Polyoxymethylene (POM)

Polyoxymethylene (POM), or acetal or polyacetal, is an engineering thermoplastic used in precision parts requiring high stiffness, low friction, and excellent dimensional stability. It is a polymer derived from formaldehyde known for its high mechanical strength and rigidity, making it suitable for various industrial applications. For more detailed information on this polymer, read the article until the end.

Polyoxymethylene (POM) is a high-performance engineering thermoplastic characterized by its repeating units of formaldehyde monomers. The chemical structure of Polyoxymethylene monomer can be simplified to the formula (CH₂O)ₙ, forming long polymer chains. This semi-crystalline Polyoxymethylene structure, with tightly packed polymer chains, gives POM its notable strength, rigidity, and excellent dimensional stability. These properties make it ideal for precision parts requiring high stiffness and low friction, such as gears, bearings, and fasteners.

There are two primary forms of polyoxymethylene (POM): copolymer POM and homopolymer POM. Each type is employed in a variety of applications based on its unique qualities.

• Composition: Made solely from the polymerization of formaldehyde monomers.
• Properties: Offers excellent mechanical properties, high stiffness, and exceptional dimensional stability. It typically exhibits higher tensile strength compared to copolymer POM.
• Applications: Commonly used in applications requiring high strength and rigidity, such as gears, bearings, and automotive components. However, it may suffer from issues like centerline porosity during processing and higher formaldehyde outgassing.

• Composition: Produced by copolymerizing formaldehyde with a small amount of a comonomer, often an acetaldehyde derivative.
• Properties: Provides improved resistance to thermal degradation and hydrolysis, making it suitable for more demanding environments. It generally has lower formaldehyde outgassing and better processing characteristics than homopolymer POM.
• Applications: Ideal for applications requiring good chemical resistance and lower moisture absorption, such as in medical devices and food service equipment.

In addition to the two main types, there are several modified grades of POM tailored for specific applications:

• Impact-modified POM: Incorporates impact modifiers to enhance toughness and resistance to shock, suitable for automotive interiors and sporting goods.
• Reinforced POM: Formulated with additives like glass or carbon fibers to improve mechanical properties such as strength and stiffness, often used in structural components.
• Low-friction POM: Designed to have a lower coefficient of friction, reducing wear in sliding or rotating applications like gears and bearings.
• Food-grade POM: Specifically formulated to meet safety standards for food contact applications.

When it comes to choosing between homopolymer POM and copolymer POM, understanding their differences can help you make the best decision for your specific needs. Let’s break down their performance and application differences:

1. Mechanical Properties

Homopolymer POM generally boasts greater mechanical strength and stiffness compared to copolymer POM. This makes it a strong contender for applications that require robust structural integrity.

2. Thermal Stability

On the other hand, copolymer POM is more resilient to thermal deterioration. This quality makes it ideal for applications that involve higher temperatures, where heat resistance is crucial.

3. Chemical Resistance

When it comes to chemical exposure, copolymer POM often outperforms homopolymer POM in resisting certain chemicals and solvents. This enhanced resistance opens up new possibilities for its use in various environments.

4. Processability

Copolymer POM also features a lower melt viscosity, which simplifies manufacturing processes, especially when creating complex part geometries. This can lead to more efficient production methods.

1. Automotive

In the automotive sector, while copolymer POM is suitable for parts that require superior heat stability and chemical resistance, homopolymer POM is typically favored for applications demanding strong mechanical strength and wear resistance.

2. Medical

For medical applications, copolymer POM is often the preferred choice due to its biocompatibility and ability to withstand cleaning solvents, ensuring safety and reliability in healthcare settings.

3. Electronics

In electronics and electrical engineering, copolymer POM is commonly used where higher chemical and heat resistance is needed, making it an excellent option for various components.

Automotive Industry

• Precision Components: POM is extensively used in automotive applications such as gears, bearings, fuel system components (fuel pumps, rails), and interior parts (door handles, latches) due to its durability and dimensional stability.
• Low Friction Applications: Parts like windshield wiper gears and power steering components benefit from POM’s low friction properties, enhancing performance and longevity.

2. Electronics

Electrical Insulation: POM’s excellent electrical insulation properties make it ideal for connectors, switches, and circuit breakers. Its low dielectric constant further enhances its suitability for electronic applications.

3. Food Processing

FDA-Compliant Uses: POM is used in food contact applications such as conveyor systems, dosing pumps, and food chutes. Its resistance to fats and oils makes it suitable for various food processing equipment.

4. Medical Devices

Biocompatibility: The material is utilized in medical devices like inhalers and insulin pens due to its purity and stabilizability. It is also found in components for dialysis machines and respiratory devices.

5. Consumer Goods

• Household Appliances: POM is employed in components of various appliances such as coffee makers, dishwashers, and vacuum cleaners. Its resistance to household chemicals makes it ideal for parts like impellers and control knobs.
• Stationery: It is commonly used for making pen bodies and caps due to its precision and durability.

6. Sports Equipment

Paintball and Airsoft: POM is used in paintball markers and airsoft guns for parts that require low weight but high durability, such as handles and bolts.

7. Miscellaneous Applications

• Furniture Hardware: POM is utilized in locks, hinges, and rollers for sliding mechanisms in furniture.
• Musical Instruments: Due to its acoustic properties, it is used in picks, flute mouthpieces, and other instrument components.

Because of its many well-known qualities, polyoxymethylene is an excellent choice for precision engineering applications. Let’s examine each of these characteristics in more detail:

• High Strength and Stiffness: POM exhibits remarkable tensile strength, with values typically ranging from 60 to 75 MPa for homopolymers and slightly lower for copolymers. Its stiffness can reach up to 3,400 MPa, making it suitable for structural applications.
• Impact Resistance: POM has good impact strength, allowing it to withstand sudden shocks without significant damage, which is crucial for mechanical components.

• Low Shrinkage and Creep Resistance: POM maintains dimensional stability under varying temperatures and humidity levels. Its shrinkage rate is generally between 1.2% and 3.5%, depending on the formulation used. It also shows low creep under long-term loads, ensuring that it retains its shape over time.

• Low Coefficient of Friction: POM has a low coefficient of friction, which enhances its performance in sliding applications such as gears and bearings. This property minimizes wear and prolongs the life of components made from POM.

• Temperature Range: POM can operate effectively in a wide temperature range, with melting temperatures around 166°C for copolymers and 178°C for homopolymers. It remains stable at temperatures as low as -40°C.
• Heat Resistance: It can withstand short-term exposure to temperatures exceeding 100°C without significant degradation, making it suitable for various high-temperature applications.

• Solvent and Fuel Resistance: POM is resistant to many solvents, fuels, and chemicals, making it ideal for use in environments where exposure to such substances is common. However, it can be affected by strong acids and bases.
• Low Hygroscopicity: With a water absorption rate of about 0.22% to 0.25%, POM exhibits low hygroscopicity, which helps maintain its mechanical properties in humid conditions.

• Good Dielectric Strength: POM has excellent electrical insulation properties, making it suitable for electrical and electronic applications. Its high dielectric strength ensures safe operation in various electrical environments.

• Ease of Machining: POM can be easily machined into precise shapes using conventional methods, allowing for the production of intricate parts with tight tolerances.
• Narrow Processing Temperature Range: The processing temperature for POM is relatively narrow (170°C to 215°C), requiring careful control during manufacturing to avoid degradation.

Polyoxymethylene represents a pinnacle of engineering thermoplastic design, offering unparalleled performance across diverse applications. Its unique combination of mechanical strength, dimensional stability, and versatility makes it an invaluable material in modern manufacturing.