Chemical resistance polyacetals

POMlElastomer (Polyacetal or Polyoxymethylene). It has toughness, good notched Izod resistance, and chemical resistance. It is used in interior automotive, gears, cams, etc. 

The permeability of water vapor through PET is higher than that of polyolefins but lower than that of polycarbonate, polyamide, and polyacetal. Antioxidants are necessary to prevent to the oxidation of polyether segments in thermoplastic polyester elastomer. Chemical resistance of PET is generally good to acids, alkalis, and organic solvents. 

Use of polyacetal gears is increasing because of their high performance, dimensional stability, high fatigue, chemical resistance at temperatures up to 90 °C, and excellent lubricity against metals and plastic materials in automotives and precision gears [7]. 

Polyacetals are produced by reacting formaldehyde. These are also sometimes called polyoxymethylene (POM) and known widely as Delrin (DuPont). These polymers have a reasonably high molecular weight (>2 xlO g/mol) and have excellent mechanical properties. More importantly, they display an excellent resistance to most chemicals and to water over wide temperature ranges. 

For a long time, polyoxymethylene was considered resistant to stress-cracking caused by solvents or other chemicals [878]. However, more recent investigations have shown that stress-cracks can indeed be initiated, in particular by base oils of lubricants. Polyacetals are often used in tribological systems due to their good frictional and lubrication properties. 

The hydrolysis resistance of polyacetals depends on their chemical structure and to a lesser extent on their stabilization. POM copolymers are more resistant than POM homopolymers, because POM homopolymers contain hydrolysis-sensitive end groups. 

Polyoxymethylene or polyacetal is a highly crystalline polymer. POM is most noted for its high stiffness, mechanical strength, abrasion resistance and good resistance to chemicals and solvents. It also displays good low temperature impact resistance, high dimensional stability, favourable frictional properties and low water absorption. 

Some of the main applications for POM in electrical systems include mountings and brackets for lamp reflectors, gear trains for helical window lift gears, interior input control switches such as multi-function turn signal switches and master light control units, seat adjustment systems, climate control systems and door lock systems. Polyacetals are particularly valued in these applications for their chemical and high temperature resistance, dimensional stability and low wear and friction (gear trains). 

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