What is Acetal Polymer?
Acetal, better known as POM plastic or polyoxyethylene or sometimes polyacetal, is a semi-crystalline thermoplastic material containing a sophisticated functional group of carbon bonded to two -OR groups. It is highly favored by manufacturers worldwide because of its high mechanical strength, rigidity, and 100% recyclability.
POM belongs to the formaldehyde family with polymethylene glycol, polyoxymethylene glycol, and polyformaldehyde.
POM is considered an ideal thermoplastic for producing products with high dimensional stability and slithering properties. It also a good replacement for metal replacement, thanks to its phenomenal blend of mechanical and chemical properties.
What are Homopolymer and Copolymer?
POM materials or resins are produced by the traditional method of polymerization of purified formaldehyde [CH2O]. Homopolymer and Copolymer two different variations of POM having different properties and applications from each other.
Comparison: Acetal Homopolymer and Copolymer –
Acetal homopolymer is produced by anhydrous, monomeric formaldehyde, polymerized by anionic catalysis in an organic liquid reaction medium. The produced polymer will need immediate stabilizing by acetic anhydride. Homopolymer contains better mechanical properties than copolymer.
On the other hand, acetal copolymer is produced by converting formaldehyde into trioxane using cationic polymerization. After that, the trioxane will be filtered to remove access water or any other contaminations having hydrogen. In alkaline environments, copolymer provides more stability than homopolymer.
Let’s take a look at their properties:
|Greater regularity in their structure||
Supreme long term performance in terms of creep resistance, strength, fatigue
|Shorter molding cycelss||
Faster molding cycles
|Offers greater mechanical properties||
More stability in alkaline environments
|Avaible in multiple viscocity ranges||
Wider processing window
|Can help in cost reductions||
meager mold deposits
|Stiffer and stronger in unfilled form||
Minimal release of gassing and odor
|Allow slimmer and lighter part designs and geometries||
Long term quality in color maintenance
Acetal Grades –
POM grades are produced by varying degrees of polymerization, each with different properties depending on the end application.
#1 Standard Grades:
Standard grade POM plastic is used for general applications with the requirement of good dimensional stability.
#2 Reinforced Grades:
Carbon fibers and glass fibers exhibit a huge amount of tensile strength and rigidity depending upon the applications and polymer reinforcement.
#3 Grades with high slip properties:
Polyoxymethylene Plastic is modified by mixing various other reins to enhance properties. In this case, it will blend with graphite, mineral fibers (possibly PTFE) to increase abrasion resistance and slip properties substantially.
#4 High Impact Grades:
Mixing POM with TPU, Rubber, and several other polymers results in a blend with significantly higher impact strength.
#5 UV Stabilized Grades:
UV stabilizing agents are often blended with POM resin for improved UV stability. The most utilized ones are amine light stabilizers and UV absorbers.
Additives like POSS, ZnO, CNTs, etc., are utilized to produce polyoxymethylene nanocomposites.
Here is a table with the thermo-physical properties of polyacetal. Take a look.
|Molar Volume Vm||mL mol-1||22.0 – 26.4|
|Density ρ||g mL-1||1.14 – 1.36|
|Molecular Weight of Repeat unit||g mol-1||30.03|
|Van-der-Waals Volume VvW||mL mol-1||12.25|
|Solubility Parameter δ||MPa1/2||19.9 – 22.9|
|Molar Heat Capacity Cp||J (mol K)-1||62 – 66|
|Entanglement Molecular Weight Me||g mol-1||2000 – 3700|
|Index of Refraction n||–||1.44 – 1.48|
|Molar Cohesive Energy||J mol-1||10100 – 11500|
|Glass Transition Temperature Tg||K||207 – 226|
POM Plastic Benefits –
- Fantastic mechanical properties over a temperature up to 140°C and -40°C.
- Great Wear resistance
- The high degree of crystallinity and impressive dimensional stability.
- Meager moisture absorption
- Low-cooperativeness of friction
- Highly polished surfaces
- High tensile strength, rigidity, toughness for short term
- Low-tendency to creep and fatigue.
- Decent resistance to organic solvents(except phenol)
Acetal Limitations –
- Quick burning without flame retardants because of the high presence of oxygen
- Poor resistance towards strong acids and bases
- High mold shrinkage
- Prolonged exposure to UV radiation may lead to color degradation and loss of strength.
- Low surface energy makes it difficult to bond without surface treatment.
Acetal Polymer Applications –
Acetal polymer comes with many applications in several industries. The range of its swift properties makes it one the most sought after thermoplastics in:
- Consumer Goods
- Medical & Healthcare
Acetal copolymer plays an integral role in developing the fuel tank mechanism for any automobile. There are very few polymers out there that can resist the sheer aggressiveness and high temperature of the fuel and surroundings.
There is a wide range of fuel system products made by acetal polymer like fuel filler necks, fuel caps, fuel sender units, valves, fuel pumps, fuel rails, etc.
These products have long-term resistance towards diesel, gasoline, methanol, etc., and very impressive temperature resistance of 100°C.
Acetal polymer’s excellent gloss finish properties make it compatible to be utilized in the automotive interior. Products like seatbelts, control panel knobs, car locks, seatbelt adjusters some of the most prominent examples.
#2 Consumer Goods:
The fuel withstanding ability of polyoxyethylene plays an important role here also. It is also useful in small engine fuel tanks for gardens and lawn cutting devices used in our households and on-road high-range automobile applications.
The same applications can also be seen in marine engines and recreation vehicles.
#3 Medical & Healthcare:
Safety and accuracy for all medical equipment are more crucial than anything else. The equipment design allows both patients and doctors to feel comfortable in their presence and be cost-effective; it becomes economically viable to use them.
That’s where thermoplastics can play an irreplaceable role as it helps produce cost-effective and high-quality medical equipment by automated assemblies and manufacturing components in bulk.
Acetal copolymer is ideal for such applications as it can be easily processed, high-crystalline plastics with adequate mechanical properties, toughness, and lubricity in an extensive range of temperatures.
#4 Industrial Applications:
Polyoxymethylene is preferred for pumping, conveying, and irrigation applications where transporting water and other aqueous fluids. In addition, acetal polymers have made their presence felt for manufacturing products like taps, housings, couplings, pipes & fittings, etc.
Minimal moisture absorption, goof flow, and easy moldability make Acetal polymers the right fit for prolonged contact with water applications.
Processing Conditions for Acetal –
Polyoxymethylene (POM) is derived in the shop floors in granules forms. Therefore, it can easily be processed in all the major plastic processing methods like Injection molding, extrusion molding, compression molding, blow molding, or rotational molding. However, Injection and Extrusion molding are the most utilized methods.
The temperature range to process POM resins is 190 – 230°C.
Processing conditions for both Injection and extrusion are expanded below:
|Melt Temprature – 1) Homopolymer resins: 180-230°C 2) Copolymer resins: 190-210°C||
Melt temperature: 180-230°C
|Injection pressure: 70-120 MPa||
Screw speed: 33-42
|Injection speed: Medium to high||
Die temperature: 175-230°C
|Mold temperature: 50-150°C||NA|
|Applications – Structural glass, clothing zippers, insulin pens, ski bindings, etc.||
Applications – rods, pipes, profile sections, etc.
Interesting Read – What is Liquid Plastic? | Liquid Plastic Vs. Resin | An In-Depth Guide
The Future of Polyacetal –
Source - IHS Markit
According to a research study conducted by Zion Market Research, the global Polyacetal resin market will reach USD 9.95 Billion By 2025 with a CAGR of 7.9% between 2019 and 2025.
The numbers will deficiently decrease substantially because of the Covid-19 pandemic, which has taken a huge toll on the world’s manufacturing sector. Still, as of writing this piece, the covid-19 vaccine has been rolled out successfully worldwide; people are going back to work, eating, watching movies, etc.
The long-term growth prospect for polyacetal seems bright, thanks to its wide range of applications and easy processability.
The growth of the automobile sector (especially in Asia) will keep the demand for the thermoplastic intact. Industrial and consumer goods sectors can also lend good support from growth in North America and Europe.
The chart above clearly shows that China leads the world in POM consumption with more than half of its market share.
1. What is stronger, acetal or nylon?
Ans. Nylon provides better tensile strength and superior bending stiffness. It can also resist higher temperatures with higher loads. On the other hand, acetal is better in terms of impact and cold resistance.
2. What is Acetal made of?
Ans. It is compromised of a functional group of carbon bonded to two -OR groups. It is also known as polyoxyethylene, polyformaldehyde, polymethylene glycol.
3. Is Delrin same as POM?
Ans. Delrin® is a POM Brand by Dupoint™, which is ideal for replacing metal in many applications. It can combine strength and stiffness with wear resistance and low friction.
4. What is Delrin good for?
Ans. Delrin® is mostly used for industrial applications. The main applications are pumps and valve components, gears, bushings, electrical insulator parts, roller, fittings, etc.
5. Is Acetal food safe?
Ans. Certain polyacetal formulations are food safe like FDA, NSF, USDA, and Canada 3-A.
6. Which one is stronger? Polyacetal or Polycarbonate.
Ans. Both the materials have pros and cons, but polyacetal or acetal is slick and hard; that’s why It’s used for glides and sacrificial wear-pads. On the other hand, polycarbonate is tough and has a high heat deflection temperature. That’s why it is used in high-temp applications and making automotive interiors and exteriors, meaning the applications where any crack or fracture is unacceptable.
Final Thoughts –
Thus were my thoughts on Acetal polymers. I have tried my best to keep the piece brief and informative. Polyacetal is certainly a versatile polymer with several applications. I’ve been in a plastic workshop, and I know the importance and benefits of working with adaptable and resourceful material.
Kindly share your reviews in the comment box.
Have a wonderful day 🙂