Polyethylene terephthalate

{{Short description|Polymer}} {{Redirect|PETE|other uses|Pete}} {{Use dmy dates|date=July 2020}} {{Chembox | Verifiedfields = change | Watchedfields = changed | verifiedrevid = 477001662 | Name = | ImageFile = | ImageFile1 = 300px|class=skin-invert-image|Strukturformel von Polyethylenterephthalat (PET) | ImageSize1 = 250px | ImageName1 = | ImageFile2 = Polyethylene-terephthalate-3D-spacefill.png | ImageClass2 = bg-transparent | ImageSize2 = 250px | ImageAlt2 = PET polymer chain | ImageFile3 = Polyethylene-terephthalate-3D-balls.png | ImageClass3 = bg-transparent | ImageSize3 = 250px | ImageAlt3 = A short section of a PET polymer chain | IUPACName = Poly(ethylene terephthalate) | OtherNames = Terylene (trademark); Dacron (trademark). | SystematicName = Poly(oxyethyleneoxyterephthaloyl) | Section1 = {{Chembox Identifiers | Abbreviations = PET, PETE | CASNo = 25038-59-9 | CASNo_Ref = {{cascite|correct|CAS}} | UNII_Ref = {{fdacite|correct|FDA}} | UNII =5YSH70HE6K | PubChem = | ChEBI = 53259 | SMILES = | ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}} | ChemSpiderID = None }} | Section2 = {{Chembox Properties | Formula = (C10H8O4)n<ref name="van der Vegt">{{cite book|last1=van der Vegt|first1=A. K.|last2=Govaert|first2=L. E.|date=2005|title=Polymeren, van keten tot kunstof|publisher=VSSD|isbn=978-90-71301-48-3}}{{page needed|date=February 2025}}</ref> | MolarMass = 10–50{{nbsp}}kg/mol, varies | Appearance = | Density = {{ubl | 1.38{{nbsp}}g/cm3, 20{{nbsp}}°C<ref name="GESTIS">{{GESTIS|ZVG=530566|Name=Polyethylenterephthalat|Date=7 November 2007}}</ref> | 1.370{{nbsp}}g/cm3,<ref name="van der Vegt" /> amorphous | 1.455{{nbsp}}g/cm3,<ref name="van der Vegt" /> single crystal }} | Solubility = Practically insoluble<ref name="GESTIS"/> | MeltingPt = > | MeltingPtC = 250 | MeltingPt_ref = <ref name="GESTIS"/> 260{{nbsp}}°C<ref name="van der Vegt" /> | BoilingPt = > | BoilingPtC = 350 | BoilingPt_notes= (decomposes) | ThermalConductivity = 0.15<ref name="Lange_16ed">{{Cite book |last1=Speight |first1=J. G. |url=https://archive.org/details/langeshandbookof70edlang/page/2807 |title=Lange's Handbook of Chemistry |last2=Lange |first2=Norbert Adolph |year=2005 |isbn=0-07-143220-5 |editor-last=McGraw-Hill |edition=16th |pages=[https://archive.org/details/langeshandbookof70edlang/page/2807 2807–2758] |url-access=registration}}</ref> to 0.24{{nbsp}}W/(m·K)<ref name="van der Vegt"/> | RefractIndex = 1.57–1.58,<ref name="Lange_16ed" /> 1.5750<ref name="van der Vegt" /> | LogP = 0.94540<ref name="chemsrc">{{Cite web|url=https://www.chemsrc.com/en/cas/25038-59-9_894380.html|title=poly(ethylene terephthalate) macromolecule_msds}}</ref> }} | Section3 = {{Chembox Hazards | MainHazards = | FlashPt = | AutoignitionPt = }} | Section4 = {{Chembox Thermochemistry | DeltaHc = | DeltaHf = | Entropy = | HeatCapacity = 1.0{{nbsp}}kJ/(kg·K)<ref name="van der Vegt" /> }} | Section5 = | Section6 = | Section8 = {{Chembox Related | OtherFunction_label = monomers | OtherFunction = Terephthalic acid Ethylene glycol }} }}

'''Polyethylene terephthalate''' (or '''poly(ethylene terephthalate)''',<ref name="Plastics Europe">{{Cite web |title=Plastics - the Facts 2022 • Plastics Europe |url=https://plasticseurope.org/knowledge-hub/plastics-the-facts-2022/ |access-date=2025-03-15 |website=Plastics Europe |language=en-GB}}</ref> '''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, and thermoformed parts for manufacturing, and in combination with glass fibre for engineering resins.<ref name="De Vos-2021">{{cite journal |last1=De Vos |first1=Lobke |last2=Van de Voorde |first2=Babs |last3=Van Daele |first3=Lenny |last4=Dubruel |first4=Peter |last5=Van Vlierberghe |first5=Sandra |title=Poly(alkylene terephthalate)s: From current developments in synthetic strategies towards applications |journal=European Polymer Journal |date=December 2021 |volume=161 |article-number=110840 |doi=10.1016/j.eurpolymj.2021.110840 |bibcode=2021EurPJ.16110840D |hdl=1854/LU-8730084 |url=https://biblio.ugent.be/publication/8731343 |hdl-access=free }}</ref>

In 2025, annual global production of PET was 31 million tons with 2031 projections showing over 40 million tons.<ref>{{cite web |author= |date=2026-01-06 |title=Polyethylene Terephthalate (PET) Market Size & Share Analysis - Growth Trends and Forecast (2026 - 2031) |url=https://www.mordorintelligence.com/industry-reports/polyethylene-terephtalate-market |website=mordorintelligence.com |access-date=2026-05-08}}</ref> 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. PET used in non-fiber applications (i.e. for packaging) makes up about 6% of world polymer production by mass. Including the >60% fraction of polyethylene terephthalate produced for use as polyester fibers, PET is the fourth-most-produced polymer after polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC).<ref name="Plastics Europe" />

PET consists of repeating (C10H8O4) units. PET is commonly recycled, and has the digit 1 (♳) as its resin identification code (RIC). The National Association for PET Container Resources (NAPCOR) defines PET as: "Polyethylene terephthalate items referenced are derived from terephthalic acid (or dimethyl terephthalate) and mono ethylene glycol, wherein the sum of terephthalic acid (or dimethyl terephthalate) and mono ethylene glycol reacted constitutes at least 90 percent of the mass of monomer reacted to form the polymer, and must exhibit a melting peak temperature between 225 °C and 255 °C, as identified during the second thermal scan in procedure 10.1 in ASTM D3418, when heating the sample at a rate of 10 °C/minute."<ref>{{Cite news|title=What is PET? |url=https://napcor.com/about-pet/ |work=NAPCOR |access-date=2020-07-08 |language=en-US}}</ref>

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 nm) or opaque and white (particle size up to a few micrometers) depending on its crystal structure and particle size.

One process for making PET uses bis(2-hydroxyethyl) terephthalate, which can be synthesized by the esterification reaction between terephthalic acid and ethylene glycol with water as a byproduct (this is also known as a condensation reaction), or by transesterification reaction between ethylene glycol and dimethyl terephthalate (DMT) with methanol as a byproduct. It can also be obtained by recycling of PET.<ref>{{Cite web |title=Polyethylene terephthalate is an often-recycled plastic, but industry is still seeking major improvements |url=https://cen.acs.org/environment/recycling/recyclers-break-polyester-barrier/101/i39?ref=search_results |access-date=2025-03-15 |website=Chemical & Engineering News |language=en}}</ref> Polymerization is through a polycondensation reaction of the monomers (done immediately after esterification/transesterification) with water as the byproduct.<ref name="De Vos-2021" />

{| class="wikitable floatright" style="clear:right; width:300px;" |- | Young's modulus, ''E'' | 2800–3100 MPa |- | Tensile strength, ''σ''t | 55–75 MPa |- | Elastic limit | 50–150% |- | Notch test | 3.6 kJ/m2 |- | Glass transition temperature, ''T''g | 67–81 °C |- | Vicat ''B'' | 82 °C |- | Linear expansion coefficient, ''α'' | {{val|7|e=-5|u=K−1}} |- | Water absorption (ASTM) | 0.16 |- ! colspan="2" style="text-align:left;" | Source<ref name="van der Vegt" /> |}

==Uses==

===Textiles===

Polyester fibres are widely used in the textile industry. The invention of the polyester fibre is attributed to J. R. Whinfield.<ref>{{cite journal |last1=Whinfield |first1=J.R. |title=The Development of Terylene |journal=Textile Research Journal |date=May 1953 |volume=23 |issue=5 |pages=289–293 |doi=10.1177/004051755302300503 }}</ref> It was first commercialized in the 1940s by ICI, under the brand 'Terylene'.<ref>The name Terylene was formed by inversion of (polyeth)ylene ter(ephthalate) and dates to the 1940s. [https://web.archive.org/web/20120930041817/http://oxforddictionaries.com/definition/english/Terylene Oxford Dictionary]. Terylene was first registered as a UK trademark in April 1946.{{Citation needed|date=May 2016}} UK Intellectual Property Office {{UK trademark|646992|UK00000646992}}</ref> Subsequently E. I. DuPont launched the brand 'Dacron'. As of 2022, there are many brands around the world, mostly Asian.

Polyester fibres are used in fashion apparel often blended with cotton, as heat insulation layers in thermal wear, sportswear and workwear and automotive upholstery.

===Rigid packaging=== Plastic bottles made from PET are widely used for soft drinks, both still and 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 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=https://patents.google.com/patent/US20070068842|access-date=2016-11-20}}</ref> Both amorphous PET and biaxially oriented PET (BoPET) are transparent to the naked eye. 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}}

In the early 2000s, the global PET packaging market grew at a compound annual growth rate of 9% to €17 billion in 2006.<ref>{{Cite web |last=Patton |first=Dominique |date=2008-01-16 |title=Salzgitter to buy SIG Beverages unit |url=https://www.beveragedaily.com/Article/2008/01/16/Salzgitter-to-buy-SIG-Beverages-unit |access-date=2023-11-01 |website=Beverage Daily}}</ref>

===Flexible packaging=== Biaxially oriented PET (BOPET) film can be aluminized by evaporating a thin film of metal onto it to reduce its permeability, and to make it reflective and opaque (MPET). These properties are useful in many applications, including flexible food packaging and thermal insulation (such as space blankets).

===Photovoltaic modules=== BOPET is used in the backsheet of photovoltaic modules. Most backsheets consist of a layer of BOPET laminated to a fluoropolymer or a layer of UV stabilized BOPET.<ref>{{cite web |title=COVEME PHOTOVOLTAIC Backsheets and Frontsheets for PV modules |url=https://www.coveme.com/files/documenti/divisioni-brochure/solare/coveme_photovoltaics_brochure_2020_eng.pdf |access-date=4 March 2022}}</ref>

PET is also used as a substrate in thin film solar cells.

===Thermoplastic resins=== PET can be compounded with glass fibre and crystallization accelerators, to make thermoplastic resins. These can be injection moulded into parts such as housings, covers, electrical appliance components and elements of the ignition system.<ref>{{cite web |title=Rynite PET Design Guide |url=http://foremostplastic.com/wp-content/uploads/2015/04/DuPont-Module-IV-Rynite.pdf |publisher=DuPont |access-date=4 March 2022}}</ref>

===Other applications===

* 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 cylinders. PET works as a much better barrier to oxygen than earlier used low density polyethylene (LDPE).<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 polyethylene terephthalate glycol (PETG). In 3D printing PETG has become a popular material<ref>{{Cite journal |last1=Santana |first1=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 |journal=Matéria (Rio de Janeiro) |language=pt |volume=23 |issue=4 |pages=e12267 |doi=10.1590/S1517-707620180004.0601 |doi-access=free }}</ref> - used for high-end applications like surgical fracture tables.<ref>{{Cite journal |last1=Bow |first1=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 |journal=PLOS ONE |volume=17 |issue=7 |article-number=e0270328 |doi=10.1371/journal.pone.0270328 |pmc=9286293 |pmid=35839177 |bibcode=2022PLoSO..1770328B |doi-access=free }}</ref> And in the automotive and aeronautical sectors, among other industrial applications.<ref>{{Cite journal |last1=Valvez |first1=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 |journal=Polymers |volume=14 |issue=13 |page=2564 |doi=10.3390/polym14132564 |pmc=9269443 |pmid=35808611 |doi-access=free }}</ref> The surface properties can be modified to make PETG self-cleaning for applications like the fabrication of traffic signs for the manufacture of LED spotlights.<ref>{{Cite journal |last1=Barrios |first1=Juan M. |last2=Romero |first2=Pablo E. |date=January 2019 |title=Improvement of Surface Roughness and Hydrophobicity in PETG Parts Manufactured via Fused Deposition Modeling (FDM): An Application in 3D Printed Self–Cleaning Parts |journal=Materials |volume=12 |issue=15 |page=2499 |doi=10.3390/ma12152499 |pmc=6696107 |pmid=31390834 |bibcode=2019Mate...12.2499B |doi-access=free }}</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 name="Green 124070">{{cite journal |last1=Green |first1=Dannielle Senga |last2=Jefferson |first2=Megan |last3=Boots |first3=Bas |last4=Stone |first4=Leon |title=All that glitters is litter? Ecological impacts of conventional versus biodegradable glitter in a freshwater habitat |journal=Journal of Hazardous Materials |date=January 2021 |volume=402 |article-number=124070 |doi=10.1016/j.jhazmat.2020.124070 |pmid=33254837 |bibcode=2021JHzM..40224070G }}</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 name="Green 124070"/><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 adhesive tapes. Digitalization has caused the virtual disappearance of the magnetic audio and videotape application. * 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}}</ref>

<gallery mode=packed> File:PETling.jpg|PET preform for injection stretch blow moulding of a bottle File:Clean the Bay 2012 (7324648864).jpg|A finished PET bottle File:Pet plastic crystallisation.jpg|A PET bottle which has been heated by a candle and has recrystallized, making it opaque. File:PET-Verpackung-offen.jpg|PET clamshell packaging, used to sell fruit, hardware, etc. File:Buso de Algodon y Poliester.JPG|Polyester yarn Mikrofaser-Handtuch für Unterwegs.JPG|Microfiber towels and cleaning cloths File:Nottingham Pride MMB 45.jpg|Aluminized Mylar balloons filled with helium </gallery>

==History== PET was patented in 1941 by John Rex Whinfield, James Tennant Dickson and their employer the Calico Printers' Association of Manchester, England. E. I. DuPont de Nemours in Delaware, United States, first produced Dacron (PET fiber) in 1950 and used the trademark Mylar (boPET film) in June 1951 and received registration of it in 1952.<ref>{{cite web |title=The Complete History Of Polyester |url=https://qualitynylonrope.com/the-complete-history-of-polyester/ |access-date=2 November 2024 |website=Quality Nylon Rope|date=14 December 2016 }}</ref><ref>Whinfield, John Rex and Dickson, James Tennant (1941) "Improvements Relating to the Manufacture of Highly Polymeric Substances", UK Patent 578,079; "Polymeric Linear Terephthalic Esters", {{US Patent|2465319}} Publication date: 22 March 1949; Filing date: 24 September 1945; Priority date: 29 July 1941</ref> It is still the best-known name used for polyester film. The current owner of the trademark is DuPont Teijin Films.<ref>[http://www.teijin.com/terms_conditions/trademark.html TEIJIN: Trademarks] {{Webarchive|url=https://web.archive.org/web/20130502034436/http://www.teijin.com/terms_conditions/trademark.html |date=2 May 2013 }} "''Mylar and Melinex are the registered trademarks or trademarks of Dupont Teijin Films U.S. Limited Partnership and have been licensed to Teijin DuPont Films Japan Limited''"</ref>

In the Soviet Union, PET was independently developed in the laboratories of the Institute of High-Molecular Compounds of the USSR Academy of Sciences in 1949, and its Russian name "Lavsan" is an acronym thereof ('''ла'''боратории Института '''в'''ысокомолекулярных '''с'''оединений '''А'''кадемии '''н'''аук СССР).<ref>{{cite book|author1=Ryazanova-Clarke, Larissa |author2=Wade, Terence |title=The Russian Language Today|url=https://books.google.com/books?id=J_OFr8TgcwMC&pg=PA49|date=31 January 2002|publisher=Taylor & Francis|isbn=978-0-203-06587-7|pages=49–}}</ref>

The PET bottle was invented in 1973 by Nathaniel Wyeth<ref>{{cite web |title=Nathaniel Wyeth – Got a lot of bottle |url=https://www.thechemicalengineer.com/features/cewctw-nathaniel-wyeth-got-a-lot-of-bottle/ |website=www.thechemicalengineer.com |access-date=3 March 2022}}</ref> and patented by DuPont.<ref>{{cite web |last1=Wyeth |first1=N. |last2=Roseveare |first2=R. |title=US patent US3733309 "Biaxially oriented poly(ethylene terephthalate) bottle" |url=https://patents.google.com/patent/US3733309A/en?oq=3733309 |date=15 May 1973}}</ref>

==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 spinnakers 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 non-crystalline (amorphous) or crystalline articles. Its amenability to drawing in manufacturing makes PET useful in fibre and film applications. It is strong and 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>

Transparent products can be produced by rapidly cooling molten polymer below the glass transition temperature (Tg) to form a non-crystalline 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> Amorphous PET forms by rapidly cooling the melt. This glassy state tends to crystallize upon heating the material above Tg, a process known as cold crystallization.<ref name="c741">{{cite journal | last=Pingping | first=Zhu | last2=Dezhu | first2=Ma | title=Study on the double cold crystallization peaks of poly(ethylene terephthalate) (PET): 2. Samples isothermally crystallized at high temperature | journal=European Polymer Journal | volume=35 | issue=4 | date=1999 | doi=10.1016/S0014-3057(98)00179-7 | pages=739–742 | url=https://linkinghub.elsevier.com/retrieve/pii/S0014305798001797 | access-date=2025-05-28| url-access=subscription }}</ref> Amorphous PET also crystallizes and becomes opaque when exposed to some solvents, such as chloroform or toluene.<ref>NPCS Board of Consultants & Engineers (2014) Chapter 6, p. 56 in ''Disposable Products Manufacturing Handbook'', NIIR Project Consultancy Services, Delhi, {{ISBN|978-9-381-03932-8}}</ref>

A more crystalline product can be produced by cooling the molten polymer slowly. Rather than forming one large single crystal, this material has a number of spherulites (crystallized areas) each containing many small crystallites (grains). Light tends to scatter as it crosses the boundaries between crystallites and the amorphous regions between them, causing the resulting solid to be translucent.<ref name="q705">{{cite journal | last=Jabarin | first=Saleh A. | title=Optical properties of thermally crystallized poly(ethylene terephthalate) | journal=Polymer Engineering & Science | volume=22 | issue=13 | date=1982 | issn=0032-3888 | doi=10.1002/pen.760221305 | pages=815–820 | url=https://4spepublications.onlinelibrary.wiley.com/doi/10.1002/pen.760221305 | access-date=2025-05-28| url-access=subscription }}</ref> Orientation also renders polymers more transparent.{{Clarification needed|reason=Orientation of what?|date=June 2024}} This is why BOPET film and bottles are both crystalline, to a degree, and transparent.{{Citation needed|date=June 2024}}

=== Flavor absorption === PET has an affinity for hydrophobic flavors, and drinks sometimes need to be formulated with a higher flavor dosage, compared to those going into glass, to offset the flavor taken up by the container.<ref name="Ashurst-2009">{{Cite book |last1=Ashurst |first1=P. |url=https://books.google.com/books?id=FQykAgAAQBAJ&pg=PA105 |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=115}} When returned for re-use, as in some EU countries, the propensity of PET to absorb flavors makes it necessary to conduct a "sniffer test" on some returned bottles to avoid cross-contamination of flavors.<ref name="Ashurst-2009"/>{{Rp|page=115}}

===Intrinsic viscosity=== Different applications of PET require different degrees of polymerization, which can be obtained by modifying the process conditions. The molecular weight of PET is measured by solution viscosity. Viscosity is highly dependent on molecular parameters such as chain length and molecular weight. Due to the structural complexity of branched polymers, viscosity-based determination of molecular weight is best used with linear polymers. With dilute solutions, an empirical relationship can be derived between the viscosity and the hydrodynamic volume and molecular weight distribution.<ref name="s718">{{cite journal | last=Sanches | first=N.B. | last2=Dias | first2=M.L. | last3=Pacheco | first3=E.B.A.V. | title=Comparative techniques for molecular weight evaluation of poly (ethylene terephthalate) (PET) | journal=Polymer Testing | volume=24 | issue=6 | date=2005 | doi=10.1016/j.polymertesting.2005.05.006 | pages=688–693 | url=https://linkinghub.elsevier.com/retrieve/pii/S0142941805000863 | access-date=2025-05-28| url-access=subscription }}</ref> The preferred method to measure this viscosity is the intrinsic viscosity (IV) of the polymer.<ref>Thiele, Ulrich K. (2007) ''Polyester Bottle Resins, Production, Processing, Properties and Recycling'', Heidelberg, Germany, pp. 85 ff, {{ISBN|978-3-9807497-4-9}}</ref> Intrinsic viscosity is a dimensionless measurement found by extrapolating the relative viscosity (measured in (dℓ/g)) to zero concentration. Shown below are the IV ranges for common applications:<ref>Gupta, V.B. and Bashir, Z. (2002) Chapter 7, p. 320 in Fakirov, Stoyko (ed.) ''Handbook of Thermoplastic Polyesters'', Wiley-VCH, Weinheim, {{ISBN|3-527-30113-5}}.</ref> {| class="wikitable" |+ !Application !IV |- |Textile fibers |0.40–0.70 |- |Technical fibers (e.g. tire cord) |0.72–0.98 |- |Biaxially oriented PET film (BOPET) |0.60–0.70 |- |Sheet grade film for thermoforming |0.70–1.00 |- |General purpose bottles |0.70–0.78 |- |Carbonated drink bottles |0.78–0.85 |- |Monofilaments and engineering plastics |1.00–2.00 |}

== Copolymers == {{Unreferenced section|date=June 2024}} PET is often copolymerized with other diols or diacids to optimize the properties for particular applications.<ref>{{cite web |title=What is PETG? (Everything You Need To Know) |publisher=Wankai New Materials Co., Ltd. |date=July 18, 2024 |location=China |url=https://wkaiglobal.com/blogs/pet-vs-petg-what-s-the-difference |access-date=October 28, 2024}}</ref><ref>{{cite web |title=What is PETG? (Everything You Need To Know) |publisher=TWI Ltd. |url=https://www.twi-global.com/technical-knowledge/faqs/what-is-petg |archive-url=https://web.archive.org/web/20250404222034/https://www.twi-global.com/technical-knowledge/faqs/what-is-petg |archive-date=April 4, 2025}}</ref>

===PETG=== thumb|class=skin-invert-image|right|PETG: Ethylene glycol units are marked in blue, and cyclohexane-1,4-dimethanol units are marked in yellow

For example, cyclohexanedimethanol (CHDM) can be added to the polymer backbone, replacing some of the ethylene glycol. Since this building block is much larger (six additional carbon atoms) than the ethylene glycol unit it replaces, it does not fit in with the neighboring chains the way an ethylene glycol unit would. This interferes with crystallization and lowers the polymer's melting temperature. In general, such PET is known as PETG or PET-G (polyethylene terephthalate glycol-modified). It is a clear amorphous thermoplastic that can be injection-molded, sheet-extruded or extruded as filament for 3D printing. PETG can be colored during processing. Replacing all of the ethylene glycol with CHDM gives PCT.

===Isophthalic acid=== [[File:Phthalic acid isomers.PNG|class=skin-invert-image|thumb|Replacing terephthalic acid (right) with isophthalic acid (center) creates a kink in the PET chain, interfering with crystallization and lowering the polymer's melting point.]] Another common modifier is isophthalic acid, replacing some of the 1,4-(''para-'') linked terephthalate units. The 1,2-(''ortho-'') or 1,3-(''meta''-) linkage produces an angle in the chain, which also disturbs crystallinity.

===Advantages=== Such copolymers are advantageous for certain molding applications, such as thermoforming, which is used for example to make tray or blister packaging from co-PET film, or amorphous PET sheet (A-PET/PETA) or PETG sheet. On the other hand, crystallization is important in other applications where mechanical and dimensional stability are important, such as seat belts. For PET bottles, the use of small amounts of isophthalic acid, CHDM, diethylene glycol (DEG) or other comonomers can be useful: if only small amounts of comonomers are used, crystallization is slowed but not prevented entirely. As a result, bottles are obtainable via stretch blow molding ("SBM"), which are both clear and crystalline enough to be an adequate barrier to aromas and even gases, such as carbon dioxide in carbonated beverages.

==Production== Polyethylene terephthalate is produced largely from purified terephthalic acid (PTA), as well as to a lesser extent from (mono-)ethylene glycol (MEG) and dimethyl terephthalate (DMT).<ref name=polyesters>{{Ullmann's | title = Polyesters | doi = 10.1002/14356007.a21_227 |volume=A21|pages=233–238}}</ref><ref name="De Vos-2021" /> As of 2022, ethylene glycol is made from ethene found in natural gas, while terephthalic acid comes from p-xylene made from crude oil. Typically an antimony or titanium compound is used as a catalyst, a phosphite is added as a stabilizer and a bluing agent such as cobalt salt is added to mask any yellowing.<ref>{{cite journal |last1=MacDonald |first1=W A |title=New advances in poly(ethylene terephthalate) polymerization and degradation |journal=Polymer International |date=October 2002 |volume=51 |issue=10 |pages=923–930 |doi=10.1002/pi.917 }}</ref>

=== Processes ===

==== Dimethyl terephthalate process ==== class=skin-invert-image|thumb|Polyesterification reaction in the production of PET In the dimethyl terephthalate (DMT) process, DMT and excess ethylene glycol (MEG) are transesterified in the melt at 150–200 °C with a basic catalyst. Methanol (CH3OH) is removed by distillation to drive the reaction forward. Excess MEG is distilled off at higher temperature with the aid of vacuum. The second transesterification step proceeds at 270–280 °C, with continuous distillation of MEG as well.<ref name=polyesters/>

The reactions can be summarized as follows: ;First step : C6H4(CO2CH3)2 + 2 HOCH2CH2OH → C6H4(CO2CH2CH2OH)2 + 2 CH3OH

;Second step : ''n'' C6H4(CO2CH2CH2OH)2 → [(CO)C6H4(CO2CH2CH2O)]n + ''n'' HOCH2CH2OH

==== Terephthalic acid process ==== class=skin-invert-image|thumb|Polycondensation reaction in the production of PET In the terephthalic acid process, MEG and PTA are esterified directly at moderate pressure (2.7–5.5 bar) and high temperature (220–260 °C). Water is eliminated in the reaction, and it is also continuously removed by distillation:<ref name = polyesters/>

: ''n'' C6H4(CO2H)2 + ''n'' HOCH2CH2OH → [(CO)C6H4(CO2CH2CH2O)]n + 2''n'' H2O

==== Bio-PET ==== '''Bio-PET''' is the bio-based counterpart of PET.<ref>[https://www.roadtobio.eu/uploads/news/2017_October/RoadToBio_Drop-in_paper.pdf Bio-based drop-in, smart drop-in and dedicated chemicals]</ref><ref>[https://www.wur.nl/nl/Onderzoek-Resultaten/Onderzoeksinstituten/food-biobased-research/Oplossingen/Duurzame-bioplastics-op-basis-van-hernieuwbare-grondstoffen.htm Duurzame bioplastics op basis van hernieuwbare grondstoffen]</ref> Essentially in Bio-PET, the MEG is manufactured from ethylene derived from sugar cane ethanol. A better process based on oxidation of ethanol has been proposed,<ref>{{cite journal |title=New route planned to biobased ethylene glycol |journal=C&EN Global Enterprise |date=20 November 2017 |volume=95 |issue=46 |page=10 |doi=10.1021/cen-09546-notw6 |last1=Alex Tullo }}</ref> and it is also technically possible to make PTA from readily available bio-based furfural.<ref>{{cite journal |last1=Tachibana |first1=Yuya |last2=Kimura |first2=Saori |last3=Kasuya |first3=Ken-ichi |title=Synthesis and Verification of Biobased Terephthalic Acid from Furfural |journal=Scientific Reports |date=4 February 2015 |volume=5 |issue=1 |page=8249 |doi=10.1038/srep08249 |pmid=25648201 |pmc=4316194 |bibcode=2015NatSR...5.8249T }}</ref>

=== Bottle processing equipment === {{Unreferenced section|date=June 2024}}thumb|upright|A finished PET drink bottle compared to the preform from which it is made

There are two basic molding methods for PET bottles, one-step and two-step. In two-step molding, two separate machines are used. The first machine injection molds the preform, which resembles a test tube, with the bottle-cap threads already molded into place. The body of the tube is significantly thicker, as it will be inflated into its final shape in the second step using stretch blow molding.

In the second step, the preforms are heated rapidly and then inflated against a two-part mold to form them into the final shape of the bottle. Preforms (uninflated bottles) are now also used as robust and unique containers themselves; besides novelty candy, some Red Cross chapters distribute them as part of the Vial of Life program to homeowners to store medical history for emergency responders. The two-step process lends itself to third party production remote from the user site. The preforms can be transported and stored by the thousand in a much smaller space than would finished containers, for the second stage to be carried out on the user site on a 'just in time' basis. In one-step machines, the entire process from raw material to finished container is conducted within one machine, making it especially suitable for molding non-standard shapes (custom molding), including jars, flat oval, flask shapes, etc. Its greatest merit is the reduction in space, product handling and energy, and far higher visual quality than can be achieved by the two-step system.{{Citation needed|date=March 2013}}

===Degradation=== PET is subject to degradation during processing. If the moisture level is too high, hydrolysis will reduce the molecular weight by chain scission, resulting in brittleness. If the residence time and/or melt temperature (temperature at melting) are too high, then thermal degradation or thermooxidative degradation will occur resulting in discoloration and lowered molecular weight, as well as the formation of acetaldehyde, and the formation "gel" or "fish-eye" formations through cross-linking. Mitigation measures include copolymerisation with other monomers like CHDM or isophthalic acid, which lower the melting point and thus the melt temperature of the resin, as well as 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=978-3-446-17571-6 |page=92 |edition=4th }}</ref>

====Acetaldehyde==== Acetaldehyde, which can form by degradation of PET after mishandling of the material, can cause an off-taste in bottled water. As well as high temperatures (PET decomposes above 300 °C or 570 °F) and long barrel residence times, high pressures and high extruder speeds (which cause shear raising the temperature), can also contribute to the production of acetaldehyde. Photo-oxidation can also cause the formation of acetaldehyde. This conversi proceeds via a Type II Norrish reaction.<ref name="Wiles&DayIII">{{cite journal |last1=Day |first1=M. |last2=Wiles |first2=D. M. |title=Photochemical degradation of poly(ethylene terephthalate). III. Determination of decomposition products and reaction mechanism |journal=Journal of Applied Polymer Science |date=January 1972 |volume=16 |issue=1 |pages=203–215 BHET|doi=10.1002/app.1972.070160118}}</ref> class=skin-invert-image|600px|center

When acetaldehyde is produced, some of it remains dissolved in the walls of a container and then diffuses into the product stored inside, altering the taste and aroma. This is not such a problem for non-consumables (such as shampoo), for fruit juices (which already contain acetaldehyde), or for strong-tasting drinks like soft drinks. For bottled water, however, low acetaldehyde content is quite important, because if nothing masks the aroma, even extremely low concentrations (10–20 parts per billion in the water) of acetaldehyde can produce an off-taste.<ref>{{cite journal |last1=Nawrocki |first1=J |last2=Dąbrowska |first2=A |last3=Borcz |first3=A |title=Investigation of carbonyl compounds in bottled waters from Poland |journal=Water Research |date=November 2002 |volume=36 |issue=19 |pages=4893–4901 |doi=10.1016/S0043-1354(02)00201-4|pmid=12448533 |bibcode=2002WatRe..36.4893N }}</ref>

==Safety and environmental concerns== Commentary published in ''Environmental Health Perspectives'' in April 2010 suggested that PET might yield endocrine disruptors under conditions of common use and recommended research on this topic.<ref>{{cite journal|author=Sax, Leonard |title=Polyethylene Terephthalate May Yield Endocrine Disruptors|journal=Environmental Health Perspectives|year=2010|volume=118 |issue=4|doi=10.1289/ehp.0901253|pmid=20368129|pmc=2854718|pages=445–8|bibcode=2010EnvHP.118..445S }}</ref> Proposed mechanisms include leaching of phthalates as well as leaching of antimony. An article published in ''Journal of Environmental Monitoring'' in April 2012 concludes that antimony concentration in deionized water stored in PET bottles stays within EU's acceptable limit even if stored briefly at temperatures up to 60 °C (140 °F), while bottled contents (water or soft drinks) may occasionally exceed the EU limit after less than a year of storage at room temperature.<ref>{{cite journal |last1=Tukur |first1=Aminu |last2=Sharp |first2=Liz |last3=Stern |first3=Ben |last4=Tizaoui |first4=Chedly |last5=Benkreira |first5=Hadj |title=PET bottle use patterns and antimony migration into bottled water and soft drinks: the case of British and Nigerian bottles |journal=Journal of Environmental Monitoring |date=2012 |volume=14 |issue=4 |pages=1237–1247 |doi=10.1039/c2em10917d |pmid=22402759 }}</ref><ref>{{cite journal |last1=Sax |first1=Leonard |title=Polyethylene Terephthalate May Yield Endocrine Disruptors |journal=Environmental Health Perspectives |date=April 2010 |volume=118 |issue=4 |pages=445–448 |doi=10.1289/ehp.0901253 |pmid=20368129 |pmc=2854718 |bibcode=2010EnvHP.118..445S }}</ref>

===Antimony=== Antimony (Sb) is a metalloid element that is used as a catalyst in the form of compounds such as antimony trioxide (Sb2O3) or antimony triacetate in the production of PET. After manufacturing, a detectable amount of antimony can be found on the surface of the product. This residue can be removed with washing. Antimony also remains in the material itself and can, thus, migrate out into food and drinks. Exposing PET to boiling or microwaving can increase the levels of antimony significantly, possibly above US EPA maximum contamination levels.<ref>{{cite journal |last1=Cheng |first1=Xiaoliang |last2=Shi |first2=Honglan |last3=Adams |first3=Craig D. |last4=Ma |first4=Yinfa |title=Assessment of metal contaminations leaching out from recycling plastic bottles upon treatments |journal=Environmental Science and Pollution Research |date=August 2010 |volume=17 |issue=7 |pages=1323–1330 |doi=10.1007/s11356-010-0312-4 |pmid=20309737 |bibcode=2010ESPR...17.1323C }}</ref> The drinking water limit assessed by WHO is 20 parts per billion (WHO, 2003), and the drinking water limit in the United States is 6 parts per billion.<ref>[http://epa.gov/ogwdw/pdfs/factsheets/ioc/antimony.pdf Consumer Factsheet on: Antimony] {{Webarchive|url=https://web.archive.org/web/20140607005920/http://epa.gov/ogwdw/pdfs/factsheets/ioc/antimony.pdf |date=7 June 2014 }}, EPA [https://web.archive.org/web/20030623135029/http://www.epa.gov/ogwdw000/contaminants/dw_contamfs/antimony.html archive 2003-06-23]</ref> Although antimony trioxide is of low toxicity when taken orally,<ref name="who.int">[https://www.who.int/water_sanitation_health/dwq/chemicals/antimonysum.pdf Guidelines for drinking – water quality]. who.int</ref> its presence is still of concern. The Swiss Federal Office of Public Health investigated the amount of antimony migration, comparing waters bottled in PET and glass: The antimony concentrations of the water in PET bottles were higher, but still well below the allowed maximum concentration. The Swiss Federal Office of Public Health concluded that small amounts of antimony migrate from the PET into bottled water, but that the health risk of the resulting low concentrations is negligible (1% of the "tolerable daily intake" determined by the WHO). A later (2006) but more widely publicized study found similar amounts of antimony in water in PET bottles.<ref>{{cite journal |doi=10.1039/b517844b |title=Contamination of Canadian and European bottled waters with antimony from PET containers |year=2006 |author=Shotyk, William |journal=Journal of Environmental Monitoring |volume=8 |pages=288–92 |pmid=16470261 |issue=2 |display-authors=etal}}</ref> The WHO has published a risk assessment for antimony in drinking water.<ref name="who.int" />

Fruit juice concentrates (for which no guidelines are established), however, that were produced and bottled in PET in the UK were found to contain up to 44.7 μg/L of antimony, well above the EU limits for tap water of 5 μg/L.<ref>{{cite journal|title=Elevated antimony concentrations in commercial juices|journal=Journal of Environmental Monitoring|author=Hansen, Claus |volume=12|issue=4|pages=822–4|year=2010|pmid=20383361|doi=10.1039/b926551a|display-authors=etal}}</ref>

=== Shed microfibres === Clothing sheds microfibres in use, during washing and machine drying. Plastic litter slowly forms small particles. Microplastics which are present on the bottom of the river or seabed can be ingested by small marine life, thus entering the food chain. As PET has a higher density than water, a significant amount of PET microparticles may be precipitated in sewage treatment plants. PET microfibers generated by apparel wear, washing or machine drying can become airborne, and be dispersed into fields, where they are ingested by livestock or plants and end up in the human food supply. A study published in the journal Science of the Total Environment found PET accounted for 18% of microplastics in human lung tissue samples, and that there were 0.69 ± 0.84 microplastics per gram of lung tissue.<ref>{{cite journal |last1=Jenner |first1=Lauren C. |last2=Rotchell |first2=Jeanette M. |last3=Bennett |first3=Robert T. |last4=Cowen |first4=Michael |last5=Tentzeris |first5=Vasileios |last6=Sadofsky |first6=Laura R. |title=Detection of microplastics in human lung tissue using μFTIR spectroscopy |journal=Science of the Total Environment |date=July 2022 |volume=831 |article-number=154907 |doi=10.1016/j.scitotenv.2022.154907 |pmid=35364151 |bibcode=2022ScTEn.83154907J }}</ref> SAPEA have declared that such particles 'do not pose a widespread risk'.<ref>{{cite web |title=SAPEA report: Evidence on microplastics does not yet point to widespread risk - ALLEA |date=10 January 2019 |url=https://allea.org/sapea-report-microplastics/ |access-date=5 March 2022}}</ref> PET is known to degrade when exposed to sunlight and oxygen.<ref>{{cite journal |last1=Chamas |first1=Ali |last2=Moon |first2=Hyunjin |last3=Zheng |first3=Jiajia |last4=Qiu |first4=Yang |last5=Tabassum |first5=Tarnuma |last6=Jang |first6=Jun Hee |last7=Abu-Omar |first7=Mahdi |last8=Scott |first8=Susannah L. |last9=Suh |first9=Sangwon |date=9 March 2020 |title=Degradation Rates of Plastics in the Environment |journal=ACS Sustainable Chemistry & Engineering |volume=8 |issue=9 |pages=3494–3511 |doi=10.1021/acssuschemeng.9b06635 |doi-access=free }}</ref> As of 2016, scarce information exists regarding the life-time of the synthetic polymers in the environment.<ref>{{cite journal |last1=Ioakeimidis |first1=C. |last2=Fotopoulou |first2=K. N. |last3=Karapanagioti |first3=H. K. |last4=Geraga |first4=M. |last5=Zeri |first5=C. |last6=Papathanassiou |first6=E. |last7=Galgani |first7=F. |last8=Papatheodorou |first8=G. |date=22 March 2016 |title=The degradation potential of PET bottles in the marine environment: An ATR-FTIR based approach |journal=Scientific Reports |volume=6 |issue=1 |article-number=23501 |bibcode=2016NatSR...623501I |doi=10.1038/srep23501 |pmc=4802224 |pmid=27000994}}</ref>

==Polyester recycling== {{main|PET bottle recycling}}

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 name="Malik Kumar PET waste recycling">{{cite journal |last1=Malik |first1=Neetu |last2=Kumar |first2=Piyush |last3=Shrivastava |first3=Sharad |last4=Ghosh |first4=Subrata Bandhu |title=An overview on PET waste recycling for application in packaging |journal=International Journal of Plastics Technology |date=June 2017 |volume=21 |issue=1 |pages=1–24 |doi=10.1007/s12588-016-9164-1 }}</ref><ref>{{cite journal |last1=Imran |first1=Muhammad |last2=Kim |first2=Do Hyun |last3=Al-Masry |first3=Waheed A. |last4=Mahmood |first4=Asif |last5=Hassan |first5=Azman |last6=Haider |first6=Sajjad |last7=Ramay |first7=Shahid M. |title=Manganese-, cobalt-, and zinc-based mixed-oxide spinels as novel catalysts for the chemical recycling of poly(ethylene terephthalate) via glycolysis |journal=Polymer Degradation and Stability |date=April 2013 |volume=98 |issue=4 |pages=904–915 |doi=10.1016/j.polymdegradstab.2013.01.007 }}</ref> PET bottles lend themselves well to recycling (see below). In many countries PET bottles are recycled to a substantial degree,<ref name="Malik Kumar PET waste recycling"/> for example about 75% in Switzerland.<ref>{{cite web |title=RAPPORT DE GESTION 2019 |url=https://www.petrecycling.ch/tl_files/content/PDF/Medien/Geschaeftsberichte/PET-Recycling_Schweiz_Rapport_de_gestion_2019.pdf |access-date=5 March 2022 |publisher=Swiss PET Recycling Association |page=5 |language=fr}}</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 |title=Recycling of PET |journal=European Polymer Journal |date=July 2005 |volume=41 |issue=7 |pages=1453–1477 |doi=10.1016/j.eurpolymj.2005.02.005 |bibcode=2005EurPJ..41.1453A }}</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>

The prime uses for recycled PET are polyester fiber, strapping, and non-food containers.{{Citation needed|date=June 2024}} Because of the recyclability of PET and the relative abundance of post-consumer waste in the form of bottles, PET is also 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> PET, like many plastics, is also an excellent candidate for thermal disposal (incineration), as it is composed of carbon, hydrogen, and oxygen, with only trace amounts of catalyst elements (but no sulfur).{{Citation needed|date=June 2024}} In general, PET can either be chemically recycled into its original raw materials (PTA, DMT, and EG), destroying the polymer structure completely;{{Citation needed|date=June 2024}} mechanically recycled into a different form, without destroying the polymer;{{Citation needed|date=June 2024}} or recycled in a process that includes transesterification and the addition of other glycols, polyols, or glycerol to form a new polyol. The polyol from the third method can be used in polyurethane (PU foam) production,<ref>{{Cite journal |last=Makuska |first=Ricardas |date=2008 |title=Glycolysis of industrial poly(ethylene terephthalate) waste directed to bis(hydroxyethylene) terephthalate and aromatic polyester polyols |url=https://mokslozurnalai.lmaleidykla.lt/publ/0235-7216/2008/2/29-34.pdf |journal=Chemija |volume=19 |pages=29–34 |number=2}}</ref><ref>{{Cite web |title=Arropol {{!}} Arropol Chemicals |url=https://arropol.com/ |access-date=2019-01-02 |language=en-US}}</ref><ref>{{cite journal |last1=Shirazimoghaddam |first1=Shadi |last2=Amin |first2=Ihsan |last3=Faria Albanese |first3=Jimmy A |last4=Shiju |first4=N. Raveendran |title=Chemical Recycling of Used PET by Glycolysis Using Niobia-Based Catalysts |journal=ACS Engineering Au |date=15 February 2023 |volume=3 |issue=1 |pages=37–44 |doi=10.1021/acsengineeringau.2c00029 |pmc=9936547 |pmid=36820227 }}</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. |title=Organocatalysis for depolymerisation |journal=Polymer Chemistry |date=2019 |volume=10 |issue=2 |pages=172–186 |doi=10.1039/C8PY01284A |hdl-access=free |hdl=2117/365711}}</ref> or 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 |title=Epoxy-based paints from glycolysis products of postconsumer PET bottles: synthesis, wet paint properties and film properties |journal=Journal of Coatings Technology and Research |date=May 2017 |volume=14 |issue=3 |pages=747–753 |doi=10.1007/s11998-016-9895-0 }}</ref>

In 2023 a process was announced for using PET as the basis for supercapacitor production. PET, being stoichiometrically carbon and {{chem2|H2O}}, can be turned into a form of carbon containing sheets and nanospheres, with a very high surface area. The process involves holding a mixture of PET, water, nitric acid, and ethanol at a high temperature and pressure for eight hours, followed by centrifugation and drying.<ref>{{cite journal |last1=Karmela Padavic-Callaghan |title=Plastic bottles can be recycled into energy-storing supercapacitors |journal=New Scientist |date=Aug 23, 2023 |url=https://www.newscientist.com/article/2388697-plastic-bottles-can-be-recycled-into-energy-storing-supercapacitors/}}</ref><ref>{{cite web|display-authors=etal |last1=Wang |first1=Shengnian |title=Upcycling drink bottle waste to ball-sheet Intercalated carbon structures for supercapacitor applications |url=https://acs.digitellinc.com/sessions/574935/view |website=ACS Fall 2023 - Sessions |publisher=American Chemical Society |date=2023}}</ref>

Significant investments were announced in 2021 and 2022 for chemical recycling of PET by glycolysis, methanolysis,<ref>{{cite news |last1=Laird |first1=Karen |date=18 January 2022 |title=Loop, Suez select site in France for first European Infinite Loop facility |url=https://www.plasticsnews.com/news/loop-industries-suez-select-site-normandy-first-european-infinite-loop-facility |access-date=11 March 2022 |work=Plastics News |language=en}}</ref><ref>{{cite news |last1=Toto |first1=Deanne |date=1 Feb 2021 |title=Eastman invests in methanolysis plant in Kingsport, Tennessee |url=https://www.recyclingtoday.com/article/eastman-chemical-recycling-plastics-investment/ |access-date=11 March 2022 |work=Recycling Today |language=en}}</ref> and enzymatic recycling<ref>{{cite news |last1=Page Bailey |first1=mary |date=24 February 2022 |title=Carbios and Indorama to build first-of-its-kind enzymatic recycling plant for PET in France |url=https://www.chemengonline.com/carbios-and-indorama-to-build-first-of-its-kind-enzymatic-recycling-plant-for-pet-in-france/?printmode=1 |access-date=11 March 2022 |work=Chemical Engineering |language=en}}</ref> to recover monomers. Initially these will also use bottles as feedstock but it is expected that fibres will also be recycled this way in future.<ref>{{cite journal |last1=Shojaei |first1=Behrouz |last2=Abtahi |first2=Mojtaba |last3=Najafi |first3=Mohammad |title=Chemical recycling of PET: A stepping-stone toward sustainability |journal=Polymers for Advanced Technologies |date=December 2020 |volume=31 |issue=12 |pages=2912–2938 |doi=10.1002/pat.5023 }}</ref>

PET is also a desirable fuel for waste-to-energy plants, 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 |date=6 January 2021 |title=Analysis of the polyester clothing value chain to identify key intervention points for sustainability |journal=Environmental Sciences Europe |volume=33 |issue=1 |page=2 |doi=10.1186/s12302-020-00447-x |pmid=33432280 |doi-access=free |pmc=7787125 }}</ref>

===Biodegradation=== PET biodegrades by ester hydrolysis.<ref>{{Cite journal|last1=Koshti|first1=Rupali|last2=Mehta|first2=Lincohn|last3=Samarth|first3=Nikesh|date=2018|title=Biological Recycling of Polyethylene Terephthalate: A Mini-Review|journal=Journal of Polymers and the Environment|volume=26|issue=8|pages=3520–3529|doi=10.1007/s10924-018-1214-7|s2cid=139274331}}</ref> Some hydrolase enzymes depolymerize (break apart) PET. The enzymes are PETase and MHETase, which afford 2-hydroxyethyl terephthalic acid and then ethylene glycol and terephthalic acid. Discovered in 2016,<ref>{{cite journal | vauthors = Yoshida S, Hiraga K, Takehana T, Taniguchi I, Yamaji H, Maeda Y, Toyohara K, Miyamoto K, Kimura Y, Oda K | display-authors = 6 | title = A bacterium that degrades and assimilates poly(ethylene terephthalate) | journal = Science | volume = 351 | issue = 6278 | pages = 1196–9 | date = March 2016 | pmid = 26965627 | doi = 10.1126/science.aad6359 | bibcode = 2016Sci...351.1196Y }}</ref> these enzymes and their host organisms have received intense scrutiny as possible routes for recycling PET or at least destroying PET waste.<ref name="Vincent">{{cite journal |last1=Tournier |first1=Vincent |last2=Duquesne |first2=Sophie |last3=Guillamot |first3=Frédérique |last4=Cramail |first4=Henri |last5=Taton |first5=Daniel |last6=Marty |first6=Alain |last7=André |first7=Isabelle |title=Enzymes' Power for Plastics Degradation |journal=Chemical Reviews |date=10 May 2023 |volume=123 |issue=9 |pages=5612–5701 |doi=10.1021/acs.chemrev.2c00644 |pmid=36916764 |url=https://oskar-bordeaux.fr/handle/20.500.12278/186875 }}</ref> A number of hurdles remain, such as the thermal instability of the enzymes and slow rates for crystalline PET.<ref name="esterase">{{cite journal |last1=Oda |first1=Kohei |last2=Wlodawer |first2=Alexander |title=Development of Enzyme-Based Approaches for Recycling PET on an Industrial Scale |journal=Biochemistry |date=2024 |article-number=acs.biochem.3c00554 |doi=10.1021/acs.biochem.3c00554 |pmid=38285602 }}</ref>

==See also== {{Portal|Chemistry}} * BoPET (biaxially oriented PET) * Bioplastic * Plastic recycling * Polycyclohexylenedimethylene terephthalate—a polyester with a similar structure to PET * Solar water disinfection—a method of disinfecting water using only sunlight and plastic PET bottles

==References== {{Reflist|35em}}

==External links== {{Commons category|Polyethylene terephthalate}} * [https://arropol.com/ Arropol commercial producer of polyol from post-consumer PET fiber] * [https://web.archive.org/web/20060702121701/http://www.plasticsinfo.org/beveragebottles/index.html American Plastics Council: PlasticInfo.org] * [http://www.kenplas.com/project/pet/ KenPlas Industry Ltd.: "What is PET (Polyethylene Terephthalate)"]; {{Webarchive|url=https://web.archive.org/web/20071210020300/http://www.kenplas.com/project/pet/ |date=10 December 2007 }} * [https://wkaiglobal.com/blogs/pet-vs-petg-what-s-the-difference PET vs PETg: What's the Difference?] * [https://web.archive.org/web/20100309112752/http://wavepolymertechnology.com/PROCESSING.aspx "WAVE Polymer Technology: PET (Polyethylene Terephthalate) flakes processing"]

{{DEFAULTSORT:Polyethylene Terephthalate}} Category:Biomaterials Category:Commodity chemicals Category:English inventions Category:Flexible electronics Category:Food packaging Category:Household chemicals Category:Plastics Category:Polyesters Category:Polymers Category:Terephthalate esters Category:Thermoplastics Category:Transparent materials