Alexei Volkov
Plastic is a broad category of synthetic and semi-synthetic materials that contain polymers as their primary constituent. The chemical composition of plastics varies, but the majority 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. The versatility of plastics is due to their plasticity, which allows them to be moulded, extruded, or pressed into a diverse range of solid forms. While most plastics are produced from non-renewable natural gas and petroleum, some are now being produced from renewable resources such as polylactic acid.
| Characteristics | Values |
|---|---|
| Chemical composition | Polymers made of carbon and hydrogen, often mixed with additives for different properties |
| Additives | Colorants, plasticizers, stabilizers, fillers, reinforcements, anti-degradants, flame retardants |
| Molecular weight | Between 10,000 and 500,000 amu; higher molecular weights are associated with longer molecular chains and greater entanglement |
| Polymerization | Addition and condensation |
| Polymer chains | Repeating units of at least 1,000 links |
| Polymer structure | Carbon chains with or without oxygen, nitrogen, or sulfur atoms; chains are entangled within each other |
| Types | Thermoplastics, thermosetting polymers, engineering plastics, commodity plastics, specialty resins, high-performance plastics |
| Thermoplastics | Polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC) |
| Thermosetting polymers | Epoxy resin, polyimide, Bakelite |
| Engineering plastics | Polyacetal, polyamide (nylon), polytetrafluoroethylene (Teflon), polycarbonate, polyphenylene sulfide, polyetheretherketone |
| Commodity plastics | Polyurethanes (PURs) |
| High-performance plastics | Aramids, ultra-high-molecular-weight polyethylenes (UHMWPE), polyetheretherketone (PEEK), polyetherimide (PEI) |
| Raw materials | Crude oil, natural gas, coal |
| Production process | Extraction of raw materials, refining, distillation, cracking, polymerization, moulding |
| Production by-products | Alkenes/alkanes |
| Production waste | Between 1950 and 2017, 9.2 billion metric tons of plastic were produced, with over 400 million metric tons produced in 2023 alone |
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What You'll Learn
Plastic is a broad category of synthetic materials
The polymer used to make plastic is usually a chain of carbon atoms, with or without attached oxygen, nitrogen, or sulphur atoms. These chains are formed from monomers, which are bonded together through a chemical reaction, resulting in a three-dimensional network of long individual polymer chains. The monomers may be arranged in a linear fashion, or they may form long side chains off the main backbone, resulting in a branched structure. The polymerization process can be performed in two ways: steam cracking and catalytic cracking. Steam cracking uses high temperatures and pressure to break hydrocarbon chains without a catalyst, while catalytic cracking uses a catalyst to achieve the same result at lower temperatures and pressures.
Plastics are classified based on the chemical structure of the polymer's backbone and side chains. Important groups classified in this way include acrylics, polyesters, silicones, polyurethanes, and halogenated plastics. The properties of plastics depend on their chemical composition, the arrangement of subunits, and the processing method. The polymer's backbone and side chains influence its properties, with the side chains hanging from the backbone to customize the characteristics of the plastic.
Plastics can also be classified into two distinct categories based on their chemical composition: thermoplastics and thermosetting polymers (thermosets). Thermoplastics can be reshaped by heating multiple times without undergoing a chemical change, while thermosets can only melt and take shape once. After solidifying, thermosets stay solid and retain their shape permanently. If reheated, they decompose instead of melting.
The versatility of plastics has led to their widespread use, with approximately a third of plastic production being used for packaging, and another third for siding and piping. However, the environmental impact of plastics, particularly their resistance to biodegradability, has become a significant issue.
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Polymers are the primary component of plastics
The structure of polymers can vary, with different arrangements of monomers and the presence of additives, resulting in unique characteristics and properties. For example, the monomers can form straight chains or branched structures with side chains attached to the main backbone. The degree of crystallinity in the polymer also affects its properties, influencing its transparency and strength. The polymerization process itself can introduce variation, resulting in polymer chains of unequal lengths, known as polydispersity.
The versatility of polymers allows plastics to exhibit a wide range of properties, including low weight, durability, flexibility, chemical resistance, low toxicity, and low-cost production. Different types of polymers, such as carbon-chain and heterochain polymers, exhibit varying characteristics. High-performance plastics, for instance, can withstand high temperatures, are highly resistant to chemical corrosion, and possess excellent mechanical and electrical properties.
The properties of plastics are also influenced by the additives mixed with the polymers. Additives such as fillers, reinforcements, stabilizers, and plasticizers can enhance the mechanical, thermal, and chemical resistance properties of plastics. The selection of the correct type of plastic depends on the specific requirements of the application. Thermoplastics, for instance, can be reshaped by heating multiple times, while thermosetting polymers solidify permanently and cannot be remelted and reformed.
The production of plastics involves extracting raw materials, refining them to obtain monomers, and then polymerizing the monomers to create polymer chains. These chains are then processed into the desired plastic products. The widespread use of plastics has led to significant environmental concerns due to their resistance to biodegradability.
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Plastic's chemical composition varies widely
Plastics are polymers, which are large molecules made up of repeating units known as monomers. The monomers are bonded together through a chemical reaction known as polymerization, which results in the formation of multiple individual polymer chains. These chains are made of carbon atoms, with or without the attachment of oxygen, nitrogen, or sulfur atoms. The polymer used to make plastic is almost always mixed with additives, including colorants, plasticizers, stabilizers, fillers, and reinforcements, which affect the plastic's chemical composition, properties, and cost.
The polymerization process is carefully controlled but has some inherent variation, resulting in polymer chains of unequal length. This variation in length is called polydispersity. Commercial plastics have polymers with a molecular weight distribution, which represents the relative amounts of polymers of different molecular weights within a given specimen. The molecular weight of a polymer is the sum of the atomic weights of the atoms comprising it. For example, the molecular weight of polyethylene is calculated by multiplying the molecular weight of the repeating ethylene functional group by the number of units in the chain.
The properties of plastics depend on the chemical composition of the subunits, the arrangement of these subunits, and the processing method. The polymer's backbone and side chains determine how plastics are classified chemically. The backbone is the part of the chain that links together a large number of repeat units, while different molecular groups called side chains hang from this backbone, influencing the polymer's properties. The degree of crystallinity in a polymer, or the arrangement of its subunits, determines its transparency, with higher crystallinity resulting in less light passing through.
Plastics can be divided into two distinct categories based on their chemical composition: carbon-chain and heterochain polymers. For each polymer type, there can be many subtypes, as industrial producers can offer variations for specific applications. Plastics can also be classified as thermoplastics or thermosetting polymers. Thermoplastics do not undergo a chemical change when heated and can be molded repeatedly, while thermosetting polymers can only melt and take shape once, permanently solidifying after they cool. Thermosetting polymers are also known as thermosets and have infinite molecular weight, while thermoplastics typically have a molecular weight between 20,000 and 500,000 atomic mass units.
The raw materials for plastic production are largely derived from crude oil and natural gas, which are separated into lighter components through distillation. One of these components, naphtha, is crucial for plastic production. The raw materials are then converted into monomers, which are joined together through polymerization to form long chains of carbon atoms. These chains are then processed into resins, which are used to make plastic products.
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Plastic is derived from natural gas, petroleum, and renewable resources
Plastic is a polymeric material that can be moulded or shaped, with properties like low density, low electrical conductivity, transparency, and toughness. The chemical composition of plastic varies based on its type and the process used to create it. While most plastics are derived from natural gas and petroleum, a growing number are produced from renewable resources.
Natural gas and petroleum are fossil fuels, and the vast majority of plastics are produced from these sources. The process of creating plastic from natural gas and petroleum begins with the extraction of raw materials, which are then refined to create different petroleum products. Crude oil, for example, is heated in a furnace and sent to a distillation unit, where it separates into lighter components called fractions. One of these fractions, naphtha, is a crucial compound for making plastic. The distillation step converts long-chain hydrocarbons into simpler hydrocarbons, which can then be turned into important chemicals used to prepare plastics. This process, known as cracking, can be performed through steam or catalytic cracking.
The next step involves converting raw material molecules into monomers, such as ethylene, propylene, and butene. These monomers contain double bonds, allowing carbon atoms to react and form polymers. Polymerisation is the process of linking these hydrocarbon monomers together through chemical mechanisms to produce polymers. This process generates thick, viscous substances known as resins, which are used to make plastic products. For example, the ethylene monomer, when subjected to heat, pressure, and a catalyst, forms long, repeating carbon chains that become a plastic resin called polyethylene (PE).
While natural gas and petroleum are the primary sources of plastic production, a growing minority of plastics are produced from renewable resources. These renewable sources include waste biomass, animal-waste products, and other renewable materials like carbohydrates, fats, and oils. The increasing demand for limited oil reserves is driving the need for newer plastics derived from these renewable resources.
The shift towards renewable resources is particularly important given the environmental concerns associated with plastics derived from fossil fuels. The production and use of plastics have led to significant environmental issues, including plastic pollution. As the world recognises the dangers of plastic pollution, the deep connection between the fossil fuel and plastic industries continues to drive investments in expanding plastic production, exacerbating the problem.
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Plastic is classified by its polymer's backbone and side chains
Plastic is a polymeric material that can be moulded or shaped, with other properties such as low density, low electrical conductivity, transparency, and toughness. The majority of polymers used in plastics are formed from chains of carbon atoms, with or without oxygen, nitrogen, or sulphur atoms. These chains are made up of thousands of repeating units formed from monomers. The backbone of a polymer is the part of the chain that links together a large number of these repeat units.
To customize the properties of a plastic, different molecular groups called side chains hang from the backbone. 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. The side chains are usually attached to the monomers before the monomers themselves are linked together to form the polymer chain.
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.
The raw materials for plastic are largely derived from crude oil and natural gas, which are then refined to yield useful chemicals including "monomers". The monomers are then linked together by chemical polymerisation to produce polymers. The polymerisation process generates thick, viscous substances as resins, which are then employed to make plastic products.
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Frequently asked questions
Plastic is a broad category of synthetic or semi-synthetic materials that contain polymers as their primary constituent.
Polymers are large molecules made up of repeating units of shorter molecules, called monomers. The monomers form long chains, which are linked together to create the polymer.
Most plastics are produced from non-renewable crude oil, natural gas, and petroleum. However, a growing number are produced from renewable resources, such as polylactic acid.
There are many different types of plastics, which can be classified in several ways. One way is by their chemical structure, such as the polymer backbone and side chains. Another way is by their properties, such as thermoplastics and thermosetting polymers.
Some commonly used plastics include polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyurethanes (PURs), and polycarbonates (PC).
