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Depending on its processing and thermal history, polyethylene terephthalate may exist both as an amorphous (transparent) and as a [[semi-crystalline polymer]]. The semicrystalline material might appear transparent (particle size less than 500 [[nanometre|nm]]) or opaque and white (particle size up to a few [[micrometre|micrometer]]s) depending on its crystal structure and particle size.
One process for making PET uses [[bis(2-hydroxyethyl) terephthalate]],{{
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Plastic bottles made from PET are widely used for [[soft drink]]s, both still and [[carbonation|sparkling]]. For beverages that are degraded by oxygen, such as beer, a multilayer structure is used. PET sandwiches an additional [[polyvinyl alcohol]] (PVOH) or [[polyamide]] (PA) layer to further reduce its oxygen permeability.
Non-oriented PET sheet can be [[thermoforming|thermoformed]] to make packaging trays and [[blister packs]].<ref>{{Citation|last=Pasbrig|first=Erwin|title=Cover film for blister packs|date=29 March 2007|url=http://www.google.com/patents/US20070068842|access-date=2016-11-20}}</ref> Crystallizable PET withstands freezing and oven baking temperatures.<ref>{{Cite book |last=Mishra |first=Munmaya |url=https://books.google.com/books?id=buiCDwAAQBAJ&dq=crystalline+pet+oven&pg=PA1378 |title=Encyclopedia of Polymer Applications, 3 Volume Set |date=2018-12-17 |publisher=CRC Press |isbn=978-1-351-01941-5 |language=en}}</ref>{{Rp|page=1378}} Both amorphous PET and BoPET are transparent to the naked eye. Color-conferring dyes can easily be formulated into PET sheet.
PET is permeable to oxygen and carbon dioxide and this imposes shelf life limitations of contents packaged in PET.<ref>{{Cite book |last1=Ashurst |first1=P. |url=https://books.google.com/books?id=FQykAgAAQBAJ&pg=PA104 |title=Soft Drink and Fruit Juice Problems Solved |last2=Hargitt |first2=R. |date=2009-08-26 |publisher=Elsevier |isbn=978-1-84569-706-8 |language=en}}</ref>{{Rp|page=104}}
===Flexible packaging===
[[BoPET|Biaxially oriented PET]] (BOPET) film (often known by one of its trade names, "Mylar") can be aluminized by [[evaporation|evaporating]] a [[thin-film deposition|thin film]] of metal onto it to reduce its permeability, and to make it reflective and opaque ([[metallized polyethylene terephthalate|MPET]]). These properties are useful in many applications, including flexible food [[packaging and labeling|packaging]] and [[thermal insulation]] (such as [[space blanket]]s).
===Photovoltaic modules===
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* A waterproofing barrier in [[undersea cables]].
* As a [[film base]].
* As a fibre, spliced into bell rope tops to help prevent wear on the ropes as they pass through the ceiling.
* Since late 2014 as liner material in type IV composite high pressure [[gas cylinder]]s. PET works as a much better barrier to oxygen than earlier used (LD)PE.<ref>[https://www.plasteurope.com/news/SIPA_t229769/ SIPA: Lightweight compressed gas cylinders have plastic liners / PET provides high oxygen barrier] https://www.plasteurope.com, 18 November 2014, retrieved 16 May 2017.</ref>
* As a [[3D printing]] filament, as well as in the 3D printing plastic [[#Copolymers|PETG]] (polyethylene terephthalate glycol). In 3D printing PETG has become a popular material<ref>{{Cite journal |last=Santana |first=Leonardo |last2=Alves |first2=Jorge Lino |last3=Sabino Netto |first3=Aurélio da Costa |last4=Merlini |first4=Claudia |date=2018-12-06 |title=Estudo comparativo entre PETG e PLA para Impressão 3D através de caracterização térmica, química e mecânica |url=https://www.scielo.br/j/rmat/a/dpWDvBJzSXYtzbKnJdDqHVg/?lang=pt |journal=Matéria (Rio de Janeiro) |language=pt |volume=23 |pages=e12267 |doi=10.1590/S1517-707620180004.0601 |issn=1517-7076}}</ref> - used for high-end applications like surgical fracture tables<ref>{{Cite journal |last=Bow |first=J. K. |last2=Gallup |first2=N. |last3=Sadat |first3=S. A. |last4=Pearce |first4=J. M. |date=2022-07-15 |title=Open source surgical fracture table for digitally distributed manufacturing |url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0270328 |journal=PLOS ONE |language=en |volume=17 |issue=7 |pages=e0270328 |doi=10.1371/journal.pone.0270328 |issn=1932-6203 |pmc=
* As one of three layers for the creation of glitter; acting as a plastic core coated with aluminum and topped with plastic to create a light reflecting surface,<ref name="Green 124070">{{Cite journal |last=Green |first=Dannielle Senga |last2=Jefferson |first2=Megan |last3=Boots |first3=Bas |last4=Stone |first4=Leon |date=2021-01-15 |title=All that glitters is litter? Ecological impacts of conventional versus biodegradable glitter in a freshwater habitat |url=https://www.sciencedirect.com/science/article/pii/S0304389420320604 |journal=Journal of Hazardous Materials |language=en |volume=402 |pages=124070 |doi=10.1016/j.jhazmat.2020.124070 |issn=0304-3894}}</ref> although as of 2021 many glitter manufacturing companies have begun to phase out the use of PET after calls from organizers of festivals to create bio-friendly glitter alternatives.<ref
▲* As a [[3D printing]] filament, as well as in the 3D printing plastic [[#Copolymers|PETG]] (polyethylene terephthalate glycol). In 3D printing PETG has become a popular material<ref>{{Cite journal |last=Santana |first=Leonardo |last2=Alves |first2=Jorge Lino |last3=Sabino Netto |first3=Aurélio da Costa |last4=Merlini |first4=Claudia |date=2018-12-06 |title=Estudo comparativo entre PETG e PLA para Impressão 3D através de caracterização térmica, química e mecânica |url=https://www.scielo.br/j/rmat/a/dpWDvBJzSXYtzbKnJdDqHVg/?lang=pt |journal=Matéria (Rio de Janeiro) |language=pt |volume=23 |pages=e12267 |doi=10.1590/S1517-707620180004.0601 |issn=1517-7076}}</ref> - used for high-end applications like surgical fracture tables<ref>{{Cite journal |last=Bow |first=J. K. |last2=Gallup |first2=N. |last3=Sadat |first3=S. A. |last4=Pearce |first4=J. M. |date=2022-07-15 |title=Open source surgical fracture table for digitally distributed manufacturing |url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0270328 |journal=PLOS ONE |language=en |volume=17 |issue=7 |pages=e0270328 |doi=10.1371/journal.pone.0270328 |issn=1932-6203 |pmc=PMC9286293 |pmid=35839177}}</ref> to automotive and aeronautical sectors, among other industrial applications.<ref>{{Cite journal |last=Valvez |first=Sara |last2=Silva |first2=Abilio P. |last3=Reis |first3=Paulo N. B. |date=2022 |title=Optimization of Printing Parameters to Maximize the Mechanical Properties of 3D-Printed PETG-Based Parts |url=https://www.mdpi.com/2073-4360/14/13/2564 |journal=Polymers |language=en |volume=14 |issue=13 |pages=2564 |doi=10.3390/polym14132564 |issn=2073-4360 |pmc=PMC9269443 |pmid=35808611}}</ref> The surface properties can be modified to make PETG self-cleaning for applications like the fabrication of traffic signs for the manufacture of light-emitting diode LED spotlights. <ref>{{Cite journal |last=Barrios |first=Juan M. |last2=Romero |first2=Pablo E. |date=2019-01 |title=Improvement of Surface Roughness and Hydrophobicity in PETG Parts Manufactured via Fused Deposition Modeling (FDM): An Application in 3D Printed Self–Cleaning Parts |url=https://www.mdpi.com/1996-1944/12/15/2499 |journal=Materials |language=en |volume=12 |issue=15 |pages=2499 |doi=10.3390/ma12152499 |issn=1996-1944 |pmc=PMC6696107 |pmid=31390834}}</ref>
▲* As one of three layers for the creation of glitter; acting as a plastic core coated with aluminum and topped with plastic to create a light reflecting surface,<ref>{{Cite journal |last=Green |first=Dannielle Senga |last2=Jefferson |first2=Megan |last3=Boots |first3=Bas |last4=Stone |first4=Leon |date=2021-01-15 |title=All that glitters is litter? Ecological impacts of conventional versus biodegradable glitter in a freshwater habitat |url=https://www.sciencedirect.com/science/article/pii/S0304389420320604 |journal=Journal of Hazardous Materials |language=en |volume=402 |pages=124070 |doi=10.1016/j.jhazmat.2020.124070 |issn=0304-3894}}</ref> although as of 2021 many glitter manufacturing companies have begun to phase out the use of PET after calls from organizers of festivals to create bio-friendly glitter alternatives.<ref>{{Cite journal |last=Green |first=Dannielle Senga |last2=Jefferson |first2=Megan |last3=Boots |first3=Bas |last4=Stone |first4=Leon |date=2021-01-15 |title=All that glitters is litter? Ecological impacts of conventional versus biodegradable glitter in a freshwater habitat |url=https://www.sciencedirect.com/science/article/pii/S0304389420320604 |journal=Journal of Hazardous Materials |language=en |volume=402 |pages=124070 |doi=10.1016/j.jhazmat.2020.124070 |issn=0304-3894}}</ref><ref>{{Cite web |last=Street |first=Chloe |date=2018-08-06 |title=61 UK festivals are banning glitter - make the switch to eco sparkle |url=https://www.standard.co.uk/beauty/music-festivals-ban-glitter-microbeads-microplastic-a3812661.html |access-date=2023-03-25 |website=Evening Standard |language=en}}</ref>
* Film for tape applications, such as the carrier for [[magnetic tape]] or backing for [[pressure-sensitive tape|pressure-sensitive adhesive tapes]]. Digitalization has caused the virtual disappeance of the magnetic audio and videotape application.
* [[Papermaking|Water-resistant paper]].<ref>{{cite web|author=Teijin|author-link=Teijin|title=Teijin Develops Eco-friendly Wet-strong Printing Paper Made 100% with Recycled Polyester Derived from Used PET Bottles|url=http://www.teijin.com/news/2013/ebd130312_00.html|publisher=Teijin Group|access-date=March 12, 2013|archive-url=https://web.archive.org/web/20130825005928/http://www.teijin.com/news/2013/ebd130312_00.html|archive-date=August 25, 2013|url-status=dead}}</ref>
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==Physical properties==
[[File:Thistle dinghy with skipper Terry Lettenmaier sailing downwind.jpg|thumb|[[Sailcloth]] is typically made from PET fibers also known as polyester or under the brand name Dacron; colorful lightweight [[spinnaker]]s are usually made of [[nylon]].]]
PET in its most stable state is a colorless, semi-crystalline resin. However it is intrinsically slow to crystallize compared to other semicrystalline polymers. Depending on processing conditions it can be formed into either amorphous or crystalline articles. Its amenability to drawing makes PET useful in fibre and film applications. Like most aromatic polymers, it has better barrier properties than aliphatic polymers. It is strong and [[toughness|impact-resistant]]. PET is [[hygroscopic]].<ref>{{Cite book |last=Margolis |first=James M. |url=https://books.google.com/books?id=5wcCEAAAQBAJ&pg=PA12 |title=Engineering Thermoplastics: Properties and Applications |date=2020-10-28 |publisher=CRC Press |isbn=978-1-000-10411-0 |language=en}}</ref>
About 60% crystallization is the upper limit for commercial products, with the exception of polyester fibers. Transparent products can be produced by rapidly cooling molten polymer below T<sub>g</sub> [[glass transition temperature]] to form an [[amorphous solid]].<ref>{{Cite book|title=Modern polyesters : chemistry and technology of polyesters and copolyesters|date=2003|publisher=John Wiley & Sons|author1=Scheirs, John |author2=Long, Timothy E. |isbn=0-471-49856-4|location=Hoboken, N.J.|oclc=85820031}}</ref> Like glass, amorphous PET forms when its molecules are not given enough time to arrange themselves in an orderly, crystalline fashion as the melt is cooled. At room temperature the molecules are frozen in place, but, if enough heat energy is put back into them by heating above T<sub>g</sub>, they begin to move again, allowing crystals to [[nucleation|nucleate]] and grow. This procedure is known as solid-state crystallization.
When allowed to cool slowly, the molten polymer forms a more crystalline material. This material has [[Spherulite (polymer physics)|spherulites]] containing many small [[crystallite]]s when crystallized from an amorphous solid, rather than forming one large single crystal. Light tends to scatter as it crosses the boundaries between crystallites and the amorphous regions between them, causing the resulting solid to be translucent.
Orientation also renders polymers more transparent. This is why BOPET film and bottles are both crystalline to a degree and transparent.
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*reduced molecular weight
*formation of [[acetaldehyde]],
*[[cross-link]]ing ("gel" or "fish-eye" formation).
Mitigation measures include
*[[copolymer
*The addition of [[polymer stabilisers]] such as [[phosphites]].<ref>{{cite book |author1=F Gugumus |editor1-last=Gaechter and Mueller |title=Plastics additives handbook : stabilizers, processing aids, plasticizers, fillers, reinforcements, colorants for thermoplastics |date=1996 |publisher=Hanser |location=Munich |isbn=3446175717 |page=92 |edition=4th }}</ref>
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===End of life===
====Recycle====
PET bottles lend themselves well to recycling (see below). In many countries PET bottles are recycled to a substantial degree,<ref name="link.springer.com">{{Cite journal |last1=Malik |first1=Neetu |last2=Kumar |first2=Piyush |last3=Shrivastava |first3=Sharad |last4=Ghosh |first4=Subrata Bandhu |date=June 2017 |title=An overview on PET waste recycling for application in packaging |url=http://link.springer.com/10.1007/s12588-016-9164-1 |journal=International Journal of Plastics Technology |language=en |volume=21 |issue=1 |pages=1–24 |doi=10.1007/s12588-016-9164-1 |s2cid=99732501 |issn=0972-656X}}</ref> for example about 75% in Switzerland.<ref>{{cite web |url=https://www.petrecycling.ch/tl_files/content/PDF/Medien/Geschaeftsberichte/PET-Recycling_Schweiz_Rapport_de_gestion_2019.pdf |title=RAPPORT DE GESTION 2019|language=fr|publisher=Swiss PET Recycling Association|access-date=5 March 2022|page=5}}</ref> The term rPET is commonly used to describe the recycled material, though it is also referred to as R-PET or post-consumer PET (POSTC-PET).<ref>{{Cite journal |last1=Awaja |first1=Firas |last2=Pavel |first2=Dumitru |date=2005-07-01 |title=Recycling of PET |url=https://www.sciencedirect.com/science/article/pii/S0014305705000728 |journal=European Polymer Journal |language=en |volume=41 |issue=7 |pages=1453–1477 |doi=10.1016/j.eurpolymj.2005.02.005 |issn=0014-3057}}</ref><ref>{{Cite web |last= |date=2020-05-08 |title=PET and its eco-friendly alternative: rPET |url=https://www.preventedoceanplastic.com/pet-and-its-eco-friendly-alternative-rpet/ |access-date=2022-10-09 |website=Prevented Ocean Plastic |language=en-GB}}</ref>
====Energy recovery====
PET is a desirable fuel for [[Waste-to-energy plant]]s, as it has a high calorific value which helps to reduce the use of primary resources for energy generation.<ref>{{cite journal |last1=Palacios-Mateo |first1=Cristina |last2=van der Meer |first2=Yvonne |last3=Seide |first3=Gunnar |title=Analysis of the polyester clothing value chain to identify key intervention points for sustainability |journal=Environmental Sciences Europe |date=6 January 2021 |volume=33 |issue=1 |pages=2 |doi=10.1186/s12302-020-00447-x |pmid=33432280 |pmc=7787125 |issn=2190-4715}}</ref>
====Littering====
Nevertheless, [[
====Dumping of apparel====
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Worldwide, 480 billion plastic drinking bottles were made in 2016 (and less than half were recycled).<ref>Sandra Laville and Matthew Taylor, [https://www.theguardian.com/environment/2017/jun/28/a-million-a-minute-worlds-plastic-bottle-binge-as-dangerous-as-climate-change "A million bottles a minute: world's plastic binge 'as dangerous as climate change'"], [[TheGuardian.com]], 28 June 2017 (page visited on 20 July 2017).</ref>
While most thermoplastics can, in principle, be recycled, [[PET bottle recycling]] is more practical than many other plastic applications because of the high value of the resin and the almost exclusive use of PET for widely used water and carbonated soft drink bottling.<ref
Because of the recyclability of PET and the relative abundance of [[post-consumer waste]] in the form of bottles, PET is rapidly gaining market share as a carpet fiber.<ref>{{cite web |title=R-PET: Schweizer Kreislauf – PET-Recycling |url=https://www.petrecycling.ch/fr/savoir/recycling-pet/r-pet-schweizer-kreislauf-kopie |website=www.petrecycling.ch |language=fr|access-date=6 March 2022}}</ref> [[Mohawk Industries]] released everSTRAND in 1999, a 100% post-consumer recycled content PET fiber. Since that time, more than 17 billion bottles have been recycled into carpet fiber.<ref>[http://carpet-inspectors-experts.com/old/everstrand-smartstrand.htm everSTRAND]{{dead link|date=March 2018 |bot=InternetArchiveBot |fix-attempted=yes }} Carpet-inspectors-experts.com [https://web.archive.org/web/20080317233830/http://carpet-inspectors-experts.com/everstrand-smartstrand.htm archive 2008-03-17]</ref> Pharr Yarns, a supplier to numerous carpet manufacturers including Looptex, Dobbs Mills, and Berkshire Flooring,<ref>[http://www.simplygreencarpet.com/ Simply Green Carpet – A Berkshire Flooring Brand]. simplygreencarpet.com</ref> produces a BCF (bulk continuous filament) PET carpet fiber containing a minimum of 25% post-consumer recycled content.
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#The chemical recycling back to the initial raw materials purified [[terephthalic acid]] (PTA) or [[dimethyl terephthalate]] (DMT) and [[ethylene glycol]] (EG) where the polymer structure is destroyed completely, or in process intermediates like [[bis(2-hydroxyethyl) terephthalate]]
#The mechanical recycling where the original polymer properties are being maintained or reconstituted.
#The chemical recycling where transesterification takes place and other glycols/polyols or glycerol are added to make a polyol which may be used in other ways such as polyurethane production or PU foam production<ref>{{Cite journal|last=Makuska|first=Ricardas|date=2008| number= 2 |title=Glycolysis of industrial poly(ethylene terephthalate) waste directed to bis(hydroxyethylene) terephthalate and aromatic polyester polyols|journal=Chemija|volume=19|pages=29–34 |url=https://mokslozurnalai.lmaleidykla.lt/publ/0235-7216/2008/2/29-34.pdf }}</ref><ref>{{Cite web|url=https://arropol.com/|title=Arropol {{!}} Arropol Chemicals|language=en-US|access-date=2019-01-02}}</ref><ref>{{Cite journal |last1=Shirazimoghaddam |first1=Shadi |last2=Amin |first2=Ihsan |last3=Faria Albanese |first3=Jimmy A |last4=Shiju |first4=N. Raveendran |date=2023-01-03 |title=Chemical Recycling of Used PET by Glycolysis Using Niobia-Based Catalysts |url=https://pubs.acs.org/doi/10.1021/acsengineeringau.2c00029 |journal=ACS Engineering Au |language=en |pages=acsengineeringau.2c00029 |doi=10.1021/acsengineeringau.2c00029 |s2cid=255634660 |issn=2694-2488|pmc=9936547 }}</ref><ref>{{Cite journal |last1=Jehanno |first1=Coralie |last2=Pérez-Madrigal |first2=Maria M. |last3=Demarteau |first3=Jeremy |last4=Sardon |first4=Haritz |last5=Dove |first5=Andrew P. |date=2018-12-21 |title=Organocatalysis for depolymerisation |url=https://pubs.rsc.org/en/content/articlelanding/2019/py/c8py01284a |journal=Polymer Chemistry |language=en |volume=10 |issue=2 |pages=172–186 |doi=10.1039/C8PY01284A |s2cid=106033120 |issn=1759-9962|hdl=2117/365711 |hdl-access=free }}</ref> In addition, PET can even be recycled chemically into epoxy based products including paints.<ref>{{Cite journal |last1=Bal |first1=Kevser |last2=Ünlü |first2=Kerim Can |last3=Acar |first3=Işıl |last4=Güçlü |first4=Gamze |date=2017-05-01 |title=Epoxy-based paints from glycolysis products of postconsumer PET bottles: synthesis, wet paint properties and film properties |url=https://doi.org/10.1007/s11998-016-9895-0 |journal=Journal of Coatings Technology and Research |language=en |volume=14 |issue=3 |pages=747–753 |doi=10.1007/s11998-016-9895-0 |issn=1935-3804}}</ref>
Chemical recycling of PET will become cost-efficient only applying high capacity recycling lines of more than 50,000 tons/year. Such lines could only be seen, if at all, within the production sites of very large polyester producers. Several attempts of industrial magnitude to establish such chemical recycling plants have been made in the past but without resounding success. Even the promising chemical recycling in Japan has not become an industrial breakthrough so far. The two reasons for this are: at first, the difficulty of consistent and continuous waste bottles sourcing in such a huge amount at one single site, and, at second, the steadily increased prices and price volatility of collected bottles. The prices of baled bottles increased for instance between the years 2000 and 2008 from about 50 Euro/ton to over 500 Euro/ton in 2008.
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