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ResourcesMaterialsAcetal Plastic: What You Need to Know

Acetal Plastic: What You Need to Know

Picture of Dean McClements
Written by
picture of Joel Schadegg
Updated by
 5 min read
Published April 29, 2022
Updated September 10, 2024

Learn about this material, its properties, uses, advantages, and alternatives.

Acetal plastic granules. Image Credit: XXLPhoto/Shutterstock.com

What is Acetal Plastic?

POM plastic (polyacetal) is a semi-crystalline thermoplastic that is based on the formaldehyde molecule. For this reason, it can also be found as polyformaldehyde, polyethylene glycol, or polyoxymethylene glycol. Its polymers consist of carbon functional groups bonded to two -OR groups, leading to an exceptional blend of mechanical and chemical properties.

Acetal plastic is commonly used as an alternative to metals, thus it finds applications in mechanical gears, electrical components, automotive products, sports equipment, medical products, food equipment, hardware, construction tools, and much more. 

Acetal
Acetal

Properties of Acetal Plastic

Acetal plastic is coveted for its excellent dimensional stability and machining profile, rivaling even metals in its properties. Below is a table including some useful properties of acetal plastic (note this table is not exhaustive).

PropertyASTM TestValue
Property

Density

ASTM Test

-

Value

1.39-1.43 g/cm3

Property

Tensile Strength

ASTM Test

D638

Value

10,000 psi

Property

Flexural Modulus of Elasticity

ASTM Test

D790

Value

420 ksi

Property

Tensile Modulus of Elasticity

ASTM Test

D638

Value

450 ksi

Property

Water absorption (when immersed for 24 hrs)

ASTM Test

D570

Value

0.25%

Property

Heat Deflection Temperature (66 psi & 264 psi)

ASTM Test

D648

Value

336 °F & 257 °F

Property

Coefficient of Friction

ASTM Test

Dynamic

Value

0.20

Data Source: Acetal Material Properties | Curbell Plastics

How Acetal is Formed

The formation of Acetal plastics begins by distilling hydrocarbon chains into smaller parts and then polymerizing them using catalysts. The method of formulation will depend on the type of acetal plastic and is generally split into homopolymer acetal and copolymer acetal processes.

The organic chemistry of acetal polymers can give even scientists a headache—but a brief description of the process used for the formulation of this semi-crystalline thermoplastic follows below.

The Differences Between Copolymer and Homopolymer Acetal Plastics

In the acetal homopolymer plastic process, aqueous formaldehyde building blocks are mixed with alcohols. They react together to form hemiformal, which is then distilled/dehydrated to release the formaldehyde. These monomers are polymerized in the presence of a catalyst to ultimately form the acetal homopolymer.

The copolymer process is much more involved; it first begins when formaldehyde is acid-catalyzed to form 1,3,5-trioxane. Separately, co-monomers dioxolane or ethylene oxide are formed by reacting ethylene glycol with aqueous formaldehyde in catalysis. The trioxane and dioxolane are polymerized together (again, in catalysis), and the resulting polymer is stabilized via melt or solution hydrolysis to remove unstable byproducts and introduce fillers, lubricants, stabilizers, etc.

Below is a table showing a brief comparison between acetal homopolymer vs. copolymer. In general, one would choose homopolymers over copolymers for their increased mechanical properties, while copolymers are generally more stable.

Acetal homopolymersAcetal copolymers
Acetal homopolymers

More structurally regular

Acetal copolymers

Enhanced performance in long-term applications (better creep and fatigue resistance)

Acetal homopolymers

Molding cycles are shorter

Acetal copolymers

More stable in alkaline environments and in chemical attacks

Acetal homopolymers

Enhanced mechanical characteristics (tensile strength, impact strength)

Acetal copolymers

Minimal odor/gas release

Acetal homopolymers

Stiffer and stronger

Acetal copolymers

Wider range of processing temps/times

Acetal homopolymers

Allows for thin wall designs and lighter parts

Acetal copolymers

Better protected from UV exposure

Acetal homopolymers

Comes in a variety of viscosities

Acetal copolymers

More dimensionally stable

Acetal homopolymers

Generally cheaper

Acetal copolymers

Good color retention and requires no heavy metals for coloring

Advantages of Acetal Plastic

  • Exhibits dimensional stability and creep resistance when machined or worked
  • Low friction coefficient (or “slippy”), leading to resistance to wear and abrasion
  • Low moisture absorption in both wet and dry environments
  • High tensile strength and rigidity
  • Chemically resistant to fuels and organic solvents
  • Low smoke emission
  • Highly aesthetic surface finishes
  • FDA approved and is 100% recyclable
  • Can be impregnated/ blended with graphite, rubbers, glass-filled, nanocomposites, metals, etc., for additional unique material properties.

Disadvantages of Acetal Plastic

  • Chemically weak to strong acids, bases, and oxidizers
  • Prone to quick-burning (without flame retardants) due to high oxygen concentration
  • Shrinks in mold significantly
  • Poor resistance to UV radiation without additives; will degrade in color and strength if left in the sun
  • Difficult to bond/glue without significant surface treatment
  • Must manage temperatures when working/machining due to small working range
  • Harder to machine than metals
  • Toxic if inhaled/ingested in liquid form

Common Uses of Acetal Plastic in Manufacturing

  • Mechanical components such as gears, pumps, valves, nuts, fasteners, etc.
  • Food equipment such as pumps, conveyors, tanks, etc.
  • Automotive components such as power window components, door locks, knobs, indicators, etc.
  • Medical device components
  • Fixtures, plumbing parts, bearings

Common Alternatives to Acetal Plastic

Acetal plastic comes in a variety of blends and similar formulations, making it easy to find an alternative if it doesn’t exactly fit the necessary material profile. Below is a brief exploration into other plastics that can function in the place of acetal plastics, given some key considerations.

Delrin: Delrin is a brand-specific POM homopolymer from DuPont and is widely utilized in industry. It is distinct from general acetal plastic, as acetal plastic is typically in a copolymer form, while Delrin is a specific homopolymer blend from DuPont. Delrin is generally specified in industrial applications such as valve components, pumps, gears, insulators, rollers, etc.

Nylon: Nylon is a thermoplastic that sports higher temperature resistance, tensile strength, stiffness, and lower costs than acetal plastic, making it a common alternative. Nylon can generally be used in place of acetal plastics; however, it is less dimensionally stable, less chemically/wear-resistant, and much more affected by humidity and moisture. Nylon is used throughout general-purpose applications and can be found in clothing, consumer goods, electronics, etc.

Xometry sample part made of nylon
Xometry sample part made of nylon

Summary

Polybutylene Terephthalate (PBT): PBT is sometimes exchangeable with acetal plastics, as it is nearly identical in mechanical characteristics. The primary consideration with PBT is that it will require more dehumidification and cannot be used in wet environments and has lower shrinkage than acetals. PBT is commonly used in electronics, sports clothing, bathroom fixtures, computer keyboards, household appliance components, etc.

Xometry provides 3D printing services and plastic injection molding services for all of your production needs. Get your quote today!

Disclaimer

The content appearing on this webpage is for informational purposes only. Xometry makes no representation or warranty of any kind, be it expressed or implied, as to the accuracy, completeness, or validity of the information. Any performance parameters, geometric tolerances, specific design features, quality and types of materials, or processes should not be inferred to represent what will be delivered by third-party suppliers or manufacturers through Xometry’s network. Buyers seeking quotes for parts are responsible for defining the specific requirements for those parts. Please refer to our terms and conditions for more information.

Picture of Dean McClements
Dean McClements
Dean McClements is a B.Eng Honors graduate in Mechanical Engineering with over two decades of experience in the manufacturing industry. His professional journey includes significant roles at leading companies such as Caterpillar, Autodesk, Collins Aerospace, and Hyster-Yale, where he developed a deep understanding of engineering processes and innovations.

Read more articles by Dean McClements

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