Acetal Copolymer — POM-C Plastic Guide (Celcon, Hostaform)

Acetal copolymer (POM-C) is the copolymer variant of polyoxymethylene: a precision engineering plastic that incorporates periodic comonomer units — typically dioxolane — into the POM chain. The result is a material that avoids the centerline porosity problems of acetal homopolymer in large cross-sections, resists hot water and hydrolysis far better than Delrin (POM-H), and offers slightly lower cost with only a modest trade-off in tensile strength and fatigue endurance. Major commercial brands are Celcon (Celanese), Hostaform (Ticona/Celanese), Ultraform (BASF), and Tenac-C (Asahi Kasei).

At a glance:

• Chemistry: acetal copolymer (POM-C); comonomer disrupts chain regularity vs. POM-H
• Tensile strength: 9,500–10,000 psi (natural grade)
• Continuous use temperature: 185°F (85°C); short-term to 220°F (104°C)
• Key advantage over POM-H (Delrin): better hydrolysis/hot-water resistance; no centerline porosity
• Key trade-off vs. POM-H: slightly lower tensile strength and fatigue endurance limit
• Brands: Celcon (M25, M90, M270), Hostaform (C13021, C9021), Ultraform, Tenac-C
• Forms: rod, sheet, tube — white (natural), black, and colored options

What Is Acetal Copolymer (POM-C)?

Acetal copolymer is produced by copolymerizing trioxane (the cyclic trimer of formaldehyde) with a comonomer — most commonly 1,3-dioxolane or ethylene oxide — at controlled ratios of 1–5 mol%. The periodic comonomer units break up the all-oxymethylene chain regularity of POM homopolymer, reducing the tendency for the polymer to depolymerize from chain ends (unzipping) under thermal stress and, critically, reducing the void formation that causes centerline porosity in large extruded POM-H stock.

POM-C vs. POM-H: The Fundamental Difference

Both acetal homopolymer and acetal copolymer are polyoxymethylene — they share the same repeating oxymethylene unit and, at first glance, appear nearly identical in a property table. The differences are real but nuanced:

The lower melting point of POM-C (165°C vs. 175°C for POM-H) is a consequence of reduced chain regularity. This also means POM-C is slightly more flexible in processing and less sensitive to narrow processing windows.

For a full side-by-side, see the Delrin vs. acetal copolymer comparison.

Commercial Brands: Celcon, Hostaform, Ultraform, Tenac-C

Unlike Delrin (a single-brand POM-H), the acetal copolymer market has multiple manufacturers:

Celcon (Celanese)

Celcon is Celanese's flagship POM-C brand, one of the longest-established acetal copolymer lines. Standard grades include Celcon M25 (high viscosity, extrusion), M90 (medium viscosity, injection molding), and M270 (low viscosity, thin-wall molding). Celcon grades include lubricated, UV-stabilized, antistatic, and reinforced formulations. For stock shapes in rod and sheet, Celcon M25 and M90 are most commonly referenced. See the Celcon grades page for the full grade matrix.

Hostaform (Ticona/Celanese)

Hostaform is the European brand name for the same Celanese POM-C chemistry, sold primarily in Europe and Asia under that name. Hostaform C 9021 and C 13021 are the standard injection molding grades; Hostaform C 52021 is glass-fiber reinforced. In stock-shape form, Hostaform-branded material is functionally equivalent to the corresponding Celcon grade — the same polymer from the same production lines, branded differently by geography. See the Hostaform grades page.

Ultraform (BASF)

Ultraform is BASF's POM-C brand, produced at BASF's Ludwigshafen site. Ultraform N 2320 and W 2320 are standard injection molding grades. Ultraform material appears in some European-sourced stock shapes.

Tenac-C (Asahi Kasei)

Tenac-C is Asahi Kasei's acetal copolymer brand, primarily serving the Asian market. Tenac-C grades are engineered for low-formaldehyde emission — increasingly important for automotive interior components subject to VOC regulations.

Acetal Copolymer Properties

The property envelope of POM-C closely parallels POM-H (Delrin) with the key distinctions noted above. Engineers who have worked with Delrin will find acetal copolymer immediately familiar.

Mechanical Properties (Standard Grade, 73°F)

Thermal Properties

Key Advantages of Acetal Copolymer

1. Hot-Water and Hydrolysis Resistance

The primary engineering advantage of POM-C over POM-H is hydrolytic stability in hot-water service. The comonomer interruptions in the chain backbone eliminate the easy-unzipping degradation pathway that makes POM-H susceptible to hot water above 60–80°C. POM-C grades can operate continuously in warm water (to ~80°C with standard grades; to ~90°C with heat-stabilized grades) with minimal loss of mechanical properties over years of service.

This makes acetal copolymer the correct material choice for:

• Dishwasher internal components (wash-arm brackets, rack guides, pump housings)
• Hot-water valve bodies and handles
• Coffee machine and vending machine internals
• Water meter components and irrigation fittings

2. No Centerline Porosity in Large Cross-Sections

Acetal homopolymer (Delrin) develops a porous centerline zone in extruded rod diameters above approximately 3 inches, caused by volumetric shrinkage during solidification. The comonomer in POM-C changes the solidification kinetics enough to largely eliminate this problem. Acetal copolymer rod in diameters up to 6–8 inches typically shows uniform, pore-free cross-section throughout.

This matters for:

• Large-diameter rod turned into flanges, pulleys, and structural components
• Parts where through-bores are centered on the rod axis and would intersect a porosity zone
• Applications in which gas-tightness of machined surfaces is required

3. Better Chemical Resistance in Alkaline Environments

POM-C shows improved resistance to dilute alkalis compared to POM-H. In industrial cleaning environments, dishwashers, and alkaline process fluids, copolymer formulations are more durable.

Acetal Copolymer Grades

The major grade distinctions in POM-C parallel those in POM-H:

Standard (natural/black) — Unfilled copolymer; the majority of stock-shape rod, sheet, and tube is supplied in this form. Properties as tabulated above.

Lubricated — Internally compounded with lubricant (often PTFE or silicone); reduces CoF and improves wear life without external lubrication. Celcon and Hostaform both offer lubricated grades.

Glass fiber reinforced (GF) — Typically 15–25% glass fiber. Raises tensile strength to 13,000–16,000 psi, improves creep resistance, reduces CTE. Less common in stock shapes than in molding compounds.

UV-stabilized — Carbon-black or UV-absorber compounded grades for outdoor applications or UV-lit environments.

Heat-stabilized — Formulations engineered for extended hot-water and elevated-temperature service. Key differentiator for dishwasher and hot-water valve applications.

Low-emission — Low-formaldehyde grades (Tenac-C and specialty Celcon grades) for automotive interior applications.

For a full grade comparison including Celcon and Hostaform specific designations, see acetal copolymer grades.

Stock Shapes: Rod, Sheet, and Tube

Acetal Copolymer Rod

Standard diameters: 0.125" through 8.0" (and to 12" in some grades). Natural (white) and black available. Key advantage over Delrin rod in diameters above 3": uniform cross-section without centerline porosity. Standard lengths: 4 ft; some diameters available in 6 ft. For sizing, tolerances, and ordering, see acetal copolymer rod.

Acetal Copolymer Sheet

Standard thicknesses: 0.062" through 4.0". Standard sheet sizes: 24"×48" and 48"×96". Natural and black. Flatness and thickness tolerances comparable to Delrin sheet. See acetal copolymer sheet.

Acetal Copolymer Tube

Extruded tube in OD ranges from 0.5" through 8.0". Uniform wall consistency through the cross-section — no centerline porosity to contend with in tube geometry regardless of OD. See acetal copolymer tube.

Applications Overview

Acetal copolymer is the preferred choice over Delrin in the following categories:

Hot-water and hydrolysis-sensitive service — Dishwasher components, hot-water valves, irrigation fittings, water meter housings, coffee machine internals.

Large-diameter machined parts — Flanges, pulleys, large bushings, and structural components where centerline porosity would compromise POM-H.

Alkaline chemical environments — Where caustic cleaning agents, alkaline process fluids, or bleach-based sanitizers are used.

General-purpose machined parts (cost-sensitive) — When the application does not specifically benefit from POM-H's higher fatigue endurance, copolymer is often specified due to slightly lower cost.

For detailed application guidance, see acetal copolymer applications.

Machining Acetal Copolymer

Acetal copolymer machines in essentially the same manner as Delrin. The same carbide tooling, speeds, and feeds apply. Slight differences:

• POM-C has a slightly lower melting point (165°C vs. 175°C for POM-H) — keep heat generation in check for thin-wall parts
• POM-C chips are slightly more stringy in some formulations; chip breaker geometry matters in production turning
• No pre-annealing required for standard stock shapes

For full machining parameters, see machining acetal copolymer.

Compliance: FDA, NSF, and RoHS

FDA-compliant acetal copolymer grades are broadly available from Celcon and Hostaform in natural color formulations meeting 21 CFR 177.2480. Unlike Delrin (which designates specific "SA" grades), many standard Celcon and Hostaform natural grades meet FDA requirements — verify with lot documentation. NSF 51 (food equipment) and NSF 61 (drinking water contact) approved grades are available.

For full compliance details, see acetal copolymer FDA food-grade compliance.

More related guides

Compare to other materials

• Delrin vs. Acetal Copolymer (POM-H vs POM-C)
• Acetal Copolymer vs. Nylon
• PEEK vs. Acetal

Forms

• Acetal Copolymer Rod
• Acetal Copolymer Sheet
• Acetal Copolymer Tube

Acetal family

• Delrin Material Hub (POM-H)
• Celcon Grades
• Hostaform Grades

Frequently asked questions — Acetal Copolymer FAQ