Sofia Martinez
Plastic is a polymeric material that can be moulded or shaped, with other properties such as low density, low electrical conductivity, transparency, and toughness. The most common plastic is polyethylene, or polythene, which has the chemical formula (C2H4)n. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes and containers including bottles, cups, and jars). Polyethylene is derived from crude oil, natural gas, or coal, and is produced by polymerisation, which involves converting light olefin gases (gasoline) such as ethylene, propylene, and butylene (monomers) into higher molecular weight hydrocarbons (polymers).
| Characteristics | Values |
|---|---|
| Composition | Plastics are polymeric materials derived from crude oil, natural gas, or coal. |
| Chemical Formula | The chemical formula for polyethylene, the most common type of plastic, is (C2H4)n. |
| Properties | Plastics can be moulded or shaped, have low density, low electrical conductivity, transparency, and toughness. |
| Types | Engineering plastics include polyacetal, polyamide (nylon), polytetrafluoroethylene (Teflon), polycarbonate, polyphenylene sulfide, epoxy, and polyetheretherketone. Commodity plastics include polyethylene (PE) and polyvinyl chloride (PVC). |
| Uses | Plastics are used in a wide range of products, including packaging, automobile interiors, and compact discs. |
| Recycling | Plastics can be recycled, but some types, such as polyethylene, can be long-lived and decomposition-resistant pollutants if not disposed of properly. |
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What You'll Learn
- Polyethylene, or polythene, is a commonly used plastic with the chemical formula (C2H4)n
- Polyethylene terephthalate is commonly referred to as PET
- Polyvinyl chloride, or PVC, is used in plumbing and is also known as vinyl
- Polystyrene is often used in packaging and is commonly known as Styrofoam
- Plastics are derived from crude oil, natural gas, and coal
Polyethylene, or polythene, is a commonly used plastic with the chemical formula (C2H4)n
Polyethylene, also known as polythene, is the most commonly used plastic in the world. It is a polymer, primarily used for packaging, including plastic bags, plastic films, geomembranes, bottles, cups, jars, and containers. It is also used in agricultural mulch, wire and cable insulation, toys, and housewares.
The chemical formula for polyethylene is typically written as (C2H4)n, where 'n' represents the degree of polymerization or the mean quantity of structural units. The formula reflects the structure of ethylene molecules, which are composed of two methylene units (CH2) linked by a double bond between carbon atoms. This structure can be represented as CH2=CH2.
During polymerization, ethylene molecules undergo a reaction where the double bond is broken, and the resulting single bond is used to link to a carbon atom in another ethylene molecule. This process creates a repeating unit within a larger, polymeric molecule. The polymerization of ethylene to polyethylene can be described by the chemical equation: n CH2=CH2 (gas) → [−CH2−CH2−]n (solid).
The basic polyethylene composition can be modified by including other elements or chemical groups, or by copolymerizing ethylene with other monomers such as vinyl acetate or propylene. Different types of polyethylene, such as LDPE, LLDPE, HDPE, and UHMWPE, are synthesized with varying molecular weights and chain architectures. These variations in structure result in different physical and mechanical properties, such as flexibility, ductility, and tensile strength.
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Polyethylene terephthalate is commonly referred to as PET
Polyethylene terephthalate, commonly known as PET, is a type of polyester commonly used for single-use bottles and packaging. It is a strong, stiff synthetic fibre and resin and a member of the polyester family of polymers. PET is made up of a polymer matrix of ethylene terephthalate monomers with repeating (C10H8O4) units. It is produced from the polycondensation of ethylene glycol and terephthalic acid. Ethylene glycol is a colourless liquid obtained from ethylene, and terephthalic acid is a crystalline solid obtained from xylene. When heated together under the influence of chemical catalysts, they produce PET in the form of a molten, viscous mass that can be spun directly into fibres or solidified for later processing as a plastic.
PET is widely used to fabricate carbonated beverage bottles because it has high strength and toughness, good abrasion and heat resistance, low creep at elevated temperatures, good chemical resistance, and excellent dimensional stability. It is also commonly recycled and has a resin identification code (RIC) of 1. PET bottles and containers are often melted down and spun into fibres for fibrefill or carpets. When collected in a suitably pure state, PET can be recycled into its original uses, and methods have been devised for breaking the polymer down into its chemical precursors for resynthesis into PET.
In 3D printing, PETG (polyethylene terephthalate glycol) has become a popular material for various applications, from surgical fracture tables to the automotive and aeronautical sectors. The surface properties of PETG can be modified to make it self-cleaning, which is useful for applications such as traffic signs or LED spotlights. PETG is also used as a plastic core coated with aluminium and topped with plastic to create a light-reflecting surface for glitter. However, as of 2021, many glitter manufacturing companies have started to phase out the use of PET due to calls for bio-friendly alternatives.
PET is also used in non-fibre applications, such as packaging, which accounts for about 6% of world polymer production by mass. The biggest application of PET is in fibres, with bottle production accounting for about 30% of global demand. In the context of textile applications, PET is referred to by its common name, polyester. PET is produced largely from purified terephthalic acid (PTA) and, to a lesser extent, from (mono-) ethylene glycol (MEG) and dimethyl terephthalate (DMT).
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Polyvinyl chloride, or PVC, is used in plumbing and is also known as vinyl
Polyvinyl Chloride (PVC) is a synthetic polymer made from vinyl chloride monomers. It is a versatile thermoplastic material known for its durability, chemical resistance, and affordability. These characteristics make it useful across a wide range of industries, from construction to manufacturing to medicine.
PVC is commonly used in plumbing systems due to its corrosion resistance and strength. Known for its strong resistance to chemicals, sunlight, and oxidation from water, PVC has almost entirely replaced cast iron for plumbing and drainage, being used for waste pipes, drainpipes, gutters, and downspouts. It is also used for medical applications, such as blood bags, medical tubing, and IV bags.
PVC is produced by polymerization of the vinyl chloride monomer (VCM). This process involves reacting ethylene with chlorine using a catalyst, forming vinyl chloride gas. The gas is then subjected to polymerization, where the monomer molecules combine to form long chains of PVC polymer.
PVC is available in two main forms: flexible and rigid. Flexible PVC is formed by adding compatible plasticizers to PVC, reducing its crystallinity. Rigid PVC, on the other hand, is a stiff and cost-effective plastic with high resistance to impact, water, weather, and corrosive environments. It is also known as UPVC, PVC-U, or uPVC.
In addition to plumbing, PVC is used in a variety of other applications. It is used in the production of phonograph records, also known as vinyl records. PVC piping is also used as a cheaper alternative to metal tubing in musical instrument making. In the building and construction industry, PVC is used to produce door and window profiles, replacing traditional building materials such as wood, metal, and concrete.
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Polystyrene is often used in packaging and is commonly known as Styrofoam
Plastic is a synthetic polymer with a chemical formula that varies based on its type and the monomers used in its production. One common type of plastic is polystyrene, often used in packaging and commonly known as Styrofoam.
Polystyrene, with the chemical formula C8H8, is a synthetic polymer made from styrene monomers, an aromatic hydrocarbon. It was first manufactured by the company I.G. Farben in Ludwigshafen around 1931 as a potential replacement for die-cast zinc. Polystyrene can be solid or foamed, and it is naturally transparent, although it can be coloured with various additives.
Polystyrene is widely used in packaging due to its excellent insulating properties, lightweight nature, and low cost. It helps keep food fresh for longer and is approved by the FDA for food contact applications. In the food industry, polystyrene is used for meat and poultry trays, egg cartons, and food containers. It is also commonly used for shipping and protective packaging, such as packing peanuts and CD/DVD cases.
The foamed version of polystyrene, known as expanded polystyrene (EPS) or extruded polystyrene (XPS), is particularly popular in packaging. EPS, commonly referred to as Styrofoam, is a rigid, closed-cell foam made of pre-expanded polystyrene beads. It is lightweight, with around 95% air content, and provides excellent thermal insulation. Styrofoam is a trademark of The Dow Chemical Company, specifically for its extruded closed-cell polystyrene foam products. However, the term "Styrofoam" is often used generically to refer to all foamed polystyrene products.
While polystyrene offers advantages in packaging, it is important to note that it is not entirely waterproof or vapour-proof. Additionally, there are concerns about the environmental impact of polystyrene waste, as it is not biodegradable. However, EPS packaging can be recycled and extruded back into solid polystyrene pellets.
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Plastics are derived from crude oil, natural gas, and coal
Synthetic plastics are derived from crude oil, natural gas, and coal. Biobased plastics, on the other hand, are made from renewable products such as carbohydrates, starch, vegetable fats and oils, bacteria, and other biological substances. The majority of plastic in use today is synthetic due to the ease of manufacturing methods involved in processing crude oil. However, the growing demand for limited oil reserves is driving the need for newer plastics from renewable resources.
Natural gas is another source of plastic. Ethane, commonly found mixed in with oil and natural gas deposits, can be turned into the building blocks of plastics. At a facility called an ethane cracker, ethane is heated to around 1,500 degrees. This causes the cracking or breaking of molecular bonds, leading to the formation of ethylene, a molecule with a double carbon bond. Ethylene is useful because it easily reacts with other chemicals and can be linked into long molecular chains. When ethylene molecules are snapped together, they form polyethylene, a common plastic.
Coal is also used in the production of synthetic plastics. However, it is unclear how coal is specifically utilized in this process.
Overall, the process of creating plastic involves forming polymers, which are larger molecules composed of many repeating units of smaller molecules called monomers. The monomers are derived from the refining of crude oil, natural gas, and coal.
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Frequently asked questions
Plastic is a polymeric material that can be moulded or shaped. The chemical formula for plastic varies as there are many different types of plastic. Polyethylene, or polythene, is the most commonly produced plastic and has the chemical formula (C2H4)n.
Polyethylene is used for packaging, including plastic bags, films, geomembranes, and containers. It is also used for softening PVC foils and in the cable and rubber industry.
Other common plastics include polyvinyl chloride (PVC) and polystyrene, but their chemical formulas are not provided in the sources. Plastics can be divided into two categories based on their chemical composition: carbon-chain and heterochain polymers.
