Acetal VS Delrin ：How to select appropriate material?

In our daily work, we were often asked about the difference between Acetal material and Delrin material, here I would like to post this article to show you key differences, which will be helpful for you to select the most proper material to use.

Firstlly, let us understanding their similarity among Acetal POM C and Delrin POM H.

Both acetal copolymer (Acetal POM-C) and acetal homopolymer( Delrin POM-H), offer a range of excellent performance attributes including high mechanical strength, stiffness, and hardness, great resilience and resistance to creep, high impact strength at low temperatures, low water absorption for great dimensional stability, and food-contact compatibility.

Although, there are some significant differences between the two grades which are important to know when selecting Acetal and Delrin.

Then, what are the key differences between Acetal POM C and Delrin POM H?

1. From the chemical r structure and composition perspective to learn

Acetal (POM-C) is a copolymer version of POM, made by polymerizing formaldehyde with a comonomer (typically dioxolane). The copolymer structure gives it improved thermal stability and chemical resistance compared to homopolymers.

Delrin (POM-H) is a homopolymer version of POM, synthesized directly from anhydrous formaldehyde. It offers higher mechanical strength, rigidity, and crystallinity than POM-C, but may be more sensitive to thermal degradation.

2. From the property perspective to learn

Ø Thermal Stability: Acetal (POM-C) is better than Delrin (POM-H)

Delrin (POM-H) is more susceptible to thermal degradation during processing, especially at high temperatures. This sensitivity can lead to the release of formaldehyde, which may cause warping or discoloration. Acetal (POM-C), on the other hand, has better thermal stability, making it easier to process without degradation.

Ø Chemical resistance: Acetal (POM-C) is in a higher level and Delrin (POM-H) is in a moderate level.

POM-C generally has better resistance to acidic and alkaline environments due to its copolymer structure. This makes it a preferred choice for parts exposed to harsh chemicals or humid environments. POM-H, while still resistant to many solvents and fuels, may degrade more easily in strong acids or bases.

Ø Mechanical Strength: Acetal (POM-C) is slightly lower while the Delrin (POM-H) is higher in this point.

POM-H typically exhibits superior mechanical properties such as tensile strength, stiffness, and creep resistance. These characteristics make it ideal for applications that require high load-bearing capacity and dimensional stability under stress. POM-C, while slightly less rigid, still offers good mechanical performance and is often chosen for applications where moderate strength is sufficient.

Ø Processing and Fabrication: Acetal (POM-C) is easier while the Delrin (POM-H) is more chanllenging

Because of its lower thermal sensitivity, POM-C is easier to process using standard injection molding and extrusion techniques. POM-H requires more precise temperature control during processing to avoid degradation, which can increase production complexity and cost.

Ø Hydrolysis Resistance: Acetal POM-C is better than Delrin POM-H

Acetal POM-C has better resistance to hydrolysis, meaning it performs better in wet or high-humidity environments. This makes it suitable for outdoor applications or parts that may be exposed to water or steam. Acetal POM-H may experience hydrolytic degradation over time under such conditions.

3. From the cost perspective to learn

 Acetal POM-C is often more readily available and can be a more cost-effective choice, Delrin POM-H  is more expensive than Acetal POM-H, and this is down to the superior mechanical strength of acetal copolymer.

Finally, now let’s see how to choose between POM-C and POM-H based on their differences:

Selecting the appropriate material depends on the specific requirements of the application. Here are some guidelines based on typical use cases:

1. When to Choose Acetal (POM-C)

Chemical Exposure: Applications involving exposure to acids, alkalis, or other aggressive chemicals.

Humid or Wet Environments: Parts used in plumbing, outdoor equipment, or medical devices that may be sterilized.

Ease of Processing: When simpler manufacturing is desired, especially for large-scale production.

Moderate Mechanical Requirements: Applications where high strength is not the primary concern.

Examples: Pump components, valve seats, gears in humid environments, food processing equipment.

2. When to Choose Delrin (POM-H)

High Mechanical Performance: Applications requiring high strength, stiffness, and wear resistance.

Dimensional Stability: Precision parts where minimal creep and high rigidity are crucial.

Low-Friction Applications: Bearings, bushings, and sliding components where low coefficient of friction is important.

Short-Term Thermal Exposure*: Applications with intermittent exposure to elevated temperatures.

Example: Gears, rollers, conveyor components, automotive fuel system parts.

Conclusion

When selecting between POM-C and POM-H, it's important to evaluate the specific needs of the application, including environmental conditions, mechanical requirements, and processing considerations. Consulting with material suppliers or engineers can further ensure the best choice for long-term performance and cost-effectiveness.

In summary, understanding the differences between Acetal POM-C and Delrin POM-H enables engineers and designers to make informed decisions that optimize part performance, durability, and manufacturability.