Sofia Martinez
Plastic is derived from organic materials such as cellulose, coal, natural gas, salt, and crude oil. Crude oil is a complex mixture of thousands of compounds and needs to be processed before it can be used. The production of plastics involves the distillation of crude oil in an oil refinery, which separates the heavy crude oil into lighter components called fractions. Each fraction is a mixture of hydrocarbon chains, which differ in terms of their molecular size and structure. Plastics are formed through a process of polymerisation or polycondensation, which involves linking chains of molecules (monomers) together to create a large molecule (a polymer). The resulting polymers are then melted and blended to make formulations for plastics, which are then transformed into finished or semi-finished products through extrusion or moulding processes.
| Characteristics | Values |
|---|---|
| Definition | Plastic is a material that can be moulded into shape and then set. |
| Origin of the word | The word plastic comes from the Latin 'plasticus' and the Greek 'plastikos' and ['polymer'], meaning 'fit for moulding' or 'capable of being moulded'. |
| Composition | Plastics are polymers, which are made by linking chains of molecules (monomers) together to create a large molecule. |
| Plasticity | Plasticity is the property that allows a material to deform irreversibly without breaking. |
| Additives | Plastic is mixed with various chemicals and other materials, known as additives, to improve lifespan, workability or appearance. |
| Production | Plastic is derived from natural, organic materials such as cellulose, coal, natural gas, salt and crude oil. |
| Environmental impact | Plastic waste is a major environmental issue, with an estimated 8-12 million tons of plastic entering oceans annually. |
| Recycling | The majority of plastic is not recycled, with only ~9% of plastics recycled globally. |
| Future production | Going forward, plastics will be increasingly made from waste, renewable materials or CO2. |
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What You'll Learn
Plastic is formed from natural materials
Plastic is derived from natural, organic materials such as cellulose, coal, natural gas, salt, and crude oil. Crude oil is a complex mixture of thousands of compounds and needs to be processed before it can be used to make plastic. The production of plastics begins with the distillation of crude oil in an oil refinery, which separates the heavy crude oil into groups of lighter components, called fractions. Each fraction is a mixture of hydrocarbon chains (chemical compounds made up of carbon and hydrogen), which differ in terms of the size and structure of their molecules.
One of these fractions, naphtha, is a crucial compound for the production of plastics. Naphtha is a mixture of C5 to C10 hydrocarbons obtained from the distillation of crude oil. Steam cracking uses the feedstocks from hydrocarbons mixtures from various fractions such as reactant gases (ethane, propane, or butane) from natural gas, or liquids (naphtha or gas oil). For example, the decane hydrocarbon is cracked down into products such as propylene and heptane, the former of which is then used to make poly(propylene).
Raw materials are converted into monomers such as ethylene, propylene, and butene, which are then linked together to form long polymer chains in a process known as polymerization. These polymer chains are long flexible chains of chemical compounds and they represent the main structure of plastics. In this process, the two elements ethylene and propylene are transformed into the resins polyethylene and polypropylene thanks to the addition of a catalyst.
The word plastic comes from the Latin 'plasticus' and the Greek 'plastikos', both meaning 'fit for moulding'. Indeed, the plasticity of plastics allows them to be moulded, extruded, or pressed into solid objects of various shapes. The development of plastics started with natural materials that exhibited plastic properties, and the first fully synthetic plastic, Bakelite, was invented in 1907 by Leo Baekeland.
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Plastic is moulded into shape
The word plastic comes from the Latin "plasticus" and the Greek "plastikos", both of which refer to the ability of plastics to be moulded. Plasticity, in the context of materials science, refers to the deformability of the materials used in the manufacture of plastics, allowing them to be moulded into a variety of shapes.
Plastic is typically derived from natural, organic materials such as cellulose, coal, natural gas, salt, and crude oil. Crude oil is separated into groups of lighter components called fractions, which are then mixed with additives such as stabilizers, plasticizers, and dyes. The plastic is then moulded into shape through various processes, including:
Thermoforming
Thermoforming involves heating a large sheet of plastic until it is soft and flexible, then stretching it over a single-sided custom mould. Vacuum pressure or compressed air is then used to press the thermoplastic against the mould, creating the desired shape.
Injection Moulding
Injection moulding involves melting plastic into a liquid and injecting it into a mould using a highly pressurised injector. The plastic fills the mould, creating the desired shape, and is then cooled and ejected for finishing. This process is ideal for producing thin, hollow-walled pieces such as water bottles or soda bottles.
Blow Moulding
Blow moulding is similar to injection moulding, but instead of injecting the liquid plastic into the mould, a plastic tube (parison) is heated and inflated inside the mould to form hollow products such as bottles and toys.
Extrusion Moulding
Extrusion moulding involves forcing liquid plastic into a die to form a shape. This method is primarily used to manufacture long, straight pieces such as tubing, hoses, or pipes.
Compression Moulding
Compression moulding is often used with thermoset plastics, which change chemically when melted and cooled, resulting in a hard, rigid final product. The plastic resin is heated to a soft, putty-like state and placed into a heated mould. It is then pressed into shape by the mould and allowed to cool. This type of moulding is often used to manufacture plastics that replace metal, such as in vehicle parts, building materials, and machine parts.
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Plastic is derived from crude oil
Plastic is a synthetic material derived from natural, organic materials such as cellulose, coal, natural gas, salt, and crude oil. Crude oil is a complex mixture of thousands of compounds and needs to be processed before it can be used to form plastic. The production of plastic begins with the distillation of crude oil in an oil refinery, which separates the heavy crude oil into groups of lighter components called fractions. Each fraction is a mixture of hydrocarbon chains (chemical compounds made up of carbon and hydrogen), which differ in terms of the size and structure of their molecules. One of these fractions, naphtha, is a crucial compound for the production of plastics.
Naphtha is a mixture of C5 to C10 hydrocarbons and is decomposed thermally at high temperatures (around 800°C) in a steam cracker in the presence of water vapour. This process splits the naphtha into lighter hydrocarbons, such as ethylene and propylene, which are the main raw materials for oil-based plastics. These hydrocarbons are then subjected to heat, pressure, and catalysts, causing them to join together into long, repeating carbon chains through a process called polymerisation.
During polymerisation, monomers like ethylene and propylene are linked together to form long polymer chains. These monomers are derived from the cracking of hydrocarbons like decane, which breaks down into smaller products such as propylene and heptane. These monomers then undergo chemical polymerisation to produce polymers, which are thick, viscous substances known as resins. These resins are then employed to make plastic products through processes like injection moulding and blow moulding.
The additives are added during the compounding stage and can include substances like stabilisers, plasticisers, and dyes, which enhance the lifespan, workability, or appearance of the final product. The compounding process involves melt blending, where various blends of materials are mixed by melting, and the resulting mixture is pelletised. These pellets are then transformed into finished or semi-finished plastic products through extrusion or moulding processes. The final products can vary widely in terms of colour, flexibility, rigidity, and other physical properties.
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Plastic is made through polymerisation
Addition polymerisation involves adding monomers together in a long chain, one monomer at a time. This is achieved by introducing a catalyst, typically a peroxide. Common examples of addition polymers are polyethylene, polystyrene, and polyvinyl chloride.
Condensation polymerisation involves joining two or more different monomers by removing small molecules such as water. In this case, two monomers combine to form a dimer (two units) by releasing a byproduct. Dimers can then join to form tetramers (four units) and so on. These byproducts are necessary to be removed for the reaction to succeed.
The polymerisation process generates thick, viscous substances as resins, which are used to make plastic products. For example, ethylene is a gaseous hydrocarbon that, when subjected to heat, pressure, and a catalyst, joins together into long, repeating carbon chains. These joined molecules (polymers) are a plastic resin known as polyethylene (PE).
PE-based plastic is processed in a factory to make plastic pellets. The pellets are poured into a reactor, melted into a thick liquid, and cast into a mould. The liquid cools down to harden into a solid plastic and produce a finished product. The processing of the polymer also includes the addition of plasticizers, dyes, and flame-retardant chemicals.
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Plastic is made from waste and renewable materials
Plastic is a material with a wide range of uses and is valued for its durability, flexibility, and low production cost. However, the majority of plastic is derived from crude oil, which is a non-renewable resource. With the growing demand for limited oil reserves, there is a need to develop plastic from renewable resources.
One alternative to oil-based plastic is bio-based or bioplastic, which is made from renewable biomass, such as waste from the industry, carbohydrates, fats, and oils. Bioplastics can be used to create biodegradable products such as packaging films and bottles. For example, in 2019, a researcher from the University of Sussex created a transparent plastic film from fish-skin waste and algae, called MarinaTex. However, it is important to note that bioplastics may not always be a more sustainable option, as they require resources for production and may not biodegrade in all climates.
Another way to create plastic from renewable resources is through the use of inventive recovery technologies that transform plastic waste into valuable materials. This process, known as plastic recycling circularity, aims to keep used plastics out of the environment and in the circular economy. By converting plastic waste into new products through recycling technologies, less waste ends up in landfills or as environmental pollution.
Additionally, plastic can be formed through compounding, where various blends of materials are melt-blended and then pelletized. These pellets are then processed into plastic objects of unique designs, sizes, shapes, and colours. This process allows for the creation of plastic products with targeted properties such as toughness, flexibility, elasticity, and colour.
Overall, there is a growing trend towards developing plastic from renewable and waste materials to reduce the environmental impact of plastic production and promote sustainability.
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Frequently asked questions
Plastic is a material made from polymers, which are long chains of molecules called monomers. The word 'polymer' means 'of many parts'.
Polymers are organic materials, like wood or wool. They are made from natural, organic materials such as cellulose, coal, natural gas, salt and crude oil.
The process of making plastic involves joining monomers together into a chain through a process called polymerisation. There are two methods of polymerisation: addition and condensation.
Polymerisation is a process that creates thick, viscous substances as resins, which are used to make plastic products.
Plastic is used to make a wide range of products, from packaging and food containers to vehicle parts, machine parts, and construction materials.
