Acetal Copolymer FAQ — Common Questions on POM-C Plastic

Frequently asked questions about acetal copolymer (POM-C): chemistry, brand differences, property comparisons to Delrin, hot-water use, machining, and FDA compliance.

What is acetal copolymer?

Acetal copolymer (POM-C) is a semicrystalline engineering thermoplastic produced by copolymerizing trioxane with a periodic comonomer — typically 1,3-dioxolane — at 1–5 mol% incorporation. The result is a polyoxymethylene chain with occasional comonomer units that interrupt the otherwise all-oxymethylene sequence of acetal homopolymer.

Properties: tensile strength ~9,500–10,000 psi, continuous use to 185°F (85°C), excellent machinability, low friction, good chemical resistance. Available as rod, sheet, and tube for machined parts.

For the complete overview, see the acetal copolymer material hub.

What is the difference between acetal copolymer and acetal homopolymer (Delrin)?

Both are polyoxymethylene (POM), but they are made differently and have different properties:

In short: acetal copolymer is better for hot-water service and large cross-sections; Delrin is better for high-cycle fatigue applications. See the Delrin vs. acetal copolymer comparison.

What brands of acetal copolymer are there?

The major commercial brands are:

• Celcon (Celanese Corporation) — the most common US-market brand
• Hostaform (Ticona/Celanese) — same polymer as Celcon, European brand name
• Ultraform (BASF) — widely used in Germany and parts of Europe
• Tenac-C (Asahi Kasei) — primarily Asian market; known for low formaldehyde emission

All four are acetal copolymer (POM-C). In most engineering applications, they are interchangeable as long as the grade meets ASTM D6100 property requirements. See the acetal copolymer grades page for the grade-by-grade breakdown.

Is Celcon the same as Hostaform?

Yes — functionally. Celcon and Hostaform are both produced by Celanese Corporation using the same POM-C chemistry and manufacturing processes. Hostaform is the European/Asian brand name; Celcon is the US brand name. The same polymer is sold under both names in different geographies.

Grade designations differ between the two brands: Celcon M90 corresponds roughly to Hostaform C 9021 (both are standard injection-molding grades with medium melt flow). Request Celanese's cross-reference table for direct grade equivalences. For stock-shape rod and sheet, either brand's standard natural grade to ASTM D6100 is acceptable for most applications.

Can acetal copolymer be used in hot water?

Yes — to a higher temperature than Delrin (POM-H). Standard acetal copolymer (POM-C) is suitable for sustained hot-water contact up to approximately 160°F (71°C); heat-stabilized grades (Hostaform C 9021 HS, Celanese HS grades) extend this to approximately 180°F (82°C).

This is the primary engineering reason to specify acetal copolymer over Delrin in hot-water applications: dishwasher components, hot-water valves, coffee machine internals, irrigation systems exposed to sun-warmed water.

Do not confuse "hot-water resistant" with "steam resistant." Above 100°C (212°F), both POM-H and POM-C degrade; neither is a steam-service material. For steam applications, evaluate PEEK, polysulfone, or PVDF.

Is acetal copolymer FDA food-grade?

Many standard natural-color Celcon and Hostaform grades meet FDA 21 CFR 177.2480 (Acetal resins, repeated-use food contact) because they are formulated with only FDA-listed adjuvants. Unlike Delrin (which designates specific "SA" grades for food contact), the compliance of POM-C is a grade formulation question, not a grade-name question.

To confirm compliance:

1. Request a 21 CFR 177.2480 compliance letter from Celanese (or BASF for Ultraform) for the specific grade
2. Specify natural (white) color — black and colored grades may use non-listed pigments
3. For NSF 51 or NSF 61 certification, request current listing documentation

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

Does acetal copolymer have centerline porosity in large-diameter rod?

No. This is one of the key advantages of acetal copolymer over Delrin for large cross-section applications. Acetal copolymer (POM-C) rod does not develop the centerline porosity characteristic of POM-H (Delrin) in diameters above 3 inches.

The comonomer in POM-C changes the solidification kinetics during extrusion, resulting in more uniform shrinkage and substantially reduced void formation at the center. Acetal copolymer rod in 4"–8" diameters typically shows a uniform, pore-free cross-section suitable for parts where through-bores are centered on the rod axis.

For applications requiring large-diameter rod and centerline-porosity-free material, always specify acetal copolymer rod.

How does acetal copolymer machine compared to Delrin?

Nearly identically. Both materials:

• Cut cleanly with carbide tooling without smearing or burning
• Hold tolerances of ±0.001–0.002" on CNC lathe and mill
• Produce short-to-medium chips that evacuate easily
• Machine well dry or with light coolant
• Do not require pre-annealing for standard operations
• Must not be laser-cut (formaldehyde gas generation from all POM materials)

Minor differences: POM-C has a slightly lower melting point (165°C vs. 175°C for POM-H), so surface glazing can occur slightly sooner at high SFM without adequate chip load. POM-C also tends to produce slightly longer, more stringy chips in some turning geometries. Neither difference requires changing the machining approach meaningfully.

For full parameters, see the acetal copolymer machining guide.

When should I choose acetal copolymer instead of Delrin?

Choose acetal copolymer (POM-C) when any of the following apply:

1. Hot water above 140°F (60°C) — dishwashers, hot-water valves, coffee equipment, irrigation with warm water
2. Large-diameter rod (>3") — POM-C has no centerline porosity
3. Alkaline chemical exposure — POM-C has better alkali resistance
4. Cost sensitivity, general machined parts — POM-C is slightly less expensive; if fatigue endurance is not the constraint, POM-C is adequate
5. Broad FDA compliance without specific "SA" grade designation — many standard POM-C natural grades meet 21 CFR 177.2480

Choose Delrin (POM-H) when:

1. High-cycle gear tooth or snap-fit fatigue life is the governing criterion
2. The print or specification explicitly calls out Delrin by grade name
3. Maximum stiffness and HDT within the acetal family is required

What sizes does acetal copolymer rod and sheet come in?

Rod: Standard diameters from 0.125" through 8.0" (natural white) in 4-foot lengths. Common sizes in black available. See acetal copolymer rod for the full size table.

Sheet: Standard thicknesses 0.062" through 4.0" in 24"×48" and 48"×96" sheets (natural and black). See acetal copolymer sheet for the full size table.

Tube: OD from 0.500" through 8.0" in standard wall thicknesses. See acetal copolymer tube.

What happens to acetal copolymer in strong acids or oxidizers?

Strong mineral acids (pH < 2: concentrated HCl, H₂SO₄, HNO₃) and strong oxidizing agents (concentrated bleach, H₂O₂ above ~10%) attack the POM-C backbone and degrade the material — loss of mechanical properties, surface attack, and potential formaldehyde release. For these environments, specify chemically resistant materials: PTFE, PVDF, or PEEK.

For dilute acids (pH > 4) and common industrial solvents, fuels, and oils, acetal copolymer is suitable. See the acetal copolymer properties page for the chemical resistance table.

More related guides

Compare to other materials

• Delrin vs. Acetal Copolymer
• Acetal Copolymer vs. Nylon

Frequently asked questions

• Delrin FAQ (POM-H)
• Acetal Copolymer Material Hub