Omar Khalid
Plastic is an extremely useful and flexible material that has become an integral part of our daily lives. From packaging to construction, it is everywhere. However, not all plastics are created equal. Different types of plastics have varying impacts on the environment, and some are more easily recycled than others. The Society of the Plastics Industry introduced the Resin Identification Code (RIC) system in 1988 to categorize plastic resins into seven groups, aiding recycling efforts. These groups include PET, HDPE, LDPE, PVC, PP, PS, and UHMWPE, each with distinct characteristics and applications. Understanding these differences can help consumers make informed choices and contribute to more effective recycling practices.
| Characteristics | Values |
|---|---|
| Number of different types of plastics | Dozens |
| Plastic production in 2023 | Over 400 million metric tons |
| Annual global plastic production by 2060 | 1.3 billion tons |
| Plastic usage | Packaging (40%), building and construction (20%), automobiles (up to 20%), furniture, toys |
| Plastic disposal | 14% incinerated, less than 10% recycled |
| Plastic classification | Thermoplastics, thermosets, conductive polymers, biodegradable plastics, engineering plastics, elastomers |
| Thermoplastics | Can be easily recycled, 80% of plastic manufactured |
| Thermosets | Cannot be easily melted and reshaped, used for products with a long life |
| Resin Identification Code | Developed by Society of the Plastics Industry in 1988, standardised by ASTM International |
| RIC usage | Indicates plastic type and recyclability |
| Types of plastic | PET, HDPE, LDPE, MDPE, UHMWPE, PVC, PP, PS, PE, PC, acrylics, polyesters, silicones, polyurethanes, halogenated plastics |
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What You'll Learn
- Acrylics, polyesters, silicones, polyurethanes, and halogenated plastics
- Thermoplastics, thermosets, conductive polymers, biodegradable plastics, engineering plastics, and elastomers
- Polyethylene, a common plastic with varying densities
- Polypropylene, the second-most widely produced commodity plastic
- Polyvinyl chloride (PVC), a widely produced plastic used in construction
Acrylics, polyesters, silicones, polyurethanes, and halogenated plastics
Acrylics
Acrylic, also known as Plexiglass, is a versatile plastic material with a variety of purposes and benefits. It is available in a spectrum of colours and opacities and can be purchased in sheets, rods, or tubes. Acrylic combines a wide variety of options with numerous benefits, and it can be fashioned into a diverse range of useful products. It is highly durable, cost-effective, and lightweight. Acrylic is 10 times more impact-resistant than glass, and if it does break, it will fracture into dull-edged pieces.
Polyesters
Polyester is a category of polymers that contain one or two ester linkages in every repeat unit of their main chain. The most common type of polyester is polyethylene terephthalate (PET). Polyesters include some naturally occurring chemicals, such as those found in plants and insects. Natural polyesters and a few synthetic ones are biodegradable, but most synthetic polyesters are not. Synthetic polyesters are used extensively in clothing and fabrics for the home and car interiors.
Silicones
Silicone (siloxane) is a synthetic plastic polymer with a backbone made of silicon and oxygen, and hydrocarbon side groups. It is derived from fossil fuels and silica (silicon dioxide). Silicone is often used for baby nipples, cookware, utensils, and toys. It is also used for insulation, sealants, adhesives, lubricants, gaskets, and medical applications.
Polyurethanes
Polyurethane is a class of polymers composed of organic units joined by carbamate (urethane) links. Polyurethanes can be produced from a wide range of starting materials, resulting in polymers with different chemical structures and applications. Polyurethane is used in rigid and flexible foams, coatings, adhesives, electrical potting compounds, and fibres.
Halogenated Plastics
Halogenated polymers are a special class of polymer compounds that contain halogen elements such as fluorine, chlorine, and bromine. These polymers are widely used in the medical field and have been found to be useful as high-efficiency solar cell acceptor materials. They can also be used as polymer additives to prepare high-performance coatings. The main purpose of halogenation is to improve the performance of materials, especially flame retardancy.
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Thermoplastics, thermosets, conductive polymers, biodegradable plastics, engineering plastics, and elastomers
Thermoplastics are plastics that can be melted and reshaped and are therefore 100% recyclable through mechanical and chemical recycling. They can be used in 3D printing, medical devices, clothing, upholstery, and carpets. Examples include acrylonitrile butadiene styrene (ABS), polypropylene, and polyphenyl sulfone (PPSU).
Thermosets, on the other hand, are plastics that cannot be melted and reshaped after they are cured. They are generally stronger than thermoplastics due to their three-dimensional network of bonds (crosslinking). Thermosets are used in a wide range of applications, including adhesives, coatings, composites, and electrical insulation. Examples of thermosets include polyurethanes, polyureas, and furan resins.
Conductive polymers are a type of plastic that can carry an electric current. They are prepared by many methods, most commonly by oxidative coupling of monocyclic precursors. Conductive polymers have important applications in organic light-emitting diodes (OLEDs), solar cells, and transistors. Examples of conductive polymers include polyacetylene, polypyrrole, polyindole, and polyaniline.
Biodegradable plastics are plastics that can be decomposed by living organisms, usually microbes, into water, carbon dioxide, and biomass. They are commonly produced with renewable raw materials, micro-organisms, petrochemicals, or combinations of these. Biodegradable plastics are often used for disposable items such as packaging, cutlery, and food service containers. Examples of biodegradable plastics include polyhydroxyalkanoates (PHAs), polylactic acid (PLA), and starch blends.
Engineering plastics are a group of plastic materials that have better mechanical or thermal properties than commodity plastics. They are more expensive and are therefore produced in lower quantities, typically for smaller objects or low-volume applications. Engineering plastics have replaced traditional engineering materials such as metal, glass, and ceramics in many applications due to their superior strength, weight, and ease of manufacturing. Examples of engineering plastics include polyamides (nylons), polycarbonates, and poly(methyl methacrylate) (PMMA).
Elastomers are viscoelastic polymers that are sticky and very elastic. Natural elastomers, such as rubber, are made from latex, while synthetic elastomers are made from petroleum. Elastomers are flexible, durable, and resistant to the passage of air, gases, and fluids. They are commonly used in liquid and gas handling systems, seals, and O-rings.
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Polyethylene, a common plastic with varying densities
Polyethylene, or polythene, is the most common plastic in the world. It is a thermoplastic polymer, primarily used for packaging, including plastic bags, plastic films, geomembranes, and containers such as bottles, cups, and jars. Polyethylene is also used in computer hardware packaging, toys, and casings. It is further used in the construction industry, for example, in the form of construction films and pipes.
Polyethylene is made by copolymerizing ethylene with 1-butene and smaller amounts of 1-hexene and 1-octene. The resultant structure has a linear backbone but short, uniform branches that prevent the polymer chains from packing closely together. The long, chain-like molecules, in which hydrogen atoms are connected to a carbon backbone, can be produced in linear or branched forms. Branched versions are known as low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE). Linear versions are known as high-density polyethylene (HDPE) and ultrahigh-molecular-weight polyethylene (UHMWPE).
The different types of polyethylene have different densities and melting points. The melting point for average commercial low-density polyethylene is typically 105 to 115 °C (221 to 239 °F), while for medium- and high-density polyethylene, the melting point is typically in the range of 120 to 130 °C (248 to 266 °F). The melting point varies with the type of polyethylene, but the theoretical upper limit of melting is reported to be 144 to 146 °C (291 to 295 °F).
Polyethylene is a good electrical insulator and has excellent chemical resistance. It is also nontoxic and chemically resilient, contributing to its popularity as a multi-use plastic. However, its chemical resilience also makes it a long-lived and decomposition-resistant pollutant when disposed of improperly.
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Polypropylene, the second-most widely produced commodity plastic
Polypropylene, also known as polypropene, is a thermoplastic polymer with a wide variety of applications. It is produced through the chain-growth polymerization of the monomer propylene. This process involves linking together many propylene molecules to form long chains, and the arrangement of these chains gives rise to different types of polypropylene with distinct properties.
Polypropylene is the second-most widely produced commodity plastic, after polyethylene. It is a white, mechanically rugged material with a high chemical resistance. While it shares similarities with polyethylene, polypropylene is slightly harder and more heat-resistant. Its density, which is the lowest among commodity plastics, ranges from 0.895 to 0.93 g/cm3. This low density makes it ideal for lightweight applications.
Polypropylene's flexibility, durability, and chemical resistance have led to its use in numerous industries. It is commonly used in packaging, automotive parts, consumer goods, and medical applications. In the packaging industry, polypropylene is favoured for its low cost and flexibility, serving as a substitute for paper and cellophane in products such as bottles, jars, food containers, and bags. Its resistance to chemicals, bacteria, and steam sterilisation makes it suitable for medical uses, including syringes, Petri dishes, and pill containers.
In the automotive sector, polypropylene is often chosen for its cost and pliability. It is used for manufacturing battery cases, bumpers, interior and door trim, and instrumental panels. Additionally, polypropylene's ability to be melted and reshaped multiple times makes it well-suited for injection moulding processes. This versatility, combined with its resistance to chemicals, makes it a popular choice for manufacturing applications.
Polypropylene also has some drawbacks. It is highly flammable and prone to oxidation. It is sensitive to sunlight, chlorinated solvents, and aromatics. Furthermore, it can break easily in cold weather and is susceptible to microbial attacks such as mould. Despite these limitations, polypropylene is considered a safe plastic by organisations like the FDA and EPA. It is BPA-free and approved for food containers, although more research is needed to understand the potential environmental and health impacts of polypropylene microplastics.
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Polyvinyl chloride (PVC), a widely produced plastic used in construction
Polyvinyl chloride (PVC) is the world's third-most widely produced synthetic plastic polymer. It is a synthetic polymer made from the vinyl chloride monomer. It is a versatile thermoplastic material known for its durability, chemical resistance, and affordability. It is widely used in applications such as pipes, medical devices, and wire and cable insulation.
PVC is widely available in two broad categories: flexible and rigid. Rigid PVC is a stiff and cost-effective plastic that shows high resistance to impact, water, weather, chemicals, and corrosive environments. It is largely used in the building and construction industry to produce door and window profiles and pipes (drinking and wastewater). It is also used for window frames, siding, and door frames.
Flexible PVC is formed by the addition of compatible plasticizers to PVC, which lower the crystallinity. These plasticizers act like lubricants, resulting in a much clearer and flexible plastic. This type of PVC is sometimes called PVC-P.
PVC is used in construction due to its strength and durability. It is also lightweight, which makes it suitable for various applications. It is easily workable, mouldable, and thermo-formable or cold-formable. It is also 100% recyclable.
PVC has been linked to cancer since 1973, and environmentalists and health advocates have raised concerns about the possible ill effects of exposure to substances such as residual vinyl chloride monomer, hydrogen chloride, organometallic stabilizers, and phthalates.
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Frequently asked questions
PET, or Polyethylene Terephthalate, is a plastic that is used to make bottles for soda, water, and other drinks. It is also used to make cooking oil containers, plastic peanut butter jars, and food containers. PET products can be recycled and are accepted by most curbside recycling programs.
High-Density Polyethylene (HDPE) is a plastic that is commonly used to make milk jugs, shampoo bottles, detergent bottles, plastic bottles, piping for water and sewer, snowboards, boats, and folding chairs. HDPE products can be recycled and are accepted at most recycling centers worldwide.
Low-Density Polyethylene (LDPE) is a plastic that is used to make plastic bags, grocery bags, plastic wraps, six-pack rings, and various containers. LDPE is not often recycled through curbside programs.
Polypropylene (PP) is a plastic that is used to make food containers for products like yogurt, sour cream, and margarine. It is also made into straws, rope, carpet, bottle caps, and automotive parts. PP products can sometimes be recycled.
