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Views: 50 Author: Site Editor Publish Time: 2024-08-15 Origin: Site
PET, short for Polyethylene Terephthalate, is a type of thermoplastic polymer. You might also hear it referred to as PETE, and in the past, it was known as PETP or PET-P. PET’s thermoplastic nature means it can be heated, melted, and then cooled to form various shapes, making it especially popular in the packaging industry, both for soft and rigid packaging. Additionally, PET is a strong, inert material that doesn’t react with food, which is a big reason why it’s widely used for food packaging and beverage bottles. Plus, it's cost-effective, which further drives its popularity.
PET ranks as the fourth most-produced polymer, right behind PE (Polyethylene), PP (Polypropylene), and PVC (Polyvinyl Chloride). By 2016, PET was already being used in over 60% of fiber applications, and PET bottles accounted for about a third of global demand, making it a staple in both the textile and packaging industries.
PET
PE
PP
PVC
PET is made up of repeating units of C10H8O4. In most cases, PET is produced from PTA, though some is made from MEG and DMT. As of 2022, the ethylene glycol in PET is still derived from ethylene, a natural gas, and the terephthalic acid comes from paraxylene, which is sourced from crude oil. During PET production, antimony or titanium is used as a catalyst, phosphites serve as stabilizers, and cobalt salts along with bluing agents are added to mask any yellowing.
PET’s slow crystallization rate makes it easier to stretch during production, which is why it’s ideal for making fibers and films.
polyester fiber
polyester fiber
As an aromatic polymer, PET offers better barrier properties than aliphatic polymers and is also hydrophobic.
Commercial PET products typically have a crystallinity of up to 60%. By rapidly cooling the molten polymer down to the glass transition temperature, transparent products can be produced. Slower cooling results in semi-transparent products. Orientation during production can also enhance transparency, explaining why BOPET films and bottles are both clear and crystalline.
PET is widely used for making plastic bottles that hold soft drinks, including both carbonated and non-carbonated beverages. For beverages that degrade easily, like beer, PET is often layered with other materials to reduce oxygen permeability.
In flexible packaging, PET is typically biaxially oriented to create BOPET film, a material you might know better by its trade name, Mylar. After orientation, additional treatments like metallization can further reduce permeability, making the film reflective and opaque, which is why it's so widely used in food packaging and insulation materials.
PET is extensively used in the textile industry due to its excellent ductility, as previously mentioned. These polyester fibers are commonly found in fashion apparel, often blended with cotton, and are used for thermal wear, sportswear, workwear, and automotive upholstery.
While most thermoplastics can be recycled, PET stands out for being particularly easy to recycle. This is partly due to its high value and the fact that PET is commonly used for water bottles, making it a popular choice for recycling. Unlike other plastics like PVC (used for cling wrap), PP (food containers), and PS (disposable cups), PET can be recycled repeatedly into the same products, significantly reducing waste. Many countries use the universal recycling symbol with the resin identification code (RIC) 1 (♳) on the bottom of PET products to indicate this.
Moreover, PET production consumes less energy and generates fewer carbon emissions compared to other materials. The lighter weight of PET products also means lower carbon emissions during transportation.
PVC Cling Film
PP Box
PS PP Disposable Chopsticks
PET Recycling Sign
Recycled PET is often referred to as RPET or R-PET, and post-consumer PET (POSTC PET) is also commonly used. Beyond being recycled into the same products, PET can be repurposed into strapping bands and non-food containers. In 2023, a new process was introduced to produce supercapacitors from PET, converting it into carbon-containing sheets and nanospheres. Additionally, PET is an ideal fuel for energy plants due to its high heat content, which helps reduce reliance on non-renewable resources.
PET Type
PET Container
If PET isn’t manually recycled and is instead discarded, there’s no need to worry. Certain bacteria in the genus Nocardia can degrade PET using lipase enzymes. These bacteria are widely found in soil, so PET can be naturally broken down.
Nocardia
Nocardia
Before discussing potential issues with PET, it’s important to mention antimony. This metalloid element is typically used as a catalyst in PET production. After PET products are completed, residual antimony can be detected on the product’s surface. Over time, these antimony elements may migrate into the contents, such as food and beverages. Exposing PET to microwaves can significantly increase antimony levels, potentially exceeding the EPA’s maximum standard. While the health risks are minimal, it’s still a concern.
Antimony
Antimony
Since PET is widely used in the textile industry, many clothes may shed fibers during use and washing. Some of these fibers break down into small particles, which can settle in rivers or oceans and be ingested by fish, entering the food chain. Other fibers may travel through the air and eventually be consumed by livestock and plants, ultimately entering our food supply.
PET is an environmentally friendly material that’s easier to recycle and has a higher recycling value compared to its counterparts. Although it may have some potential safety concerns, these are minimal compared to its advantages. As more countries take action against plastic pollution, PET offers a viable solution for many industries.
