POM - Polyacetal (Delrin)

Polyacetal (POM), also known as polyoxymethylene or by the trade name Delrin, is a high-performance semi-crystalline engineering thermoplastic widely recognized for its exceptional stiffness, low friction coefficient, outstanding dimensional stability, and superior fatigue resistance. First commercialized by DuPont in 1960, POM has become the material of choice for precision mechanical components that were traditionally manufactured from metals such as zinc, brass, and aluminum.

The global polyacetal market was valued at approximately $5.5 billion in 2024 and is projected to grow at a compound annual growth rate (CAGR) of 5.0% through 2030, driven by increasing metal replacement in automotive components, expanding demand for precision consumer electronics mechanisms, and growing applications in medical devices and plumbing systems. Global POM production exceeds 1.5 million tonnes annually, with automotive accounting for approximately 40% of total consumption according to industry data from Technavio.

Polyacetal resins comply with ASTM D4181 specifications for acetal (POM) molding and extrusion materials. Select grades are approved for food contact under FDA 21 CFR 177.2470, NSF/ANSI 61 for drinking water system components, and meet UL 94 HB classification. Grades for automotive fuel system applications comply with relevant SAE and EPA permeation standards.

Key properties of polyacetal include:

• High stiffness and strength with a flexural modulus of 2,600–3,200 MPa and tensile strength of 60–70 MPa — among the highest of any unreinforced semi-crystalline thermoplastic.
• Exceptionally low coefficient of friction (0.20–0.35 against steel) and excellent wear resistance, enabling gears, bearings, and sliding components to operate for millions of cycles without lubrication.
• Outstanding dimensional stability with low and predictable shrinkage, minimal moisture absorption (0.20–0.25%), and excellent creep resistance under sustained load.
• Superior fatigue endurance — POM withstands repeated cyclic loading better than virtually any other unreinforced engineering thermoplastic, critical for spring elements, snap-fit assemblies, and living hinges.
• Good chemical resistance to aldehydes, esters, ethers, hydrocarbons, and most automotive fuels and lubricants. POM is particularly resistant to organic solvents that attack many other engineering plastics.
• Excellent spring-back properties and elastic recovery, making POM ideal for snap-fit connections, spring clips, and flexible integral hinges.
• Natural lubricity and low noise generation during operation, important for consumer electronics mechanisms, automotive interior components, and appliance drives.

Homopolymer vs. Copolymer

Polyacetal is commercially available in two distinct forms, each offering different performance characteristics:

• POM Homopolymer (e.g., Delrin): Produced by polymerization of formaldehyde, POM homopolymer offers higher mechanical strength, stiffness, and hardness compared to copolymer. It has a higher melting point (178°C vs. 165°C) and slightly better short-term mechanical properties. Homopolymer is preferred where maximum mechanical performance and impact resistance are required.
• POM Copolymer (e.g., Celcon, Hostaform): Produced by copolymerization of trioxane with small amounts of comonomer (typically ethylene oxide). Copolymer offers better thermal stability during processing, improved resistance to hot water and alkaline environments, lower centerline porosity in thick sections, and wider processing windows. Copolymer is preferred for parts in contact with hot water, thin-walled components, and applications requiring extended hot-runner processing.

Available Grades

Standard Homopolymer POM delivers the highest mechanical strength, stiffness, and fatigue resistance among unreinforced acetal grades. These grades are the benchmark for precision gears, cam mechanisms, and structural components requiring maximum mechanical performance.

Standard Copolymer POM provides excellent thermal processing stability, superior hot-water resistance, and broader processing latitude compared to homopolymer. Copolymer grades are preferred for plumbing fittings, hot-water applications, and thin-walled precision parts.

Low-Friction and PTFE-Filled POM grades incorporate PTFE (polytetrafluoroethylene), silicone, or other lubricant additives to further reduce the already low coefficient of friction. These grades are essential for applications where POM-on-POM or POM-on-metal sliding contact occurs, including printer mechanisms, conveyor guides, and automotive seat adjusters.

UV-Stabilized POM grades contain UV absorbers and stabilizers for outdoor applications where POM would otherwise degrade under prolonged ultraviolet exposure. These grades are used in garden equipment, automotive exterior mechanisms, and outdoor hardware.

Glass-Fiber-Reinforced POM grades containing 10% to 25% glass fiber provide increased stiffness, higher heat deflection temperature (up to 170°C), and reduced thermal expansion while maintaining good wear properties. These grades serve structural brackets, pump components, and precision housings requiring tight dimensional tolerances across temperature ranges.

Processing

Polyacetal is processed primarily by injection molding with recommended melt temperatures of 190–230°C for copolymer and 200–220°C for homopolymer, with mold temperatures of 60–120°C. Higher mold temperatures (80–120°C) improve crystallinity, surface finish, and dimensional stability. POM has relatively low moisture absorption, but drying at 80–90°C for 2–3 hours is recommended for optimal surface quality.

POM is also processed by extrusion (rod, sheet, profile), CNC machining of extruded stock shapes, and blow molding for hollow containers. Post-processing options include ultrasonic welding, hot-plate welding, spin welding, snap-fit assembly, press-fit insertion, and mechanical fastening. POM does not accept adhesive bonding or painting readily due to its low surface energy, though plasma and flame surface treatments can improve adhesion when required.