Delrin

Delrin is DuPont's trand name for Polyoxymethylene (POM). Polyoxymethylene is a thermoplastic with high stiffness, low friction, is chemically resistant, has low water absorption, and has high dimensional stability. As a result, it is an excellent material for parts that require a high precision. However, the material suffers from low impact strength, low melting temperature, high rigidity, and very high thermal expansion. Chemically the material is resistant to hydrolysis by bases, but sensitive acid hydrolysis and chlorine attack.

Delrin is made from the acetal homopolymer resin variant, which tends to suffer from porosity problems and thus is considered unsuitable for certain applications. In this case, the Acetal copolymer (ex: Acetron GP) is often used as a replacement

Details
Polyoxymethylene is defines my the molecular formula $$(CH_2O)_n$$. Like most plastics, it has a relatively low density ($$~1.5g/cm^3M$$). It is semi-crystalline (75%-85% crystalline) with a melting point of $$175^\circ C/347^\circ F$$ as a homopolymer and $$163^\circ C/325.4^\circ F$$ as a copolymer.

Synthesis
Polyoxymethylene homopolymer is created using anhydrous formaldehyde, which can be synthesized by reacting aqueous formaldehyde with an alcohol (-O- group) to create a hemiformal which is treated through dehydration then heat treated to release the formaldehyde. The formaldehyde is the polymetized by an anionic catalysis then stabilized with acetic anhydride.

Polyoxymethylene copolymer is created by converting formaldehyde to trioxane. The formaldehyde is treated by acid catalysis, typically with sulfuric acid or acidic ion exchange resins, after which the trioxane is removed through distillation or extraction. The trioxane is then dried to remove the water and hydrogen-containing impurities. The co-monomer is usually dioxolan, but ethylene oxide can be used. Diolan can be formed by the reaction of ethylene glyol with a formadahyde source such as trioxane ot an concentrated aqueous formaldehyde over an acid catalyst. Likewise, dioxolane can be substituted with other diols.

Trioxane and dioxoland are polymerized using an acid catalyst such as boron trifluoride etherate ($$BF_3*OEt_2$$. This can take place at room temperature in a non-polar solvent which produces a slurry, or melted for extrusion.

After polymerization, the acid catalyst must be deactivated, then the polymer must be stabilized by heat.

Most Polyoxymethylene contains added thermal and oxidative stabilizers, lubricants, and fillers.

Crafting
Granulated POM can be formed into a desired shape using heat or pressure, typically using injection molding and extrusion. Likewise, POM can be machined using traditional methods such as milling, drilling, turning, etc., and is also cuttable. Due to the low friction, lubricant is not necessary, but is recomended to reduce heat.

POM is notoriously difficult to bond, but with a properly prepared surface can by bonded with epoxies, polyurethanes, and cyanoacrylates (ex: super glue). Solvent welding is typically unsuccessful or very weak, although the material responds well to thermal welding.

POM, like most acetal resins, is susceptible to acid hydrolysis, oxidation, and chlorine. Over time, even the low levels of chlorine in normal tap water (1-3ppm) can cause the material to break down and develop cracks.