What is Acetal?
An acetal or polyacetal is an organic molecule wherein a central carbon atom is bonded to two separate oxygen atoms through single bonds. Its structure can be written as R2C(OR’)2.
Acetal plastic is commonly called acetal or polyoxymethylene (POM). Its functional group consists of a carbon molecule bonded to two -OR groups. Its molecular structure takes the form of (CH2O)n.
Moreover, it is a formaldehyde-based and semi-crystalline engineering thermoplastic. It is no surprise that POM is of utmost importance because of its different properties and uses.
Learn more about this high-performance plastic below!
Key Properties and Characteristics of Acetal
Polyacetal offers numerous excellent properties and characteristics as an engineering material.
- Dimensional stability: It can withstand fluctuating temperatures and retain its precise dimensions over time.
- Low moisture absorption: Ranges between 0.2% to 0.25% at saturation.
- High hardness and rigidity: Despite its low specific gravity, it maintains its form even under large loads.
- High strength: High tensile strength (2.6 N/mm²), meaning POM can withstand significant force before stretching and breaking.
- Excellent abrasion resistance: POM plastic parts are used for bearings because of this property.
- Low friction: This means POM is very slippery. It is ideal for situations where components must glide or move smoothly against each other without encountering too much resistance.
- High fatigue endurance: POM can withstand repeated stress and strain cycles without significant degradation or failure.
- Outstanding chemical resistance: Known to resist various fuels, oils, and organic solvents.
- Thermal properties: It has a broad temperature range of -40°C to 120°C
- Electrical properties: POM doesn’t conduct electricity, making it great for electrical insulation.
Now, let’s explore its benefits.
What Are the Advantages of Polyoxymethylene?
POM serves as an excellent alternative to metals due to its numerous characteristics mentioned above. It is one of the top alternatives to steel and aluminum.
Additionally, POM produced through CNC machining is known for its superior dimension stability. With that, acetal thermoplastic materials are used to make high-precision parts.
Due to their exceptional physical properties, acetal plastic sheets are used for their resistance to creep. Due to their creep and fatigue rigidity, this means that despite exposure to high levels of stress, these acetal sheets will not easily deform over time.
Disadvantages of POM
Despite its tremendous benefits, POM is not without its drawbacks.
Compared to other materials, acetal resin typically has longer molding cycle times. This refers to the time it takes for the plastic to take its shape in the mold cavity. It can also shrink significantly in its mold.
Without the use of flame retardants, it also has a propensity or tendency for quick burning. This is due to the high presence of oxygen in the environment. The surrounding temperatures around POM must be managed properly. If let in the sun, its color and strength may degrade due to its poor resistance without additives.
Lastly, all of these excellent acetal material properties and usages come with high costs.
What Is Polyoxymethylene Used for?
POM is one of the most commonly used plastics in the manufacturing industry. Considering its outstanding physical and chemical characteristics, this general purpose engineering plastic has a wide range of uses.
Automotives
POM is used in gears, bushings, clips, and values. This low friction engineering plastic is also very useful in fuel system components due to its wear resistance.
Consumer goods
POM’s wear resistance, durability, and low friction find excellent use in consumer goods as well. It is used in the fabrication of buckles, handles, fasteners, and even toys.
Electrical Insulation
Due to its top-notch electrical properties such as its dimensional stability and Electrical insulation, it is used for various electronic uses. These include switches, connectors, and relay housings, among others.
Healthcare
POM is also utilized in dental components, surgical instruments, and orthopedic implants. This is because of its chemical resistance and biocompatibility.
Industrial machines
Additionally, POM is utilized in various industrial machinery applications where high strength, dimensional stability, and low friction are needed. Even as a stiff plastic, acetal sheets can be formed into gears, tubes, valves and other precision mechanical parts.
What Are the Types of Acetal?
POM is mainly categorized as copolymer (POM-C) and homopolymer acetal plastic (POM-H).
- Copolymers are composed of different types of monomer units in a polymer chain.
- Homopolymers are made up of one repetitive monomer unit.
What Is the Key Difference Between Copolymer and Homopolymer Acetal Plastic?
The structural differences lead to variations in their performance.
Melting Points
Regarding melting points, POM-C melts at 162-173 to 343.4°C. Their homopolymer counterparts have a slightly higher melting point at 175°C.
Chemical Resistance
POM-C is said to have more chemical and abrasion resistance. This is due to their superior dimensional stability.
Mechanical Properties difference
POM-H is reported to have higher tensile strength. They exhibit better stiffness and hardness. With that, they are used more for applications that require higher impact strength and room temperatures.
Not only that, their homopolymer counterparts contain higher crystallinity. Although acetal copolymer has lower crystallinity, this gives way to their better friction resistance.
Applications difference
Acetal copolymers are typically used in wet environments such as in food processing. In fact, acetals used in this industry offer excellent wear properties. These are also used in manufacturing seals and valves due to their resistance to corrosion. If you are in need of plastics or machined parts in electrostatics, these copolymers are one of the top choices for you.
On the other hand, homopolymers will do the job for you if you need materials that are smaller in diameter. These include thin-walled bushings and bearings. Homopolymers are also used for different electrical components and components that handle fluid.
More Expensive
POM-H is more costly than acetal copolymer owing to its better physical and performance attributes.
Which Acetal Type is Best for Your Needs?
POM-C and POM-H differ primarily in their molecular structure. POM-C is a copolymer made from two different monomers. This gives POM-C a more stable and flexible structure, increasing its chemical resistance and decreasing its tendency to crystallize, hence reducing brittleness.
In contrast, POM-H is a homopolymer, which means it is made up of one kind of monomer. This uniform structure produces higher crystallinity, which improves POM-H’s mechanical properties such as tensile strength and stiffness. This increased crystallinity, however, may make POM-H less resistant to hydrolysis and more susceptible to chemical attack.
POM-C is often used in applications that need high chemical resistance and simplicity of machining. POM-H is consequently used for situations demanding increased mechanical strength and stiffness.
Want to learn more about their differences? Click here for more information!
How Does Acetal Plastic Affect Human Health?
Even though Acetal/POM is FDA-approved for applications in the food industry, this does not rid it of its potential detrimental effects on human health.
Acetal plastics release formaldehyde when they are burned or overheated. This poses a significant health hazard to nearby personnel. If its invisible fumes are ignited, it can also become extremely dangerous.
Although no major studies have shown the long-term health effects of chronic exposure to this plastic, some individuals have reported increased general health issues due to regular exposure to its vapors or gaseous form. Some have even reported cases of cancer or thyroid problems.
Is Acetal Plastic Toxic?
Like any industrial component, Acetal/POM contains levels of toxicity when it is inhaled in its liquid or vapor form. However, when Acetal/POM is used in its solid crystalline form, it is no longer considered toxic. As a matter of fact, this plastic is used in manufacturing food processing equipment as it has been graded as food-safe.
FAQS ABOUT Acetal
Is acetal a metal or plastic?
Although this material possesses different properties common in metals, such as high strength, toughness, and rigidity, it is a versatile engineering thermoplastic.
What Are the Alternatives to Acetal Plastic?
Aside from Delrin, acetal plastic has other alternatives.
- Nylon: Nylon is a strong thermoplastic that is also resistant to high temperatures. It is also used for its tensile strength and stiffness. An advantage of this material compared to acetal is that it is cheaper. However, acetal is more dimensionally stable. This means it is more affected by chemicals, wear, moisture, and humidity.
- Polybutylene Terephthalate (PBT): PBT is usually easily interchangeable with Acetal in the industry. This is because of their identical mechanical characteristics. However, PBT is not preferred in environments with higher humidification.
Is acetal plastic strong?
Yes, acetal plastic is definitely a strong material. These high performance plastics are resistant to hydrocarbons and different solvents. Its desirable mechanical properties such as its high strength and hardness make it one of the commonly used plastics in the industry.