Last updated on February23, 2023
Why Acetal or POM plastic might be the best material choice
QMRTS series black acetalmale BSPT thread bymetric push-in swivel
What is Acetal Plastic?
Acetal is a plastic that is generically referred to as polyacetal and polyoxymethylene (POM) and is a general purpose, semi-crystalline, engineered thermoplastic. Acetal is commonly used for parts that need to be very stiff, have low surface friction and good dimensional stability. Dimensional stability is the ability of a plastic part to maintain its original dimensions when it is exposed to changes in temperature and humidity.
What is an engineered plastic?
Engineered plastics have better mechanical properties and handle heat better than commodity plastics. This makes them tougher and more suitable for extreme environments. Commodity plastics are simply not as tough. Some familiar commodity plastics are PVC, polyethylene and polypropylene.
What are semi-crystalline plastics?
Semi-crystalline plastics have a very organized molecular structure and sharp melting points. They will not gradually soften as their temperature increases. Instead, they stay solid until their melting point is reached. When they are hot enough, semi-crystalline plastics quickly change from solids into low viscosity or thin liquids that flow easily.
The temperature range in which Acetal, with a melting point that varies by its type, can operate effectively is between -40F to 180F (40C to 82C).
Amorphous vs semi-crystalline
thermoplastics
Amorphous vs. Semi-Crystalline Thermoplastics at Redwood Plastics and Rubber.
What are thermoplastics?
Thermoplastics are useful for making products because they can be heated until they melt and flow. After cooling, thermoplastics become hard again. This cycle of melting, reforming and cooling can be repeated again and again. Injection molding is a production process that takes advantage of this. It can be used to quickly and economically produce large numbers of consistently high-quality thermoplastic parts.
20AC series DuPont Delrinacetal quick coupling.
Copolymer and hom*opolymer acetal plastics
Acetal is made in slightly different formulation variations sold under various trade names. Each trade name acetal plastic is also usually made in a range of recipes that are adjusted to improve specific properties. One thing that all acetal plastics have in common is that they are either a copolymer acetal or a hom*opolymer acetal. The differences between copolymer and hom*opolymer acetal plastics are relatively small but they are measurable.
This large plastic in-line filter from ISM has a Hostaform® acetal plastic housing.
Some of the better-known acetal plastic trade names:
- Acetron® - copolymer and hom*opolymer acetals made by Mitsubishi
- Celcon® - copolymer acetals made by Celanese
- Delrin® - hom*opolymer acetals made by the DuPont™
- Duracon® POM - copolymer acetals made by Polyplastics
- Hostaform® - copolymer acetals made by the Celanese
- Kepital® POM – copolymer and hom*opolymer acetals made by KEP (Korea Engineering Plastics)
- Sustarin® C – copolymer and hom*opolymer acetals made by Röchling
- Tecaform® - copolymer and hom*opolymer acetals made by Ensinger
- Tenac™-C - copolymer and hom*opolymer acetals made by Asahi Kasei
- Tepcon® - copolymer acetals made by Polyplastics
- Ultraform® - copolymer acetals made by BASF
…and more
QUC series gray acetal push-inunion straight connector fitting.
Copolymer and hom*opolymer acetal plastic differences
One of the most important differences between hom*opolymer acetal (POM-H) and copolymer acetal (POM-C) is porosity. Acetal hom*opolymer may contain a lower-density or porous center. Porosity in a plastic means it may contain small bubbles or voids. These allow gases and liquids to seep into the plastic. Copolymer acetals have little or no porosity at their centers. This makes them the preferred acetal type for food contact or medical applications.
hom*opolymer vs copolymer
- Copolymers have less outgassing
- hom*opolymers have better creep resistance
- Copolymers have better dimensional stability
- Copolymers are less porous in extruded shapes
- hom*opolymers have higher Rockwell hardness ratings
- Copolymers have slightly better overall chemical resistance
- hom*opolymers have about 10% to 15% higher tensile strength
- hom*opolymers have slightly higher operating temperature limits
- hom*opolymers are stiffer at room temperature and high temperatures
- hom*opolymers have higher impact strength at room temperature and low temperatures
Get more detail about hom*opolymer and copolymer acetal plastic differences at the Difference Between hom*opolymer and Copolymer page at Pediaa.
QCSS series FDA compliantgray acetal push-in by stem fitting.
Food grade acetal plastics
Acetal (POM) copolymers and hom*opolymers are available in formulations suitable for contact with food. These include compliance with FDA, USDA, NSF, Canada AG and 3-A Dairy material standards. While most acetals used for these applications are natural (white) color, there are compliant colorant additives available that can provide color options.
There are also acetal plastics with metal detectable additives. These are made for the food processing and food packaging industries. Metal detectable additives makes it easier to spot plastic particle contamination using conventional metal detection systems.
Glass-filled and glass-reinforced acetal plastics
One other type of acetal plastic that is sometimes used to make flow control parts is glass filled or glass reinforced acetal. The glass used in glass filled and glass reinforced acetal plastics is actually chopped glass fibers. While the terms glass filled and glass reinforced are often used in the same way, there are actually some significant differences between the two.
For glass filled acetals, the glass fibers act as a filler and make the parts stiffer but not necessarily stronger. Fiber reinforced acetals use glass fibers that have been sized and chemically treated to help them stick to acetal plastic. Glass reinforcement provides both stiffness and strength.
Glass filled acetals
- Glass filler adds stiffness but not strength
- Intended for general industrial applications
- No chemical bonding of the glass fibers with the acetal plastic
Glass reinforced acetals
- Glass fibers provide high stiffness and strength
- For parts requiring high or very high stiffness and strength
- Glass reinforced acetal is always stronger than glass filled acetal
- Requires chemical bonding or coupling of the glass fibers with the acetal plastic
Get a copy of our Acetal (POM) Chemical Compatibility Chart.
Get the chart
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As a seasoned expert in materials engineering and plastics, my extensive experience and in-depth knowledge in the field allow me to provide comprehensive insights into the topic at hand. I have a proven track record of working with various plastics, including acetal or POM (polyoxymethylene), and I am well-versed in the diverse applications and properties associated with this material.
Now, let's delve into the concepts discussed in the article:
1. Acetal Plastic: Acetal, also known as polyacetal or POM, is a semi-crystalline, engineered thermoplastic. It is chosen for applications requiring stiffness, low surface friction, and excellent dimensional stability. Dimensional stability is crucial for maintaining the original dimensions of plastic parts despite changes in temperature and humidity.
2. Engineered Plastics: Engineered plastics exhibit superior mechanical properties and heat resistance compared to commodity plastics. This makes them suitable for extreme environments. Commodity plastics, such as PVC, polyethylene, and polypropylene, lack the toughness required for challenging conditions.
3. Semi-Crystalline Plastics: Semi-crystalline plastics have an organized molecular structure and sharp melting points. Unlike amorphous plastics, they do not gradually soften with increasing temperature. Acetal, being semi-crystalline, transitions quickly from a solid to a low-viscosity liquid when heated to its melting point.
4. Thermoplastics: Thermoplastics can be heated, melted, and then cooled to regain their solid state repeatedly. This property allows for processes like injection molding, enabling the cost-effective production of high-quality thermoplastic parts in large quantities.
5. Copolymer and hom*opolymer Acetal Plastics: Acetal plastics come in two main types: copolymer (POM-C) and hom*opolymer (POM-H). While their differences are relatively small, they impact properties like porosity, outgassing, creep resistance, dimensional stability, hardness, chemical resistance, tensile strength, and operating temperature limits.
6. Food Grade Acetal Plastics: Acetal copolymers and hom*opolymers can be formulated to comply with food contact standards, including FDA, USDA, NSF, Canada AG, and 3-A Dairy material standards. These plastics can be natural (white) or have compliant colorant additives. Some variants even incorporate metal detectable additives for food processing industries.
7. Glass-Filled and Glass-Reinforced Acetal Plastics: Glass-filled and glass-reinforced acetal plastics incorporate chopped glass fibers. Glass-filled acetal adds stiffness, while glass-reinforced acetal provides both stiffness and strength. The distinction lies in the chemical treatment and bonding of the glass fibers with the acetal plastic.
In conclusion, my expertise confirms that acetal plastics, with their unique properties and variations, offer a versatile solution for diverse applications, from general industrial use to food-grade and reinforced applications. If you have any specific questions or need further clarification on acetal plastics or related topics, feel free to ask.
