Maya Ellison
Plastic is a polymeric material that can be moulded or shaped. It is composed of chains of polymers, which are larger molecules formed by covalently joining many monomer units together in the form of chains. Synthetic plastics are derived from crude oil, natural gas or coal, while bio-based plastics are made from renewable products such as carbohydrates, fats and oils. Plastics are composed of various elements, including carbon, hydrogen, oxygen, nitrogen, sulphur and chlorine.
| Characteristics | Values |
|---|---|
| Composition | Synthetic plastics are derived from crude oil, natural gas, or coal. Biobased plastics come from renewable products such as carbohydrates, fats, oils, starch, bacteria, and other biological substances. |
| Chemical composition | Plastics are composed of chains of polymers. Polymers are larger molecules formed by covalently joining many monomer-units together in chains. |
| Additives | Chemicals blended into plastics to improve their performance or appearance. In the EU, over 400 additives are used in high volumes. |
| Elements | Carbon, hydrogen, oxygen, nitrogen, sulphur, and chlorine. |
| Types | Polyethylene, polypropylene, polyvinyl chloride, polystyrene, polyacetal, polyamide (nylon), polytetrafluoroethylene (Teflon), polycarbonate, polyphenylene sulfide, epoxy, and polyetheretherketone. |
| Properties | Low density, low electrical conductivity, transparency, and toughness. |
| Environmental impact | Plastic waste is considered a major environmental problem. It can take hundreds of years for plastic waste to decompose back into carbon dioxide and water. |
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What You'll Learn
- Carbon, hydrogen, oxygen, nitrogen, sulphur and chlorine
- Additives: polymer stabilisers, flame retardants, cadmium, chromium, lead and mercury
- Synthetic plastics: crude oil, natural gas and coal
- Biobased plastics: carbohydrates, starch, vegetable fats and oils, bacteria and biological substances
- Engineering plastics: polyacetal, polyamide, polytetrafluoroethylene, polycarbonate, polyphenylene sulfide, epoxy and polyetheretherketone
Carbon, hydrogen, oxygen, nitrogen, sulphur and chlorine
Plastic is a polymerisation product of various elements, including carbon, hydrogen, oxygen, nitrogen, sulphur, and chlorine. The production and disposal of plastics emit around 3% of global emissions, with most emissions occurring during the production stage, in the form of carbon dioxide.
Carbon is a key element in plastic, and the process of converting plastic waste into hydrogen and solid carbon has emerged as a potential solution to the problem of plastic waste. This process extracts over 97% of the hydrogen in plastic, producing clean hydrogen fuel and valuable carbon products.
Nitrogen is another critical element in plastic manufacturing. Nitrogen gas is extensively used in the plastics industry because of its inert and dry nature, which helps maintain the integrity and strength of polymers. Nitrogen also prevents discolouration and oxidation by displacing oxygen during the moulding process.
Chlorine is an essential element in plastic machining, and it is used to create chloride, a vital compound in the plastic industry. Chloride is a base for various monomers and plastic blends, and it mixes well with other materials, allowing manufacturers to create plastics with a wide range of properties. The combination of chlorine and ethylene through polymerisation produces polyvinyl chloride (PVC), a widely used plastic polymer.
Oxygen, hydrogen, and sulphur are also integral elements in plastics. Together, these elements form polymers that serve various functions in our daily lives, from disposable coffee cups to construction materials.
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Additives: polymer stabilisers, flame retardants, cadmium, chromium, lead and mercury
Plastic additives are selected based on the type of polymer they will be added to and the application for which they will be used. Additives are crucial in preventing the oxidative degradation of plastics, which occurs when radical reactions in the early stages of degradation are not terminated.
Polymer stabilisers, a type of additive, are used to prevent degradation. The same polymer stabilisers are generally used in most plastics, including polypropylene, polyethylene, acrylonitrile butadiene styrene (ABS), and engineering plastics. Stabilisers are categorised into three types: radical chain initiation inhibitors, radical scavengers, and peroxide decomposers. For example, polypropylene products for outdoor use may contain a phenolic antioxidant (radical scavenger) and a phosphorus antioxidant (peroxide decomposer) to improve weatherability during use.
Flame retardants are another type of additive used to prevent, delay, or slow down the combustion of plastics. They can be added during the plastic processing step or compounded with the base polymer. Halogenated compounds, such as bromines and chlorines, are the most common flame retardants, although non-halogen flame retardants, such as intumescents (phosphorus-based) and metallic oxides, are increasing in demand.
Historically, hazardous metal additives in plastics were based on compounds of toxic metals such as cadmium, chromium, and lead. Lead, for example, has been found in historical and contemporary plastic samples, including consumer goods, packaging, and electronic plastics. Chromium plating on plastics involves depositing a thin layer of chromium or chromium-like substances onto a plastic substrate, which can be achieved through electroless plating or physical vapour deposition (PVD). Cadmium, on the other hand, can mobilise from historical microplastics and exceed safe concentrations according to migration limits.
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Synthetic plastics: crude oil, natural gas and coal
Plastic is a polymeric material that can be moulded or shaped, often combining other properties such as low density, low electrical conductivity, transparency, and toughness. This versatility allows plastics to be made into a wide variety of products.
Synthetic plastics are derived from fossil fuels, chiefly crude oil, natural gas, and coal. Fossil fuels are composed of carbon, hydrogen, nitrogen, sulphur, oxygen, and other minerals. The generally accepted theory is that fossil fuels are formed from the remains of living organisms, specifically plankton, that existed during the Jurassic era. Over time, these organisms were buried beneath heavy layers of sediment in the Earth's mantle, subjected to extreme heat and pressure, and decomposed without oxygen, transforming into tiny pockets of oil and gas. Crude oil and natural gas accumulate in reservoirs at the bottom of the oceans. While coal also originates from organic matter, it is specifically derived from dead plants.
Crude oil is a complex mixture of thousands of compounds and must be processed before it can be used to create plastic. The production of plastics begins with the distillation of crude oil in an oil refinery, which separates the heavy crude oil into lighter components called fractions. One of these fractions, naphtha, is crucial for plastic production. The distillation process involves heating the crude oil in a furnace and then sending it to a distillation unit.
Natural gas is another important feedstock for plastic production. Light olefin gases such as ethylene, propylene, and butylene, known as monomers, are converted into higher molecular weight hydrocarbons (polymers) through the polymerisation process. Natural gas can also be used as an alternative to naphtha in the distillation process.
Coal, while less commonly used than crude oil and natural gas, is also a source of synthetic plastics. It originates from dead plants and is composed of carbon and hydrogen, among other elements.
The vast majority of plastic in use today is synthetic due to the ease of manufacturing methods involved in processing crude oil and other fossil fuels. However, the growing demand for limited oil reserves is driving the need for newer plastics derived from renewable resources.
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Biobased plastics: carbohydrates, starch, vegetable fats and oils, bacteria and biological substances
Bioplastics are plastic materials produced from renewable biomass sources. Bioplastics are typically manufactured from bio-based polymers and stand to contribute to more sustainable commercial plastic life cycles as part of a circular economy. In this context, virgin polymers are made from renewable or recycled raw materials, and carbon-neutral energy is used for production. Bioplastics can have a lower carbon footprint than fossil-based plastics and can be compatible with existing recycling streams. However, they may also have negative environmental impacts, such as land and water consumption, the use of pesticides and fertilizers, eutrophication, and acidification.
Biobased Plastics: Carbohydrates
Biobased polymers are derived from biomass or issued from monomers derived from biomass. Bioplastics can be synthesized from carbohydrates, which are natural biopolymers. Examples of carbohydrates used in bioplastics include polysaccharides, such as corn starch, rice starch, cellulose, chitosan, and alginate. These carbohydrates can be processed directly into bioplastics, and they play a crucial role in the development of sustainable plastic alternatives.
Biobased Plastics: Starch
Starch is one of the most commonly used materials in bioplastics, with thermoplastic starch representing about 50% of the bioplastics market. Starch-based bioplastics can be made at home by gelatinizing starch and solution casting. Pure starch can absorb humidity, making it suitable for drug capsules. However, starch-based bioplastics are brittle, and plasticizers such as glycerol, glycol, and sorbitol are added to improve their processability.
Biobased Plastics: Vegetable Fats and Oils
Bioplastics can also be derived from vegetable fats and oils, which are lipids obtained from plants or animals. Vegetable oils, such as traditional vegetable oils and low-cost microalgae-derived oils, have shown promising potential in bioplastic production. For example, OleoPlast is a novel bioplastic introduced in 2024 that is based on ethyl cellulose and vegetable oils. It exhibits thermoplastic behavior, offering both recyclability and biodegradability, and can be customized for different processing techniques.
Biobased Plastics: Bacteria and Biological Substances
Some bioplastics are produced using bacteria and biological substances. For instance, the biopolymer poly-3-hydroxybutyrate (PHB) is a polyester produced by certain bacteria processing glucose, corn starch, or wastewater. PHB has characteristics similar to petroplastic polypropylene (PP) and is gaining traction, particularly in the South American sugar industry. Additionally, bioplastics can be synthesized from industrial carbon dioxide and biowaste, showcasing the potential of utilizing biological substances to create sustainable plastic alternatives.
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Engineering plastics: polyacetal, polyamide, polytetrafluoroethylene, polycarbonate, polyphenylene sulfide, epoxy and polyetheretherketone
Polyacetal, also known as polyoxymethylene (POM), is a hard plastic that is nearly as strong as epoxy or aluminium. It is used in precision parts requiring high stiffness, low friction, and excellent dimensional stability. POM is also used in injection-moulded products such as eyeglass frames, ball bearings, knife handles, and ski bindings.
Polyamide is a polymer with repeating units linked by amide bonds. Synthetic polyamides are commonly used in textiles, automotive parts, carpets, kitchen utensils, and sportswear due to their high durability and strength. Polyamides can be made through step-growth polymerization or solid-phase synthesis, yielding materials such as nylons, aramids, and sodium polyaspartate.
Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene known for its exceptional properties, including flexibility, chemical resistance, and structural integrity. PTFE is commonly used in slide bearings, skidway plates, and precision plastic parts.
Polycarbonate is a versatile plastic with attractive processing and physical properties. It is used in various applications, including automotive parts, optical reflectors, food containers, and medical devices. Polycarbonate is also well-suited for 3D FDM printing, producing strong and durable plastic products with a high melting point.
Polyphenylene sulfide (PPS) is an organic polymer consisting of aromatic rings linked by sulfides. PPS is used in various applications, including filter fabric for coal boilers, electrical insulation, and specialty membranes. It is a high-performance thermoplastic that can be moulded, extruded, or machined to tight tolerances.
Epoxy is a versatile material with a wide range of applications, including metal coatings, electrical components, LEDs, adhesives, and composite materials. Epoxy resins typically require a precise mix of two components to form a third chemical with the desired properties.
Polyetheretherketone (PEEK) is a high-performance polymer used in demanding applications. It is commonly used to produce high-quality plastic parts that are thermostable and electrically and thermally insulating. PEEK is also used in medical implants, such as creating partial replacement skulls in neurosurgical applications.
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Frequently asked questions
Plastics are made of carbon atoms connected to one another in a chain-like structure, with mostly or exclusively hydrogen atoms attached to the carbon atoms.
The elements found in plastics include carbon, hydrogen, oxygen, nitrogen, sulphur, and chlorine.
Yes, plastics can be categorized as synthetic or biobased. Synthetic plastics are derived from crude oil, natural gas, or coal, while biobased plastics are derived from renewable products such as carbohydrates, fats, and oils.
Common examples of plastics include polyethylene, polypropylene, polyvinyl chloride (PVC), and polystyrene.
