Sofia Martinez
Plastic is a catch-all term for a range of synthetic or semisynthetic chemical substances composed primarily of polymers. These polymers are formed by covalently joining many monomer units together in the form of chains. The resulting polymer chains can be composed of various elements, including carbon, hydrogen, oxygen, nitrogen, sulphur, and chlorine. The plasticity of these polymeric materials allows them to be moulded, extruded, or pressed into a diverse range of solid forms, giving rise to the many products we encounter daily.
| Characteristics | Values |
|---|---|
| Chemical composition | Polymers with aliphatic (linear) carbon atoms in their backbone chains or heterochain polymers with atoms such as oxygen, nitrogen, or sulfur in their backbone chains |
| Types | Synthetic plastics, biobased plastics, thermoplastics, condensation polymers, silicone |
| Additives | Stabilizers, plasticizers, dyes, polymer blends, masterbatch granules |
| Production process | Injection molding, blow molding, rotational molding, compounding, extrusion, pelletizing, molding |
| Properties | Low density, low electrical conductivity, transparency, toughness, durability, flexibility, chemical resistance, low toxicity, low cost |
| Disposal | Burning can release toxic gases, recycling is encouraged |
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What You'll Learn
- Plastic is a polymeric material with moulding capabilities
- Plastics are categorised by their chemical composition
- Common plastics include polyethylene, polyethylene terephthalate, and polypropylene
- Additives are blended into plastics to improve lifespan, workability, and appearance
- Plastic is derived from crude oil, natural gas, coal, or renewable resources
Plastic is a polymeric material with moulding capabilities
Plastic is a term used to refer to a wide range of synthetic or semisynthetic polymeric materials composed primarily of polymers. These polymers are usually organic and of high molecular weight, and they are often mixed with other substances. The word "plastic" comes from the Latin "plasticus" and the Greek "plastikos," both of which mean "capable of moulding." This property of plasticity, often found in combination with other characteristics such as low density, low electrical conductivity, transparency, and toughness, allows plastics to be moulded into a great variety of products.
Plastics can be divided into two main categories based on their chemical composition: those made up of polymers with only aliphatic (linear) carbon atoms in their backbone chains and those made up of heterochain polymers. The first category includes most commodity plastics, such as polypropylene, while the second category includes most engineering plastics, like polycarbonate.
The process of creating plastics involves the use of condensation polymerisation, where two or more different monomers are joined by removing small molecules like water, forming chains like pearls on a string. This process requires a catalyst and is known as step growth. Common examples of condensation polymers include polyester and nylon.
The versatility of plastics is further enhanced by the addition of various blends of materials and additives. These additives, such as stabilizers, plasticizers, and dyes, are introduced during the compounding stage to improve the lifespan, workability, and appearance of the final product. The compounding process involves melting and mixing the plastic with additives, and it is carried out by specialised companies called Compounders.
The moulding capabilities of plastics are utilised through various techniques such as injection moulding, blow moulding, and rotational moulding. Injection moulding involves injecting molten plastic into a mould cavity under high pressure, while blow moulding uses a heated plastic tube that is inflated inside a mould to create hollow products. Rotational moulding combines heating with rotation, allowing plastic powder to melt and stick to the walls of the mould to form thick-walled hollow parts. These moulding processes enable the creation of a diverse array of solid forms, contributing to the widespread use of plastics in our daily lives.
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Plastics are categorised by their chemical composition
Plastic is a general term for a wide range of synthetic or semisynthetic materials composed primarily of polymers. These polymers are large molecules formed by covalently joining many smaller molecules called monomers. The monomers are joined together in the form of chains, similar to pearls on a string. The word "polymer" itself comes from the Greek "poly" meaning "many" and "mer" meaning "repeating unit".
Plastics can be categorised into two distinct groups based on their chemical composition. The first category includes plastics made up of polymers containing only aliphatic (linear) carbon atoms in their backbone chains. An example of this type of plastic is polypropylene, where a methyl group (CH3) is attached to every other carbon atom. The second category consists of plastics made up of heterochain polymers, which contain atoms such as oxygen, nitrogen, or sulfur in their backbone chains, in addition to carbon. Polycarbonate, composed of molecules containing two aromatic (benzene) rings, is an example of a heterochain polymer.
The versatility of plastics comes from the fact that they can be moulded, extruded, or pressed into a diverse range of solid forms. This property, known as plasticity, is a result of the chemical composition of polymers and the ability to vary different parameters such as elements, monomer types, and their arrangement. By changing these parameters, the shape, molecular weight, and other chemical/physical properties of the polymer can be altered to suit specific applications.
Plastics are derived from various sources, including crude oil, natural gas, coal, and renewable resources such as carbohydrates, fats, oils, and polylactic acid. The specific chemical composition of a plastic determines its properties and applications. For example, polyethylene terephthalate (PET) is commonly used in soft drink bottles due to its lightweight and tough nature, while polyvinyl chloride (PVC) is used in sanitary plumbing because of its durability and flexibility.
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Common plastics include polyethylene, polyethylene terephthalate, and polypropylene
Plastic is a catch-all term for a wide range of synthetic or semisynthetic materials composed primarily of polymers. These polymers are usually made from natural gas and petroleum, but an increasing number are produced from renewable resources, such as polylactic acid.
Polyethylene (PE) is a widely used plastic with a simple chemical structure, making it very easy and cheap to process. It is often used for plastic shopping bags and plastic films, and to make some toys. It is formed from many monomers of ethene. Polyethylene comes in a number of varieties, including high-density polyethylene (HDPE) and low-density polyethylene (LDPE).
Polyethylene terephthalate (PET) is another commonly used plastic, often utilised for food and drink packaging. It is particularly good at preventing oxygen from getting in and spoiling the product, and at keeping carbon dioxide in carbonated drinks. PET is used to make soft-drink bottles, and it is also the most likely type of plastic to be recycled. However, it does contain antimony trioxide, a carcinogen.
Polypropylene (PP) is a type of plastic that offers an excellent balance of thermal, chemical, and electrical properties. It is an economical alternative to HDPE or ABS. The structure of polypropylene can be used as an example of the first category of plastics mentioned above: those made up of polymers having only aliphatic (linear) carbon atoms in their backbone chains. Attached to every other carbon atom in polypropylene is a pendant methyl group (CH3).
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Additives are blended into plastics to improve lifespan, workability, and appearance
Plastic is a polymeric material that can be moulded or shaped, usually by applying heat and pressure. This property of plasticity, often found in combination with other special properties such as low density, low electrical conductivity, transparency, and toughness, allows plastics to be made into a wide variety of products.
To improve the lifespan, workability, and appearance of plastics, various additives are blended into them. These additives are chemical substances that enhance the properties of plastics and make them more useful. Additives can be mineral-based or natural substances that improve strength and reduce costs. They can also be used to prevent the decomposition of polymers during processing by acting as heat stabilisers. For example, antioxidants help extend the lifespan of plastics by preventing them from bonding with oxygen molecules and growing mould or bacteria. Light and heat stabilisers are also used to make plastics more durable by protecting them from the elements.
To improve workability, internal lubricants are added to plastics to lower the viscosity and improve the flow of the material during processing. High-polymeric processing aids also improve the flowability of PVC compounds. Additionally, acid scavengers are added to plastics to prevent unwanted chemical reactions, making the plastic parts more durable and less reactive to external chemicals.
Additives also play a crucial role in enhancing the appearance of plastics. Pigments are commonly used as additives to introduce colours and specific shades to plastics. There are thousands of pigment options available, allowing for a wide range of customisation.
Overall, additives are essential in improving the lifespan, workability, and appearance of plastics. They make plastics safer, tougher, and more colourful, while also reducing production costs and prolonging the lifespan of plastic products.
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Plastic is derived from crude oil, natural gas, coal, or renewable resources
Plastic is a term used to refer to a wide range of synthetic or semisynthetic materials composed primarily of polymers. These polymers are derived from natural, organic materials such as cellulose, coal, natural gas, salt, and crude oil. Crude oil, in particular, is a complex mixture of thousands of compounds that need to be processed before they can be used to create plastic.
The production of plastics derived from crude oil begins with the distillation of crude oil in an oil refinery. This process involves heating the oil in a furnace and sending it to a distillation unit, where heavy crude oil separates into lighter components called fractions. One of these fractions, naphtha, is crucial for plastic production.
Natural gas is another significant source of feedstock for plastic production. It provides the necessary hydrocarbons, such as ethylene, propylene, and butylenes, which serve as direct inputs for plastics manufacturing. Additionally, natural gas processing yields feedstocks that contribute to the creation of plastics.
Coal, although not as prominent as crude oil and natural gas, is also used in the production of synthetic plastics. It provides the carbon necessary for forming the hydrocarbon base of plastics.
In recent years, there has been a growing trend toward producing plastics from renewable resources. These biobased plastics are derived from renewable products such as carbohydrates, fats, and oils. Polylactic acid, for example, is a renewable resource that can be used to create plastic.
Overall, the derivation of plastics from crude oil, natural gas, coal, or renewable resources involves complex processes that transform these raw materials into the versatile and widely used substance known as plastic.
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Frequently asked questions
Plastic is a catch-all term for a range of synthetic or semisynthetic chemical substances composed primarily of polymers.
Polymers are the molecules that make up plastics. They are formed by covalently joining many monomer-units together in the form of chains.
Some examples of polymers used in plastics are polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polyethylene (PE).
Most plastics are produced from natural gas and petroleum, but a growing number are produced from renewable resources like polylactic acid. Synthetic plastics are derived from crude oil, natural gas, or coal, while bio-based plastics come from renewable products like carbohydrates, fats, and oils.
