Plastics play an important and ubiquitous role in our everyday lives. They are found in packaging, building and construction, textiles, consumer products, transportation, electronics and industrial machinery. But what exactly is plastic? Essentially, plastic is a petrochemical, engineers use heat to separate petroleum into gasoline, kerosene, naphtha, light oil, heavy oil etc. Naphtha is then decomposed to form ethylene and propylene, the raw materials needed for plastics. To create a high-molecular compound however, one must first create a low-molecular compound and bond them together. The low-molecular compounds are known as monomers and the high-molecular-weight compounds are called polymers, you may have picked up that ‘mono’ means ‘single’ while ‘poly’ means ‘many’. The formation of polymers from monomers uses heat, light, and additives such as enzymes (polymerization initiators). Through this process, ethylene and propylene are polymerized into polyethylene and polypropylene.
However, plastics can be divided into two main groups, thermoplastics and thermoset plastics. Thermoset plastics are irreversibly hardened when cooled, the starting material is usually a liquid and when it cools it cannot be melted down and reshaped. Attempts to reheat a thermoplastic would result in burning and consequently, the chemical composition would be irreversibly altered. Thermoplastics are not hindered by this property which makes them much more versatile, something that will be discussed at length in this paper.
The term ‘plastics’ encompasses a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. A key property of plastics is that they can be moulded, extruded or pressed into any shape and then retain that shape. Thermoplastic is a subset of plastics made of polymer resins that do not undergo chemical change in their composition when heated and thus can be melted and reshaped repeatedly. This particular property makes thermoplastics particularly useful for moulding as they can be heated until molten and injected into steel moulds at high pressures. This means you can easily make a plastic mould of almost anything. But thermoplastics can be further divided into two groups, commodity and engineering plastics. This blog will discuss their differences and help you decide which kind of plastic is right for you.
In short, commodity plastics do not have any exceptional properties and can be produced en-mass, often they are only intended to be single-use products. They are inexpensive to produce and exhibit relatively weak mechanical properties. Common uses of commodity plastics are for packaging, clothing, bottles, household products, toys, cutlery, disposable cups etc. Let’s look at some of the most common commodity plastics and their properties.
Polypropylene is made from a combination of propylene monomers and has unique properties that make it one of the most common types of plastic. It has a high melting point so it is used for applications like microwave-safe containers. It also doesn’t react with water, detergents, acids or bases and therefore won’t break down easily. It’s resistant to cracking and stress even when flexed so it works as a living hinge, a thin piece of plastic that will bend without breaking. A living hinge is not useful for structural applications like holding up a heavy door but exceptionally useful for non-load-bearing applications such as the lid on a medicinal or shampoo bottle.
Polyvinyl chloride (PVC)
Polyvinyl chloride is, by volume, the second most common thermoplastic behind polyethylene and polypropylene. It’s an economical and versatile thermoplastic polymer that is cheap to produce, flame retardant, a good insulator, durable, and chemically resistant. Due to these properties, it is widely used in the building and construction industry to produce door profiles, plumbing pipes, wire and cable insulation and medical devices.
Low-Density Polyethylene (LDPE)
Lightweight and durable, polyethylene has a variable crystalline structure and is made from the polymerisation of ethylene monomers. It is one of the most widely used thermoplastics in the world with tens of millions tons produced annually. It has a low melting point and good chemical resistance to detergents, acids and alkalis. It’s very flexible and has low tensile strength, meaning it can withstand a lot of stretching before it actually breaks. These properties make it particularly suitable for plastic grocery bags, clear food wrap, bottles and laminations. However, like most plastics, this means it is not biodegradable and is a large source of waste. For instance, supermarkets are transitioning away from their use of single-use plastic grocery bags in an effort to reduce waste.
Polystyrene is a hard, stiff, transparent synthetic resin produced by the polymerisation of styrene. It is used widely in the food industry as rigid trays, containers, disposable eating utensils, electronics, automobile parts and toys. However, when most people think about polystyrene, they think about foam polystyrene which is valued for its insulating and cushioning properties. Foam polystyrene can be 95 percent air and is widely used to make home insulation, lightweight protective packaging, surfboards, food service, and food packaging.
Polyester – Polyethylene Terephthalate (PETE)
Polyethylene Terephthalate, better known in the textile industry by the trade name polyester, is naturally transparent and semi-crystalline plastic. Widely used as a fibre for clothing, and a moisture barrier with applicability in bottling and packing. It is chemically resistant, very strong for its weight, transparent and shatterproof making it a good substitute for glass as a container. This combination of properties makes it ideal for consumable product packaging.
Polyurethane is made of two main chemical compounds, polymers and urethane groups which can form to create a versatile solution that can take many forms. For that reason, polyurethane is a class of polymers rather than a distinct compound. This allows for polyurethanes with very different physical properties, leading to an equally wide range of applications including; rigid and flexible foams, varnishes and coatings, adhesives, electrical potting compounds and fibres such as spandex and polyurethane laminate. Unlike other synthetic polymers, polyurethanes are heat resistant which is why they can be used in the insulation of refrigerators and freezers.
Engineering plastics are manufactured to withstand various mechanical and environmental conditions. They have highly sought after properties that make them ideal for engineering, industrial, medical and automotive applications. These properties include heat resistance, mechanical strength, chemical stability, malleability, impact resistance, transparency and others. These plastics are often made in smaller quantities to meet a specific engineering outcome, meaning they’re usually harder to make and as a result, are more expensive than commodity plastics.
High-Density Polyethylene (HDPE)
HDPE is a thermoplastic polymer produced from the monomer ethylene. It has a high strength-to-density ratio, is relatively low cost, malleable, heat resistant, corrosion-resistant, and can be easily recycled. HDPE is used in plastic bottles, corrosion-resistant piping, geomembranes, chemical containers, and plastic lumber has been shown to be recyclable at least ten times. ESE World B.V. carried out tests and demonstrated that plastic injection moulding and shredding techniques do not alter the material properties over the life of the product.
Acetal – Polyoxymethylene Plastic (POM)
Polyoxymethylene, better known as Acetol, is an engineering plastic used in the production of precision parts for applications demanding high stiffness, good dimensional stability and low friction. It has applications in automotive, electrical and electronic, industrial and drug delivery industries.
Acrylonitrile Butadiene Styrene (ABS)
Acrylonitrile Butadiene Styrene or ABS is formed by the polymerisation of styrene and acrylonitrile in the presence of polybutadiene. The material is resistant to corrosive chemicals, has high impact resistance, low production cost and has a low melting point meaning it can be melted and moulded easily. The combination of these properties makes it the ideal material for LEGO, computer keyboards, power tools and plastic face guards.
Polyamides or Nylon was the first wholly synthetic fibre ever produced. It is strong, elastic, abrasion resistant, mildew resistant, and has good shape holding properties. It’s an important fibre in hosiery, lingerie, stretch fabrics and sports garments, soft-sided luggage, furniture upholstery, and carpets. Additionally, extruded and moulded plastics made from nylon exhibit high melting points, stiffness, toughness, strength, and chemical inertness. As a result, they are useful in gear wheels, oil seals, bearings, and temperature-resistant packaging film.
Polyether Ether Ketone (PEEK)
Polyether Ether Ketone is a colourless organic thermoplastic polymer with excellent mechanical and chemical resistance properties that are retained at high temperatures. It is used to fabricate items for demanding applications including bearings, piston parts, pumps, high-performance liquid chromatography columns, compressor plate valves and electrical cable insulation. It is one of only a few plastics compatible with ultra-high vacuum applications, that is, pressures lower than 100 nano pascals. Meaning it’s suitable for aerospace, automotive, and chemical industries. PEEK is a high-performance polymer but its high price restricts its use to only the most demanding applications.
Polycarbonates are a group of thermoplastic polymers containing carbonate groups in their chemical structure. They are naturally transparent and allow for the internal transmission of light in nearly the same capacity as glass. They are also pliable, heat-resistant, strong, and incredibly impact-resistant, which makes them ideal for engineering applications like bulletproof glass, plastic lenses in eyewear, medical devices, automotive components, protective gear, greenhouses, digital disks, and exterior lighting fixtures.
Plastics constitute a significant portion of waste generated by human activity, but advancements in recycling technologies have reduced our environmental footprint. HDPE is one of the world’s most recycled plastics. Used HDPE is shredded, melted down and cooled into pellets that can be reused since the recycling process has little effect on the properties of the plastic. The beauty of engineering thermoplastics is that you can usually find a business willing to buy your used engineering plastics because they are able to process and sell it at a profit because most of the original properties are retained.
The commodity plastics we throw in our yellow bins go through a similar process but on a larger and more generalised scale. Once collected, the plastics are sorted into polymer types and then are balled up and sent to a processor where large contaminants are removed. The balled plastic is shredded and washed to remove further contaminants and then passed under a magnet to capture any metal. Then the plastic is melted and pushed through an extruded (which is a bit like a spaghetti maker) where it is then pressed and chopped in granules. These granules can be easily transported and melted down again to be spun into fibres to make various products like plastic bottles, fleeces, sleeping bags, pens, carpets, tables and chairs.
Industrial Plastics specialises in the fabrication and manufacturing of custom plastic solutions and we utilise many of the engineering plastics mentioned in this paper. Whether it be ABS, acrylic, HDPE, polycarbonate, polypropylene, or UHMWPE. The Industrial Plastics engineering design team are experts at finding the right material for your needs. The applications can be anything from a HDPE prototype, insulated glycol tanks for HVAC systems, customer acrylic balustrades fabrications, or PVC chemical bunds, we are the experts in plastics fabrication.
Disclaimer: Please note that Industrial Plastics does not offer all of the plastics mentioned in this article. Refer to our website for our product range or for more information, contact us via email at [email protected] or telephone 1300 465 888.