Ethan Clarke
Plastic is everywhere, from food containers to packaging and wrapping. One of the most commonly used plastics is PET, or polyethylene terephthalate, which is identified by the number 1 inside a recycling symbol on the packaging. While PET is often marketed as highly recyclable, BPA-free, and safe, it has been associated with the leaching of harmful chemicals, especially when exposed to high heat or stored for long periods. These chemicals can have negative health effects, including endocrine and reproductive issues, and can also impact the environment. With growing concerns about plastic pollution and toxicity, it is important for consumers to be aware of the potential risks associated with different types of plastics and take steps to reduce their exposure to toxic chemicals.
| Characteristics | Values |
|---|---|
| Flame test | A yellow flame with dark smoke could be PET or Polycarbonate |
| Float test | PET will sink in water |
| Smell | PET smells similar to burnt sugar |
| Health | Antimony, a metalloid element with toxic qualities, leaches from PET |
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What You'll Learn
The float test
To perform the float test, simply fill a container with water and place the plastic item in question on the surface of the water. If the item floats, it is likely PET. This is because PET has a lower density than water, allowing it to float.
It is important to note that the float test is not 100% accurate, as other types of plastic may also float due to their low density. However, this test can be a quick and easy way to narrow down the type of plastic you are dealing with.
Additionally, it is worth mentioning that while PET is a popular and versatile plastic, it has come under scrutiny for its potential health and environmental risks. PET is intended for single use only, as repeated use may cause toxic chemicals to leach into food or drinks, especially when exposed to high heat or stored for long periods. These chemicals, such as antimony trioxide and phthalates, can have negative effects on human health, including endocrine and reproductive issues. Therefore, it is recommended to avoid using PET for food and beverage packaging whenever possible and opt for safer alternatives like glass, stainless steel, or wood.
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The burn test
Burning plastic is a common method used to identify different types of plastic polymers. This process is often used in recycling companies to identify and separate different types of plastics before processing.
If you decide to perform the burn test, you will need a candle or lighter, tweezers or pliers, and a sample of the plastic you want to identify. Hold the plastic sample with the tweezers or pliers and carefully bring it close to the flame. Observe the colour of the flame and any soot release, as well as whether the flame self-extinguishes. Different types of plastics will exhibit different behaviours when exposed to a flame. For example, PET (polyethylene terephthalate), which is commonly used for bottles, will produce a yellow flame with soot release.
In addition to the visual cues, experienced recyclers can also identify the type of plastic through the odour of the smoke. Each polymeric family has a distinct smell when burned, allowing for more precise identification. For example, the polyamide family, which includes members like polyamide 6 and polyamide 6.6, has a unique odour that can be recognised through experience.
By combining the observations of flame colour, soot release, self-extinguishing behaviour, and the odour of the smoke, you can get a good indication of the type of plastic you are working with. However, it is important to prioritise safety and only perform the burn test when necessary, as some plastics can release toxic fumes when burned.
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Chemical makeup
Polyethylene terephthalate (PET) is a type of plastic commonly used in single-use water bottles, food containers, and beverage bottles. It is also known as PETE, polyester, or polyethylene terephthalate glycol (PETG).
The chemical makeup of PET involves the polymerization of monomers, specifically the monomer bis(2-hydroxyethyl) terephthalate, which is synthesized through an esterification reaction between terephthalic acid and ethylene glycol, with water as a byproduct. This process can also be achieved through a transesterification reaction between ethylene glycol and dimethyl terephthalate (DMT), resulting in methanol as a byproduct. Polymerization occurs through a polycondensation reaction of the monomers, which takes place immediately after esterification or transesterification, yielding water as the byproduct.
PET can also be produced through the recycling of existing PET materials. Additionally, it has been found that at least one species of bacterium in the genus Nocardia can degrade PET using an esterase enzyme, which cleaves the ester bond between two oxygen atoms linking the subunits of PET.
PET is often chosen for its lightweight, durable, and water and bacteria-resistant properties. However, its widespread use has led to significant environmental concerns. PET is known to leach toxic chemicals, such as the heavy metal antimony trioxide, which is used in its production. Studies have detected antimony in bottled drinks and fruit juice concentrates packaged in PET, exceeding safe limits.
Furthermore, the production of PET contributes to the release of cancer-causing chemicals and environmental pollutants. The proposed expansion of PET plants, such as the Corpus Christi Polymers plant in Texas, has raised concerns about the increased production of PET and its environmental impact.
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Odour
Some plastics have a strong tangy odour, which is often associated with cheap items, especially those from China. This odour can be difficult to remove, even with soap, baking soda, or acid. While the exact source of this smell is hard to pinpoint without professional analysis, there are a few potential causes. One possibility is the presence of residual monomers or other substances used during the manufacturing process, such as terephthalic acid, which may be found in PET plastic. Another reason could be the addition of odour-masking substances to cover up other smells. Tangy smells, in particular, are often a symptom of some kind of ester.
In some cases, the odour may be due to polycyclic aromatic hydrocarbons (PAHs), although these compounds have been banned in commercial products in the EU and Italy since the 1980s. More recently, there has been a trend to add cheap orange flavouring to plastic to disguise other odours.
It is worth noting that PET plastic is often chosen for its odour-resistant properties. For example, PET plastic shoes are marketed as odour-free, as bacteria find it challenging to cling to the soft surface.
Additionally, when identifying plastic types, it is important to consider other factors such as the recycling codes and the flame and float tests. The recycling codes, indicated by a number inside a triangle, can provide information about the plastic's composition and the possibility of Bisphenol A (BPA) presence. PET plastic, for example, is identified by the code 1 and is known to be BPA-free. The flame test can also help distinguish between certain types of plastics, as different plastics produce distinct flame colours when ignited. For instance, a yellow flame with dark smoke could indicate either PET or polycarbonate.
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Density
PET, or polyethylene terephthalate, is a type of plastic with a density ranging from 1.3 to 1.4 g/cm³. In its amorphous state, PET has a density of 1.30–1.33 g/cm³, while in its crystalline state, the density increases to 1.33–1.40 g/cm³. This density range gives PET excellent heat resistance, corrosion resistance, and mechanical strength. Due to these properties, PET is widely used in manufacturing bottles, films, fibres, and other plastic products.
The density of PET is higher than that of some other plastics, such as low-density polyethylene (LDPE) and polypropylene (PP), which have densities ranging from 0.91 to 0.96 g/cm³ and 0.895–0.905 g/cm³, respectively. However, PET's density is lower than that of glass and metal, making it a lightweight alternative for packaging applications. For example, PET bottles weigh only about 7% of glass bottles, significantly reducing packaging weight and transportation costs.
The density of plastics can be altered by adding fillers or through different polymerization methods. For example, high-density polyethylene (HDPE) has a higher density than standard polyethylene (PE) due to a different polymerization method, resulting in a stronger and harder material.
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Frequently asked questions
PET stands for Polyethylene Terephthalate.
If the recycling symbol on your plastic container has a "'1'" in it, it's made of PET.
PET is used in the production of single-use plastic products like water and soda bottles, polyester clothing, and cuddly toys. It is also used in food and beverage packaging.
PET is commonly marketed as "'safe'", "highly recyclable", and "BPA-free". However, studies have shown that toxic chemicals can leach from PET plastic into food and drinks, especially when the container is heated or contains acidic food. These chemicals can have negative health effects, including endocrine and reproductive issues, early puberty, endometriosis, and infertility.
