page_title: Polyethylene terephthalate
section_title: Purification and decontamination
hierarchical_section_title: Polyethylene terephthalate / Polyester recycling industry / PET bottle recycling / Purification and decontamination
caption_attribution_description: English: Bales of crushed PET bottles sorted according to the colour to green, transparent and blue ones. In Olomouc, the Czech Republic. Čeština: Balíky PET lahví (roztříděné na zelené, průhledné a modré) připravené ke transportu a zpracování.
context_page_description: Polyethylene terephthalate, commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is the most common thermoplastic polymer resin of the polyester family and is used in fibres for clothing, containers for liquids and foods, thermoforming for manufacturing, and in combination with glass fibre for engineering resins.
  It may also be referred to by the brand names Terylene in the UK, Lavsan in Russia and the former Soviet Union, and Dacron in the US.
  The majority of the world's PET production is for synthetic fibres, with bottle production accounting for about 30% of global demand. In the context of textile applications, PET is referred to by its common name, polyester, whereas the acronym PET is generally used in relation to packaging. Polyester makes up about 18% of world polymer production and is the fourth-most-produced polymer after polyethylene, polypropylene and polyvinyl chloride.
  PET consists of polymerized units of the monomer ethylene terephthalate, with repeating units. PET is commonly recycled, and has the number "1" as its resin identification code.
context_section_description: The success of any recycling concept is hidden in the efficiency of purification and decontamination at the right place during processing and to the necessary or desired extent.
  In general, the following applies: The earlier in the process foreign substances are removed, and the more thoroughly this is done, the more efficient the process is.
  The high plasticization temperature of PET in the range of 280 °C (536 °F) is the reason why almost all common organic impurities such as PVC, PLA, polyolefin, chemical wood-pulp and paper fibers, polyvinyl acetate, melt adhesive, coloring agents, sugar, and protein residues are transformed into colored degradation products that, in their turn, might release in addition reactive degradation products. Then, the number of defects in the polymer chain increases considerably. The particle size distribution of impurities is very wide, the big particles of 60–1000 µm—which are visible by naked eye and easy to filter—representing the lesser evil, since their total surface is relatively small and the degradation speed is therefore lower. The influence of the microscopic particles, which—because they are many—increase the frequency of defects in the polymer, is relatively greater.
  The motto "What the eye does not see the heart cannot grieve over" is considered to be very important in many recycling processes. Therefore, besides efficient sorting, the removal of visible impurity particles by melt filtration processes plays a particular part in this case.
  In general, one can say that the processes to make PET bottle flakes from collected bottles are as versatile as the different waste streams are different in their composition and quality. In view of technology there isn't just one way to do it. Meanwhile, there are many engineering companies that are offering flake production plants and components, and it is difficult to decide for one or other plant design. Nevertheless, there are processes that are sharing most of these principles. Depending on composition and impurity level of input material, the general following process steps are applied.
  Bale opening, briquette opening
  Sorting and selection for different colors, foreign polymers especially PVC, foreign matter, removal of film, paper, glass, sand, soil, stones, and metals
  Pre-washing without cutting
  Coarse cutting dry or combined to pre-washing
  Removal of stones, glass, and metal
  Air sifting to remove film, paper, and labels
  Grinding, dry and / or wet
  Removal of low-density polymers (cups) by density differences
  Hot-wash
  Caustic wash, and surface etching, maintaining intrinsic viscosity and decontamination
  Rinsing
  Clean water rinsing
  Drying
  Air-sifting of flakes
  Automatic flake sorting
  Water circuit and water treatment technology
  Flake quality control
caption: Bales of crushed PET bottles sorted according to color: green, transparent, and blue.
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