Acetal vs. Delrin®: Their Differences
Learn about the differences in characteristics and applications for these two polymers.
Delrin® and copolymer acetal are both polyoxymethylene (POM) polymers. Delrin® is a homopolymer whereas more generic acetal materials are copolymers. Both materials have excellent properties. Of the two, acetal is better suited to continuous high-temperature exposure. On the other hand, Delrin® is the better choice for continuous cyclic loading applications. This article will compare acetal vs. Delrin®, explain how they differ, and outline their key characteristics.
Acetal is a semi-crystalline engineering thermoplastic that is also called polyoxymethylene (POM). POM comes in two forms, namely: homopolymer and copolymer. The terms, “POM” and “acetal” can often be used interchangeably. In practical terms, though, “acetal” generally refers to the copolymer version. Acetal copolymer is a chain of CH2O molecules with additional comonomers added in after every 70 to 100 units of CH2O. These comonomers disrupt the regular ordering of the molecular chains and thus make the material less crystalline. Below is an image of gears made from acetal:
Acetal polymers have good thermal and chemical resistance. Some typical acetal plastic properties are listed below:
- Reinforcing: Acetal copolymers readily accept reinforcing materials like glass fiber. A chemical process known as coupling allows the polymer molecules to chemically bond to the glass fiber. This results in significant increases in strength and stiffness.
- Low Coefficient of Friction: A low friction coefficient means that acetal has good wear- and abrasion-resistant properties.
- Chemical Resistance: Acetal copolymer is resistant to both organic and inorganic solvents and acids.
- Lower Relative Cost: Acetal copolymer tends to be cheaper than homopolymer POMs like Delrin®.
- Low Porosity: Acetal has low porosity characteristics, meaning that centreline porosity is unlikely. Centreline porosity is the phenomenon wherein voids form in the center of an extruded profile or sheet.
- Resistance to Hot Water: Acetal resists degradation caused by prolonged exposure to hot water, helping it maintain dimensional stability.
- High Continuous Service Temperature: Acetal copolymers can withstand prolonged exposure to high temperatures without serious reductions in mechanical properties.
Acetal polymers are used in almost every industry from automotive to consumer electronics. Some typical applications are listed below:
- Insulin pens
- Dry powder inhalers
- Electric toothbrushes
- Electrical connectors
- Fuel sender units
- Door locks
- Vehicle fuel tanks
To learn more, see our guide on What is Acetal Plastic?
Delrin® is the trade name for a semicrystalline homopolymer POM developed by DuPont. It is one of the strongest and stiffest unreinforced polymers. Delrin® is a homopolymer which means it has a uniform backbone made with repeating units of CH2O. This homogenous molecular makeup makes it possible to create larger crystalline blocks of Delrin® than of other POMs. It must be noted that there are different types of Delrin®, some of which have fillers like glass fiber and PTFE. The image below is of standard Delrin® sheet stock:
Teflon sheet on a white background.
Image Credit: enes efe/Shutterstock.com
Delrin® polymer is a tough and high-strength engineering polymer. Some of the key Delrin® material properties are listed below:
- Easy to Mold: Delrin® acetal resin flows well in liquid form. It fills injection molds better than similar materials and also enables short cycle times.
- Crystalline: Delrin® has a high degree of crystallinity. That gives it excellent mechanical properties such as strength, stiffness, and springback.
- High Yield Strain: Delrin® can flex with very little permanent deformation. This is an ideal characteristic for snap-fit connectors.
- High Toughness: Delrin® has excellent toughness, a helpful property that does not vary over a temperature range of -40॰C to 90॰C.
- Temperature Resistance: Delrin® is able to withstand high intermittent temperatures of up to 120॰C. It cannot sustain that temperature for extended periods, however.
- Fatigue Strength: Delrin® is well suited to applications that undergo continuous cyclic loading because it resists fatigue very well.
Delrin® is popular for its excellent mechanical properties, especially fatigue resistance and toughness. Some typical applications are listed below:
- Conveyor system parts
- Implants & prosthetics
- Safety restraints
- Door system parts
- Zip fasteners
- Linear guide rails
Copolymer acetal and homopolymer POM (Delrin®) differ primarily in their molecular makeup (Delrin® has a more ordered crystalline structure). The strength of any POM depends largely on the strength of the molecular chain bonds between regions of high crystallinity. Bond strength within a crystalline region is much higher than between two adjacent crystalline regions. This means that the material’s strength is determined by the inter-region bonds. When a load is applied, these inter-region chains will first stretch and ultimately peel away from nearby crystalline regions. Improvements in inter-region bonds translate into greater strength.
Delrin® has more crystalline regions, so it contains more inter-region bonds. A more ordered crystalline structure will result in improved strength. The image below shows the difference between the molecular structure of Delrin® and copolymer acetal:
The key differences between acetal vs Delrin® are listed in the table below:
Resistant to organic and inorganic solvents and acids.
Does not perform well in the presence of acids, bases, or oxidizing agents.
Has a wider processing window, meaning it is not as sensitive to variations in temperature. It will not degrade as readily at high temperatures.
Needs to be processed in a very narrow temperature band to prevent degradation. Due to its high crystallinity, it has a very precise melting temperature.
Effect of Reinforcing Additives
Glass-filled acetal has better mechanical properties. This is due to the way the copolymer bonds chemically to the glass.
Additives like glass fiber do not bond chemically to the polymer chains. This means that additives behave as fillers and only increase the stiffness of the material.
Better long-exposure temperature resistance. Acetal does not oxidize when exposed to high temperatures for long periods
Higher instantaneous temperature resistance but tends to degrade when exposed to high temperatures for long periods of time.
Mechanical properties are not as good as Delrin®. However, acetal retains its mechanical properties at elevated temperatures for long periods.
High fatigue resistance in cyclic loading applications. Better creep resistance when exposed to long-term loading.
Table 1. Key Differences Between Acetal Copolymer vs Delrin®
The common properties of both acetal copolymer and Delrin® are:
- Very easy to machine (in the proper temperature range).
- Exhibits some centerline porosity. This is the process where the material becomes porous at the center of extruded profiles due to outer surfaces cooling first and reducing density at the center. It must be noted that acetal experiences less of this problem than Delrin®, which is very prone to centreline porosity.
- Poor flame resistance with a UL94 rating of HB.
This article provided a comparison of acetal copolymer vs homopolymer (Delrin®) to help you decide which material is best suited to your specific application.
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- Delrin® is a registered trademark of E.I. Du Pont De Nemours and Company, Wilmington, DE.
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