Alexei Volkov
Polyethylene terephthalate (PET) is a type of polyester plastic derived from petroleum. It is commonly used in various fields, including the creation of fibre materials, plastic bottles, and engineering plastics. PET is known for its durability and malleability, and it can be both transparent and semi-crystalline. In its raw form, PET is typically transparent and colourless, but it can be modified and coloured during processing. For example, recycled PET flakes may turn yellow after heating, and coloured PET is becoming increasingly popular for packaging.
| Characteristics | Values |
|---|---|
| Color | Raw PET is clear and transparent. However, recycled PET may turn yellow. |
| State | PET is a semi-crystalline thermoplastic polymer resin. |
| Texture | PET is lightweight, durable, and malleable. |
| Uses | PET is used in fibers for clothing, containers for liquids and foods, thermoforming for manufacturing, and in combination with glass fiber for engineering resins. |
| Recyclability | PET is commonly recycled and has a resin identification code of 1 (♳). |
| Flexibility | PET has higher tensile strength and rigidity, making it suitable for applications requiring structural integrity. |
| Temperature Resistance | PET has good heat resistance and low creep at elevated temperatures. |
| Chemical Resistance | PET has excellent chemical resistance. |
| Electrical Properties | PET has good electrical insulation properties. |
| Barrier Properties | PET provides a barrier against liquids and is used for packaging and bottles. |
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What You'll Learn
Polyethylene terephthalate (PET) is a thermoplastic polymer resin
Polyethylene terephthalate, commonly known as PET, is the most common thermoplastic polymer resin of the polyester family. It is produced from the polycondensation of ethylene glycol and terephthalic acid. PET is everywhere, playing a crucial role in various industries due to its versatility, lightweightness, chemical resistance, and electrical insulation properties.
When used as a fabric or fibre, PET is generally referred to as "polyester". In more solid forms, like packaging or containers, it is called "PET" or "PET resin". PET is made with a mix of two elements that form a polymer chain: ethylene glycol and purified terephthalic acid. The raw materials involved in the manufacturing of PET are more expensive than those of PE. Terephthalic acid usually comes from natural gas, while purified terephthalic acid is derived from crude oil.
PET is commonly recycled and has a resin identification code (RIC) of 1. It can also be obtained by recycling PET itself. It is known to degrade when exposed to sunlight and oxygen. PET is used in fibres for clothing, containers for liquids and foods, and thermoforming for manufacturing. It is also combined with glass fibre for engineering resins. In 2016, the annual production of PET was 56 million tons, with the biggest application being in fibres (over 60%) and bottle production accounting for about 30% of global demand.
PET is a transparent, amorphous thermoplastic when rapidly cooled, and a semicrystalline plastic when slowly cooled or cold-drawn. It can be processed using common moulding methods like injection moulding, blown moulding, and extrusion. It is suitable for fabricating thin-layer products like stretched film and thermoforming. PET is widely used for carbonated beverage bottles due to its high strength, toughness, good abrasion and heat resistance, low creep at elevated temperatures, and excellent dimensional stability. It also has lower gas permeation compared to other polymer materials, which improves the shelf life of carbonated beverages.
A modified version of PET is PETG or PET-G (polyethylene terephthalate glycol-modified), which is a clear amorphous thermoplastic that can be injection-moulded, sheet-extruded, or extruded as a filament for 3D printing. PETG can be coloured during processing, making it ideal for point-of-sale stands and retail displays.
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PET is derived from terephthalic acid and ethylene glycol
Polyethylene terephthalate (PET) is a thermoplastic polymer resin of the polyester family. It is one of the most versatile bulk materials used in our daily lives, with applications in textiles, packaging, automotive, construction, medical goods, and electrical and electronic devices. PET is derived from terephthalic acid and ethylene glycol through a process of polycondensation. This process involves the esterification reaction between terephthalic acid and ethylene glycol, with water as a byproduct. This reaction is also known as a condensation reaction. Alternatively, PET can be derived by a transesterification reaction between ethylene glycol and dimethyl terephthalate (DMT), with methanol as a byproduct.
The raw materials for PET, terephthalic acid and ethylene glycol, are derived from crude oil or natural gas. As of 2022, terephthalic acid is obtained from p-xylene, which is made from crude oil, while ethylene glycol is made from ethene found in natural gas. The production of these raw materials has environmental impacts, particularly in the combustion of fossil fuels, which contributes to human toxicity. However, advancements in catalytic processes for the conversion of biomass have led to more technically effective and cheaper methods for the synthesis of green PET monomers.
The process of deriving PET from terephthalic acid and ethylene glycol results in a transparent, amorphous thermoplastic when rapidly cooled, while slow cooling yields a semicrystalline plastic. This variation in crystallization is important for different applications, such as seat belts, where mechanical and dimensional stability are crucial. PET can be processed using common moulding methods like injection moulding, blown moulding, and extrusion. It is also suitable for fabricating thin-layer products like stretched film and thermoforming.
PET is widely used in the production of carbonated beverage bottles due to its high strength, toughness, and excellent dimensional stability. It serves as a barrier to aromas and gases, making it suitable for containing carbonated beverages. Additionally, PET is used in artificial fibres for textiles, commonly found in clothing items. The polyester fibres provide heat insulation and are often blended with cotton.
The versatility of PET extends to its ability to be recycled, making it one of the most acceptable plastic materials. Mechanical recycling involves collecting, sorting, cleaning, shredding, melting, and reprocessing plastic materials into new products. PET's recyclability contributes to its sustainability profile, positioning it as the most recycled plastic in municipal and commercial recycling facilities in the United States and Europe.
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It can be coloured during processing
Polyethylene terephthalate, commonly known as PET, is a type of polyester plastic derived from petroleum. It is known for its durability, malleability, and widespread use in various fields, including fibre materials, plastic bottles, and engineering plastics. One of its unique characteristics is its ability to be coloured during processing.
During the manufacturing process, PET can be modified to achieve different colours. This colouring process can be done through the addition of various additives, such as nucleating agents, hazing agents, fluorescers, and other visual and technical effect enhancers. These additives not only enhance the appearance of the PET but also impart specific technical properties to the plastic.
The versatility of PET in terms of colour customisation makes it a popular choice for a variety of applications. For instance, PET is widely used in the packaging industry, where coloured packaging has become an emerging trend. Brands are increasingly adopting coloured packaging as a marketing strategy to create visually appealing products that stand out on retail shelves.
However, the introduction of coloured PET, particularly in the milk packaging, home, and personal care markets, has presented challenges for recyclers. The Plastics Recyclers of Europe (PRE) has warned that the influx of coloured PET bottles, including black, white, and other opaque and translucent colours, could result in additional sorting requirements in recycling plants. This issue arises because coloured PET cannot be easily recycled and reused like its unpigmented counterpart, which has traditionally been the most valuable form of PET for recycling.
To address this challenge, recycling organisations such as the Association of Postconsumer Plastic Recyclers (APR) have provided guidelines and best practices for colour changes during the moulding process. By optimising the raw-material infeed, handling, and reprocessing steps, recyclers can minimise losses in time, material, and labour when dealing with coloured PET. Additionally, advancements in sorting technology have enabled the differentiation between certain colours of PET, such as white PET, facilitating more efficient recycling processes.
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$56.99
PET is highly recyclable
Polyethylene terephthalate (PET) is a thermoplastic polymer resin of the polyester family. It is commonly used in fibres for clothing, containers for liquids and foods, and thermoforming for manufacturing. PET is highly recyclable and has a resin identification code (RIC) of 1 (♳).
The process of recycling PET typically involves six steps: collection, sorting, cleaning, shredding, melting, and reprocessing. Firstly, used plastic materials are collected from various sources, such as recycling bins, drop-off centres, and waste management facilities. These collected items are then sorted based on the type and colour of the plastic. The sorted plastics are then cleaned with water and detergents to remove contaminants. Next, the cleaned plastics are shredded into smaller pieces, such as pellets or flakes, to increase the surface area and facilitate the melting process. The plastic pieces are then melted and reprocessed by extruding them into new products.
One of the benefits of PET is that it can be recycled repeatedly through bottle-to-bottle recycling. However, if the quality of the recycled PET is not high enough for this process, it can be flaked, washed, heated, and stretched into fibres. These fibres are then spun into recycled polyester yarn, which can be used for various applications, including seat belts, bags, carpets, roofing insulation, and clothing. Recycled PET, also known as rPET, is safe for use in food packaging and has been approved by agencies and governments worldwide.
Despite PET's recyclability, there are challenges to its sustainability. The lack of efficient recycling infrastructure and collection systems contributes to low recycling rates. For example, in the United States in 2021, only about 28.6% of PET bottles and packaging were recycled, while the rest ended up in landfills, incinerators, or the environment. Additionally, as PET is recycled, the quality of the material may degrade, resulting in rPET that is weaker and less durable than virgin PET. This quality degradation also limits the number of times PET can be recycled.
Furthermore, PET accounts for 12% of global solid waste, highlighting the importance of encouraging bottle recycling. In 2023, the United States collected 1,962 million pounds of bottles for recycling, contributing to the highest level of bottle recycling in decades (33% in 2023). Recycling PET bottles helps reduce emissions and lower the carbon footprint compared to glass bottles. The recycled material can be used not only for bottles but also for fibres, films, thermoformed packaging, and strapping.
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It has a wide range of applications
Polyethylene terephthalate (PET) is a colourless, semi-crystalline resin with a wide range of applications. It is a type of polyester, which is a common thermoplastic polymer resin. In its raw form, PET is highly flexible and can be moulded into almost any shape.
One of the major applications of PET is in the textile industry. Polyester fibres are widely used in clothing, often blended with cotton as a heat insulation layer. In the context of textiles, PET is referred to as polyester, and it is the fourth-most-produced polymer for this use, with an annual production of 56 million tons in 2016.
PET is also commonly used in packaging, particularly for food and beverages. It is well-suited for this purpose due to its excellent combination of properties, including mechanical, thermal, and chemical resistance, as well as dimensional stability. PET is often used to produce films and sheets that can be thermoformed for food packaging. It is also used for bottling, accounting for about 30% of global demand for PET.
Another important application of PET is in the automotive and aeronautical sectors. PET can be used as a 3D printing filament to create high-end products such as surgical fracture tables, automotive parts, and aeronautical components. PETG, a modified version of PET, is especially popular for 3D printing due to its ease of use and excellent formability.
Furthermore, PET finds applications in the medical field, electrical and electronic devices, construction, and industrial applications. It can be blended with other materials to improve its performance and open up new possibilities for use. Overall, the versatility, lightweight nature, chemical resistance, and electrical insulation properties of PET make it a crucial material in various industries.
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Frequently asked questions
Polyethylene terephthalate, commonly known as PET, is a transparent, amorphous thermoplastic. It is known for its exceptional durability and malleability.
Yes, PET can be coloured during processing.
PET is widely used for the manufacture of packaging for drinking water, carbonated drinks, and food. It is also used for artificial fibres in textiles and clothing.
