POM is the abbreviation for ‘polyoxymethylene’ (also known as ‘polyacetal’ … or just plain old ‘acetal’) synthesised from formaldehyde. It’s a readily available starting material, but, despite humble beginnings, is an engineering thermoplastic suitable for metal replacement.
For around 100 years it has been possible to form a polymer from formaldehyde but the pathetic thermal stability of polyformaldehyde (paraformaldehyde) meant that its only use was as a temporary store of gaseous formaldehyde in a solid form.
Just over 50 years ago DuPont and Celanese independently solved the thermal stability problem by stopping the unzipping reaction. The former by end capping the polymer chains (homopolymer) and the latter by incorporating a comonomer (copolymer).
The two versions of POM (homopolymer and copolymer) differ slightly in their properties but both have a low glass transition temperature (-80oC) meaning that POM is in its rubbery state at room temperature. However the high crystallinity makes the POM very rigid. So you can think of POM as an extremely stiff rubber, which explains its outstanding properties of toughness, resilience and fatigue endurance, making it the nearest thing to a metal spring and ideal for gears and bearings. POM is the best thermoplastic for snap fit assemblies.
Trade names: Delrin, Hostaform, Iupital, Kepital, Lucel, Ultraform
A word of warning to processors.
Polyoxymethylene is still thermally unstable if mishandled at high temperatures. That can bring tears to your eyes, both literally and metaphorically !
Written by Dr.Charlie Geddes for Hardie Polymers
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