POM Copolymer: Properties, Uses & Cost Guide
Tensile data verified against MatWeb.com database & manufacturer datasheets · Last updated July 2026
Published: 2026-06-10
POM (polyoxymethylene) copolymer is the workhorse engineering thermoplastic for precision mechanical components. Unlike POM homopolymer, the copolymer grade offers superior thermal stability, resistance to alkaline environments, and a wider...
POM (polyoxymethylene) copolymer is the workhorse engineering thermoplastic for precision mechanical components. Unlike POM homopolymer, the copolymer grade offers superior thermal stability, resistance to alkaline environments, and a wider processing window — making it the preferred choice for complex injection molded gears, cams, and fuel system components.
POM copolymer exhibits excellent dimensional stability, low moisture absorption (0.2% at saturation), and outstanding fatigue resistance — critical for components subjected to cyclic loading such as gear teeth. Its natural lubricity eliminates the need for external lubricants in many applications. The material is widely used in automotive fuel sender units, window regulator mechanisms, printer gears, and conveyor chain links.
Key processing parameters: melt temperature 190-210 °C, mold temperature 60-90 °C. POM copolymer processes easily on standard injection molding machines with medium-flow grades available for thin-wall applications. Pre-drying is typically not required for sealed containers. Overheating above 230 °C can cause formaldehyde generation — ensure proper ventilation.
Polyplastics Duracon (Japan) is the global benchmark for POM copolymer, with tight molecular weight control yielding consistent molding performance. Grade selection depends on melt flow rate: M90 (standard flow), M270 (high flow for thin-wall), and M25 (low flow for extrusion).
Recommended Applications
POM Copolymer Duracon M90 is commonly specified for:
⚠ Not Recommended For
POM Copolymer Duracon M90 is not recommended for:
- Strong acid environments (sulfuric, nitric — POM hydrolyzes rapidly below pH 4)
- UV-exposed outdoor applications without carbon black loading (UV degrades rapidly)
- Continuous service above 100°C (use PPS or PEEK for high-temp structural instead)
Selection & Application Guide
POM (acetal/Delrin) is the premium choice for precision mechanical components requiring tight tolerances, low friction, and excellent dimensional stability. Choose POM over nylon when moisture absorption and dimensional stability are critical — POM absorbs 10× less moisture than nylon. Choose POM over PBT when fatigue resistance and creep resistance are needed. POM's low friction and wear resistance make it the standard for gears, bearings, and sliding mechanisms.
Real-World Applications
POM's low friction (μ=0.1-0.3), excellent fatigue resistance, and dimensional stability make it the standard material for small precision gears in office equipment, automotive actuators, and consumer products.
POM's resistance to gasoline, ethanol blends, and diesel fuel, combined with low permeability, makes it standard for fuel sender units, fuel caps, and valve bodies.
POM's wear resistance and low friction suit it for conveyor chain links, wear strips, and guide rails in packaging and material handling systems.
POM's precision moldability, low friction, and biocompatibility (USP Class VI) make it ideal for metered-dose inhaler valves and dose counters.
Processing & Cost Considerations
Manufacturing Tips
- POM processes easily at 185-215°C melt temperature with mold temperatures of 80-100°C. It has a narrow processing window — avoid temperatures above 220°C as POM decomposes with formaldehyde release. Ensure adequate ventilation.
- POM is highly crystalline and shrinks significantly (1.8-2.5%). Mold design must account for this shrinkage, especially for precision gear teeth and bearing surfaces. Post-molding shrinkage continues for 24-48 hours.
- Homopolymer acetal (Delrin) has higher tensile strength and stiffness; copolymer acetal (Duracon/Celcon) has better chemical resistance to hot water and strong bases. Choose homopolymer for maximum mechanical performance; copolymer for chemical exposure.
POM costs $5-10/kg — slightly more than nylon but offering superior dimensional stability and lower friction. The total cost advantage of POM over nylon often comes from eliminating secondary operations (no moisture-conditioning needed, tighter as-molded tolerances). POM is not a high-temperature polymer (max 100°C continuous); for higher temperatures, consider PPS or PEEK.
Technical Properties
| Density | 1.41 g/cm³ |
|---|---|
| Tensile Strength | 62 MPa |
| Melting Point | 165 °C |
| Shrinkage Rate | 1.8-2.0% |
| Flexural Modulus | 2.6 GPa |
| Hdt | 110 °C at 1.82 MPa |
| Continuous Service Temp | 100 °C |
| Coefficient Of Friction | 0.20 (dynamic, vs steel) |
| Tensile Modulus | 2.6 GPa |
| Yield Strength | 65 MPa |
| Elongation At Break | 35% |
Engineering Tool: Shrinkage & Cost Estimator
Calculate part weight, mold cavity dimensions accounting for shrinkage, and material cost — all locally in your browser.
Equivalents & Cross-References
| Equivalent / Alternate | Action |
|---|---|
| Polyplastics Duracon M90-44 | |
| Celcon M90 | |
| Delrin 500P | |
| Ticona Hostaform C9021 |
Frequently Asked Questions
What is the difference between POM copolymer and POM homopolymer (Delrin)?
POM copolymer has superior thermal stability and chemical resistance (especially to alkalis and hot water) at a slight trade-off in tensile strength (62 MPa vs 70 MPa for homopolymer). Copolymer also has a wider processing window, lower mold deposit, and lower centerline porosity — generally preferred for complex injection molded parts.
What melt temperature should I use for Duracon M90 injection molding?
190-210 °C is the recommended melt temperature range. Never exceed 230 °C as POM degrades with formaldehyde gas evolution. Mold temperature should be 60-90 °C for optimal crystallinity.
Why is POM copolymer so widely used in Japanese automotive manufacturing?
POM copolymer dominates Japanese auto fuel systems because of its excellent resistance to gasoline, diesel, ethanol blends, and biodiesel — combined with low permeation rates. Toyota and Honda specify Duracon-grade POM for fuel pump assemblies, window regulators, and door lock mechanisms.
What is the difference between homopolymer and copolymer POM?
Homopolymer (Delrin) has higher tensile strength (70 MPa vs 61 MPa), stiffness, and fatigue endurance. Copolymer (Duracon/Celcon) has better thermal stability, chemical resistance to hot water and alkalis, and less formaldehyde outgassing during processing. For most mechanical applications, homopolymer is preferred; for hot water or chemical exposure, copolymer is safer.
Can POM be used for drinking water applications?
Copolymer POM grades are certified to NSF/ANSI 61 for potable water contact. Homopolymer POM generally does not have this certification due to residual formaldehyde. For plumbing components in contact with drinking water, always specify NSF-certified copolymer POM.
Is POM suitable for snap-fit assembly?
Yes, POM is excellent for snap-fits due to its high fatigue endurance and elastic recovery. However, POM has low elongation at break (15-25% for homopolymer), so snap-fit designs must avoid excessive strain during assembly. The allowed strain for POM snap-fits is typically 4-6% for unreinforced grades.
Why does POM release formaldehyde during processing?
POM is a polyoxymethylene that can depolymerize (unzip) from chain ends when overheated, releasing formaldehyde gas. This is more pronounced in homopolymer than copolymer. The copolymer's C-C bond in the backbone interrupts the unzipping reaction. Always process POM within the recommended temperature range and ensure adequate ventilation.
Can POM be bonded with adhesives?
POM is notoriously difficult to bond due to its low surface energy and chemical inertness. Mechanical fastening and snap-fits are preferred. When adhesive bonding is necessary, surface treatment (plasma, corona, or chemical etching) plus cyanoacrylate or two-part epoxy provides moderate bond strength. Welded joints (ultrasonic, hot plate) are stronger than adhesive bonds.
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References & Industry Standards
- ASTM International. Standard Specifications for Engineering Plastics & Thermoplastics. astm.org
- UL Prospector. Plastics & Elastomers Material Database. ulprospector.com
- MatWeb. Material Property Data for Engineering Thermoplastics. matweb.com
- ISO 1043. Plastics — Symbols and Abbreviated Terms. iso.org