Ethan Clarke
Plastic is everywhere. From beverage bottles to computer parts, plastics are used to make our lives easier and more straightforward. But not all plastics are the same. There are hundreds of types of plastic, each with unique properties and uses. The wide range of plastics can be classified by their chemical composition, their synthesis, their physical properties, or their reactions to various substances. The most common plastics are classified into seven groups, with polyethylene being the most common plastic in the world. However, the vast majority of plastic in use today is synthetic, derived from crude oil, natural gas, or coal, and only a small fraction of plastic is made from renewable materials. With the growing demand for limited oil reserves, there is a need to develop newer plastics from renewable resources.
| Characteristics | Values |
|---|---|
| Variety | There are hundreds of types of plastic, but only a handful are commonly encountered. |
| Chemical composition | Plastics are made up of polymers, which are composed of monomers. |
| Polymer types | Plastics can be made up of aliphatic (linear) carbon atom polymers or heterochain polymers, which contain atoms such as oxygen, nitrogen, or sulfur in addition to carbon. |
| Backbone chains | The polymer backbone chains can have different molecular groups called side chains attached to them, influencing the properties of the polymer. |
| Classification | Plastics can be classified by chemical structure, chemical synthesis process, physical properties, or resistance and reactions to substances and processes. |
| Production | Plastics are produced by the polymerization of their starting materials (monomers), which are usually petrochemical. |
| Sources | Most plastic is derived from fossil fuels such as crude oil, natural gas, and coal, but a small fraction comes from renewable materials. |
| Durability | The chemical structure of most plastics makes them resistant to natural degradation processes, leading to persistence in the environment. |
| Uses | Plastics are used in a wide range of products, including packaging, building and construction, electronics, textiles, automotive parts, and medical devices. |
| Recycling | The complexity of plastic recycling is determined by the different types of plastic, with some being more recyclable than others. |
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What You'll Learn
Plastic is a synthetic or semisynthetic polymer
Plastics are synthetic or semisynthetic materials that use polymers as their main ingredient. Polymers are substances made of many repeating units, derived from the Greek words "poly", meaning many, and "meros", meaning parts or units. A polymer can be thought of as a chain where each link is a monomer (single unit). Monomers can be chemically joined through addition polymerization or condensation polymerization. The first totally synthetic polymer, Bakelite, was produced in 1907, and the first semisynthetic fibre, rayon, was developed from cellulose in 1911. However, the mass production of synthetic polymers only began during World War II when natural sources like latex, wool, and silk became scarce. Synthetic rubber was needed for tires, and nylon, produced through condensation polymerization, replaced silk in parachutes.
Today, synthetic polymers are widely used in the form of plastics, and the plastics industry is one of the fastest-growing industries globally, especially in the United States. The industry produces approximately 150 kilograms of polymers per person annually in the US. Plastics are valued for their durability, resulting from their chemical structure, which makes them resistant to many natural degradation processes. They can be easily moulded, extruded, or pressed into solid objects of various shapes, making them versatile and adaptable to a wide range of applications.
Plastics can be categorized into synthetic and naturally occurring types, both of which can be shaped when soft and then hardened to retain the given shape. Examples of synthetic polymers include polyethylene, used in plastic bags; polystyrene, used in Styrofoam cups; polypropylene, used for fibres and bottles; and polyvinyl chloride, used for food wrap, bottles, and drain pipes. Polyethylene, polystyrene, and acrylic are formed through addition polymerization and are often thermoplastic in nature, allowing them to be heated, softened, and hardened when cooled. These polymers are easily recyclable.
On the other hand, condensation polymerization, where a small molecule is eliminated as monomers join, results in nylons, some polyesters, and urethanes. These polymers can be thermoplastic or thermosetting. Thermoset polymers, once formed, cannot be melted and reformed. Plastics can be found in a variety of shapes, colours, and types, each with distinct uses. Some plastics are reusable and recyclable, while others are not due to the chemicals they contain. Polycarbonate, a type of plastic included in group number 7, is known for its strength and toughness, being used to create strong products.
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Plastic is derived from natural gas, crude oil, or coal
Plastic can be categorised as either 'synthetic' or 'biobased'. Synthetic plastics are derived from fossil fuels such as crude oil, natural gas, and coal. Biobased plastics, on the other hand, are derived from renewable sources such as carbohydrates, starch, vegetable fats and oils, bacteria, and other biological substances.
The majority of plastic in use today is synthetic due to the ease of manufacturing methods involved in processing crude oil. Crude oil is the principal source of carbon for modern plastic, but variants are also manufactured from renewable materials. The main ingredient in most plastic materials is a derivative of crude oil and natural gas.
Crude oil is a source of raw material (feedstock) for making plastics, but it is not the major source of feedstock for plastics production in the United States. Natural gas and its derivatives are the primary sources of feedstock for plastics production in the US. Petrochemical feedstock naphtha and other oils refined from crude oil are also used as feedstocks for petrochemical crackers that produce the basic building blocks for making plastics.
Natural gas is a fossil fuel that is composed mostly of methane, a hydrocarbon with the chemical formula CH4. Carbon has a valency of four, meaning it has four electrons in its outermost shell. It can pair up with four other electrons from any element on the periodic table to form chemical bonds. In the case of hydrocarbons, carbon pairs with hydrogen. Hydrogen has only one electron in its outermost shell, so four hydrogen atoms can pair with one carbon atom by forming single bonds, resulting in a CH4 molecule. This molecule is the simplest hydrocarbon and is known as methane, the first member of the Alkane family.
Coal is another fossil fuel source from which plastic is derived. The growing demand for limited oil reserves is driving the need for newer plastics derived from renewable resources.
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Plastic is durable and resistant to degradation
Plastic is a synthetic or semisynthetic material that uses polymers as its main ingredient. The chemical structure of most plastics makes them durable and resistant to degradation. This durability is a result of the high molecular weight and hydrophobicity of plastics, as well as the absence of functional groups that are susceptible to attack by microbial enzymes, light, water, etc.
Polyolefins, for example, are a type of plastic that is particularly durable due to their chemical and biological inertness. This inertness also makes them ideal for applications such as food packaging, sterile medical uses, and construction. Additionally, the recalcitrance and impermeability of polyolefins contribute to their long life when they are discarded, becoming a source of environmental concern.
Polyethylene terephthalate (PET), a widely used polymer, is highly resistant to environmental biodegradation. Its accumulation in the environment has led to concerns about its absorption and concentration of organic pollutants, hazardous effects on marine wildlife, and the dissemination of potentially invasive species. Despite the presence of bonds that are normally readily hydrolysed, PET is essentially non-degradable under normal conditions due to its aromatic groups.
Other types of plastics, such as PVC and polypropylene, also exhibit durability and resistance to degradation. PVC, or polyvinyl chloride, can be manufactured to possess rigid or flexible properties, making it suitable for a wide range of applications. Polypropylene, on the other hand, is known for its flexibility, strength, heat resistance, and acid resistance.
While the durability of plastics has contributed to their widespread use, it has also become an environmental challenge, with plastic accumulation in the world's oceans and the persistence of plastic waste over centuries.
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Plastic is lightweight, flexible, and tough
Plastic is a versatile material with numerous applications in our daily lives. Its unique properties, such as being lightweight, flexible, and tough, make it a popular choice for a wide range of products.
One of the key advantages of plastic is its lightweight nature. This makes it ideal for various applications where weight is a critical factor. For example, in the automotive industry, plastic components help reduce vehicle weight, leading to improved fuel efficiency. Additionally, in packaging, lightweight plastic materials are preferred to minimize transportation costs and provide convenience to consumers.
The flexibility of plastics is another remarkable feature. Plastics can be easily molded, extruded, or pressed into various shapes, allowing for a diverse range of applications. From shopping bags and disposable packaging to electrical cable insulation and medical tubing, the flexibility of plastics enables their use in countless everyday items. Furthermore, flexible plastics like polyvinyl chloride (PVC) can be blended with other materials, enhancing their versatility.
Plastics are also known for their toughness and durability. Certain types of plastics, such as polycarbonate, are highly impact-resistant and are used in engineering applications. Polypropylene, another widely used plastic, retains its flexibility while being strong enough to withstand repeated stress without cracking. This toughness makes plastics suitable for products like automotive parts, laboratory equipment, and construction materials.
The combination of being lightweight, flexible, and tough makes plastics a preferred choice in many industries. They contribute to weight reduction, ease of manufacturing, and product durability. However, it is essential to note that not all plastics possess these characteristics to the same degree. Different types of plastics have unique properties, and some may be more lightweight, flexible, or tough than others, catering to specific requirements.
In summary, the versatility of plastics lies in their ability to be lightweight, flexible, and tough. These properties have led to their widespread use and popularity, shaping numerous aspects of our modern lives.
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Plastic is classified by its chemical structure
Plastic is a polymeric material that can be moulded or shaped, and it is usually classified by the chemical structure of the polymer's backbone and side chains. The polymerization process is a chemical reaction that results in the formation of multiple individual polymer chains made up of repeating units. These chains are not covalently bonded to each other but are kept together by intermolecular forces.
The fundamental differences in the properties of different types of polymers are due to the varying functional groups within the molecular structure. These differences include mechanical, thermal, and chemical resistance properties. The chemical structure of plastics also determines their degradation process. While most plastics are resistant to many natural degradation processes due to their chemical structure, recent studies have shown that ocean plastics decompose faster than previously thought due to exposure to environmental conditions.
Plastics can be broadly divided into two categories based on their chemical composition. The first category includes plastics made up of polymers with only aliphatic (linear) carbon atoms in their backbone chains. Examples of this type include polypropylene, polyethylene, polyacetal, and nylon. The second category consists of plastics with other types of carbon atoms in their backbone chains.
Additionally, plastics can be classified based on the chemical processes used in their synthesis, such as condensation, polyaddition, and cross-linking. They can also be classified by their physical properties, such as hardness, density, tensile strength, and thermal resistance. Other classifications are based on qualities relevant to manufacturing or product design, including thermoplastics, thermosets, conductive polymers, biodegradable plastics, engineering plastics, and elastomers.
The Society of the Plastics Industry introduced the Resin Identification Code (RIC) system in 1988, which categorised plastic resins into seven groups to facilitate recycling. Some of the well-known plastics in these groups include polyvinyl chloride (PVC), polyethylene terephthalate (PET), polystyrene, polypropylene, and polycarbonates (PC).
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Frequently asked questions
Plastics are synthetic or semisynthetic materials that use polymers as a main ingredient. Most plastics are derived from natural gas, petroleum, and crude oil.
All plastics are polymeric materials that can be moulded or shaped, usually with the application of heat and pressure. They are durable, flexible, lightweight, and inexpensive to produce.
Plastics can differ in their chemical structure, physical properties, and synthesis processes. There are hundreds of types of plastics, but only a handful are commonly encountered. Some plastics are reusable and recyclable, while others are not due to the chemicals they contain.
Some common plastics include polyethylene terephthalate (PET), polyvinyl chloride (PVC), polystyrene, and polycarbonate. PET is often used for beverage bottles, while PVC is used for plumbing pipes and electrical cables. Polycarbonate is known for its strength and impact resistance, and is used in products like sunglasses and DVDs.
