Omar Khalid
Plastics are classified into hundreds of types, but only a handful are commonly encountered. Plastics are typically classified by their chemical structure, but they can also be classified by the chemical process used in their synthesis, their physical properties, or their resistance and reactions to various substances and processes. The most common plastics in the world are collectively polyethylenes, which are classified into three types: high-density, low-density, and linear low-density. Other commonly used plastics include polyvinyl chloride (PVC), polypropylene (PP), and polystyrene (PS).
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What You'll Learn
Plastic classifications by synthesis, physical properties, and reactions
Plastics are classified in various ways, including by their chemical structure, polarity, and applications. They can also be classified by their synthesis, physical properties, and reactions.
Synthesis
Plastics can be classified by the chemical processes used in their synthesis. For instance, thermoplastics can be moulded repeatedly without undergoing chemical changes when heated. Examples of thermoplastics include polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC). On the other hand, thermosets, or thermosetting polymers, can only take shape once and will decompose if heated after solidification. Examples of thermosets include epoxy resin, polyimide, and Bakelite.
Physical Properties
Plastics can be classified by their physical properties, such as hardness, density, tensile strength, thermal resistance, and glass transition temperature. For example, polystyrene is known for its low cost and ease of manufacturing, while polyvinyl chloride (PVC) is valued for its strength and durability.
Reactions
Plastics can also be classified by their reactions to various substances and processes, such as exposure to organic solvents, oxidation, and ionizing radiation. Biodegradable plastics, for instance, break down upon exposure to factors such as sunlight, ultraviolet radiation, moisture, bacteria, and enzymes.
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Plastics used in food-grade, cosmetics, and chemicals
Plastic is a broad term for a group of materials made from polymers, or chemical compounds. There are hundreds of types of plastic, but only a few are commonly used. Plastics are classified into several groups, including food-grade, cosmetics and chemicals, technical and construction materials, and materials used for clothing.
Food-grade plastics include polypropylene (PP), HDPE (high-density polyethylene), LDPE (low-density polyethylene), PS (polystyrene), and PET (polyethylene terephthalate). These plastics are used for food packaging and storage. For example, LDPE is used for bread bags and produce bags, while PET is used for single-serve beverage bottles and condiment bottles. HDPE is commonly used for milk jugs and grocery bags, and it is considered safe for long-term food storage due to its durability and high melting point. Polypropylene is also used for food storage, as it is durable and has high heat resistance, making it safe for use in the microwave and dishwasher.
However, some plastics used for food packaging and storage have been found to contain harmful chemicals such as BPAs, which can leach into food and cause potential health risks. BPAs are endocrine disruptors, which means they can interfere with hormone production and regulation. Other chemicals found in food packaging include phthalates, which are plasticizers used to make plastic more flexible and durable. These chemicals have been found in almost all tested foods and are particularly concerning due to their widespread presence.
Plastics used in the production of cosmetics and chemicals include poly(ethylene oxide) (PEG) and sodium polyacrylate. These plastics have unique properties that make them suitable for specific applications in the cosmetics and chemicals industries.
In summary, plastics used in food-grade, cosmetics, and chemicals applications vary in their specific types, properties, and potential health concerns. While some plastics are safe for food storage and packaging, others may contain harmful chemicals that can leach into food, emphasizing the importance of using the right types of plastics for specific applications.
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Plastics used in technical and construction materials
There are hundreds of types of plastic, but only a handful are commonly used. Plastics are classified into several groups, including food-grade plastics, plastics used in cosmetics and chemicals, and plastics used in technical and construction materials.
Polycarbonate is a type of thermoplastic that has become increasingly common in building and construction projects. PC panels are transparent and stronger than acrylic, making them popular for exterior design elements like windows, skylights, cladding, and roofing.
Other plastics used in construction include polyethylene (PE), which includes variations like high-density polyethylene (HDPE) and low-density polyethylene (LDPE). Polypropylene (PP) is also used in construction, often for carpeting, piping systems, roofing sheets, building insulation, and electrical cable insulation. It is the most widely produced plastic after PE and is used when heat, fatigue, or shatter resistance is required.
Plastics are also used in heavy equipment and machinery, complementing or replacing metals, wood, and glass. Materials like UHMW, ABS, nylon, and polycarbonate are used in construction, agriculture, road construction, and maintenance.
The construction industry has contributed significantly to the rise of plastic consumption globally, with concerns being raised about the environmental impact and health implications of plastics.
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Plastics used in the production of clothing
Plastics are classified into seven main types, each with distinct properties and applications. These types include Polyvinyl Chloride (PVC), High-Density Polyethylene (HDPE), Low-Density Polyethylene (LDPE), Polypropylene (PP), Polystyrene (PS), Polyethylene Terephthalate (PET), and Polycarbonate (PC). While these categories encompass a wide range of plastic items, it's important to note that there are hundreds of specific types of plastic, or polymers, with new applications being discovered regularly.
Now, let's delve into the specific types of plastics used in the production of clothing. The fashion industry relies heavily on synthetic fabrics derived from plastic, with an estimated 60% of clothing materials being plastic-based. These synthetic fabrics are favoured for their lightweight, durable, affordable, and flexible nature. The most common types of plastics used in clothing production include:
Polyester
Polyester, or polyethylene terephthalate (PET), is a dominant fibre in the synthetic fabric market, accounting for 52% of the overall fibre market and around 80% of synthetic fibres. It is derived from petroleum-based products obtained from fossil fuels, making its production environmentally detrimental. Polyester is widely used in clothing due to its breathability and ability to provide warmth, making it suitable for both sportswear and winter garments. However, it is important to note that polyester is a significant contributor to microfibre pollution, as it sheds tiny plastic fibres during washing that end up in the ocean and have even been found in human blood and placenta.
Acrylic
Acrylic is another popular synthetic fabric used in clothing production, known for its affordability and versatility. However, it also contributes to microfibre pollution, with a single 6kg wash of acrylic clothing releasing approximately 728,789 fibres.
Nylon
Nylon is a synthetic fibre commonly used in clothing, often blended with other fibres such as polyester or cotton. It is lightweight and durable, making it desirable for various garment types.
Polyvinyl Chloride (PVC)
PVC is used in the production of pleather or faux leather clothing, such as trousers or jackets. While PVC has versatile applications, it is considered the most dangerous plastic to human health due to its ability to leach toxic chemicals throughout its lifecycle.
Other Plastics
Plastics can also be found in clothing in less obvious ways. For example, plastic is often used in zippers, threads, labels, and elastic waistbands. Additionally, plastic-based materials provide stiffness and reinforcement in certain garments, such as padding in bras for structure and support.
While the use of plastics in clothing provides functionality and affordability, it is important to recognise the environmental and health impacts associated with these materials. The fashion industry is working towards sustainable practices, including reducing microfibre release, developing new materials, and encouraging recycling initiatives to minimise the harm caused by plastic-based clothing.
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Microplastics
Plastics are classified into hundreds of types, but only a handful are commonly encountered. These are numbered according to their recycling codes, from 1 to 7. If a plastic cannot be identified within the first six groups, it is classified as number 7.
One particular type of plastic that has come under scrutiny is microplastics. These are plastic particles smaller than 5mm in size, or about the size of a pencil eraser. They can form when larger plastic pieces break apart, or they can be intentionally designed as such, called microbeads, commonly found in health and beauty products.
Primary microplastics are small pieces of plastic that are purposefully manufactured. They are usually used in facial cleansers and cosmetics, or in air-blasting technology. They have also been used in medicine as vectors for drugs. These microplastic "scrubbers" have replaced natural ingredients such as ground almond shells, oatmeal, and pumice in exfoliating hand cleansers and facial scrubs.
Secondary microplastics arise from the degradation of larger plastic products through natural weathering processes. Sources of secondary microplastics include water and soda bottles, fishing nets, plastic bags, microwave containers, tea bags, and tire wear. Both types of microplastics are recognised to persist in the environment, particularly in aquatic and marine ecosystems, causing water pollution.
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