Properties
POM is characterized by its high strength, hardness and rigidity to ~40 °C. POM is intrinsically opaque white, due to its high crystalline composition, but it is available in all colors. POM has a density of ρ = 1.410-1.420 g/cm3.
POM homopolymer is a semi-crystalline polymer (75-85% crystalline) with a melting point of 175° Celsius. The POM copolymer has a slightly lower melting point of 162 – 173° Celsius.
POM is a tough material with a very low coefficient of friction. However, it is susceptible to polymer degradation catalyzed by acids, which is why both polymer types are stabilized. Both homopolymer and copolymer have chain end groups (introduced via end capping) which resist depolymerization. With the copolymer, the second unit normally is a C2 (ethylene glycol) or C4 (1,4-butanediol) unit, which is introduced via its cyclic acetal (which can be made from the diol and formaldehyde) or cyclic ether (e.g. ethylene oxide). These units resist chain cleavage, because the O-linkage is now no longer an acetal group, but an ether linkage, which is stable to hydrolysis. POM is sensitive to oxidation, and an anti-oxidant is normally added to molding grades of the material.
POM advantages:
- High abrasion resistance
- Low coefficient of friction
- High heat resistance
- Good electrical and dielectric properties
- Low water absorption
Read more about this topic: Polyoxymethylene
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