09 Aug Polymers Used by Injection Moulders
There are two main types of polymers, thermoplastics and thermosets. The main physical difference is that thermoplastics can be re-melted into liquid plastic. Whereas, thermosets remain in a permanent solid state and cannot be put back into the process.
Commonly, plastic injection moulders use thermoplastics. Common polymers used by moulders are Acrylonitrile Butadiene Styrene (ABS), Polyethylene, Polycarbonate, Polyamide (also known as Nylon) and Polypropylene.
Types of Polymers
Acrylonitrile Butadiene Styrene (ABS)
ABS is an opaque thermoplastic and amorphous polymer. An amorphous polymer is a polymer that doesn’t exhibit a crystalline form. ABS a terpolymer, a polymer synthesised from three different monomers, Acrylonitrile, Butadiene, and Styrene. Together they create a product that is flexible and light in weight.
The advantage of ABS is that it combines the strength and rigidity of the Acrylonitrile and styrene polymers with the toughness of the Butadiene. The final property of ABS is influenced partly by the conditions under which the material is processed. For example, moulding at high temperatures improves the gloss and heat resistance of the product. Whereas, the highest impact resistance and strength are obtained by moulding at low temperatures.
The limitations to ABS are that it is sensitive to thick sections in plastic parts which may cause voids, bubbles or sink. It also has poor resistance to weather and is attacked easily by hydrocarbons and organic solvents; heat resistance is also low and the price of the material is relatively high.
In addition to moulded plastics, ABS is used in drain pipe systems, plastic clarinets, golf club heads, automotive parts, common appliances in a kitchen, LEGO bricks, and many other products.
Polyethylene
Polyethylene is a thermoplastic polymer with variable crystalline structure and an extremely large range of applications depending on the specific type. It is one of the most versatile and most popular plastics in the world. The two most common types of Polyethylene are high-density polyethylene (HDPE) and low-density polyethylene (LDPE).
HDPE is flexible and translucent, weatherproof and is easy to process via most moulding methods. HDPE is also cost effective as it isn’t expensive in comparison to other thermoplastic polymers. The flexible nature of HDPE means it has a variety of applications such as toys, cable insulations and kitchenware
LDPE is very similar to HDPE, but it isn’t as flexible nor does it have the tensile strength of HDPE. LDPE also has a low water absorption rate and as such as ideal for bottles and pipes.
The advantages of polyethylene are high levels of ductility, tensile strength, impact resistance, resistance to moisture absorption, and recyclability. The higher the density of the polyethylene material used, the stronger, more rigid, and more heat resistant the plastic is.
The major disadvantage with Polyethylene is that it is typically more expensive than Polypropylene, another thermoplastic which is used for similar components.
Polycarbonate
Polycarbonate (PC) plastics are a naturally transparent, amorphous thermoplastic. They are used to produce a variety of components with excellent toughness and thermal stability. Unlike most thermoplastics, PC can undergo large plastic deformations without cracking or breaks. PC is one of the most used thermoplastics and is commonly used for greenhouses, digital disks like DVDs, eyewear lenses, medical devices, automotive components, and cellular phones.
Like the majority of thermoplastics there are different grades available such as film, flame retardant, reinforced and stress crack resistant, branched (for applications requiring high melt strength) and other speciality grades. PC can also be blended with ABS, something which is widely used for the automotive industry.
The disadvantages to PC are that some grades aren’t ideal for food use due to the release of Bisphenol from hydrolysis. PC is also susceptible to scratching, despite its tough nature, meaning it isn’t ideal for clear surfaces that require an immaculate finish.
Polyamide (Nylon)
The name Nylon’s refers to the group of plastics known as Polyamide’s. Nylon’s provide a broad range of properties which are ideal for various applications. This is because of its electrical properties, toughness, wear resistance and chemical resistance. Nylon has a high level of stability and is resistant to many external factors like abrasion, impact, and chemicals. This material produces plastic parts used in many industries such as medical, automotive, industrial, sports equipment, apparel and high impact polystyrene.
Disadvantages of Nylon include high shrinkage, susceptible to moisture, easily attacked by oxidising agents and strong acids. However, Nylon can be blended with other plastics to improve its performance and make it suitable for other uses where on its own it would not work.
Polypropylene
Polypropylene (PP) is one of the most versatile polymers available and is a very common plastic that is known for its flexibility. PP is a very dynamic plastic and has been compounded for a wide range of properties. Some characteristics of this plastic are its high melting point, high resistance to stress and cracking, excellent impact strength, and its resistance to water, acids, and detergents.
PP is safe for use as food containers because it does not leak chemicals into food products. It can be commonly found in household goods such as utensils, athletic apparel, area rugs, and automotive parts such as car batteries.
The disadvantages to PP are that Polypropylene has limited temperature applications; it is also susceptible to UV degradation; has poor resistance to chlorinated solvents and aromatics; susceptible to oxidation and PP is highly flammable.
The named thermoplastics above are only a handful of the ones that Malton Plastics process on a day-to-day basis. Malton Plastics have the scope and ability to process many thermoplastics. For more information on what thermoplastics Malton Plastics process or which plastic would best suit your component or product, please contact us via phone or email below.
Email: sales@maltonplastics.com
Phone: +44 (0) 1751 4777 20
Fax: +44 (0) 1751 4777 60
