Polyethylene terephthalate (PET) is one of the most common polymers in its polyester family. Its global market size was estimated to be worth US$37.25 billion in 2021. Polyethylene terephthalate is used in several applications such as; textile fibres, bottles, rigid/flexible packaging, and electronics. However, it accounts for 12% in global solid waste. This is why bottle recycling is highly encouraged and has reached its highest level in decades (33% in 2023). In 2023, the US collected 1,962 million pounds of bottles for recycling. Compared to glass bottles, the PET bottle is lightweight and has a lower carbon footprint in production and transportation. Recycling further reduces emissions. The recycled material can be put back into bottles, fibres, film, thermoformed packaging and strapping. After collecting the bottles from landfills, they are sorted, cleaned and grinded. This grinded material is "bottle flake", which is then processed by either:
"Basic" or "physical" recycling. Bottle flake is melted into its new shape directly with basic changes in its physical properties. "Chemical" or "advanced" recycle. Bottle flake is partially or totally depolymerized then enabling purification. The resulting oligomers or monomers are repolymerized to PET polymer, which is then processed in the same way as virgin polymer. In either case, the resulting feedstock is known as "r-PET" or "rPET" ("recycled PET"). This recycled PET's carbon footprint is 79% lower than virgin PET's, namely 0.45 kg CO2 per kg instead of 2.5 kg C02 per kg.
Bottle manufacturing PET and rPET are both used in the creation of bottled water (still and carbonated). Bottled water companies have been voluntarily using rPET in the production and many companies are producing bottles using 100% rPET nowadays. Such companies include Dasani, Fiji and Nestlé Pure Life. Other goods bottled in PET include oil, vinegar, milk, and shampoo. These bottles are closed with polyolefin screw closure with antitamper ring, and have a label which may be printed on paper or plastic and may be glued on. The resin may be colourless or tinted blue, green or brown, or pigmented white.
When manufacturing these water bottles, the energy used to mold the resin into its shape varies based on the bottle shape and its thickness. Some bottles have complex shapes such as Dasani while other bottles have a very simple form such as Smartwater. Therefore, the energy used to create these bottles can range from 8.33 - 20 MJ/kg where the units "MJ" represent megajoules, a unit for energy. The emissions associated with the production range from 0.034 – 0.046 kg C02-eq per 500mL.
Collection and sorting
The empty PET packaging is discarded by the consumer after its use and becomes PET waste. In the recycling industry, this is referred to as "post-consumer PET". All types of PET packaging, including bottles are usually marked with the recycle symbol 1. The bottles are sent to trash centers (materials recovery facilities) and get sorted out from the other disposable items. There are times when the recyclables are taken to a transfer station first. At this facility, the materials are stored, sorted, and compacted before being transported to a true recycling facility where they are further processed. This step is especially common in areas where MRFs are located far from collection points Here the PET bottles are sorted and separated from other objects and bottles made of other materials
Collection and sorting process in Switzerland Source:
recyclables collected from bins and sent to facility metal collection ballistic sorting (items that fall slower or faster in air such as dust, films, glass bottles and stones are removed here) metal separation again spectral sorting: sensors detect polymer type and colour sorting on a conveyor belt (manual) baling: the flattened bottles are compressed into bales for shipment to the processing centre
Types of sorting at MRFs Air classifiers: Stream of air directed towards conveyor belt that lifts away lighter materials (paper and light plastics) Eddy current / magnetic separators: Use magnets to separate magnetized and non-magnetized metals Manual separation: Workers stationed along conveyor belt that sort out items and contaminants (usually assisting the machines and catching what they missed) Optical sorters: A camera or laser sorts items based on color, shape, and other properties (still a new technology) Screens: Rotating screens that separate materials based on size (like a colander)
The sorted post-consumer PET bottless are flattened, pressed into bales and offered for sale to recycling companies. Colourless/light blue post-consumer PET attract higher sales prices than the darker blue and green fractions. The mixed color fraction is the least valuable due simply to the fact unlike aluminium, there are few standards when it comes to the coloration of PET. Unlike clear varieties, PET with unique color characteristics are only useful to the particular manufacturer that uses that color. For material recovery facilities, colored PET bottles are therefore a cause for concern as they can impact the financial viability of recycling such materials. The Plastics Recyclers Europe (PRE, Brussels, Belgium), that an upsurge in a variety of PET colors would be a problem because no market exists for them in the current recycling climate. From there, there are two types of recycling; chemical or mechanical.
Types of collections Deposit: some countries have legislated a deposit for packaging including PET bottles. In the EU, deposit schemes average an 86% recovery rate. Collect: waste collectors pick up PET bottles mixed into some other stream (54% recovery in EU). Bring: consumers take PET bottles and place them into a container (43% recovery in EU). Different countries have opted for different systems.
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