POLYOXYMETHYLENE

CAS Number  :  9002-81-7 
Chemical formula :  (CH2O)n
Molecular Weight :  146.14
Density             :  1.41–1.42 g/cm
Melting point     :  165 °C

Other names :
-Poly(oxymethylene) glycol; polymethylene glycol

Polyoxymethylene (POM), also known as acetal,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.

Polyoxymethylene is characterized by its high strength, hardness and rigidity to −40 °C. 
Polyoxymethylene is intrinsically opaque white because of its high crystalline composition but can be produced in a variety of colors.
Polyoxymethylene has a density of 1.410–1.420 g/cm3.

Typical applications for injection-molded Polyoxymethylene include high-performance engineering components such as small gear wheels, eyeglass frames, ball bearings, ski bindings, fasteners, gun parts, knife handles, and lock systems. 
The material is widely used in the automotive and consumer electronics industry. 
Polyoxymethylene's electrical resistivity is 14×1015 Ω⋅cm making it a dielectric with a 19.5MV/m breakdown voltage.

Development of Polyoxymethylene
Polyoxymethylene was discovered by Hermann Staudinger, a German chemist who received the 1953 Nobel Prize in Chemistry.
He had studied the polymerization and structure of Polyoxymethylene in the 1920s while researching macromolecules, which he characterized as polymers. 
Due to problems with thermostability, Polyoxymethylene was not commercialized at that time.

Around 1952, research chemists at DuPont synthesized a version of Polyoxymethylene, and in 1956 the company filed for patent protection of the homopolymer.
DuPont credits R. N. MacDonald as the inventor of high-molecular-weight Polyoxymethylene.
Patents by MacDonald and coworkers describe the preparation of high-molecular-weight hemiacetal-terminated (~O−CH2OH) POM, but these lack sufficient thermal stability to be commercially viable. 
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.

In 1960, DuPont completed construction of a plant to produce its own version of acetal resin, named Delrin, at Parkersburg, West Virginia.
Also in 1960, Celanese completed its own research. 
Shortly thereafter, in a limited partnership with the Frankfurt firm Hoechst AG, a factory was built in Kelsterbach, Hessen; from there, Celcon was produced starting in 1962,with Hostaform joining it a year later. 
Both remain in production under the auspices of Celanese and are sold as parts of a product group now called 'Hostaform/Celcon POM.

Production of Polyoxymethylene
Different manufacturing processes are used to produce the homopolymer and copolymer versions of Polyoxymethylene.

Homopolymer
To make polyoxymethylene homopolymer, anhydrous formaldehyde must be generated. 
The principal method is by reaction of the aqueous formaldehyde with an alcohol to create a hemiformal, dehydration of the hemiformal/water mixture (either by extraction or vacuum distillation) and release of the formaldehyde by heating the hemiformal. 
The formaldehyde is then polymerized by anionic catalysis, and the resulting polymer stabilized by reaction with acetic anhydride. 
Due to the manufacturing process, large-diameter cross-sections may have pronounced centerline porosity.
A typical example is DuPont's Delrin.

Copolymer
The polyoxymethylene copolymer replaces about 1–1.5% of the −CH2O− groups with −CH2CH2O−.
To make polyoxymethylene copolymer, formaldehyde is generally converted to trioxane (specifically 1,3,5-trioxane, also known as trioxin). 
This is done by acid catalysis (either sulfuric acid or acidic ion-exchange resins) followed by purification of the trioxane by distillation and/or extraction to remove water and other active hydrogen-containing impurities. 
Typical copolymers are Hostaform from Celanese and Ultraform from BASF.

The co-monomer is typically dioxolane, but ethylene oxide can also be used. 
Dioxolane is formed by reaction of ethylene glycol 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 etherate, BF3OEt2. 
The polymerization can take place in a non-polar solvent (in which case the polymer forms as a slurry) or in neat trioxane (e.g. in an extruder). 
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.

Fabrication
Polyoxymethylene 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 injection molding and extrusion. 
Rotational molding and blow molding are also possible.
Typical applications for injection-molded Polyoxymethylene include high-performance engineering components (e.g. gear wheels, ski bindings, yoyos, fasteners, lock systems). 

The material is widely used in the automotive and consumer electronics industry. 
There are special grades that offer higher mechanical toughness, stiffness or low-friction/wear properties.
Polyoxymethylene 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.

Machining
When supplied as extruded bar or sheet, Polyoxymethylene 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.

Polyoxymethylene sheets can be cut cleanly and accurately using an infrared laser, such as in a CO2 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 Polyoxymethylene can be dimensionally unstable, especially with parts that have large variations in wall thicknesses. 
Polyoxymethylene 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
Polyoxymethylene is typically very difficult to bond, with the copolymer typically responding worse to conventional adhesives than the homopolymer.
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.
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.

Once the surface is prepared, a number of adhesives can be used for bonding. 
These include epoxies, polyurethanes, and cyanoacrylates. 
Epoxies have shown 150–1,050 psi (1,000–7,200 kPa) shear strength. 
Cyanoacrylates are useful for bonding to metal, leather, rubber, cotton, 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.

Usage of Polyoxymethylene
-Mechanical gears, sliding and guiding elements, housing parts, springs, chains, screws, nuts, fan wheels, pump parts, valve bodies.
-Electrical engineering: insulators, bobbins, connectors, parts for electronic devices such as televisions, 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, ball-jointed dolls, 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.
-Furniture: hardware, locks, 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.
-Dining: fully automatic coffee brewers; knife handles (particularly folding knives).

-Horology: mechanical movement parts (e.g. Lemania 5100), watch bracelets (e.g. IWC Porsche Design 3701).
-Vapor/e-cigarette accessories: material used in the manufacturing of most "Drip Tips" (Mouthpiece).
-Tobacco products: The BIC Group uses Delrin for their lighters.
-Keyboard keycaps: Cherry uses POM for their G80 and G81 series keyboards.

Degradation of Polyoxymethylene
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. 
Thus low levels of chlorine in potable water supplies (1–3 ppm) can be sufficient to cause environmental stress cracking, a problem experienced in both the US and Europe in domestic and commercial water supply systems. 
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 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.

Polyoxymethylene, POM, people also name it as acetal resin, polyacetal, polytrioxane and polyformaldehyde, is a semi-crystalline engineering thermoplastic, normally available in homopolymer or copolymer.
Under temperatrue −40 °C, Polyoxymethylene products still with good perforamce of high strength, hardness and rigidity. 
Polyoxymethylene becomes a very good replacement for metal materials.

Applications of Polyoxymethylene
Polyoxymethylene can support high stiffness, low friction and excellent dimensional stability, popularly used in precision parts, which brings high strength, hardness and rigidity.
Polyoxymethylene is used for high-performance engineering components such as gun parts, small gear wheels, fasteners, eyeglass frames, ball bearings, ski bindings, knife handles, and lock systems.
Polyoxymethylene is widely used in the automotive and consumer electronics industry.
Polyoxymethylene is also used as a substitute for acrylic resins and metals in numerous prosthetic applications.
Typical Applications: Food conveyers, Steering columns, Bushings, Seat belt components, Fasteners, Filter housings, Insulin pens. 

Polyacetal or Polyoxymethylene is a semi-crystalline engineering thermoplastic widely used to produce high precision parts thanks to high lubricity. 
Discover how it is manufactured, what are the various types of Polyoxymethylene available (homopolymer and copolymer) and its key properties ranging from mechanical, physical and chemical. Also, get detailed information on key features which make acetal resins an ideal material of choice in applications ranging from automotive to medical, industrial and many more.

Polyacetal, also commonly known as acetal or polyoxymethylene (POM), is a formaldehyde-based, semi-crystalline engineering thermoplastic which contains the functional group of a carbon bonded to two -OR groups. 
Polyoxymethylene is 100% recyclable. 
Polyoxymethylene is known as polyformaldehyde, polymethylene glycol and polyoxymethylene glycol.

Polyoxymethylene resins are widely used in the production of precision parts for applications demanding good dimensional stability and sliding properties. 
Some of them include:
-Automotive
-Electrical & electronic
-Industrial 
-Drug Delivery 

The polymer serves as an alternative to metals due to its low friction and wear characteristics as well as its excellent balance of mechanical and chemical properties.

Properties of Polyoxymethylene
-Extremely high mechanical and impact resistance
-Wear, bending and deformation resistance
-No need for flattery
-Low friction coefficient
-High abrasion resistance
-Dimentional stability in humid ambient conditions
-Good chemical resistance

Applications of Polyoxymethylene
-Gears,
-Pulleys and rings,
-Wedges and wheels,
-Guide rollers,
-Pump equipments,
-Machine parts working in humid conditions and without flattery

Typical Applications of Polyoxymethylene:

-Bushings
-Seat belt components
-Steering columns
-Filter housings
-Food conveyers
-Fasteners
-Insulin pens

Polyoxymethylene has minimal water absorption, excellent dimensional stability and the best properties for chip machining. 
Thanks to its favorable characteristics, great hardness, rigidity and strength with good toughness, chemical resistance and its shear behaviour with abrasion resistance, Polyoxymethylene is a successful replacement for metal materials. 
Polyoxymethylene is resistant to organic solvents. 
Polyoxymethylene also features good resistance to black-light UV-radiation.

POM is the abbreviation of the chemical name polyoxymethylene (polyoxymethylene), generally also called polyoxymethylene, acetal resin.
Polyoxymethylene is a crystalline thermoplastic resin mainly composed of (-CH2O-) structural units.
Polyoxymethylene includes a homopolymer composed of a molecular chain of polyoxymethylene formed by formaldehyde, and a copolymer composed of a tri-E polymer of formaldehyde-trioxane and dioxyalkylene.

Polyoxymethylene mainly focuses on the application of gears, screws and bearings and other mechanical parts. 
Used in AV machines such as DVD players and Blu-ray disc players; OA machines such as printers and copiers; household appliances such as washing machines, refrigerators, and razors;
Fuel tank caps, fuel oil pumps, seat belt parts and automotive interior products and other auto parts. 
Polyoxymethylene is also used in residential-related fields such as window frames and shutter parts.

Polyoxymethylene plastics offer:
-High strength, rigidity and toughness
-Good impact strength, even at low temperatures
-Low moisture absorption (at saturation 0.8%)
-Outstanding wear resistance and sliding properties
-Excellent machinability
-Good creep resistance
-High dimensional stability
-Good resistance to hydrolysis (up to ~60 °C)
-Excellent resilience/recovery elasticity

Properties of Polyoxymethylene
Polyoxymethylene combines high stiffness and strength with outstanding resilience, favourable sliding friction behaviour and excellent dimensional stability, even under the effect of mechanical forces, in contact with numerous chemicals,fuels and other media as well as at elevated temperatures.

Polyoxymethylene (POM), also commonly known as Acetal, is a naturally white semi-crystalline thermoplastic. 
Polyoxymethylene is used to produce precision parts that require high resistance to abrasion and heat, low friction, good dimensional stability, resistance to water absorption, and high tolerance to organic chemical compounds (e.g. hydrocarbons). 
Polyoxymethylene is a very high tensile strength plastic with significant creep resistant properties that bridge the material properties gap between most plastics and metals. 
Typical applications include small gears, consumer electronics, plastic zippers, medical devices, and furniture components such as the plastic feet underneath a couch.

Polyoxymethylene is identified by a number of technical and industrial names (the most common of which is Acetal). 
Other technical names include the following:
-Polyacetal
-Polyformaldehyde
-Polymethylene glycol
-Polyoxymethylene glycol

Substance identity

EC / List no.: 608-494-5
CAS no.: 30525-89-4
Mol. formula:

Help
EC / List no.: 608-494-5

CAS no.: 30525-89-4

Mol. formula: (CH2O)n

Hazard classification & labelling of Polyoxymethylene
Danger! According to the classification provided by companies to ECHA in CLP notifications this substance may cause cancer, is harmful if inhaled, is harmful if swallowed, causes serious eye damage, is a flammable solid, is suspected of causing cancer, is harmful in contact with skin, is suspected of causing genetic defects, causes skin irritation, may cause an allergic skin reaction, may cause allergy or asthma symptoms or breathing difficulties if inhaled and may cause respiratory irritation.

At least one company has indicated that the substance classification is affected by impurities or additives.

Synonyms:
ETHYLIDENE DIACETATE
542-10-9
1,1-Ethanediol Diacetate
1,1-Diacetoxyethane
ethane-1,1-diyl diacetate
Ethylidene acetate
1,1-Ethanediol, diacetate
1-acetyloxyethyl acetate
Polyoxymethylenes
Delrin
KL1S8V6W25
NSC-8852
Ethylidene di(acetate)
66455-31-0
1-acetoxyethyl acetate
Diacetic acid ethylidene
UNII-KL1S8V6W25
NSC 8852
EINECS 208-800-3
MFCD00014980
1,1-diacetoxy-ethane
1,1'-Diacetoxy-ethane
AI3-24218
DSSTox_CID_7188
1-(Acetyloxy)ethyl acetate
DSSTox_RID_78341
DSSTox_GSID_27188
SCHEMBL987906
1-(Acetyloxy)ethyl acetate #
CHEMBL3187663
DTXSID1027188
ETHYLIDENE DIACETATE [MI]
NSC8852
1,1-Ethanediol, 1,1-diacetate
ZINC1648271
Tox21_200113
AKOS015900230
NCGC00248529-01
NCGC00257667-01
AS-57369
CAS-542-10-9
CS-0206532
FT-0625724
D90424
(2-BENZYLOXY-PHENYL)-HYDRAZINEHYDROCHLORIDE
Q15720555
Aldacide
Flo-Mor
Formagene
Formaldehyde polymer
Oilstop, Halowax
Paraform
PARAFORMALDEHYDE
Paraformaldehyde
Paraformaldehydum
Paraformic aldehyde
Polyformaldehyde
Polymerised formaldehyde
Polyoxymethylene
Polyoxymethylene glycol
para-formaldehyde
PARAFORMALDEHYDE
Paraformaldehyde
paraformaldehyde
Polyoxymethyleen
Polyoxymethylene
polyoxymethylene
paraformaldehyde
Polyoxymethylene
104512-58-5
104512-63-2
104814-22-4
1417997-02-4
30525-89-4
53026-80-5