Maya Ellison
Plastic is a synthetic material made from petrochemicals, with the word deriving from the Ancient Greek πλαστικός (plastikos), meaning capable of being shaped or moulded. The world's first fully synthetic plastic was Bakelite, invented in 1907, and since then, dozens of different types of plastics have been produced. The most common type of plastic is polyethylene, specifically in the form of LDPE and HDPE, accounting for over 34% of total plastic production. It is a thermoplastic polymer that is easy to mould, making it versatile and widely used in products such as plastic bags, food containers, and bottles. Other types of plastics with significant usage include polypropylene, PVC, polystyrene, and ABS.
| Characteristics | Values |
|---|---|
| Most produced plastic | Polyethylene (PE), specifically LDPE and HDPE |
| % of total plastic production | Over 34% |
| Common uses | Plastic bags, food containers, bottles, toys, pipes, medical devices |
| Other names | Polyethylene terephthalate (PET) |
| Physical properties | Lightweight, durable, transparent, impact-resistant, moisture-resistant, easily recyclable |
| Other common plastics | Polypropylene (PP), PVC, Polystyrene (PS), ABS |
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What You'll Learn
Polyethylene (PE)
Polyethylene, also known as polythene and abbreviated as PE, is the most commonly produced plastic. It is a polymer, primarily used for packaging (plastic bags, plastic films, geomembranes, and containers including bottles, cups, and jars). Polyethylene is also used in grocery bags, milk jugs, recycling bins, agricultural pipes, playground equipment, lids, shampoo bottles, and water bottles. It is a thermoplastic and a homopolymer that contains ethene molecular chains.
Polyethylene was first synthesized by German chemist Hans von Pechmann in 1898 while investigating diazomethane. It was accidentally discovered again in 1933 by Eric Fawcett and Reginald Gibson at the Imperial Chemical Industries (ICI) works in Northwich, England. In 1935, another ICI chemist, Michael Perrin, developed a reproducible high-pressure synthesis for polyethylene that became the basis for industrial low-density polyethylene (LDPE) production.
The properties of polyethylene depend on its type. Molecular weight, crosslinking, and the presence of comonomers all strongly affect its properties. LDPE is softer and more transparent than HDPE. LDPE is composed of 4,000-40,000 carbon atoms, with many short branches. It is derived via the free-radical polymerization process and is produced at high pressure (1000-3000 bar) and temperature (80-300°C). The melting point for average commercial LDPE is typically 105 to 115 °C (221 to 239 °F).
Polyethylene is strong, durable, lightweight, and resistant to chemicals, certain solvents, dilute acids, and wear and tear. It is a good insulator, making it ideal for insulating electrical components. It is also relatively affordable and easy to create and source. It can be cut into filaments, pellets, films, and threads, and although some grades are transparent, it can also be dyed. Polyethylene is widely used for plastic injection molding and is one of the easiest materials to work with. Its processing ease makes it popular in other applications, such as blow molding and film extrusion.
Despite its popularity, polyethylene is not environmentally friendly. Like most thermoplastics, it is produced as a crude oil processing byproduct and is not biodegradable. It is also a long-lived and decomposition-resistant pollutant when disposed of improperly.
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Polypropylene (PP)
Polypropylene, also known as polypropene, is a thermoplastic polymer with a wide variety of applications. It is the world's second-most widely produced commodity plastic. It is produced through the chain-growth polymerization of the monomer propylene. Its properties are similar to polyethylene, but it is slightly harder, more heat-resistant, and has a higher softening point. It is also more flexible and has a higher rigidity. Polypropylene has a high chemical resistance and is resistant to fats and almost all organic solvents at room temperature. It is also waterproof and resistant to mould, bacteria, and chemical corrosion.
Polypropylene has a white, mechanically rugged appearance and a slippery, tactile surface. It has a density of between 0.895 and 0.93 g/cm3, making it the commodity plastic with the lowest density. It is tough and flexible, especially when copolymerized with ethylene, and has good resistance to fatigue. It is reasonably economical and has a high insulation value, making it safe to use for plastic casing in electrical goods and cables.
The properties of polypropylene depend on several factors, including molecular weight and molecular weight distribution, crystallinity, and the type and proportion of comonomers used. It can exist in various crystalline modifications, including isotactic, syndiotactic, and atactic forms, with the former being the most common. The crystalline modifications are further categorized into α-, β-, and γ-modifications, as well as mesomorphic (smectic) forms.
Polypropylene is produced by slurry, solution, or gas-phase processes, where propylene monomers are subjected to heat and pressure in the presence of a catalyst system. It can be processed by almost all thermoplastic-processing methods, including extrusion blow moulding, injection moulding, and general-purpose extrusion.
Polypropylene's versatility has made it a popular material in many areas, including plastic packaging, plastic parts for machinery and equipment, fibres and textiles, and even medical applications. It is also used in the automotive industry for battery casings, trays, bumpers, and interior details.
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Polyvinyl Chloride (PVC)
PVC is an economical and versatile thermoplastic polymer. It is used in a variety of applications in the building and construction, healthcare, electronics, automobile, and other sectors. In the construction industry, it is used to produce door and window profiles and pipes (drinking and wastewater). It has strong resistance against chemicals, sunlight, and oxidation from water. It is also used in fascia, siding, or weatherboarding. PVC has almost entirely replaced the use of cast iron for plumbing and drainage, being used for waste pipes, drainpipes, gutters, and downspouts.
Polyvinyl Chloride is also used in the healthcare industry. PVC blood collection bags have enhanced ambulatory medicine and serve as the foundation for modern blood banks. It is also used for tamper-resistant over-the-counter medications and shrink wrap for consumer products.
In the electronics industry, PVC is used for wire and cable insulation. It is also used in the automobile industry for windshield system components.
PVC can be modified by chlorination, which increases its chlorine content to or above 67%. Chlorinated polyvinyl chloride (CPVC) is produced by chlorination of an aqueous solution of suspension PVC particles followed by exposure to UV light, which initiates free-radical chlorination.
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Polystyrene (PS)
Polystyrene, also known as Styrofoam, is a synthetic polymer made from styrene, an important feedstock for a variety of products. It is a durable yet lightweight plastic with incredible customization opportunities. Polystyrene is naturally transparent, but it can be coloured with colourants. It is also inexpensive and has a low softening temperature.
Polystyrene comes in two main forms: foam, also known as expanded or extruded polystyrene, and rigid, solid plastic. The foam variety is a soft, white insulating material with good damping properties, while the solid plastic form is naturally transparent, lightweight, and inexpensive to manufacture. Solid polystyrene is commonly used in medical products like Petri dishes and test tubes, as well as household products like yogurt containers, smoke detector housings, and red Solo cups. It is also used in automotive and electrical components and electronics. Polystyrene's transparency makes it suitable for optic applications like lighting fixtures.
The two most common types of standard solid plastic polystyrene are general-purpose polystyrene (GPPS) and high-impact polystyrene (HIPS). GPPS is a hard, brittle, naturally clear homopolymer that can be coloured. It is often used for CD jewel cases. HIPS, on the other hand, is opaque, less brittle, and contains a polybutadiene rubber impact modifier. It is commonly used in household and food packaging.
Polystyrene is one of the most widely used plastics, with production reaching several million tonnes per year. Its versatility, durability, and low cost make it a popular choice for various applications. However, polystyrene's poor chemical resistance and slow biodegradation have raised environmental concerns, particularly regarding its use in disposable food packaging.
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$111.75 $149
Polyethylene Terephthalate (PET)
Polyethylene terephthalate, commonly known as PET, is a type of clear, durable, and versatile plastic. It is the most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foods, and thermoforming for manufacturing. It is also combined with glass fibre for engineering resins. In 2016, the annual production of PET was 56 million tons, with the biggest application being in fibres (over 60%), and bottle production accounting for about 30% of global demand.
PET is commonly recycled and has a resin identification code (RIC) of 1. It is defined by the National Association for PET Container Resources (NAPCOR) as:
> Polyethylene terephthalate items referenced are derived from terephthalic acid (or dimethyl terephthalate) and mono ethylene glycol, wherein the sum of terephthalic acid (or dimethyl terephthalate) and mono ethylene glycol reacted constitutes at least 90 percent of the mass of monomer reacted to form the polymer, and must exhibit a melting peak temperature between 225 °C and 255 °C, as identified during the second thermal scan in procedure 10.1 in ASTM D3418, when heating the sample at a rate of 10 °C/minute.
Depending on its processing and thermal history, PET may exist as an amorphous (transparent) or semi-crystalline polymer. As a semi-crystalline plastic, it is practically shatterproof and has an impressive high strength-to-weight ratio. It is also a strong gas and moisture blocker, and a great deterrent to liquor and solvents. PET is widely used in carbonated beverage bottles due to its high strength, toughness, good abrasion and heat resistance, low creep at elevated temperatures, and excellent dimensional stability. It is also used in artificial fibres for textiles, providing outstanding wear resistance, low moisture absorption, and durability.
PET is also used as a 3D printing filament, known as PETG (polyethylene terephthalate glycol). It is a clear amorphous thermoplastic that can be injection-moulded, sheet-extruded, or extruded as a filament for 3D printing. PETG is a popular material in industrial applications such as automotive and aeronautical sectors, as well as in the fabrication of traffic signs and LED spotlights.
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Frequently asked questions
Polyethylene, specifically in the form of LDPE and HDPE, is the most commonly used type of plastic worldwide. It is used in products such as plastic bags, food containers, and bottles.
LDPE stands for Low-Density Polyethylene. It is used in trays, food containers, work surfaces, machine components, protective cases, and laundry bags.
HDPE stands for High-Density Polyethylene. It is used in products such as milk jugs, shampoo bottles, plastic bags, and recycling bins.
PET stands for Polyethylene Terephthalate. It is the most commonly used plastic after polyethylene and is widely used in beverage bottles, food packaging, and polyester clothing.
PVC stands for Polyvinyl Chloride. It is the third-most produced synthetic plastic polymer. It is used in the construction industry for products such as pipes, flooring, and upholstery.
