Alexei Volkov
Plastic is a synthetic material derived from organic compounds. It is made up of polymers, which are long chains of molecules. The properties of plastics depend on the structure of these polymers and how they are bonded. Plastics can be categorised as thermoplastics or thermosets, depending on the nature of the bonds between their polymers. Thermoplastics have weak secondary bonds that can be easily broken and reformed by heating and cooling, while thermosets have strong primary bonds that give them a rigid 3D structure. The bonds between polymers in plastics can be covalent or ionic. In a covalent bond, electrons are shared between atoms, whereas in an ionic bond, electrons are transferred between atoms, resulting in positively and negatively charged ions.
| Characteristics | Values |
|---|---|
| Definition | Plastic is a polymeric material that can be moulded or shaped, usually by applying heat and pressure. |
| Composition | Plastics are synthetic materials derived from organic (carbon-containing) compounds. |
| Sources | The most common sources for carbon compounds are oil (petroleum) and natural gas. |
| Types | There are about 50 different groups of plastics, with hundreds of varieties. The main types are thermoplastics and thermosets. |
| Structure | Thermoplastics have long, linear polymer chains that are weakly chemically bonded. Thermosets are linear chain molecules with strong primary bonds between adjacent polymer chains, giving them a rigid 3D structure. |
| Bonds | Plastics consist of covalent bonds, where the outer electrons of atoms overlap and are shared between nuclei. Some plastics may also have ionic bonds, such as those with carboxylic acid/carboxylate functional groups. |
| Malleability | Thermoplastics can be easily remoulded by heating and breaking the weak bonds between polymers. Thermosets, once moulded, cannot be reformed as they have strong, irreversible bonds. |
| Recyclability | Thermoplastics are easy to recycle as they can be melted and reshaped. Thermosets cannot be recycled. |
| Applications | Plastics are used in packaging, textiles, electrical components, automotive parts, and more. |
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What You'll Learn
Plastic is a polymeric material that can be moulded or shaped
Plastic is a synthetic polymeric material derived from petroleum, with crude oil and natural gas as its raw materials. The word 'plastic' comes from the Ancient Greek πλαστικός (plastikos), meaning "capable of being shaped or moulded". The plasticity of plastics allows them to be moulded, extruded, or pressed into a wide range of solid forms, including films, fibres, plates, tubes, bottles, and boxes. This adaptability, along with its low weight, durability, flexibility, chemical resistance, low toxicity, and low-cost production, has led to its widespread use around the world.
Plastics are composed of polymers, which are chemically bonded chains of molecules or monomers. These monomers can be simple, comprising a few atoms, or complex functional groups of atoms. The chemical composition and size of the individual monomers determine how the polymer interacts with itself and its environment. Polymers can be naturally occurring, such as cellulose, latex, and rubber, or synthetic, like nylon, polyethylene, and polypropylene. The terms "polymer" and "plastic" are often used interchangeably, but there are differences between the two. Plastics are a subset of polymers, and while all plastics are considered polymers, not all polymers are considered plastics.
The polymer chains in plastics are composed of carbon atoms covalently bonded with other atoms. Covalent bonds are formed when the outer electrons of atoms overlap and are shared between the nuclei. These bonds are very strong and only rupture under extreme conditions. In addition to covalent bonds, plastics also exhibit van der Waals forces, which are weaker bonds between molecules that allow sliding and rupture to occur.
The classification of plastics into thermoplastics and thermosets depends on the reversibility of the chemical processes used to create them. Thermoplastics have long, linear polymer chains that are weakly chemically bonded, allowing them to glide past each other when heated. As a result, thermoplastics can be remoulded, and the new shape is retained when cooled. Thermosets, on the other hand, have strong primary bonds between adjacent polymer chains, giving them a rigid 3D structure. Once a thermoset has been moulded, it cannot be reformed, and if reheated, it decomposes instead of melting.
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Plastic is made from organic compounds
Plastic is a synthetic material derived from organic compounds. In other words, plastics are human-made materials that come from carbon-containing substances. The most common sources for carbon compounds are oil (petroleum) and natural gas. Crude oil is heated in a furnace and sent to a distillation unit, where heavy crude oil separates into lighter components called fractions. One of these fractions, naphtha, is crucial for making plastic. Polymerisation is a process in the petroleum industry where light olefin gases (gasoline) such as ethylene, propylene, and butylene (monomers) are converted into higher molecular weight hydrocarbons (polymers). This occurs when monomers are chemically bonded into chains.
Plastics are polymers composed of various elements, including carbon, hydrogen, oxygen, nitrogen, sulphur, and chlorine. They can also be produced from silicon atoms (silicone). The properties of a particular plastic depend on the polymer chains' structure, how they are bonded to each other, and any additives introduced. For example, additives may be blended into plastics to give them colour or make them softer. However, these additives may have adverse effects on human health and the environment.
Plastics can also be made from renewable plant materials like cellulose and starch, known as bioplastics. The development of bioplastics is a growing field due to the limited nature of fossil fuel reserves and the rising levels of greenhouse gases caused by burning these fuels.
Plastics consist of long molecule chains, and their atoms are covalently bonded. Covalent bonds occur when the outer electrons of atoms come close enough to overlap and are shared between the nuclei, forming a strong bond. However, some plastics may also exhibit ionic bonding, as some have ionic functional groups such as carboxylic acid or carboxylate.
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Plastic is made from covalently bonded atoms
Plastic is a synthetic material derived from organic compounds, most commonly sourced from carbon-containing compounds such as oil (petroleum) and natural gas. These organic compounds are covalently bonded atoms. In a covalent bond, the outer electrons of atoms are close enough to overlap and are shared between the nuclei, forming a strong covalent bond. Each pair of shared electrons is called a covalent bond.
The specific type of plastic produced depends on the polymer chains involved, how they are bonded, and any additives introduced. For example, polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons, primarily used in packaging. Polypropylene, on the other hand, is a thermoplastic polymer used in packaging, textiles, stationery, plastic parts, and containers.
Plastics can also be categorised as thermoplastics or thermosets. Thermoplastics have long, linear polymer chains that are weakly chemically bonded. When heated, these bonds break, allowing the polymers to move past each other, which is why thermoplastics can be easily remoulded. Thermosets, on the other hand, have strong primary bonds between adjacent polymer chains, giving them a rigid 3D structure.
While most plastics are made from covalently bonded atoms, it is important to note that some plastics may also exhibit ionic bonding. For example, in "thermoset" materials, the polymer chains are often cross-linked by covalent bonds, but ionic functional groups may also be present.
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Plastic can contain ionic functional groups
Plastics are synthetic materials derived from organic (carbon-containing) compounds. The most common sources for carbon compounds are oil (petroleum) and natural gas. Plastics consist of polymers—long molecule chains often mixed with other substances such as colouring agents and softeners. The properties of a particular plastic depend on what the polymer chains look like, how they are bonded to each other, and which additives have been introduced.
Plastics can be classified into two categories: thermoplastics and thermosets. Thermoplastics have long, linear polymer chains that are only weakly chemically bonded or connected to each other. When a thermoplastic object is heated, these bonds are easily broken, allowing the polymers to glide past each other. Thermoplastics can be easily recycled by melting and reshaping them into new products. Examples of thermoplastics include PET, polyethylene, and polypropylene.
Thermosets, on the other hand, are linear chain molecules with strong primary bonds between adjacent polymer chains, giving them a rigid 3D structure. Once a thermoset has been moulded, it cannot be reformed as temperature changes do not affect it. In thermoset materials, the polymer chains are typically cross-linked through covalent bonds, creating a single giant molecule. Examples of thermosets include rubberized materials and epoxy resins.
While plastics are primarily composed of covalently bonded atoms, some plastics can contain ionic functional groups, such as carboxylic acid or carboxylate. This means that some ionic bonding may also be present within the material. Therefore, plastics can be considered molecular solids, and depending on the bonding and thermal history, they can exhibit varying degrees of crystallinity or amorphousness.
The distinction between thermoplastics and thermosets is essential in understanding the behaviour and applications of different types of plastics. The presence of ionic functional groups in plastics can also influence their properties and behaviour, contributing to the diverse range of applications that plastics offer in our modern world.
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Plastic can be recycled
Another challenge is the variety of plastic types, which can be difficult to separate and mix when melted down. Plastic items often contain multiple types of plastic and different layers, making them hard to separate and costly to recycle. Additionally, plastics can be contaminated by food and other substances, rendering them unusable for recycling. The small amounts of certain plastic types produced in some countries can also make recycling non-economical.
Despite these challenges, recycling plastic is possible and can result in incredible products. The most widely recycled plastic globally is PET, which is relatively easy to recycle and is often transformed into fashion items, such as polar fleece clothing, backpacks, and carpets. PET bottles can even be recycled into new bottles, a process made possible by blending virgin and recycled PET to strengthen the material. Other recycled plastic products include shampoo bottles, cosmetic caps, and packaging films.
Mechanical recycling is the most common form of plastic recycling, involving the collection, cleaning, sorting, shredding, melting, and forming of plastic waste into pellets for resale to producers of recycled plastic products. While this process is straightforward in theory, it is complex in practice due to the variety of plastic types and the need for diligent sorting to prevent quality degradation.
To improve plastic recycling, established technologies must be scaled up and implemented worldwide, and innovations are required to address hard-to-recycle plastics. Additionally, addressing plastic pollution at its source by reining in the production of single-use plastics is crucial.
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Frequently asked questions
Covalent bonds occur when the outer electrons of some atoms are close enough to overlap and are shared between the nuclei, forming a covalent bond. Each pair of electrons is called a covalent bond. Covalent bonds are strong primary bonds, like metallic and ionic bonds.
Ionic bonds are due to electrostatic attractive forces between positive and negative ions. In ionic bonding, one atom loses an electron, becoming positively charged, while the other atom gains an electron, becoming negatively charged. The two atoms are then held together by electrostatic forces.
Plastic is a polymeric material that can be moulded or shaped, usually with heat and pressure. All plastic materials consist of covalently bonded atoms. However, some plastics also have ionic functional groups, so some ionic bonding may be present.
Polyethylene or polythene is the most widely used plastic. Other plastics that are covalently bonded include polypropylene, polyvinyl chloride, polystyrene, and polyethylene terephthalate (PET).
