Polyoxymethylene (POM): properties and applications / Articles

Polyoxymethylene (POM), also known as polyacetal or acetal resin, is one of the most widely used engineering thermoplastics in modern industry. Chemically, POM is a polymerisation product of formaldehyde with a molecular weight of 40–120 kDa. It is a white crystalline powder that transforms into strong and wear-resistant products during processing. POM is one of the five major engineering thermoplastics (alongside polyamide, polycarbonate, polyester and polyphenylene oxide) and occupies a unique niche due to its exceptional combination of mechanical and tribological properties. The material is also known under numerous trade names: Delrin (DuPont), Celcon (Celanese), Duracon (Polyplastics), Kepital, Ultraform (BASF), Hostaform and others.

Chemical Structure and Synthesis

Polyoxymethylene is a linear polymer with the repeating unit –CH₂–O–. Its high degree of crystallinity (70–100% for homopolymer, 60–80% for copolymer) provides the material with exceptional stiffness, strength and dimensional stability.

POM production is a complex multi-stage process. The first step involves producing formaldehyde from natural gas or methanol. The formaldehyde is then concentrated and polymerised. Depending on the technology, two main types of POM are distinguished:

Homopolymer POM (POM-H) — a product of pure formaldehyde polymerisation. The technology was first developed by DuPont in 1960 under the Delrin brand. Homopolymer is characterised by higher mechanical strength, stiffness and creep resistance. However, it has a narrower processing temperature range and lower thermal stability. The melting temperature of homopolymer is 173–180 °C. Currently, only DuPont and Japan's Asahi Kasei possess the technology for homopolymer production.

Copolymer POM (POM-C) — a product of copolymerisation of formaldehyde with comonomers (typically dioxolane). The technology was developed by Celanese in 1962 under the Celcon brand. Copolymer offers improved thermal stability, a wider processing window, and better resistance to hydrolysis and alkalis. The melting temperature of copolymer is 164–172 °C. Copolymers are currently the main type of POM on the global market.

Polymerisation can be carried out using dry or wet methods. The wet method, which includes additional washing and drying stages to remove residual formaldehyde, provides higher product quality, but key technologies remained inaccessible to Chinese manufacturers for a long time due to patent restrictions. The global POM market is highly concentrated: key patents belong to DuPont, BASF, Polyplastics, Asahi Kasei and Celanese.

Physical and Mechanical Properties

POM possesses a unique combination of properties that make it indispensable in many industries.

Mechanical Strength and Stiffness. POM is characterised by high stiffness and hardness, combined with good impact strength. The tensile modulus is 2700–3100 MPa. Tensile strength reaches 70–73 MPa. Rockwell hardness is M94. POM successfully replaces metals (steel, copper, aluminium) in friction assemblies and load-bearing structures.

Fatigue Strength and Creep. POM exhibits exceptional fatigue resistance under dynamic and alternating loads. The material has low creep even at elevated temperatures, which is one of its key advantages over many other thermoplastics.

Tribological Properties. POM is a self-lubricating material with a low coefficient of friction (0.2–0.35) and high wear resistance. These properties make it ideal for plain bearings, gears and other friction assemblies.

Temperature Resistance. The long-term service temperature range of POM is from –60 to 100–135 °C. The brittle temperature is approximately –60 °C. The material retains impact strength at low temperatures. DuPont Delrin homopolymer has an operating range from –40 to 120 °C.

Dimensional Stability. POM has low moisture absorption, ensuring excellent dimensional stability even in high-humidity conditions. This property is particularly important for precision parts. Linear moulding shrinkage is approximately 1.8–1.9%. The material is recommended for precision moulding.

Chemical Resistance. POM is resistant to automotive fuels, oils, organic solvents, weak acids and alkalis. The material is resistant to virtually all neutral organic substances. However, POM is not resistant to concentrated acids and radiation.

Electrical Properties. POM has good electrical insulation properties and is widely used in the electrical industry.

Advantages and Disadvantages of POM

Key Advantages:

High mechanical strength and stiffness approaching those of metals
Low coefficient of friction and high wear resistance
Exceptional fatigue strength and low creep
Excellent dimensional stability across a wide humidity range
Chemical resistance to fuels, oils and organic solvents
Wide operating temperature range
Good machinability and laser marking capability

Main Disadvantages:

Complex processing due to narrow temperature window (especially for homopolymer)
Not resistant to concentrated acids and strong oxidisers
Susceptible to degradation under radiation
Relatively high cost compared to commodity thermoplastics

Processing and Moulding

POM is primarily processed by injection moulding, as well as extrusion and blow moulding. The material is easily machined. An important feature of POM processing is the narrow temperature interval between melting and decomposition, requiring precise temperature control. Copolymers have a wider processing window compared to homopolymers. POM is easily ultrasonically welded and allows laser marking. There is a wide range of grades available: high-flow, filled and reinforced (glass fibre, glass spheres), with improved anti-friction properties, and impact-modified blends.

Applications

Thanks to its unique combination of properties, POM finds application in a wide range of industries:

Automotive Industry — stability of properties across a wide temperature range and resistance to fuels and oils make POM indispensable for fuel system components, interior elements (levers, fasteners, clips), door systems, safety systems and seat belts. The automotive sector accounts for approximately 22% of global POM consumption.

Electrical and Electronics — POM is used for insulators, housings, connectors, switches, coils, as well as components for mobile phones, computers and tablets. This is the largest consumption segment — over 25% of the global market.

Mechanical Engineering and Precision Instrumentation — production of high-precision gears, bearings, bushes, cams, valves, fasteners, clips and pump components. POM is particularly valued in precision engineering due to its dimensional stability.

Household Appliances and Consumer Goods — production of appliance components, buttons, zippers and fasteners. The material is also used for sports equipment (ski bindings), medical devices (syringes, inhalers, drug delivery device components).

Industrial Equipment — conveyor systems, rollers, guides, pump and valve components, chemical equipment parts due to chemical resistance.

In recent years, specialised POM grades have been actively developed: low-formaldehyde-emission grades for automotive interiors, medical-grade with enhanced purity, as well as compounds with improved anti-friction properties (with silicone or PTFE additives).

Global POM Market

The global polyoxymethylene market shows steady growth. In 2025, the market was estimated at 1.72 million tonnes, with projections to reach 2.27 million tonnes by 2031 at a CAGR of 4.71%. In 2023, the market stood at 1,481.2 thousand tonnes. In monetary terms, the POM market was valued at USD 3.6 billion in 2024, with a projected growth to USD 4.8 billion.

China is the world's largest POM producer. As of 2025, China's capacity reached 76 million tonnes per year, accounting for approximately 38% of the global total. Global capacity stands at about 200 million tonnes per year. The Chinese POM market is highly concentrated: Yuntianhua has 9 million tonnes of capacity and holds approximately 15% of the Chinese market (about 25% among domestic producers). In 2026, the company announced the construction of a new plant with a capacity of 10 million tonnes with an investment of 18.57 billion yuan.

Among the world's largest producers are Celanese, Polyplastics, DuPont, Mitsubishi Gas Chemical, Asahi Kasei, BASF and Yuntianhua. Polyplastics will increase its capacity to 39.8 million tonnes per year by 2026. China is actively expanding production capacity: during 2021–2025, 31 million tonnes of new capacity were added in the country at a CAGR of 14%.

Conclusion

Polyoxymethylene (POM) is a unique engineering thermoplastic that combines high mechanical strength, exceptional wear resistance, a low coefficient of friction and excellent dimensional stability. These properties make it an indispensable material for the automotive, electrical, mechanical engineering and medical industries. Despite the complexity of processing and the high concentration of technologies among a limited number of producers, POM continues to expand its presence in the global market, especially in China, where domestic production capacities are actively developing and import substitution efforts are underway.