Polyoxymethylenes, also known as polyacetals, are high molecular weight thermoplastics. The colorless, partially crystalline polymers are mainly used for the production of molded parts by injection molding. Because of their high rigidity, low coefficients of friction and good dimensional stability, polyoxymethylenes are used for the manufacture of precision parts. A characteristic structural element is an unbranched acetal group.
The homopolymer made from formaldehyde + methanol is called POM-H. In addition to numerous acetal groups, the copolymers (abbreviation POM-C) also have – (CH2) m – O– units with 2 or 4 methylene groups. They serve to thermally stabilize the polymer. POM-C has similar properties to POM-H.
POM is characterized by high strength, hardness and stiffness in a wide temperature range. It retains its high toughness, has high abrasion resistance, a low coefficient of friction, high heat resistance, good sliding properties, good electrical and dielectric properties and low water absorption. The intrinsic color is opaque white because of the high crystallinity, but the material can be dyed in all colors.
Most POM grades meet FDA and EU regulations, and WRAS, KTW and NSF.
The crystallinity of POM-H reaches 80% and is slightly higher than that of POM-C with up to 75%. The crystallite melting point of POM-H is 175 ° C and of POM-C is 164 to 172 ° C. Because of the higher crystallite melting point, POM-H has a slightly better heat resistance. POM-C is somewhat more resistant to alkalis and hot water. In general, POM has poor weather resistance.  If the processing temperature is too high or if it is heated above 220 ° C, POM begins to thermally decompose. It forms for example Formaldehyde, which has a pungent and irritating odor.
Without special surface treatment, POM can only be bonded to a limited extent. The adhesion of adhesives (mostly epoxy resins) can be improved by special pickling of the surface
Areas of application:
POM is therefore one of the preferred construction materials, e.g. for precision parts in precision engineering. The most important areas of application are the automotive industry and electrical engineering, followed by general device and mechanical engineering as well as applications in the consumer goods sector. Gear wheels for example are made out of extruded plates or rods from POM.