Uses of Acetal

Unit Structure

POM has the composite structure (-CH2O-)n. The unit structure (the portion within the parentheses), is a carbon atom with two hydrogens and one oxygen attached. A single chain, on average, repeats this formula "n" times; the greater the value of n, the greater the molecular weight of the plastic. Adjusting the molecular weight is one way of adjusting the properties of the plastic. This polymer is sometimes called "polyformaldehyde" as the formula within the parentheses is basically formaldehyde (HCHO). When the unit structure is as shown above without modification, the plastic is called a homopolymer; when it is modified with alternating portions of a different unit structure, it is called a copolymer.

Homopolymeric acetal is a translucent white, straight-chained (rather than branch-structured) polymer. Thus, homopolymeric acetal is highly crystalline. Homopolymeric acetal is strong and resistant to solvents, dimensionally stable and is resists damage by ultraviolet light. It has a low coefficient of friction, making it useful in moving parts. It is thermosetting and it also holds up well in a wet environment. Acetal does not, however, hold up well in the presence of strong acids.

Copolymeric acetal plastics have their properties modified, and thus lose some of the qualities of homopolymeric acetal. This is especially so as branch density is increased. However, copolymeric POMs are often given greater lubricity and have good long-term electrical stability. Copolymeric POM resists even strong alkali and has excellent impact strength. It is essentially unaffected by petroleum products such as oil or brake fluid. As with homopolymeric acetal, it is not suited for an environment of strong acids. It is also not suitable for use with strong oxidizers such as hypochlorites.

Homopolymeric acetal is useful in the automotive industry for car parts ,such as cams and gears, that have internal bearings. Thanks to its solvent resistance, it is used in fuel pumps. Water resistance enables it to be used in sprayers and showerheads, and also in impellers. Copolymeric acetal finds applicability in the automotive industry as well, and also in plumbing. It makes fine wristwatch gears. Research indicates the uses of polyoxymethylene plastic, or acetal, will increase as new modifiers are discovered and utilized.