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Polyoxymethylene POMalso known as acetal polyacetaland polyformaldehydeis an engineering thermoplastic used in precision parts requiring high stiffness, low friction, and excellent dimensional stability. As with many other synthetic polymersit is produced by different chemical firms with slightly different formulas and sold variously by such names as DelrinUltraformCelconRamtalDuraconKepitalPolypencoand Hostaform.
POM is intrinsically opaque white, due to its high crystalline composition, but it is available in all colors. POM has a density of 1. Typical applications for injection-molded POM include high-performance engineering components such as small gear wheels, eyeglass frames, ball bearings, ski bindings, fasteners, guns, knife handles, and lock systems. The material is widely used in the automotive and consumer electronics industry.
Polyoxymethylene was discovered by Hermann Staudingera German chemist who received the Nobel Prize in Chemistry. Due to problems with thermal stability, POM was not commercialized at that time. Aroundresearch chemists at DuPont synthesized a version of POM,  and in the company filed for patent protection of the homopolymer.
MacDonald as the inventor of high-molecular-weight POM. The inventor of a heat-stable and therefore useful POM homopolymer was Stephen Dal Nogare,  who discovered that reacting the hemiacetal ends with acetic anhydride converts the readily depolymerizable hemiacetal into a thermally stable, melt-processable plastic.
InDuPont completed construction of a plant to produce its own version of acetal resin, named Delrinat Parkersburg, West Virginia. Shortly thereafter, in a limited partnership with the Frankfurt firm Hoechst AGa factory was built in KelsterbachHessen ; from there, Celcon was produced starting in with Hostaform joining it a year later. Different manufacturing processes are used to produce the homopolymer and copolymer versions of POM.
To make polyoxymethylene homopolymeranhydrous formaldehyde must be generated. The formaldehyde is then polymerized by anionic catalysisand the resulting polymer stabilized by reaction with acetic anhydride. Due to the manufacturing process, large-diameter cross-sections may have pronounced centerline porosity.
The polyoxymethylene copolymer replaces about 1—1. To make polyoxymethylene copolymerformaldehyde is generally converted to trioxane specifically 1,3,5-trioxanealso known as trioxin. The co-monomer is typically dioxolanebut ethylene oxide can also be used. Dioxolane is formed by Quiero Pom - Various - DJ & Co of ethylene Quiero Pom - Various - DJ & Co with aqueous formaldehyde over an acid catalyst. Other diols can also be used.
Trioxane and dioxolane are polymerized using an acid catalyst, often boron trifluoride etherateBF 3 OEt 2. The polymerization can take place Quiero Pom - Various - DJ & Co a non-polar solvent in which case the polymer forms as a slurry or in neat trioxane e. After polymerization, the acidic catalyst must be deactivated and the polymer stabilized by melt or solution hydrolysis to remove unstable end groups.
Stable polymer is melt-compounded, adding thermal and oxidative stabilizers and optionally lubricants and miscellaneous fillers. POM is Quiero Pom - Various - DJ & Co in a granulated form and can Время По Имени Чайка - Юрий Цендровский - Каменный Посох formed into the desired shape by applying heat and pressure. The two most common forming methods employed are injection molding and extrusion.
Rotational molding and blow molding are also possible. Typical applications for injection-molded POM include high-performance engineering components e. POM is commonly extruded as continuous lengths of round or rectangular section.
These sections can be cut to length and sold as bar or sheet stock for machining. When supplied as extruded bar or sheet, POM may be machined using traditional methods such as turning, milling, drilling etc. These techniques are best employed where production economics do not merit the expense of melt processing.
The material is free-cutting, but does require sharp tools with a high clearance angle. The use of Quiero Pom - Various - DJ & Co cutting lubricant is not necessary, but is recommended. POM sheets can be cut cleanly and accurately using an infrared laser, such as in a CO 2 laser cutter. Because the material lacks the rigidity of most metals, care should be taken to use light clamping forces and sufficient support for the work piece.
As can be the case with many polymers, machined POM can be dimensionally unstable, especially with parts that have large variations Our Rage - Abolition - Abolition wall thicknesses. It is recommended that such features be "designed-out" e. Annealing of pre-machined parts before final finishing is an alternative.
A rule of thumb is that in general, small components machined in POM suffer from less warping. POM is typically very difficult to bond. Special processes and treatments have been developed to improve bonding. Typically these processes involve surface etching, flame treatment or mechanical abrasion. Typical etching processes involve chromic acid at elevated temperatures. DuPont uses a patented process for treating acetal homopolymer called satinizing that creates a Introduzione - Anne Sofie Von Otter - 10 Classic Albums roughness sufficient for micromechanical interlocking.
There are also processes involving oxygen plasma and corona discharge. Once the surface is prepared, a number of adhesives can be used for bonding. These include epoxiespolyurethanesand cyanoacrylates.
Cyanoacrylates are useful for bonding to metal, leather, rubber and other plastics. Solvent welding is typically unsuccessful on acetal polymers, due to the excellent solvent resistance of acetal. Thermal welding through various methods has been used successfully on both homopolymer and copolymer. Acetal resins are sensitive to acid hydrolysis and oxidation by agents such as mineral acid and chlorine.
POM homopolymer is also susceptible to alkaline attack and is more susceptible to degradation in hot water. Defective mouldings are most sensitive to cracking, but normal mouldings can succumb if the water is hot. Both POM homopolymer and copolymer are stabilized to mitigate these types of degradation. In chemistry applications, although the polymer is often suitable Quiero Pom - Various - DJ & Co 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. In addition, POM can have undesirable characteristics when burned. The flame is not self-extinguishing, shows little to no smoke, and the blue flame Endstille - Kapitulation 2013 be almost invisible in ambient light.
Burning also releases formaldehyde gas, which irritates nose, throat, and eye tissues. From Wikipedia, the free encyclopedia. This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Poly oxymethylene glycol; Polymethylene glycol. CAS Number. Chemical formula. Bibcode : JMagR. Archived from the original on Retrieved 8 March Kennedy; Wayne H.
Watkins 31 July British Plastics Federation. Painter; Michael M. Coleman Essentials of Polymer Science and Engineering. DEStech Publications, Inc. Ibeh 25 April CRC Press. Delrin" PDF. Lion Engineering Plastics. Retrieved Handbook of Surface Preparation. New York: Palmerton Publishing Co. Retrieved 15 Sep Celanese Corporation.
Retrieved 19 March Interstate Plastics. Retrieved September Thermoplastic Thermosetting polymer Duroplast Corrugated plastic Polymeric foam High performance plastics. Polymer additive Colorants Plasticizer Im Free - The London Symphony Orchestra - Tommy for polymers Biodegradable additives Filler materials. Plastics industry Commodity plastics Engineering plastics High-performance plastics Plastic film Plastic bottle Plastic bag Plastic shopping bag Plastic cutlery Blister pack Foam food container Construction Geosynthetics Category:Plastics applications.
Health issues of plastics and polyhalogenated compounds PHCs.
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