Battle between Dupont Delrin Homopolymer and Acetal Copolymer Rages On

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( — November 18, 2013) Anaheim, CA — Have you ever seen the tiny working parts in a garden hose nozzle, audio cassette parts, food conveyors, toilet water valves, feed screws or maybe even guitar picks?  If so, then you have probably looked at one of the most versatile plastics named Acetal (Polyoxymethylene or POM). 


Acetal is an extremely durable and physically strong plastic, so it shouldn’t be a surprise to see it being used for so many different things. Acetal is a common replacement material for metal parts. It also replaces plastic materials with similar properties, like the Nylon 6/6 (Polyamide) or PBT. Acetal is the logical next level up from HDPE, which a common plastic used in food processing equipment, milk jugs and laundry detergent bottles.

Acetal plastic material is in a family of plastics called ‘thermoplastic’. What this means is that a material can be softened by heating and as it cools, the material becomes hard again, and will retain the new shape.  Because of this characteristic it is able to be molded in to many different types of objects, like the few listed above. While some thermoplastics are easily ‘formable’, Acetal is very difficult to reshape with heat after it is made into a part or into a sheet or rod.


A crystalline, rather than amorphous type resin is used to make Acetal.   Because of the uniform molecular structure of Acetal, it can be molded or machined into a huge range of different shapes and sizes for use in thousands of applications. Acetal is perfect for parts that would require a plastic material to be rigid, have excellent mechanical strength and have a low coefficient of friction. 


The two basic types of Acetal Materials

If you are searching for a plastic that that is machinable and tough, either resin will work. But for more demanding applications, you need to know some of the differences between Acetal and Dupont Delrin®.


There are two basic types of Acetal; one is a copolymer and the other a homopolymer. 

The most widely recognized Acetal is the homopolymer Acetal commonly known as Delrin®. Delrin® Acetal is produced by Dupont, and is one of the best known and popular brand names for a plastic. Dupont Delrin® is one of the only brands commonly used that is an Acetal Homopolymer.


The Acetal Copolymer is the other Acetal material. Perhaps the best known Copolymer Acetal is made by BASF; they produce a high quality copolymer called H2320. You may remember the television ads from BASF stating, “We don’t make the products you use; we make the products you use better!” One of the other manufacturers of the Acetal Copolymer is Ticona and their brand name is Celcon.


The most standard mill shapes for these materials are: Acetal Rod, Acetal Plate, Flat Sheets and a variety of tube and profiles are also produced.

Both the Dupont Delrin® and Acetal resins are produced in Natural (White) and Black, with some colors available on special order. Dupont also makes a few specialty Delrin® products, including Delrin AF (a PTFE filled Delrin®) which is a brown color and offers additional wear resistance. The most popular grade of Dupont Delrin used for extrusion is the Delrin® 150SA.


They are similar but not the same

Although the copolymer and homopolymer Acetal are very similar and may look the same, there are some significant differences in properties, and this makes them unique in their own way.  For example the copolymer will perform better than the homopolymer in these areas; thermal, impact, wear and chemical resistance.


As you investigate the copolymer characteristics, you will discover that it has a slightly lower water absorption rate.  This can be critical if you are working with moist applications such as plumbing, impellers, pumps, valve and valves stems.


The Dupont Delrin® material has a greater crystalline structure, making Delrin® stronger, with improved mechanical strength and creep resistance over its cousin, the copolymer. 

The chart shows that the Dupont Delrin® 150SA material has a higher Flexural Strength, Flexural Modulas and Rockwell Hardness. The Delrin® also has a higher temperature rating both in heat deflection and melting point.


Dupont Delrin 150SA versus Acetal Copolymer Phsyical Properties Chart
One visually obvious difference, and also a performance difference, between the copolymer and homopolymer is center line porosity.  The homopolymer (Delrin®) resin is known to be susceptible to having center line porosity, in the center of a rod, it will be seen as a very small found at the center.  The porosity in sheet is visible also, it will appear as a white line down the middle (of the thickness) of the extruded or compression molded sheet material.  This center line porosity is caused by the gasses trying to escape during the cooling processes. If a round rod is to have the center portion machined out, then Delrin® maybe the best choice.

Copolymer Acetal does not have this ‘soft center’ or porosity, and is a better choice if the part will not have the center removed.


Delrin® Homopolymer and Acetal Copolymer are both machinable

Both Delrin® and Acetal are excellent choices for machining and mechanical type applications. Also, tight tolerances may be maintained during the cutting and machining process. The materials are considered to be self lubricating, and make very good dry slide wear strips. The materials are FDA and 3A (Dairy) compliant.

We believe that you should consider the Acetal materials, either Delrin® Homopolymer or Copolymer Acetal for your demanding plastic applications.



Industrial Plastic Supply, Inc

2240 S. Dupont Drive
Anaheim, CA 92806