Acetal vs. Delrin®: What’s the Difference?
Two types of strong and durable manufacturing polymers
Copolymer acetal (more commonly known just by “acetal”) and homopolymer POM (“Delrin®”) are both polyoxymethylene (POM) polymers with great properties, like strength and durability, that make them appealing to manufacturers. We’ll talk about both of these materials in this article, and we’ve even got a side-by-side comparison table so you can decide which one is best for your needs.
What is Acetal?
Acetal is a semi-crystalline engineering thermoplastic that comes in two forms: homopolymer and copolymer. The terms “POM” and “acetal” are often used interchangeably, but in practical terms, “acetal” generally refers to the copolymer version. This copolymer is a chain of CH2O molecules with extra comonomers added in after every 70–100 units of CH2O. These disrupt the regular ordering of the molecular chains, ultimately making the material less crystalline.
Acetal copolymers readily accept reinforcing materials like glass fiber, and their molecules can be chemically bonded to the glass via coupling, which increases its strength and stiffness. Acetal has a low friction coefficient, meaning that it’s got good wear- and abrasion-resistance. It can also handle exposure to organic and inorganic solvents and acids, and prolonged exposure to hot water and high temperatures. This copolymer’s low porosity means that centerline porosity (where voids form in the center of an extruded part/sheet) will be highly unlikely. It’s also, most times, more affordable than homopolymer POMs, too.
What is Delrin?
Delrin is a semicrystalline homopolymer POM that’s one of the strongest and stiffest unreinforced polymers around. It was developed by DuPont (which patented the “Derlin” trade name). Homopolymers have a uniform backbone made with repeating CH2O units, which makes it possible to create larger crystalline blocks than other POMs. Delrin’s high crystallinity gives it excellent mechanical properties, including the aforementioned strength and stiffness, as well as spring back. There are different types of Delrin, some of which have fillers like glass fiber and PTFE. The image below shows a standard Delrin sheet stock.
Teflon sheet on a white background.
Image Credit: enes efe/Shutterstock.com
Delrin’s toughness doesn’t vary in temperatures of -40–90॰C, and it’s able to withstand high intermittent temperatures of up to 120॰C. It won’t be able to sustain that temperature for a longer time, however. As a resin, it flows well and can fill injection molds much better than similar materials with short cycle times. Its ability to flex without deforming makes it ideal for snap-fit connectors. It can resist fatigue very well, making it a common option for parts that are put under continuous cyclic loading. Unlike acetal, Delrin is prone to becoming porous at the center of extruded profiles due to its outer surfaces cooling first, reducing the center’s density.
Acetal vs. Delrin
As we’ve seen, both acetal and Delrin have some great properties, but let’s see a side-by-side comparison to really understand their differences.
| Property | Acetal | Delrin |
|---|---|---|
Property Chemical resistance | Acetal Resistant to organic/inorganic solvents and acids | Delrin Not resistant to acids, bases, or oxidizing agents |
Property Temperature resistance | Acetal Better long-exposure temperature resistance, doesn’t oxidize or degrade in high temperatures for long periods | Delrin Higher instantaneous temperature resistance, but degrades with prolonged exposure, poor flame resistance (UL94 rating of HB) |
Property Processing difficulty | Acetal Wider processing window as it’s not sensitive to temperature variations | Delrin 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 |
Property Effect of reinforcing additives | Acetal Glass-filled acetal has better mechanical properties due to the way the copolymer bonds chemically to the glass | Delrin Additives like glass fiber do not bond chemically to the polymer chains, so they behave as fillers and only increase the stiffness of the material |
Property Mechanical properties | Acetal Not as good as Delrin, but can keep its mechanical properties at high temperatures for long periods | Delrin High fatigue resistance for cyclic loading applications, better creep resistance when exposed to long-term loading |
Property Advantages | Acetal Reinforcing, low coefficient of friction, chemical resistance, low cost, low porosity, hot water resistant, high continuous service temperature | Delrin Easy to mold, high crystallinity, high yield strain, tough, temperature resistant, good fatigue strength |
Property Applications | Acetal Insulin pens, dry powder inhalers, electric toothbrushes, electrical connectors, kitchenware, gears, valves, pumps, fuel sender units, door locks, vehicle fuel tanks | Delrin Conveyor system parts, bearings, bushes, implants and prosthetics, rollers, safety restraints, door system parts, zip fasteners, linear guide rails |
Key Property Differences Between Acetal Copolymer vs. Delrin®
So, in summary, while Delrin and acetal are both POM polymers, Delrin is a homopolymer, and acetal is a copolymer. Acetal is well suited to constant high-temperature exposure, while Delrin is the better choice for continuous cyclic loading tasks. They’re both very easy to machine (in the proper temperature range), but acetal has less chance of centerline porosity than Delrin.
FAQs on Acetal and Delrin
How does a POM’s structure affect its overall strength?
POMs are made up of minuscule and tightly-packed crystalline structures that are a bit like mini blocks. These are pretty strong on their own, but the material’s overall strength depends on the bonds that connect and hold these blocks together. This is because bond strength within a crystalline block is much higher than between two blocks that are next to each other. When this material is pulled, bent, or otherwise put under stress, these connecting bonds can start to stretch. With too much force, they’ll eventually separate and weaken the material. There are ways to improve these bonds so that the material can handle more force without getting damaged.
How can POM be made even stronger?
As mentioned above, to make a POM stronger, the bonds between the crystalline blocks need to be reinforced. There are two main ways of doing this. The first is by adding reinforcing materials, like glass fibers, which works especially well for acetal (not so much for Delrin) because it can chemically bond with the glass. The second is by selective heat treatment, which could increase crystallinity and improve the bonds’ strength. Acetal reacts better to the additive method, while Delrin can sometimes benefit more from heat treatment.
How Xometry Can Help
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Copyright and Trademark Notice
- Delrin® is a registered trademark of E.I. Du Pont De Nemours and Company, Wilmington, DE.
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