The single most important thing about Delrin® is that it is unique. The revolutionary engineering of the Delrin® portfolio is a true testament to the scientific expertise of DuPont™. Compared to copolymer acetal, Delrin® delivers many mechanical advantages for superior application solutions.
Acetal is the common name for a family of thermoplastics otherwise known as polyoxymethylene (POM). Available in both copolymer and homopolymer varieties, it is widely considered that the latter is ‘purer’. Acetal is a relatively simple molecule which is made of repeating units of formaldehyde (CH₂O), but the subtle differences in formulation and manufacturing methods are what gives Delrin® the competitive edge.
All acetal is produced by converting methane into methanol and methanol into formaldehyde. It is the polymerisation method where the differentiation starts. The DuPont™ patented method of producing Delrin® results in its mechanical advantages – unrivalled by any other acetal on the market.
Delrin® homopolymer acetal is constructed of formaledehyde polymer chains which are joined together by catalysts. Molecules form endcaps which stabilise the chain and control the molecular weight. The uniformity of the formaldehyde chain structure allows for the tight packing of polymer chains and increased interconnections between blocks. This results in a typical crystallinity of 55-60%, which gives Delrin® acetal homopolymer the mechanical property advantage over standard copolymer acetal.
Standard copolymer acetal tend to feature a second monomer (which differs from producer to producer) to attempt to replicate the patented chemistry of Delrin®, but results are not comparable. The position of this second molecule in the molecular chain is random and creates disruption in the chain. This lack of order and uniformity in the chain reduces the crystallinity by 45 to 50%, explaining copolymer acetals reduced mechanical properties.
As a general rule, the lower the melt flow rate and higher the viscosity, the better the mechanical properties. Unfortunately, this can cause issues filling thinner walls in component designs with long flow paths. Conversely, the higher the melt flow rate, the easier the filling of thin wall sections is, but then mechnical properties are compromised. However, with Delrin® and its unique homopolymer chemistry, this general rule is not entirely accurate.
This standard melt 9 g/10min copolymer acetal (red bar) offers 6kJ/m2 of impact strength. Compared to the higher flowing Delrin® 511DP (MFR 15 g/10min), there is a 40% improvement in flow rate, making it much easier to fill your product design, and also a 16% improvement in impact properties as Delrin® 511DP has an impact strength of 7kJ/m2.
Delrin® homopolymer acetal is the stiffest unreinforced polymer on the market, simultaneously offering high rigidty and ductility. This is achieved by the exceptionally high crystallinity in its structure.
The uniform, crystalline Delrin® hompolymer structure improves the stiffness of the material and increases the tensile and flexural modulus by 17 to 20%. This enables thinner wall part design, saving material costs and becoming more sustainable whilst having the product strength required.
With some polymer types, high stiffness can mean low ductility or brittleness, but that isn’t the case with Delrin®.
Comparing the higher flow rate Delrin® 511DP with the standard melt 9 g/10min copolymer acetal, we can offer a 14% improvement in tensile yield stress, but also a huge 44% improvement in the yield strain, demonstrating the high ductility of Delrin® compared to copolymer. This is due to the uniform, crystalline structure of Delrin®.
If we look at a more comparable melt flow grade such as Delrin® 311DP with an MFR of 7g/10min, the yield strain improves by 77%. This is again due to the uniform, crystalline structure of Delrin®.
A simple injection moulding might have a wall section of 2mm when designed in a standard melt 9 copolymer acetal. Using Delrin® 511DP, the wall section could be reduced to 1.7mm, without compromising performance due to the high rigidity of Delrin®. Thinner wall sections lighten the overall product part.
Reducing part weights is hugely beneficial:
The rate of crystallisation (molten polymer becoming solid plastic) and therefore hold pressure time for Delrin® is on average 8 seconds per mm. With a saving of 0.3mm, there would be a 2.4 second saving in hold pressure time.
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