Chloe Zhang
Plastic is a polymeric material that can be moulded or shaped, typically using heat and pressure. Most plastic today is synthetic and derived from crude oil, natural gas, and coal. The first human-made plastic, Parkesine, was patented in 1856 by Alexander Parkes and composed of nitrocellulose. Most polymers are made up of carbon and hydrogen atoms, and plastics fall into this category. There are two main categories of plastics: those made up of polymers with only aliphatic carbon atoms, and those made up of heterochain polymers, which contain atoms such as oxygen, nitrogen, or sulfur in addition to carbon.
| Characteristics | Values |
|---|---|
| Composition | Polymers with aliphatic (linear) carbon atoms in their backbone chains or heterochain polymers with atoms such as oxygen, nitrogen, or sulfur in their backbone chains, in addition to carbon. |
| Chemical Composition | Hydrocarbons with carbon and hydrogen atoms. |
| Manufacturing | Synthetic plastics are derived from crude oil, natural gas, or coal. Biobased plastics come from renewable products such as carbohydrates, fats, and oils. |
| Properties | Low density, low electrical conductivity, transparency, and toughness. |
| Types | Commodity plastics, engineering plastics (or resins), thermoplastic elastomers, bioplastics. |
| Examples | Polypropylene, polycarbonate, nylon, Teflon, polyethylene. |
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What You'll Learn
- Plastic is a polymeric material that can be moulded or shaped
- Plastics are made from hydrocarbons derived from fossil fuels
- Plastic is defined by its engineering behaviour, not chemical composition
- Plastic was first patented in 1856 by Alexander Parkes
- Plastic can be categorised by its chemical composition
Plastic is a polymeric material that can be moulded or shaped
The majority of plastics in use today are synthetic, derived from crude oil, natural gas, or coal. These fossil fuels are composed of hydrocarbons, which are molecules formed by carbon and hydrogen atoms bonding together. Carbon, with its valency of four, can pair with four other electrons from any element on the periodic table, making it highly versatile in chemical bonding. In the case of hydrocarbons, carbon pairs with hydrogen, forming single bonds to create molecules such as methane (CH4) and ethane (C2H6).
Polymers, which are long chains of monomers, are a key component of plastics. The monomers can be of various types, with ethylene being a common example used in low-density polyethylene (LDPE) and high-density polyethylene (HDPE). The degree of branching in the chains affects the resulting plastic's density and other physical properties. For instance, HDPE has stronger and less flexible chains than LDPE due to its higher density.
Plastics can be categorised based on their chemical composition. One category consists of plastics made up of polymers with only aliphatic (linear) carbon atoms in their backbone chains. An example is polypropylene, where every other carbon atom is attached to a methyl group (CH3). The other category is composed of heterochain polymers, which contain atoms such as oxygen, nitrogen, or sulfur in their backbone chains, in addition to carbon. Polycarbonate, with its molecules containing two aromatic (benzene) rings, falls into this category.
The development of plastics has a long history, with the first human-made plastic, Parkesine, being patented in 1856 by Alexander Parkes. This early plastic was composed of nitrocellulose, making it hard, flexible, and transparent. However, it lacked commercial success due to issues with product quality control. Subsequent improvements in plasticity and the discovery of new polymer types have led to the diverse range of plastics we use today.
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Plastics are made from hydrocarbons derived from fossil fuels
Plastic is a polymeric material that can be moulded or shaped, typically when heat and pressure are applied. Plastics are derived from fossil fuels, with over 99% of plastics made from chemicals sourced from fossil fuels. Fossil fuels include crude oil, natural gas, and coal, which are composed of hydrocarbons. Hydrocarbons are formed from the remains of living organisms, specifically tiny plants and animals called plankton, which existed during the Jurassic era. Over millions of years, these organisms were buried beneath heavy layers of sediment in the Earth's mantle, subjected to immense heat and pressure, and decomposed without oxygen, transforming into small pockets of oil and gas.
Crude oil and natural gas accumulate in rocks, forming reservoirs. Oil refining of crude oil yields various chemicals, including naphtha, a mixture of hydrocarbons. Decane, a hydrocarbon, can be broken down into products like propylene and heptane, which are used to make polypropylene. Raw materials are converted into monomers, such as ethylene, propylene, and butene, which contain double bonds that allow carbon atoms to react and form polymers. The polymerisation process involves linking hydrocarbon monomers through chemical mechanisms to produce polymers. These polymers are thick, viscous substances known as resins, which are used to create plastic products.
The first commercially produced plastic, Bakelite, was invented in 1907 by Leo Hendrik Baekeland by synthesising coal tar and wood alcohol. Plastic use expanded during World War II as the US Military experimented with its applications, leading to increased commercial demand post-war. Seeking cheaper production methods, manufacturers turned to fossil fuels, which remain the primary source of plastic production today. Plastic manufacturing currently accounts for 12% of global oil consumption, and this percentage is expected to rise with increasing plastic consumption.
The connection between the fossil fuel and plastic industries has detrimental environmental consequences. Fossil fuels are responsible for over 75% of greenhouse gas emissions, and the development of plastics from fossil fuels contributes to rising emissions annually. As the world grapples with the dangers of plastic pollution, the industry is simultaneously investing heavily in expanding plastic production, exacerbating pollution risks and undermining efforts to address the plastic crisis.
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Plastic is defined by its engineering behaviour, not chemical composition
Plastic is a polymeric material with the defining characteristic of plasticity, which allows it to be moulded, extruded, or pressed into a diverse range of solid forms. It is a man-made substance, typically produced from natural gas and petroleum, with an ever-growing amount being produced from renewable resources like polylactic acid.
Plastics are classified in various ways, including by the chemical process used in their synthesis, their physical properties, and their engineering behaviour. While plastics can be categorised by their chemical composition, they are primarily defined by their engineering behaviour.
The two main categories of plastics based on chemical composition are carbon-chain polymers and heterochain polymers. Carbon-chain polymers are made up of aliphatic (linear) carbon atoms in their backbone chains. An example of this category is polypropylene, where a methyl group (CH3) is attached to every other carbon atom. Heterchain polymers, on the other hand, contain atoms such as oxygen, nitrogen, or sulfur in their backbone chains, in addition to carbon. Polycarbonate, with its molecules containing two aromatic (benzene) rings, is an example of a heterochain polymer.
The engineering behaviour of plastics, however, takes precedence in their definition. This includes their physical properties, such as hardness, density, tensile strength, and thermal resistance, as well as their responses to various substances and processes, like exposure to organic solvents and oxidation. For instance, thermoplastics are a type of plastic that can be moulded repeatedly without undergoing chemical changes when heated. This behaviour makes them suitable for specific applications, such as in the production of beverage bottles, where their low density and transparency are desirable traits.
The adaptability of plastics, combined with their unique properties, has led to their ubiquitous presence in modern life.
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Plastic was first patented in 1856 by Alexander Parkes
Plastic is a polymeric material that can be moulded or shaped, often with the application of heat and pressure. It is usually created from a combination of carbon, oxygen, nitrogen, sulphur, or other atoms.
Parkes' invention was a significant milestone, as it anticipated many of the modern aesthetic and utility uses of plastics. Parkesine was exhibited at the 1862 International Exhibition in London, showcasing its potential for various applications. The material's flexibility and mouldability, even upon repeated heating, made it a groundbreaking innovation.
Parkes was a prolific inventor, holding at least 66 patents throughout his career. Many of his patents were related to electroplating and the development of plastics. He pioneered processes for electroplating delicate objects, such as flowers, and his techniques were used to create silver-plated objects presented to notable figures like Prince Albert.
In recognition of his contributions, Parkes was posthumously inducted into the American Plastics Academy's Hall of Fame in 2005. His legacy is also commemorated with a blue plaque erected by the Birmingham Civic Society in 2004.
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Plastic can be categorised by its chemical composition
Plastic is a polymeric material that can be moulded or shaped when heat and pressure are applied. It is usually categorised based on its engineering behaviour rather than its chemical composition. However, plastics can be divided into two distinct categories based on their chemical composition.
The first category of plastics is made up of polymers with only aliphatic (linear) carbon atoms in their backbone chains. Commodity plastics like polypropylene fall into this category. Polypropylene has a pendant methyl group (CH3) attached to every other carbon atom.
The second category is made up of heterochain polymers. These compounds contain atoms such as oxygen, nitrogen, or sulphur in their backbone chains, in addition to carbon. Engineering plastics like polycarbonate are composed of heterochain polymers. Polycarbonate molecules contain two aromatic (benzene) rings.
Plastics can also be classified by the chemical process used in their synthesis, such as condensation, polyaddition, and cross-linking. They can be further classified by their physical properties, including hardness, density, tensile strength, thermal resistance, and glass transition temperature. For instance, high-performance plastics are a category of polymers that exhibit superior properties compared to commodity and engineering plastics. These plastics can withstand high temperatures, are highly resistant to chemical corrosion and degradation, and have excellent mechanical and electric properties.
Additionally, plastics are often categorised based on their intended use or specific applications. For example, the Society of the Plastics Industry introduced the Resin Identification Code (RIC) system, which divided plastic resins into seven categories to facilitate recycling. The seven types of plastic are:
- Polyethylene terephthalate (PET) - used for food and drink packaging.
- High-Density Polyethylene (HDPE) - used for grocery bags, milk jugs, and recycling bins.
- Polyvinyl chloride (PVC) - commonly used in plastic wrap.
- Polystyrene (PS) - used for beverage cups, insulation, packing materials, and disposable dinnerware.
- Polypropylene (PP) - a commodity plastic with pendant methyl groups.
- Polycarbonate (PC) - used for eye protection, mobile phones, and compact discs.
- Miscellaneous - any plastic that cannot be identified in the six types mentioned above, such as polycarbonates.
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Frequently asked questions
Plastic is a polymeric material that has the capability of being moulded or shaped, usually by the application of heat and pressure.
Most plastic in use today is synthetic and derived from crude oil, natural gas, or coal. Biobased plastics, on the other hand, are made from renewable products such as carbohydrates, fats, and oils.
Most polymers are made up of carbon and hydrogen atoms, and many plastics as well. Other elements found in plastics include oxygen, nitrogen, and sulfur.
Some common plastics include polyethylene, polyacetal, polyamide (nylon), polytetrafluoroethylene (Teflon), polycarbonate, and polypropylene.
Plastics are used in a wide variety of products due to their special properties such as low density, low electrical conductivity, transparency, and toughness. Examples include bottles, car tires, and non-stick cookware.
