Chloe Zhang
Plastic is a synthetic or semi-synthetic material that is used in a wide variety of applications. It is derived from natural, organic materials such as cellulose, coal, natural gas, salt, and, most commonly, crude oil. The process of making plastic involves the extraction, refining, polymerization, and mixing of these materials. Crude oil, for example, is heated in a furnace and sent to a distillation unit to separate the lighter components, one of which, naphtha, is crucial for plastic production. Polymerization involves bonding monomers to form long polymer chains, which are then melt-blended and formed into plastic pellets, which can be extruded or moulded into various shapes. The versatility, durability, low cost, and ease of production of plastics have led to their widespread use around the world.
| Characteristics | Values |
|---|---|
| Main Components | Carbon, oxygen, hydrogen, nitrogen, chlorine, sulfur |
| Main Sources | Petroleum, natural gas, cellulose, coal, mineral, water, plants |
| Plastic Types | Synthetic, semi-synthetic, biobased |
| Plasticising Process | Extraction, refining, polymerisation, polycondensation, compounding, moulding |
| Plasticising Machinery | Extruder, twin-screw extruder, processing machine |
| Plastic Products | Polyvinyl chloride (PVC), polyethylene, polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), high-density polyethylene (HDPE), low-density polyethylene (LDPE) |
| Plastic Applications | Packaging, construction, biomedical devices, aviation, textiles, furniture, automobiles, electronics, housewares, automotive components, medical tools |
| Plastic Qualities | Lightweight, durable, flexible, nontoxic, low cost, impact-resistant, strong, stable, transparent, resilient, corrosion-resistant, colourful |
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What You'll Learn
Plastic's synthetic nature
Plastics are a range of synthetic or semi-synthetic materials that use polymers as their main ingredient. The world's first fully synthetic plastic was Bakelite, invented in 1907 by Leo Baekeland, who coined the term "plastics". Baekeland used phenol, an acid derived from coal tar, to create the first plastic derived from fossil fuels rather than plants or animals. This breakthrough opened the floodgates to a torrent of now-familiar synthetic plastics, including polystyrene, polyester, polyvinyl chloride (PVC), polythene, and nylon.
Synthetic plastics are derived from crude oil, natural gas, or coal. While bio-based plastics come from renewable products such as carbohydrates, fats, and oils. The production of plastics begins with the distillation of crude oil in an oil refinery, which separates the heavy crude oil into lighter components called fractions. One of these fractions, naphtha, is crucial for plastic production. Two main processes are used to produce plastics: polymerisation and polycondensation. In polymerisation, monomers such as ethylene and propylene are linked together to form long polymer chains. Polycondensation involves joining two or more different monomers by removing small molecules such as water, and it also requires a catalyst for the reaction to occur.
The polymers' shape gives plastics their plasticity, allowing them to be moulded into various shapes. This adaptability, combined with their lightweight, durable, flexible, non-toxic, and inexpensive nature, has led to their widespread use around the world. However, the slow decomposition rate of plastics in natural ecosystems has also raised widespread environmental concerns. Most plastic produced has not been reused, and plastic pollution is a significant issue, particularly in oceans.
To address these concerns, strategies such as recycling and degradation (depolymerization or deconstruction) are being explored to improve sustainability through life-cycle management. Mechanical reprocessing, for example, can have a low climate impact, but it cannot handle the volumes and diversity of plastic waste on its own. Additional routes, such as selective dissolution and melt-blending with compatibilization, are necessary to improve circularity and end-of-life design.
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Plastic's origin in nature
Plastic is a term used to describe materials that can be formed and moulded under heat and pressure. The word plastic derives from the Ancient Greek πλαστικός (plastikos), meaning "capable of being shaped or moulded". Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as their main ingredient.
Before the widespread adoption of plastics, materials such as wood, metal, glass, ceramics, and animal-derived materials such as horn, bone, and leather were used. Natural materials from the bark of the rubber tree, gum (latex resin), were also used, but these were sticky and mouldable, and not useful for storage. In the 18th century, Charles Goodyear accidentally discovered rubber by adding sulphur to hot crude rubber, making it resilient and elastic.
Natural plastics such as horn, tortoiseshell, amber, rubber, and shellac have been worked with since ancient times. The first manufactured plastic, Parkesine, was invented in 1862 by Alexander Parkes. It was a cheap and colourful substitute for ivory or tortoiseshell, made from cellulose nitrate—cotton fibres dissolved in nitric and sulphuric acids and then mixed with vegetable oil.
The world's first fully synthetic plastic was Bakelite, invented in New York in 1907 by Leo Baekeland, who coined the term "plastics". Since then, dozens of different types of plastics have been produced, such as polyethylene, which is widely used in product packaging, and polyvinyl chloride (PVC), used in construction and pipes because of its strength and durability.
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Polymerisation and polycondensation
The production of plastics involves two main processes: polymerisation and polycondensation. Both these processes require specific catalysts.
Polymerisation
Polymerisation involves linking monomers such as ethylene and propylene together to form long polymer chains. In condensation polymerisation, two or more monomers combine to form a dimer (two units) by releasing a byproduct. These byproducts are necessary for the success of the reaction and are often valuable raw materials that can be recycled back into the feedstream. The most common byproduct is water, which can be treated and disposed of easily. Dimers can then join to form tetramers (four units) and so on. Common examples of condensation polymers include nylon, polyester, and polyurethane.
Polycondensation
Polycondensation is a chemical process for producing a polymer by linking single or multiple kinds of monomers to form long chains, releasing water or a similar simple substance. It is a form of step-growth polymerization, where linear polymers are produced from bifunctional monomers. Polycondensation can be homopolycondensation, where the minimum possible number of monomer types (usually two) participates, or copolycondensation, where at least one more monomer participates. Polycondensation can also be classified as equilibrium (reversible) polycondensation, where the degree of completion and the mean length of the macromolecules are limited by the equilibrium concentration of the reagents and reaction products. Solution polycondensation is a technique that allows the process to be carried out under relatively mild conditions, which is important for the synthesis of high-melting polymers as high reaction temperatures can destroy monomers and polymers.
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Plastic's lightweight nature
Plastic is a synthetic material derived from crude oil, natural gas, or coal. It can also be made from renewable sources such as carbohydrates, fats, and oils. The production of plastics involves the distillation of crude oil in an oil refinery, separating it into lighter components called fractions. One of these fractions, naphtha, is crucial for plastic production.
Plastics are known for their lightweight nature, among other desirable properties such as durability, flexibility, non-toxicity, and low production costs. This lightweight quality has made plastics highly useful in various applications, including packaging, construction, and electronics.
In packaging, plastics like polyethylene are widely used due to their lightweight and mouldable nature, making them ideal for product packaging. Polyvinyl chloride (PVC), another commonly used plastic, is valued in construction and pipes for its strength, durability, and lightweight characteristics.
The lightweight nature of plastics has also been leveraged in the development of ultra-lightweight plastic electronics. Researchers have created flexible electronic foils that are light-as-a-feather and can conform to any desired shape. These foils, deposited on ultra-lightweight plastic films, have a total thickness of just two micrometres and can be used in smart, mobile, and wearable devices, as well as biomedical applications.
While plastics offer significant advantages due to their lightweight property, they also pose environmental concerns due to their slow decomposition rate in natural ecosystems. Efforts are being made to develop sustainable alternatives, such as all-natural bioinspired structural materials that are lightweight, strong, and environmentally friendly.
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Plastic's durability
Plastic is an indispensable part of everyday life. Plastic products are lightweight, durable, flexible, non-toxic, and inexpensive to produce. They are used for packaging, bottles, bags, and technical moulded parts.
However, the durability of plastic becomes a curse when it is deposited in the environment. Plastic has a slow decomposition rate in natural ecosystems, and most plastic produced has not been reused or recycled. It ends up in landfills or as plastic pollution, with marine plastic creating garbage patches in oceans.
The chemical structure of plastic is foreign to nature, and microorganisms that break down toxic substances like bacteria and fungi have not been able to successfully dispose of plastic. This is because plastics are polymers, which consist of very long chains of molecular units with carbon as the defining element, almost always combined with hydrogen, and sometimes nitrogen, oxygen, fluorine, or chlorine. These long molecular chains make polymers strong, durable, and resistant to water.
While biodegradable plastic does exist, it is more expensive and cannot be used in applications where resilience to decomposition is required. The best way to dispose of plastic currently is through complete combustion, which produces significant amounts of useful heat.
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Frequently asked questions
Plastic is a synthetic or semi-synthetic material that usually comes from petrochemicals or things like cellulose and starch. It is derived from natural, organic materials such as cellulose, coal, natural gas, salt, and crude oil.
The process of making plastic involves the extraction, refining, polymerization, and mixing of materials. The first step is the extraction of raw materials, such as petroleum and natural gas. The second step is the refining process, which transforms crude oil into different petroleum products. These products are then converted to yield useful chemicals, including monomers. Polymerization involves linking monomers such as ethylene and propylene together to form long polymer chains. Condensation polymerization is the process of bonding two or more monomers by removing small molecules like water.
Some examples of plastic include polyethylene, polyvinyl chloride (PVC), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), high-density polyethylene (HDPE), and low-density polyethylene (LDPE).
