Polyoxymethylene
This article needs additional citations for verification. (March 2016) |
Names | |
---|---|
Other names
Poly(oxymethylene) glycol; polymethylene glycol
| |
Identifiers | |
ChemSpider |
|
UNII | |
CompTox Dashboard (EPA)
|
|
Properties | |
(CH2O)n | |
Molar mass | Variable |
Appearance | Colorless solid |
Density | 1.41–1.42 g/cm3[1] |
Melting point | 165 °C (329 °F)[2] |
Electrical resistivity
|
14×1015 Ω⋅cm[2] |
−9.36×10−6 (SI, at 22 °C) [3] | |
Thermochemistry | |
Heat capacity (C)
|
1500 J/kg·K[2] |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
|
Polyoxymethylene (POM), also known as acetal,[4] polyacetal, and polyformaldehyde, is an engineering thermoplastic used in precision parts requiring high stiffness, low friction, and excellent dimensional stability. As with many other synthetic polymers, it is produced by different chemical firms with slightly different formulas and sold variously by such names as Delrin, Kocetal, Ultraform, Celcon, Ramtal, Duracon, Kepital, Polypenco, Tenac and Hostaform.
POM is characterized by its high strength, hardness and rigidity to −40 °C. POM is intrinsically opaque white because of its high crystalline composition but can be produced in a variety of colors.[1] POM has a density of 1.410–1.420 g/cm3.[5]
Typical applications for
Development
Polyoxymethylene was discovered by
Circa 1952, research chemists at
In 1960, DuPont completed construction of a plant to produce its own version of acetal resin, named Delrin, at
Production
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Different manufacturing processes are used to produce the homopolymer and copolymer versions of POM.
Homopolymer
To make polyoxymethylene
Copolymer
The polyoxymethylene copolymer replaces about 1–1.5% of the −CH2O− groups with −CH2CH2O−.[16]
To make polyoxymethylene
The
Trioxane and dioxolane are polymerized using an acid catalyst, often
Stable polymer is melt-compounded, adding thermal and oxidative stabilizers and optionally lubricants and miscellaneous fillers.
Fabrication
POM is supplied in a granulated form and can be formed into the desired shape by applying heat and pressure. The two most common forming methods employed are
are also possible.Typical applications for injection-molded POM include high-performance engineering components (e.g. gear wheels, ski bindings,
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.
Typical mechanical properties[17][18]
POM is a hard plastic, that cannot be glued, but can be joined to POM by melting.
Melted POM does not adhere to steel tools used to shape it.
Density | 1.41 | kg/dm3 |
Melting point | 165 | °C |
Specific thermal capacity | 1500 | J/kg/K |
Specific thermal conductivy | 0.31 to 0.37 | W/m/K |
Coefficient of thermal expansion | 12 | ppm/K |
POM is a relatively strong plastic, nearly as strong as epoxy, or aluminum, but a bit more flexible:
Property | value | units |
---|---|---|
Tensile yield stress | 62 | MPa |
Tensile modulus | 2700 | MPa |
Elongation at yield | 2.5 | % |
Tensile breaking stress | 67 | MPa |
Elongation at break | 35 | % |
Impact strength | 80 | kJ/m2 |
POM is relatively wear-resistant, for a plastic :
Property | conditions | value | units |
---|---|---|---|
Coefficient of friction against steel | 0.3 m/s, 0.49 MPa | 0.31 | |
Coefficient of friction against steel | 0.3 m/s, 0.98 MPa | 0.37 | |
Specific wear against steel | 0.49 MPa | 0.65 | mm3/N/km |
Specific wear against steel | 0.98 MPa | 0.30 | mm3/N/km |
Coefficient of friction against POM | 0.15 m/s, 0.06 MPa | 0.37 |
Availability and price
POM materials can have trademarked producer-specific names, for example "Delrin".
Prices for large quantities, in october 2023, in US$/kg:[19]
- USA : 3.26, Europe 2.81, China 2.58, SEA 2.30, Middle East 1.68 .
Prices and availability retail / small wholesale :
- available in many colors, e.g. black, white, but not transparent .
- available as plates [20][ref], upto 3 meter by 1.25 meter, in thicknesses from 0.5mm to 130mm .
- available as round bars [ref], from diameter 5mm to 200mm.
Retail price november 2023 in the Netherlands : from 19 to 27 euro/dm3
Advantages and disadvantages
POM is a strong hard plastic, about as strong as plastics can be, and therefore competes with e.g. epoxy and polycarbonate.
The price of POM is about the same as that of epoxy.
There are two main differences between POM and epoxy :
- epoxy is a two-component resin that can be cast, and adheres to everything it touches,
while POM can be cast when melted and adheres to practically nothing.
- epoxy is usable up to 180°C. POM can be used long-time up to 80°C, short-time up to 100°C.
Epoxy is often used with glass-fiber reinforcement, but for POM that is not an option because it will not adhere to it.
Epoxy needs time to cure, while POM has full strength as soon as it has cooled down.
POM has very little shrinkage: from 165°C to 20°C it shrinks by 0.17%.
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 soluble cutting lubricant is not necessary, but is recommended.
POM sheets can be cut cleanly and accurately using an infrared laser, such as in a CO2
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 in wall thicknesses. It is recommended that such features be "designed-out" e.g. by adding fillets or strengthening ribs. 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.
Bonding
POM is typically very difficult to bond, with the copolymer typically responding worse to conventional adhesives than the homopolymer.[21] Special processes and treatments have been developed to improve bonding. Typically these processes involve surface etching, flame treatment, using a specific primer/adhesive system, 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 surface roughness sufficient for micromechanical interlocking. There are also processes involving oxygen plasma and corona discharge.[22][23] In order to get a high bond strength without specialized tools, treatments, or roughening, one can use Loctite 401 prism adhesive combined with Loctite 770 prism primer to get bond strengths of ~1700psi.[21]
Once the surface is prepared, a number of adhesives can be used for bonding. These include
Thermal welding through various methods has been used successfully on both homopolymer and copolymer.[24]
Usage
- Electrical engineering: telephones, etc.
- Vehicle: fuel sender unit, light/control stalk/combination switch (including shifter for light, turn signal), power windows, door lock systems, articulated shells.
- Model: model railway parts, such as trucks (bogies) and hand rails (handle bars). POM is tougher than ABS, comes in bright translucent colors, and is not paintable.
- Hobbies: radio-controlled helicopter main gear, landing skid, yo-yos, vaping drip tips, 3D printer wheels, K'Nex,[25] ball-jointed dolls,[26] etc.
- Medical: insulin pen, metered dose inhalers (MDI).
- Food industry: Food and Drug Administration has approved some grades of POM for milk pumps, coffee spigots, filter housings and food conveyors.[27]
- Furniture: handles, hinges., rollers for sliding mechanisms of furnitures
- Construction: structural glass - pod holder for point
- Packaging: aerosol cans, vehicle tanks.
- Pens: used as the material for pen bodies and caps
- Sports: paintball accessories. It is often used for machined parts of paintball markers that do not require the strength of aluminium, such as handles and reciprocating bolts. POM is also used in airsoft guns to reduce piston noise.
- Longboarding: puck material for slide gloves help the rider touch the road and lean on their hand to slow down, stop, or perform tricks.
- Clothing: zippers.
- Music: picks, Irish flutes, bagpipes, practice chanters, harpsichord plectra, instrument mouthpieces, tips of some drum sticks.[28][29]
- Dining: fully automatic coffee brewers; knife handles (particularly folding knives).
- IWC Porsche Design3701).
- Vapor/e-cigarette accessories: material used in the manufacturing of most "Drip Tips" (Mouthpiece).
- Tobacco products: The BIC Group uses Delrin for their lighters.[31]
- Keyboard keycaps: Cherry uses POM for their G80 and G81 series keyboards.[32]
Degradation
Acetal resins are sensitive to
In chemistry applications, although 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 (HCl). 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 can be almost invisible in ambient light. Burning also releases formaldehyde gas, which irritates nose, throat, and eye tissues.
See also
- Dalziel Hammick
- Forensic engineering
- Forensic polymer engineering
- Paraformaldehyde
- Polymer degradation
- Resin
References
- ^ a b "Colored Delrin". Retrieved 12 March 2021.
- ^ a b c d "Data Sheet: POM (Delrin, Acetal)" (PDF). xometry.eu. 2021. Retrieved June 19, 2022.
- S2CID 11545416.
- ^ "MatWeb:acetal".
- ^ "Ticona MSDS for Hostaform". Archived from the original on 2011-05-12.
- ^ Acetal (Polyoxymethylene)
- ^ "The Nobel Prize in Chemistry 1953". NobelPrize.org. Retrieved 8 March 2016.
- ISBN 978-1-118-41009-7.
- ^ "A History of Plastics". British Plastics Federation. Retrieved 8 March 2016.
- ^ News & Media Relations Home - DuPont EMEA[permanent dead link]
- ^ US 2768994, Macdonald, Robert Neal, "Polyoxymethylenes", published 1956-10-30, assigned to E. I. Du Pont de Nemours and Co.
- ^ US 2998409, Nogare, Stephen Dal & Punderson, John Oliver, "Polyoxymethylene carboxylates of improved thermal stability", published 1961-08-29, assigned to E. I. Du Pont de Nemours and Co.
- ISBN 978-1-932078-75-6.
- ISBN 978-1-4200-9384-1.
- ^ "Acetal Products Comparison: Acetal vs. Delrin" (PDF). Lion Engineering Plastics. Retrieved 2016-10-01.
- ^ "How to Maximise the Property Advantages of DuPont Delrin Acetal Homopolymer over Acetal Copolymer" (PDF). DuPont. 2013. Archived from the original (PDF) on 2016-05-19. Retrieved 2016-10-01.
- ^ "POM standard values" (PDF). POM_standard_values.pdf. Retrieved November 3, 2023.
- ^ "General Properties of M90-44". DURACON® POM Grade Catalog M90-44. Retrieved November 3, 2023.
- ^ "Polyoxymethylene (POM) price index". BusinessAnalytIQ. Retrieved November 3, 2023.
- ^ "POM-C staf wit Ø 100mm". Rich Kunststoffen. Retrieved November 3, 2023.
- ^ a b c "Design Guide for Bonding Plastics" (PDF). Retrieved 22 February 2020.
- ^ BASF Ultraform product information
- ^ Snogren, R. C. (1974). Handbook of Surface Preparation. New York: Palmerton Publishing Co.
- ^ "Tamshell Engineering Corner". Retrieved 15 September 2017.
- ^ "Ticona Polymer and Processing Expertise Helps Rodon Deliver Successes, Including K'NEX® Toys". celanese.com. Celanese Corporation. Retrieved 19 March 2016.
- ^ The Smart Doll Body
- ^ "Acetal Plastic Sheet, Rod, Tube and Accessories". Interstate Plastics. Retrieved September 1, 2015.
- ^ Murphy, Joe. "The Loud Buzzer". unknown. Archived from the original on 2013-10-04. Retrieved 2012-03-17.
- ^ Barry, Kenneth. "Saxscape Mouthpieces".
- ^ "Chronography 4: Lemania 5100". 19 October 2015.
- ^ "BiC® Werbefeuerzeuge für Geschäftskunden". www.bic-feuerzeuge.de (in German). Retrieved 2017-08-14.
- ^ "ABS vs PBT vs POM Keycap Plastic". numpad. 2020-01-14. Archived from the original on 2020-07-24. Retrieved 2020-01-18.
External links
- "Acetal". Machine Design. November 15, 2002. Retrieved 17 December 2019.
- "Acetal (POM) Engineering Property Data". MatWeb. Retrieved 17 December 2019.
- Michael Sepe (September 2012). "How Do You Like Your Acetal: Homopolymer or Copolymer?". Plastics Technology. Retrieved 17 December 2019.
- "Acetal Delrin Copolymer Homopolymer - What are the differences?". Retrieved 17 December 2019.