The last couple of decades have seen modifications and innovations being made in the production of new plastic materials. New plastic resins are being introduced, each with its unique set of properties and applicability. Materials like Polyethylene, Polypropylene, Polycarbonate, PVC, ABS, and Acetal thermoplastics are the commonly used ones.
Thermoplastics are defined as polymers that can be heated, melted, solidified over repeated cycles, leading to their recyclability. The application of heat transforms these polymers into a liquid state, thereby making them suitable for molding through modern techniques like plastic injection molding.
These thermoplastics find their applications in various industrial and commercial products and parts.
The article talks about the composition of Acetal thermoplastic, its properties, manufacturing, benefits, and applications in various sectors.
What is Acetal Thermoplastic?
Acetal thermoplastic is also known as Polyoxymethylene (POM). The resin occurs in a white semi-crystalline state. One of the reasons for its high demand in the plastic industry is its high tensile strength. Additionally, the polymer has significant creep resistance which makes it a perfect material to use as an alternative to metals for various applications.
As mentioned above, Acetal or Polyoxymethylene is a thermoplastic. While thermosets have been a part of the plastic industry for a long time, the inability to reheat and reuse them has been a serious limitation. Thermoset plastics burn when heated a second time.
On the contrary, thermoplastics have a different response to heat. Thermoplastics liquify at a certain temperature and can be solidified and molded into desired shapes.
Acetal homopolymer plastic melts at 175 degree Celcius whereas Acetal copolymer melts at 162-173 degrees celsius.
Repeated heating and cooling of thermoplastics like Acetal do not result in any significant chemical degradations.
Acetal polymers exhibit repetitive and orderly structural units that give them their sharp melting points as opposed to amorphous solids.
Acetal is commonly categorized as :
- Acetal Homopolymer
- Acetal Copolymer
Homopolymers consist of repetitive monomer units with a similar molecular structure exhibited by each unit.
Copolymers are made out of different types of monomer units that combine with each other to form a common polymer structure.
Both Acetal homopolymers and Acetal Copolymers are used for various applications across a wide range of sectors. Accordingly, each has its own benefits and limitations that need to be considered.
Following are some important considerations when choosing between Acetal Copolymer and Acetal Homopolymer:
- Homopolymers are stiffer, harder, slippery in texture, and have high tensile strength. Homopolymers have high operation temperature and also high room temperature impact strength.
- Copolymers have better dimensional stability and are more resistant to chemicals and abrasion.
Each of the aforementioned properties of Acetal Homopolymers and Acetal Copolymers contributes to their utility in the production of precision parts that need strong resistance to abrasion, water, and chemical attacks. Its excellent dimensional stability, low friction, and resistance to abrasion make it a good choice for applications like small gears, plastic zippers, plastic furniture, consumer electronics, and medical parts.
Acetal or POM is also known by a number of other names. Some of these include:
- Polyoxymethylene glycol
- Polymethylene glycol
Additionally, there are various industrial names given to Acetal by different manufacturing companies involved in its production. Celcon®, Delrin®, Duracon®, Kepital®-POM, Tecaform®, Tepcon®, Hostaform®, Ultraform® are some common brand names available in the market.
Acetal is known by the chemical formula : (CH2O)n.
The injection molding temperature for Acetal is between 79 to 107 degrees Celcius. The material has a density of 1.41 to 1.42 g/cm3
The tensile strength for Acetal is 63 MPa and the Flexural Strength is 90 MPa. Acetal offers a shrink rate of 2.1 to 2.9%.
Following are some other properties of Acetal which make it an excellent choice for various applications around a wide range of sectors:
- Excellent heat resistance
- Strong electrical properties
- Low water absorption
- Low coefficient
- High strength and rigidity
- High tensile strength
- 100% recyclability
Acetal has been known to have some levels of toxicity when inhaled in vapor/liquid form. However, in its solid crystalline form, it is not considered toxic. Acetal has been considered food safe and has been used in making food processing equipment and kitchen utilities.
The FDA has approved a few grades of Acetal for usage in the food industry.
However, when looking for a suitable plastic resin for the food processing and packaging equipment industry, it is suggested to confirm your requirements with material manufacturers. The need to consider the end-use environment is important for making these decisions.
Additionally, it is suggested to follow the handling instructions carefully when using Acetal in molten polymer form.
The manufacturing process of Acetal
Almost all plastics follow a similar manufacturing process. The production process of Acetal starts with the distillation of hydrocarbons into fractions which are then combined in the presence of catalysts to undergo polymerization.
Depending on the type of polymer being produced (Acetal homopolymer or Acetal Copolymer), different types of manufacturing processes are used.
Homopolymer Acetal (POM) is produced by reacting aqueous formaldehyde with alcohols to form hemiformal. This mixture is then distilled or dehydrated to release the formaldehyde which is then polymerized in the presence of catalysts to produce Acetal homopolymer.
Acetal copolymer manufacturing follows a more complex process. Formaldehyde is first converted to trioxane (in the presence of catalysts) and then distilled (for purification). Co monomers like dioxolane and ethyl oxide are also used. Trioxane and dioxolane are then polymerized in the presence of a catalyst to produce the Acetal Copolymer.
The polymerization process can follow two types of combinations.
Chain growth polymerization is the sequential linking of monomer units to form a long polymer chain. Double or triple carbon bonds are usually seen in the chain growth process.
Step growth polymerization process is a series of reactions of the monomer units to produce large units. Two monomers may combine to become a dimer, or three may combine to form a trimer and so on. Water is generally released during the process which is the reason why plastics manufactured using this process are called condensation plastics.
Acetal is available in the markets in its granulated form. Manufacturers use the process of heating and pressure application to convert it into liquid and then molding it into desired shapes.
Acetal is one of the most widely used plastics in the manufacturing sector. Its applications include engineering components that require high-performance, like those in the electronics and the automotive sectors. These include gear wheels, fasteners, lock systems, etc.
Following are some of the main applications of Acetal:
- Mechanical gears, equipment, housing parts, chains, nuts, parts of pumps, valves, etc.
- Electrical insulations, connectors, and parts of various electronic devices.
- The automotive sector like vehicle fuel sender units, power windows, door locks, turn signals, vehicle tanks, etc.
- Sports material like landing skid, yo yos, paintball accessories, airsoft guns, etc.
- Medical sector parts like an insulin pen, metered-dose inhalers, etc.
- Food industry – milk pumps. Food conveyors, etc.
- Hardware products like locks, handles, etc.
- Musical instruments and parts like picks, bagpipes, instrument mouthpieces, flutes, drum sticks tip, etc.
- Construction works like structural glass
- Kitchenware like coffee brewers, knife handles, etc.
3D printing application
Acetal is used for 3D printing by some industries. However, most machines require a good number of modifications to print with Acetal. This is perhaps the reason why Acetal is not a preferred material for 3D printing applications.
However, considering the high demand for Acetal in consumer products, various new technologies are being tested and researched for its use in 3D printing.
While Acetal has various advantages to its credit (which contribute to its huge popularity within the market), there re certain disadvantages that need to be considered before material selection. Acetal does not bond easily (owing to its high chemical resistance), especially with glues and adhesives. This makes it a poor choice for designing and modifying prototypes.
Benefits of Acetal thermoplastic
The wide usage of Acetal in various industries can be attributed to its unique properties and features.
Its strength, chemical and abrasion resistance, impact resistance make it an ideal choice for products that need to face tough functional and environmental conditions.
Its low friction coefficient and durability make it a great option for movable parts in vehicles and automobiles as well as construction units like hinges, etc.
Its wide availability in the form of sheets and blocks contributes to the easy machinability.
Additionally, Acetal can easily be colored in any shade (since it is naturally white in its original form). This makes it a good choice for parts and products that need to be visually appealing.
Various manufacturers also make use of additives like PTFE or fiberglass to enhance properties of Acetal. PTFE improves the lubricity whereas fiberglass adds more strength to the material.
Plastics are undoubtedly the innovation of the century. They are involved in almost all industries and find their usage in almost all everyday use products. Plastic consumption has seen record growth in the last decade. Innovations and research in the sector have introduced a wide range of unique plastics like Acetal.
Similar to other plastic resins, Acetal has its own characteristic features, as discussed in the article above. These features along with its physical, chemical, mechanical and electrical properties make it a highly valuable raw material for various commercial and industrial applications.