategic engineering decision that directly affects the reliability, durability and cost-effectiveness of industrial equipment. PTFE remains unsurpassed for applications requiring exceptional chemical inertness and minimal friction over a wide temperature range. PEEK is the optimal choice for critical components exposed to high mechanical loads, extreme temperatures and aggressive environments, ensuring maximum reliability. POM is ideal for precision parts where high stiffness, dimensional stability and good wear resistance at moderate temperatures are required.

UNITEC-D GmbH is a reliable partner for Ukrainian industry, offering a wide range of industrial components made of PTFE, PEEK and POM, which meet the highest quality standards and are certified according to CE and UkrSEPRO. Our experts are ready to provide qualified advice and help in choosing the optimal material to solve your unique engineering tasks.

For detailed information on available polymer components and technical support, visit our electronic catalog: UNITEC-D E-Catalog

10. Links

1. ISO 13000: Plastics — Polytetrafluoroethylene (PTFE) semi-finished products — Specification and methods of test.
2. ISO 527: Plastics — Determination of tensile properties.
3. ISO 10993: Biological evaluation of medical devices.
4. ASTM D4894: Standard Specification for Polytetrafluoroethylene (PTFE) Granular Molding and Ram Extrusion Materials.
5. Victrex (www.victrex.com) — Technical data and whitepapers on PEEK.
6. DuPont (www.dupont.com) — Technical information on Delrin (POM) and Teflon (PTFE).