Polyoxymethylene (POM), often referred to as acetal or polyacetal, is a versatile engineering plastic that answers the question, “what is polyoxymethylene?” It is used for parts requiring high strength and precision, excelling in applications from automotive to electronics. This article covers its composition, properties, and uses.
What Is Polyoxymethylene?
Polyoxymethylene, also known as acetal or polyacetal, is a high-performance engineering thermoplastic with no side chains, high density, and high crystallinity.
This semi-crystalline thermoplastic is commonly available in white or black plastic pellets and boasts excellent mechanical properties such as:
strength
modulus
wear resistance
toughness
fatigue resistance
creep resistance
POM ranks among the top five engineering plastics due to its excellent electrical insulation, solvent resistance, and ease of processing, making it ideal for diverse applications.
Chemical Composition of POM
The chemical composition of POM is primarily based on Polyoxymethylene, with the chemical formula (-CH₂-O-)n. This semi-crystalline thermoplastic is characterized by a high density of C-O bonds, which are shorter than C-C bonds, resulting in a higher cohesive energy density and overall density compared to polyethylene.
Its lack of side chains and linear polymer structure endow high molecular weight POM with remarkable rigidity and strength.
Historical Development of POM
POM’s development started in the 1920s when Hermann Staudinger investigated its polymerization and structure.
Commercial production of POM material started in the 1960s with DuPont’s Delrin and Celanese’s Hostaform. DuPont’s commercialization efforts began after patenting the homopolymer form, while Celanese Corporation introduced it under the name ‘Celcon’ in the 1950s.
Staudinger’s groundbreaking work paved the way for POM’s development, earning him the Nobel Prize in Chemistry in 1953.
Key Properties Of POM Material
POM stands out due to its metal-like hardness, strength, and rigidity, making it suitable for a wide range of applications. Self-lubrication, fatigue resistance, and elasticity across a range of temperatures and humidity levels boost its attractiveness.
The material’s chemical resistance, low moisture absorption, and excellent wear behavior make it a versatile choice for numerous industries. We will explore the physical, chemical, mechanical, and thermal properties of POM.
Physical Properties
POM exhibits impressive mechanical strength and rigidity, with a high tensile strength ranging from 60 to 70 MPa and a modulus of elasticity that rivals some metals. Its low coefficient of friction, comparable to PTFE, and excellent wear resistance make it ideal for moving parts like gears and bearings.
Additionally, it retains good dimensional stability and excellent dimensional stability under changing environmental conditions and mechanical stress.
Chemical Resistance
Polyoxymethylene’s exceptional chemical stability makes it ideal for applications with expected chemical exposure. It can withstand various solvents and chemicals, including oils, greases, and many organic compounds, without significant degradation. However, exposure to strong acids requires caution, as POM’s resistance is limited in these environments.
The copolymer variant, POM-C, offers higher chemical resistance and a lower melting point compared to the homopolymer, POM-H.
Mechanical Properties
POM is recognized for its outstanding tensile strength. This property allows it to endure heavy loads and resist deformation. Creep resistance ensures long-term performance, while machinability allows for precise manufacturing of intricate designs.
Low melt viscosity ensures smooth flow during injection molding, enabling high-precision parts with tight tolerances.
Thermal Properties
POM exhibits remarkable thermal stability, suitable for various applications across a broad temperature range. Its high melting point, typically around 165–175°C for copolymers and slightly higher for homopolymers, allows it to perform effectively in extreme environments without deformation. It performs reliably from -40°C to 100°C, or higher with additives, and its low thermal expansion coefficient maintains precision amid temperature fluctuations.
Prolonged exposure to temperatures near its melting point can cause creep or deformation, especially in homopolymers.
Types of Polyoxymethylene
Polyoxymethylene is available in two primary types: homopolymer and copolymer. Each type has unique characteristics that make it suitable for specific applications. Recognizing these differences helps in choosing the right POM material for specific needs.
Additionally, modified grades of POM are available, offering tailored properties for specialized uses.
POM Homopolymer
Homopolymer POM, like Delrin®, is noted for its high strength and rigidity, ideal for demanding applications. It has higher density, crystallinity, and melting point compared to copolymer POM but exhibits lower thermal stability and a narrower processing temperature range.
Despite limitations, the high performance of acetal copolymer makes it favored for applications needing exceptional mechanical properties, particularly those utilizing acetal polymer.
POM Copolymer
POM copolymer’s modifications enhance its properties, making it suitable for applications needing improved performance. It offers better chemical resistance and can withstand exposure to various solvents and harsh chemicals. The copolymer’s structure contributes to a lower tendency to degrade under stress, extending its usability with pom resin.
Its better thermal stability and wider processing temperature range make POM copolymer ideal for applications requiring balanced properties.
Modified POM Grades
Modified grades of POM, such as impact-modified and reinforced types, enhance toughness and are designed for specialized uses. Impact-modified POM boosts toughness and reduces brittleness, suitable for high impact resistance applications.
Reinforced grades improve strength and rigidity for demanding industrial applications. Modifying concentrates can tailor POM properties, balancing impact resistance with its inherent characteristics.
Manufacturing Processes For POM
Manufacturing processes for POM are vital for creating components that meet industry performance standards. These include injection molding, extrusion and blow molding, and machining and 3D printing.
Each method offers unique advantages and is selected based on the desired properties of the final product.
Injection Molding
Injection molding enables the production of complex POM parts with tight tolerances, suitable for high-volume manufacturing. It allows for the creation of intricate shapes with high precision, ideal for engineering plastics applications.
However, precise temperature control is necessary to avoid degradation of the material during the pom injection molding process.
Extrusion and Blow Molding
Extrusion and blow molding efficiently produce POM sheets and hollow components. Extrusion produces continuous shapes like sheets and rods, while blow molding is used for hollow parts.
These processes are crucial for manufacturing components with excellent mechanical properties.
Machining and 3D Printing
POM is known for its excellent machinability, allowing for precision manufacturing of intricate parts. High-speed operations with minimal tool wear and outstanding surface finishes are possible thanks to POM’s machinability.
3D printing with POM enables complex geometries not possible with traditional methods, making it versatile in modern manufacturing.
What Is Polyoxymethylene Used For?
POM is widely used in various industries due to its excellent mechanical properties and cost-effectiveness. It is replacing metals like zinc, brass, aluminum, and steel in many applications because of its lower cost and similar performance.
We will explore the specific uses of POM in sectors like automotive, industrial machinery, sports and recreational equipment, and electrical and electronic applications.
Automotive Industry
In the automotive industry, POM is commonly used for fuel system components, pump parts, and seals due to its chemical resistance and durability. POM withstands exposure to acids, bases, and organic solvents without degradation, ideal for demanding automotive applications.
Its ability to be shaped into complex forms to achieve the desired shape through various manufacturing processes enhances its suitability for automotive use.
Industrial Machinery
POM’s robustness and wear resistance make it perfect for parts in industrial machinery, including gears, bearings, and bushings. These components require high durability and the ability to endure heavy loads, which POM provides. Its application in industrial machinery ensures durability and reduced maintenance needs.
Sports and Recreational Equipment
Polyoxymethylene is often used in sports and recreational equipment, enhancing performance and safety. Its properties make it suitable for components in ski bindings, bicycle gears, and archery bow components.
Its durability and abrasion resistance ensure sports equipment withstands rigorous use while maintaining reliability.
Electrical and Electronic Applications
POM is essential in electrical and electronic applications, used for connectors, switches, and various pom components. Its excellent electrical insulation ensures reliability and stability in these devices.
Its ability to withstand varying temperatures and environmental conditions makes it ideal for electrical and electronic uses.
Advantages Of POM
POM’s primary advantages lie in its high performance, durability, and cost-effectiveness. It delivers exceptional mechanical strength and stiffness, often outperforming other thermoplastics in load-bearing scenarios, such as gears and bearings.
Its low friction and excellent wear resistance contribute to long-lasting durability, reducing maintenance needs in moving parts.
Additionally, POM’s ease of processing—through injection molding or machining—keeps production costs low, making it an economical choice for high-precision components.
These attributes make POM a standout choice for industries needing reliable, long-term performance without high costs.
Disadvantages Of POM
One significant limitation of POM is its sensitivity to ultraviolet (UV) light, which can degrade its mechanical properties and cause surface chalking or brittleness over time, rendering it less suitable for outdoor applications unless stabilized with additives.
Another concern is its behavior under thermal degradation or combustion, where it releases formaldehyde gas—a potentially hazardous byproduct. Careful design and handling are necessary, especially in enclosed or high-temperature environments, to mitigate health and safety risks.
Is POM Plastic Expensive?
The cost of POM plastic varies significantly depending on brand, grade, and origin. As of February 2025, POM prices range from 10,000 to 49,500 yuan per ton, with a median market price of 13,300 yuan per ton. Domestic prices range from 13,070 to 13,800 yuan per ton, while imported POM, like Dow DuPont’s (grade 100ST), is 42,000 yuan per ton in Shanghai.
Prices also vary by region and brand, with Mitsubishi Engineering POM (grade F20-03) priced at 16,600 yuan per ton in the South China market, and Taiwan Formosa POM (grade M90) at 13,200 yuan per ton in the Ningbo market.
Comparison With Nylon And Polycarbonate
Compared to nylon, POM provides better dimensional stability and lower moisture absorption, ideal for precision parts in humid conditions, though nylon is tougher and more flexible.
Polycarbonate excels in impact resistance and transparency, perfect for safety shields, but lacks POM’s low friction and wear resistance.
POM’s cost-effectiveness and self-lubricating properties make it ideal for mechanical applications, but its UV sensitivity and formaldehyde risk require careful consideration based on specific use cases.
Summary
In summary, Polyoxymethylene (POM) is a high-performance engineering thermoplastic that offers excellent mechanical properties, chemical resistance, and ease of processing.
Its applications span across various industries, including automotive, industrial machinery, sports equipment, and electronics. While POM has significant advantages, such as durability and cost-effectiveness, it also has some limitations, like UV sensitivity and formaldehyde emission.
Understanding these aspects helps in making informed decisions about using POM in specific applications.
With its unique combination of properties, POM continues to be a valuable material in engineering and manufacturing.
Frequently Asked Questions
What is Polyoxymethylene (POM)?
Polyoxymethylene (POM), also referred to as acetal or polyacetal, is a high-performance engineering thermoplastic recognized for its strength, rigidity, and superior mechanical properties. It is widely used in various applications due to these beneficial characteristics.
What are the key properties of POM?
POM is characterized by its high mechanical strength, low friction, excellent wear resistance, good dimensional stability, and notable chemical resistance. These properties make it an ideal material for various applications.
What are the main types of POM?
The main types of POM are homopolymer and copolymer, each possessing distinct characteristics tailored for specific applications. Additionally, modified grades are available for specialized uses.
What are the common applications of POM?
POM is commonly utilized in automotive components, industrial machinery parts, sports equipment, and electrical devices, owing to its exceptional durability and performance. Its diverse applications make it a vital material in various industries.
How does POM compare to nylon and polycarbonate?
POM excels in dimensional stability and moisture resistance compared to nylon, but polycarbonate outperforms it in impact resistance and transparency. While POM is cost-effective and self-lubricating, its sensitivity to UV light and formaldehyde emissions upon degradation are notable drawbacks.