Chloe Zhang
Plastic is a polymeric material known for its plasticity, or ability to be moulded or shaped. This property, often combined with other characteristics such as low density, low electrical conductivity, transparency, and toughness, allows plastics to be used in a wide range of products. While there is no one chemical symbol for plastic, there are various chemical formulas for different types of plastics. For example, the chemical formula for polyethylene, the most commonly produced plastic, is generally written as (C2H4)n.
| Characteristics | Values |
|---|---|
| Generalised chemical formula | (C2H4)n |
| Density | 0.88–0.96 g/cm³ |
| Melting point | 115–135 °C |
| Primary application | Packaging products (plastic films, plastic bags, plastic bottles, and geomembranes) |
| Types | Low-density polyethylene, high-density polyethylene, and polyethylene terephthalate |
| Additives | Colorants, plasticizers, stabilizers, fillers, and reinforcements |
| Thermal properties | Poor conductors of heat and electricity |
| Mechanical properties | Low density, low electrical conductivity, transparency, and toughness |
| Resistance | Resistant to strong acids, strong bases, gentle oxidants, and reducing agents |
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What You'll Learn
- There is no single chemical symbol for plastic
- Plastic is a polymeric material, made from chains of linked subunits called monomers
- Common plastics include polyethylene, polystyrene, polypropylene, and polyvinyl chloride
- The properties of plastics depend on their chemical composition, arrangement of subunits, and processing method
- Plastic is usually solid, but can be heated and remoulded
There is no single chemical symbol for plastic
One of the most common types of plastic is polyethylene, which has the chemical formula (C2H4)n. This formula represents a polymer formed from the monomer ethylene, which has the formula C2H4. Polyethylene is used in a wide range of applications, from packaging to geomembranes, due to its low density, low electrical conductivity, and toughness. However, its chemical resilience also makes it a persistent pollutant in the environment.
Another type of plastic is polypropylene, which has the chemical formula (C3H6)n. This plastic is a thermoplastic polymer that becomes malleable at certain temperatures, with a melting point ranging from 130°C to 171°C. Polypropylene is used in applications where a balance of strength and flexibility is desired.
Polyvinyl chloride (PVC) is another commonly used plastic with the monomer vinyl chloride, which has the formula C2H3Cl or CH2=CHCl. PVC is a synthetic polymer that can take two basic forms: rigid PVC, used in construction, and flexible PVC.
In addition to these commodity plastics, there are also engineering plastics like polyacetal, polyamide (nylon), and polytetrafluoroethylene (Teflon). These plastics offer superior mechanical and thermal properties compared to commodity plastics and are used in specific applications like plumbing, hardware, and automotive components.
The variety of plastic types and their unique chemical compositions make it challenging to assign a single chemical symbol to represent all plastics. Each type of plastic has distinct properties and behaviours that are defined by its specific chemical structure.
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Plastic is a polymeric material, made from chains of linked subunits called monomers
Plastic is a polymeric material, meaning it is made from chains of linked subunits called monomers. Polymers are substances or materials that consist of very large molecules, or macromolecules, that are formed by linking many smaller molecules, known as monomers, into a covalently bonded chain or network. This process is called polymerization. Polymers can be natural or synthetic, and they play essential and ubiquitous roles in everyday life.
The continuously linked backbone of a polymer used for the preparation of plastics consists mainly of carbon atoms. For example, the monomer of polyethylene ('polythene' in British English) is ethylene. Many other structures exist; for example, elements such as silicon form familiar materials such as silicones, and oxygen is also commonly present in polymer backbones, such as those of polyethylene glycol.
The microstructure of a polymer describes the arrangement of monomer residues along the backbone of the chain. Polymers can consist of linear macromolecules containing only one unbranched chain, or they can have a main chain and side chains, as in the case of polyethylene, where the side chains are alkyl groups. The longer the polymer chain, the higher its viscosity, or resistance to flow as a liquid, because they have a greater surface area, which makes them want to stick to neighbouring molecules.
The properties of polymers are characterised by the interaction between the solvent and the monomer subunits. In a good solvent, the polymer appears swollen and occupies a large volume, whereas in a bad solvent, the chain contracts. The inclusion of plasticizers tends to lower Tg and increase polymer flexibility.
Many commercially important polymers are synthesized by chemically modifying naturally occurring polymers. For example, the reaction of nitric acid and cellulose forms nitrocellulose, and natural rubber heated in the presence of sulfur forms vulcanized rubber.
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Common plastics include polyethylene, polystyrene, polypropylene, and polyvinyl chloride
Plastic is a polymeric material that can be moulded or shaped. It is often combined with other properties such as low density, low electrical conductivity, transparency, and toughness. This allows plastics to be made into a wide range of products.
Some of the common plastics include polyethylene, polystyrene, polypropylene, and polyvinyl chloride.
Polyethylene, or polythene, is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes, bottles, cups, jars, etc.). It is non-toxic, chemically resilient, and has excellent chemical resistance. It can be low-density or high-density polyethylene. The former was discovered in 1933 and is known as LDPE, while the latter is known as HDPE.
Polystyrene is the sixth type of plastic. It can be solid or foamed and is a very inexpensive resin per unit weight. It is easy to create and can be found in beverage cups, insulation, packing materials, egg cartons, disposable dinnerware, and bike helmets. It is also known by its commercial name, Styrofoam, and is highly inflammable.
Polypropylene is the second-most widely produced commodity plastic. It is hard and sturdy, withstanding high temperatures. It is found in Tupperware, car parts, thermal vests, yogurt containers, and disposable diapers. It has a very favourable strength-to-weight ratio and is resistant to fatigue, making it ideal for living hinges.
Polyvinyl chloride (PVC) is the world's third-most widely produced synthetic plastic polymer. It comes in two basic forms: rigid and flexible. Rigid PVC is used in the building and construction industry for door and window profiles and pipes, while flexible PVC is used in toys, cling wrap, detergent bottles, and medical tubing. It is well-known for its ability to blend with other materials. However, PVC is considered the most hazardous plastic due to the variety of toxic chemicals it may leach.
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The properties of plastics depend on their chemical composition, arrangement of subunits, and processing method
Plastics are polymers made of carbon and hydrogen, often mixed with additives to enhance their performance or appearance. They are classified as either “commodity” resins or “specialty” resins. The properties of plastics are dependent on their chemical composition, the arrangement of subunits, and the processing method.
All plastics are polymers, but not all polymers are plastics. Plastic polymers consist of chains of linked subunits called monomers. If identical monomers are joined, it forms a homopolymer, and different monomers link to form copolymers. Homopolymers and copolymers may be either straight or branched chains. The arrangement of these polymer chains can vary significantly, even with the same monomer. For example, High-Density Polyethylene (HDPE) has linear, unbranched chains that pack tightly together, making the material rigid and strong, ideal for milk jugs and pipes. On the other hand, Low-Density Polyethylene (LDPE) has branched chains that prevent tight packing, resulting in a more flexible and less dense material used for plastic bags and films.
The processing method also affects the properties of plastics. Thermoplastics, for instance, can be repeatedly softened by heating and hardened by cooling, allowing them to be remoulded. They do not undergo any chemical changes when subjected to high temperatures and can be changed into a soft state. Thermosetting plastics, on the other hand, solidify permanently and can only be moulded once. When exposed to high temperatures, they undergo degradation and become damaged.
Plastics are highly valued for their unique combination of properties. They are lightweight, durable, resistant to corrosion, chemicals, and water, and are excellent insulators due to their poor conductivity of heat and electricity. They can be easily moulded into complex shapes and sizes at a low cost and can be made rigid or flexible, opaque or transparent.
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Plastic is usually solid, but can be heated and remoulded
Plastics are usually solid, but some can be heated and remoulded. Plastic is a polymeric material that can be moulded or shaped, often in combination with other properties such as low density, low electrical conductivity, transparency, and toughness. This property of plasticity allows plastics to be made into a wide variety of products.
Plastics can be divided into two broad families of polymers: thermoplastics and thermosets. Thermoplastics are polymers that can be melted and remelted almost indefinitely. They melt when heated and harden when cooled. Thermoplastics include polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyethylene terephthalate, and polycarbonate. Thermoplastics have a simple molecular structure made up of chemically independent macromolecules. They are used in a wide range of applications, from toys and sports equipment to automotive parts and food storage containers.
Thermosets, on the other hand, never soften once moulded and remain in a permanent solid state after being cured. Thermosetting plastics are known for their strong structure due to the formation of strong cross-links during initial moulding. However, some sources suggest that thermosetting plastics can be deformed and moulded into different shapes when heated.
The process of thermoplastic injection moulding involves creating a mould, usually made of metal, and melting the thermoplastic resin into a liquid before injecting it into the mould to cool and solidify. This process requires high heat and pressure and is used to create a wide range of products, from automotive parts to medical devices and packaging materials.
Overall, while plastic is typically solid, its unique properties of plasticity and mouldability allow it to be heated and remoulded, making it a versatile material for various applications.
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Frequently asked questions
There is no single chemical symbol for plastic, as plastic can be made from a variety of polymers and additives. The most common type of plastic is polyethylene, which has the chemical formula (C2H4)n.
Polyethylene, also known as polythene, is a polymer made from the monomer ethylene (C2H4). It is the most commonly produced plastic and is used in packaging products such as plastic bags, bottles, and containers.
Other common types of plastic include polypropylene (C3H6)n and polyvinyl chloride (PVC), which has the formula CH2=CHCl or C2H3Cl.
Additives are substances mixed with polymers to modify the chemical composition, properties, and cost of plastics. Common additives include colorants, plasticizers, stabilizers, fillers, and reinforcements. Some additives, like phthalates, can be toxic and harmful to the environment.
