Maya Ellison
Plastics are a group of materials that are either synthetic or naturally occurring and can be shaped when soft and hardened to retain a given shape. They are chiefly represented by polyethylene, polypropylene, polyvinyl chloride, and polystyrene. The scientific names of plastics are derived from their chemical composition and engineering behaviour. For example, polyethylene is abbreviated as PE and has the IUPAC name polyethene or poly(methylene), derived from its ingredient rather than the resulting chemical compound. Polyvinyl chloride, commonly known as PVC, is another widely used plastic with various applications. Other plastics include polycarbonate, polymethyl methacrylate (PMMA), and polytetrafluoroethylene (Teflon). These names are based on the chemical structure of the polymer's backbone and side chains, with different molecular groups influencing their properties.
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What You'll Learn
Plastic is a group of synthetic or natural materials
Plastics are a group of synthetic or natural materials that are formed by the polymerization of small molecules called monomers. These monomers combine to create long chains of polymers, which are the building blocks of plastics. The word "polymer" comes from the Greek words "poly," meaning many, and "meros," meaning parts or units. These polymers can be natural, such as cellulose and latex, or synthetic, like polyethylene and polyvinyl chloride (PVC).
The first synthetic polymer was invented in 1869 by John Wesley Hyatt, who treated cellulose derived from cotton fiber with camphor to create a plastic that could be crafted into various shapes. However, the first fully synthetic plastic, Bakelite, was invented in 1907 by Leo Baekeland. Baekeland coined the term "plastics" and his invention was durable, heat-resistant, and suitable for mass production. Since then, dozens of different types of plastics have been produced, including polyethylene, polypropylene, and PVC, each with unique properties and applications.
Plastics are classified based on their chemical structure, particularly the backbone chains of their polymers. These backbone chains are composed of carbon atoms, sometimes with attached oxygen, nitrogen, or sulfur atoms. The structure of these chains influences the properties of the resulting plastic. For example, the degree of crystallinity in polymers affects their strength, melting point, and light transmission.
Plastics have become dominant since the early 20th century due to their adaptability and desirable properties such as low weight, durability, flexibility, and low cost. They are used in a wide range of applications, from packaging and construction to automobiles, furniture, and medical devices. However, their slow decomposition rate has led to widespread environmental concerns, with plastic pollution and microplastics affecting natural ecosystems.
While most plastics are produced from natural gas and petroleum, there is a growing trend towards using renewable resources like polylactic acid. The ability to customize the properties of plastics through different molecular groups and additives has contributed to their versatility and widespread use.
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Plastic is a polymer, made of carbon atom chains
Plastic is a synthetic material that can be moulded into various shapes and used for a wide range of applications. It is a polymer, made of carbon atom chains. The word 'polymer' comes from the Greek words 'poly', meaning 'many', and 'meros', meaning 'parts' or 'units'. Polymers are long chains of atoms linked by covalent bonds, as proposed by Hermann Staudinger in 1920. This structure allows plastics to be stretched without breaking, a property that is due to the long carbon atom chains.
Most plastics contain organic polymers, which are formed from chains of carbon atoms, with or without attached oxygen, nitrogen, or sulfur atoms. These chains are made up of thousands of repeating units formed from monomers. Each polymer chain consists of several thousand repeating units, with a backbone that links a large number of repeat units together. The backbone is the main path of the chain, and different molecular groups called side chains hang from it, influencing the properties of the polymer.
The process of combining monomers to form polymers is called polymerization. Monomers are small molecules, the smallest being two carbon atoms, which are chemically reacted to form polymers. During polymerization, monomers are added together, and free radicals are introduced to initiate the process. Free radicals are highly reactive atoms or ions with a single unpaired electron. They attack the double bond between carbon atoms and form new bonds, creating a chain reaction that results in the formation of a polymer chain.
Plastics can be classified into two categories based on their chemical composition. The first category includes plastics made of polymers with only aliphatic (linear) carbon atoms in their backbone chains, such as polypropylene. The second category consists of heterochain polymers, which contain atoms like oxygen, nitrogen, or sulfur in their backbone chains, in addition to carbon. An example of a heterochain polymer is polycarbonate, which contains two aromatic (benzene) rings in its molecules.
The versatility of plastics lies in their ability to be engineered for specific applications. Synthetic polymers can be designed with specific properties, such as strength, flexibility, and colour, making them unique materials. This customisation of properties is achieved by varying the structure of the side chains attached to the backbone of the polymer. Additionally, plastics are lightweight, durable, flexible, chemically resistant, low-cost, and easy to process, making them suitable for a wide range of applications, from medical devices to construction materials.
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Plastic is classified by polymer backbone and side chains
Plastics are a group of materials that are either synthetic or naturally occurring. They can be shaped when soft and then hardened to retain the given shape. Most plastics contain organic polymers, which are formed from chains of carbon atoms, with or without the attachment of oxygen, nitrogen, or sulfur atoms. These chains are made up of thousands of repeating units formed from monomers. Each polymer chain consists of several thousand repeating units.
The backbone of a polymer is the part of the chain that is on the main path, linking together a large number of repeat units. The continuously linked backbone of a polymer used for the preparation of plastics consists mainly of carbon atoms. A simple example of this is polyethylene, whose monomer is ethylene. The backbone can also contain other elements, such as silicon, which forms familiar materials such as silicones, or oxygen, which is commonly present in polymer backbones such as those of polyethylene glycol.
To customize the properties of a plastic, different molecular groups called side chains hang from the backbone. These side chains are usually attached to the monomers before the monomers themselves are linked together to form the polymer chain. The structure of these side chains influences the properties of the polymer. For example, dipole-dipole bonding side chains enable the polymer for high flexibility. Side chains can also lend the polymer to ionic bonding or hydrogen bonding.
Plastics are usually classified by the chemical structure of the polymer's backbone and side chains. Important groups classified in this way include the acrylics, polyesters, silicones, polyurethanes, and halogenated plastics. Block copolymers have long sequences of different monomer units, with polymers containing two or three blocks of two distinct chemical species. Graft or grafted copolymers contain side chains or branches whose repeat units have a different composition or configuration than the main chain.
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Plastic is moulded, extruded, or pressed into solid forms
Plastic is a general term for a wide range of synthetic or semi-synthetic materials that utilize organic polymers to create materials with a vast array of characteristics. The defining characteristic of plastics is their plasticity, which allows them to be moulded, extruded, or pressed into solid forms.
Moulding
Injection moulding is the most common modern method of manufacturing plastic parts. Invented in 1872, the process involves using a ram or screw-type plunger to force molten plastic or rubber into a mould cavity. As the plastic cools, it solidifies and conforms to the contour of the mould. Injection moulding is ideal for producing high volumes of identical objects. The process can also be used to create plastic parts with protruding metal screws, a technique known as insert moulding.
Extrusion
The plastic extrusion process involves five steps. First, raw plastic materials are loaded into a hopper and fed into a heated cylindrical chamber called an extruder. The plastic is then heated and forced through a small opening called a die, which shapes the plastic. As the plastic is extruded, it is fed onto a conveyor belt to cool. Finally, the plastic flows smoothly from the cylindrical profile of the extruder into its final shape.
Pressing
Plastic pressing involves using a machine called an injection moulding press to shape plastic. The process is similar to injection moulding, where molten plastic is injected into a mould using a plunger. However, it is unclear if the pressing process also involves cooling the plastic to solidify it into the desired shape.
Through these processes, plastic can be moulded, extruded, or pressed into a diverse range of solid forms. The adaptability of plastics, combined with their low weight, durability, flexibility, chemical resistance, low toxicity, and low-cost production, has led to their widespread use in various industries, including automobiles, packaging, construction, and electronics.
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Plastic is thermoplastic or thermosetting
Plastic is a group of synthetic or naturally occurring materials that can be moulded when soft and hardened to retain a given shape. Plastics are polymers, which are substances made of many repeating units known as monomers. The word polymer comes from the Greek words "poly", meaning many, and "meros", meaning parts or units.
Polymers can be formed through two types of polymerization: addition polymerization and condensation polymerization. Addition polymerization involves three basic steps: initiation, propagation, and termination. During this process, monomers join by attaching to the end of the last unit in the chain, similar to linking paper clips together. Examples of plastics formed through addition polymerization include polyethylene, polystyrene, and acrylic. These polymers are typically thermoplastic in nature, meaning they can be heated and softened or hardened when cooled. Thermoplastics can be easily processed, reprocessed, or recycled.
On the other hand, condensation polymerization involves the joining of monomers with the elimination of a small molecule. Examples of condensation polymers include nylons, some polyesters, and urethanes. These polymers can be either thermoplastic or thermosetting. Thermoplastics and thermosetting plastics are two distinct types of polymers that behave differently when exposed to heat.
Thermoplastics, such as those used in reusable plastic containers, piping systems, and electrical cable insulation, can be repeatedly heated, cooled, and reshaped without altering their chemical structure. They typically have low melting points, making them suitable for remoulding or recycling.
Thermosetting plastics, also known as thermosets, undergo a chemical reaction when heated, resulting in a three-dimensional network of irreversibly bonded molecules. This process is what sets them apart from thermoplastics, as once formed, thermosets cannot be melted or reshaped. Thermosets are commonly used in construction equipment panels, electrical components, insulators, and motor components.
While thermoplastics and thermosets sound similar, they have distinct properties and applications. Thermosets have greater physical properties than thermoplastics and can withstand higher temperatures. However, thermosets cannot be remoulded or recycled, while thermoplastics offer the advantage of being easily reheated, reshaped, and cooled without undergoing chemical changes.
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Frequently asked questions
Plastic is a general term for a group of synthetic or processed materials that are mostly thermoplastic or thermosetting polymers of high molecular weight. These polymers are often referred to as "resins".
Common plastics include polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), and polystyrene (PS). The scientific name for polyethylene, the most common plastic, is polyethene or poly(methylene).
Polymers are substances made of many repeating units, or monomers. They are the building blocks of plastics and can be natural or synthetic.
Polymers used in plastics include polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), and polyethylene terephthalate (PET). These polymers have unique properties and can be combined to create a wide range of plastic products.
