Degradation
Acetal resins are sensitive to acid hydrolysis and oxidation by agents such as mineral acids and chlorine. POM homopolymer is also susceptible to alkaline attack and is more susceptible to degradation in hot water. Both POM homopolymer and copolymer are stabilized to mitigate these types of degradation. Thus low levels of chlorine in potable water supplies (1–3 ppm) can be sufficient enough to cause stress corrosion cracking to develop, a problem which has been experienced in both the USA and Europe in domestic and commercial water supply systems. Defective mouldings are most sensitive to cracking, but normal mouldings will succumb if the water is hot.
Widespread failure of acetal mouldings in potable and hot water supplies resulted in one of the largest class actions in the USA when acetal plumbing fittings cracked and caused flooding of homes, a problem exacerbated by similar problems with polybutylene pipework. The acetal fittings tended to fail first, followed by the pipework.
In chemistry applications, whilst the polymer is often suitable for the majority of glassware work, it can succumb to catastrophic failure. An example of this would be using the polymer clips on hot areas of the glassware (such as a flask to column, column to head or head to condenser joint during distillation). As the polymer is sensitive to both chlorine and acid hydrolysis, it may perform very poorly when exposed to the reactive gases, particularly hydrogen chloride. Failures in this latter instance can occur with seemingly unimportant exposures from well sealed joints, and do so without warning and rapidly (the component will split or fall apart). This can be a significant health hazard as the glass may open or smash. Here, PTFE or a high grade stainless steel may be a more appropriate choice.
Read more about this topic: Polyoxymethylene
Famous quotes containing the word degradation:
“I suppose one has a greater sense of intellectual degradation after an interview with a doctor than from any human experience.”
—Alice James (1848–1892)
“We found nothing grand in the history of the Jews nor in the morals inculcated in the Pentateuch.... I know of no other books that so fully teach the subjection and degradation of woman.”
—Elizabeth Cady Stanton (1815–1902)
“Self-alienation is the source of all degradation as well as, on the contrary, the basis of all true elevation. The first step will be a look inward, an isolating contemplation of our self. Whoever remains standing here proceeds only halfway. The second step must be an active look outward, an autonomous, determined observation of the outer world.”
—Novalis [Friedrich Von Hardenberg] (1772–1801)