Acetal: homopolymer (Delrin) versus copolymer, are they different?

Acetal Grades

In my twenty plus years in the plastics industry, there have been materials there have always been materials that were easily confused or misunderstood in terms of their physical properties and/or potential applications. By far the most commonly confused and misunderstood material is Acetal. There are a myriad of reasons why this happens, from a lack of training at the distribution level to the political alliances and capabilities at the manufacturer level.

Either way, we still spend a lot of time explaining and educating on this topic with our customers every day. Our goal is to make sure the Job Shop gets the best material for the job! The reason why this is so important? Acetal homopolymer (or Delrin) and Acetal copolymer (known by various trade names like Tecaform or Acetron GP to name a few) are not the same, they are not equivalents. What they really are is alternatives to each other. It’s not that one is necessarily better than the other, they each have a place in the market and offer some distinct advantages. Using the wrong one can be a source of failures and returns that will cost you time, materials and maybe even a customer.

Time and again we see prints that call out for “Delrin” in the title block are being substituted with Acetal copolymer because the pricing can be more favorable on the copolymer material when compared to Acetal homopolymer. The attraction of the lower price can allow some to rationalize that they are getting the same thing, only cheaper. Take a look at the comparison chart on our website. The tensile strength, creep and fatigue resistance and toughness of homopolymer Delrin are much different than that of copolymer Acetal. Homopolymer Delrin can have increased physical properties in excess of 20% of other Acetal’s.

Black Acetal-porosity line(Click on picture for a closer look)

Center line porosity is another differentiator. Acetal homopolymer has an inherent center line porosity that is not present in Acetal copolymer. Is this a bad thing? It depends on the application, but you have to know if it matters in the end use application. If there is a concern that Acetal homopolymer center line porosity will be a problem, the design can be modified or reinforced to allow the use of Acetal copolymer.

Fatigue endurance is another area of differentiation where homopolymer Delrin will significantly outperform copolymer Acetal. This makes it a more ideal material for various industrial applications especially when maintaining or improving long-term performance is important.

Acetal ASTM

When you request a quote and you want to make sure you will be quoted and sold Acetal homopolymer Delrin, ask the seller to certify it as such. Read the certification carefully. The primary ASTM heading for both items are the same (ASTM D6100-11). The devil is in details of the second level of the specification where S-POM0111=Acetal homopolymer Delrin and S-POM0211=Acetal copolymer.

Either way, Plastics International stocks a vast inventory of both Acetal homopolymer Delrin and copolymer Acetal in natural and black in sheet and rod form. We do not have a minimum order on in stock items so you can get as little or as much of which ever Acetal is right for you. We would be happy to help you make sure you have the right material to meet your customer’s specification. Visit our website at www.plasticsintl.com for more information.

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