Ethan Clarke
Plastic is everywhere, from the cars we drive to the technology we use and the clothes we wear. It is derived from natural, organic materials such as crude oil, natural gas, coal, cellulose, salt, and carbohydrates, fats, and oils. The process of creating plastic involves several steps, including the extraction of raw materials, refining to obtain specific chemicals, breaking down large molecules into smaller ones, and reassembling them into long chains through a process called polymerization. The resulting resins can be transported and melted down to create a wide range of plastic products.
| Characteristics | Values |
|---|---|
| Raw materials | Crude oil, natural gas, coal, carbohydrates, fats, oils, cellulose, salt |
| First step | Extraction of raw materials |
| Second step | Refining process to transform crude oil into different petroleum products |
| Third step | Cracking, where large hydrocarbon molecules are broken down into smaller molecules |
| Polymerization | Smaller molecules are reassembled into long chains with the help of a catalyst to produce plastics |
| Additives | Plasticizers, stabilizers, fillers, pigments, flame retardants |
| Resins | Polyethylene, polypropylene |
| Pellets | Nurdles |
| Final product | Plastic objects of unique design, various size, shape, colour |
| Environmental impact | 3 tons of CO2 for every ton of plastic produced |
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What You'll Learn
Plastic is derived from crude oil, natural gas, or coal
Plastic can be categorised into two types: synthetic plastics and biobased plastics. Synthetic plastics are derived from crude oil, natural gas, or coal. Biobased plastics, on the other hand, are derived from renewable products such as carbohydrates, starch, vegetable fats and oils, bacteria, and other biological substances.
Synthetic plastics are the most common type of plastic in use today due to the ease of manufacturing methods involved in processing crude oil. Crude oil is the principal source of carbon for modern plastic, and it is a complex mixture of thousands of compounds that need to be processed. The refining process transforms crude oil into different petroleum products, which are then converted into useful chemicals, including "monomers" (molecules that are the basic building blocks of polymers). One of the crucial compounds derived from this process for plastic-making is naphtha.
Natural gas, another fossil fuel, is also used as a feedstock for plastic production. It is a mixture of gases, primarily methane, which is a simple hydrocarbon. Through chemical reactions, carbon can pair up with hydrogen to form a CH4 molecule, which is the simplest hydrocarbon.
Coal, the third fossil fuel source of plastic, is also a hydrocarbon derivative. While synthetic plastics rely on fossil fuels, biobased plastics are derived from renewable resources, including waste biomass and animal waste products from the industry. As the demand for limited oil reserves increases, there is a growing need to develop newer plastics from these renewable resources.
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Refining separates crude oil into lighter fractions
Plastic is a generic name given to a wide range of synthetic materials that come from natural, raw materials. Synthetic plastics are derived from crude oil, natural gas, or coal. Crude oil is a mixture of thousands of compounds that need to be processed.
The refining process transforms crude oil into different petroleum products. In this process, crude oil is heated in a furnace and sent to the distillation unit, where heavy crude oil separates into lighter components called fractions. Each fraction contains hydrocarbons with a similar number of carbon atoms, with smaller molecules towards the top and longer molecules towards the bottom of the column. The lightest fractions, such as gasoline and petroleum gas, flow to the top of the tower, while intermediate weight liquid fractions like kerosene and diesel oil distillates linger in the middle. Heavier liquids, such as gas oils, separate lower down, and the heaviest fractions, solids with the highest boiling points, remain at the base of the tower.
The process of separating crude oil into fractions is called fractional distillation. It occurs in a distillation tower or fractionating column, which can be quite tall and wide depending on the refinery. Fractional distillation separates the various hydrocarbon chains in crude oil to create different petroleum products. The separated fractions have different densities, with the least dense gases at the top and the denser heavy fuels and bitumen at the bottom.
After distillation, the obtained long-chain hydrocarbons are converted into hydrocarbons that can be turned into chemicals used to prepare a wide range of products, including plastics. These hydrocarbons are then melt-blended and processed into plastic objects of unique designs, sizes, shapes, and colours.
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Polymerization turns small molecules into long chains
Plastic is a generic name given to a wide range of synthetic materials that come from natural, raw materials. Synthetic plastics are derived from crude oil, natural gas, or coal. The process of transforming these raw materials into plastic involves several steps, one of which is polymerization.
Polymerization is a process in which small molecules called monomers chemically combine to produce long chain-like molecules called polymers. The monomer molecules may be alike or may represent two, three, or more different compounds. These monomers are the basic building blocks of polymers. In the polymerization process, the monomers are transformed into resins, which can then be molded using heat and pressure into various shapes.
The polymer chains formed during polymerization can be linear polymers or cross-linked polymers. Linear polymers are composed of chain-like molecules and may be viscous liquids or solids with varying degrees of crystallinity. They can be dissolved in certain liquids and soften or melt upon heating. Cross-linked polymers, on the other hand, have a network-like molecular structure and are thermosetting resins. They do not melt or soften upon reheating and do not dissolve in solvents.
There are two main classes of polymerization: condensation polymerization and addition polymerization. In condensation polymerization, each step of the process involves the formation of a molecule of a simple compound, often water. This type of polymerization results in a polymer that is less massive than the monomers that formed it. In addition polymerization, monomers react without forming by-products, and the process is typically carried out in the presence of catalysts.
The polymerization process can be further categorized into chain-growth polymerization and step-growth polymerization. In chain-growth polymerization, monomers are added one at a time to a growing chain with an active center, and long chains are formed from the beginning of the reaction. This process involves linking together unsaturated monomers, particularly those containing carbon-carbon double bonds. Step-growth polymerization, on the other hand, involves pairs of reactants of any length combining at each step to form longer polymer molecules. The average molar mass increases slowly, and long chains form later in the reaction.
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Compounding blends materials to make plastic formulations
Plastic compounding is a process that involves blending different additives, fillers, or reinforcements with base polymers to create customized plastic compounds with enhanced properties. The process starts with the selection of a suitable base polymer and additives, taking into account the desired characteristics and end-use requirements of the finished plastic compound. The base polymer and additives are then combined using specialized machinery, such as twin-screw extruders or internal mixers. The mixing process is done slowly and carefully to ensure complete dispersion and uniform distribution of the additives within the polymer matrix.
Compounding often occurs on a twin-screw extruder, where the pellets are then processed into plastic objects of unique design, various sizes, shapes, and colours with accurate properties according to the predetermined conditions set in the processing machine. The mixed materials are put into an extruder, where they melt, heat up, and are homogenized. The components fuse into a molten state with the help of the extruder’s application of heat and mechanical shear.
The correct mixing and dispersion of the additives throughout the polymer matrix are ensured by this procedure. After the extrusion process, the molten compound is cooled and transformed into solid pellets. These pellets are then ready for further processing, such as moulding or extrusion, to create finished engineering plastic products.
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Nurdles are plastic pellets that are transported to manufacturers
Plastic is a generic name given to a wide range of synthetic materials that come from natural, raw materials. Synthetic plastics are derived from crude oil, natural gas, or coal. The production of plastic involves extraction of raw materials, a refining process, and compounding. During compounding, various blends of materials are melt-blended and then pelletized. These pellets, known as nurdles, are the focus of this discussion.
Nurdles are small plastic pellets, typically less than 5 mm in size, that serve as the raw material for manufacturing plastic products. They are made from fossil fuels and a range of harmful chemicals, including phthalates, Bisphenol A (BPA), flame retardants, organotins, heavy metals, and PFAS. Nurdles are the building blocks for everyday items such as plastic water bottles, containers, bags, and polystyrene foam. They are melted down and transformed into various plastic products through processes like extrusion and injection molding.
The issue of nurdle pollution has gained significant attention due to frequent leaks and spills during manufacturing and transportation. Nurdles can escape from the production process through drains, spills during transport, or cargo container mishandling. Their small size makes them easily washable into drains, rivers, and oceans, and they can be blown around by the wind or float on water. This has led to their presence on shorelines and in the water bodies across the world, impacting various ecosystems.
Nurdles contribute to plastic pollution and pose a threat to wildlife and human health. They can be mistaken for food by birds and fish, leading to starvation and health issues. Additionally, nurdles act as carriers of toxins and harmful chemicals, such as persistent organic pollutants (POPs). These pollutants can accumulate and become more toxic as they move up the food chain, impacting marine life and potentially entering the human food chain.
The presence of nurdles in the environment is a pressing issue, and efforts are being made to address their impact. Citizen science programs, like Nurdle Patrol, monitor and collect nurdle specimens from water bodies and railroad tracks for future research. Additionally, initiatives such as the proposed Plastic Pellet Free Waters Act aim to prohibit the discharge of plastic pellets into waterways and hold manufacturers accountable for nurdle spills and leaks.
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Frequently asked questions
Synthetic plastics are derived from crude oil, natural gas, or coal. Crude oil and natural gas are extracted (drilled) from the ground.
The raw materials are transported to a refinery where they are heated in a furnace and sent to a distillation unit. Here, they are separated into lighter components called fractions. One of these, naphtha, is crucial for making plastic.
The fractions are converted into useful chemicals, including monomers, which are then reassembled into long chains through a process called polymerization. This process produces resins that can be melted and moulded into various shapes.
