[go: up one dir, main page]
Wikipedia

Polyethylene terephthalate: Difference between revisions

Browse history interactively
← Previous edit
Content deleted Content added
VisualWikitext
→Other applications: added the use in creating clothing for Jews.
Tags: Reverted Visual edit
Reverted 1 edit by 103.113.99.81 (talk): Rv, adds nothing
 
(31 intermediate revisions by 11 users not shown)
Line 72:
}}
 
'''Polyethylene terephthalate''' (or '''poly(ethylene terephthalate)''', '''PET''', '''PETE''', or the obsolete '''PETP''' or '''PET-P'''), is the most common [[thermoplastic]] [[polymer]] resin of the [[polyester]] family and is used in [[synthetic fibre|fibre]]s for clothing, [[packaging|containers]] for liquids and foods, and [[thermoforming]] 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 |pages=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 2016, annual production of PET was 56 million tons.<ref>{{cite web |url=https://arstechnica.com/science/2016/03/does-newly-discovered-bacteria-recycle-plastic/ |title=Newly identified bacteria cleans up common plastic |newspaper=[[Ars Technica]] |date= 19 March 2016 |author=Saxena, Shalini |access-date= 21 March 2016}}</ref> The biggest application is in fibres (in excess of 60%), with bottle production accounting for about 30% of global demand.<ref>{{cite journal|last1=Ji|first1=Li Na|title=Study on Preparation Process and Properties of Polyethylene Terephthalate (PET)|doi=10.4028/www.scientific.net/AMM.312.406|journal=Applied Mechanics and Materials|date=June 2013|volume=312|pages=406–410|bibcode=2013AMM...312..406J|s2cid=110703061}}</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.{{Citation needed|date=July 2022}} Polyester makes up about 18% of world polymer production and is the fourth-most-produced polymer after [[polyethylene]] (PE), [[polypropylene]] (PP) and [[polyvinyl chloride]] (PVC).{{Citation needed|date=July 2022}}
Line 122:
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=httphttps://wwwpatents.google.com/patentspatent/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}}
Line 138:
===Thermoplastic resins===
PET can be compounded with glass [[fiber-reinforced plastic|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>
 
=== Nanodiamonds ===
PET is stoichiometrically a mixture of carbon and {{chem2|H2O}}, and therefore has been used in an experiment involving laser-driven shock compression which created [[nanodiamond]]s and [[superionic water]]. This could be a possible way of producing nanodiamonds commercially.<ref>{{cite journal |last1=He |first1=Jhiyu |display-authors=etal |date=Sep 2, 2022 |title=Diamond formation kinetics in shock-compressed C─H─O samples recorded by small-angle x-ray scattering and x-ray diffraction |journal=Science Advances |volume=8 |issue=35 |pages=eabo0617 |bibcode=2022SciA....8O.617H |doi=10.1126/sciadv.abo0617 |pmc=10848955 |pmid=36054354 |s2cid=252046278 |hdl-access=free |hdl=10852/101445}}</ref><ref>{{cite journal |last1=Leah Crane |date=Sep 10, 2022 |title=Blasting plastic with powerful lasers turns it into tiny diamonds |url=https://www.newscientist.com/article/2336362-blasting-plastic-with-powerful-lasers-turns-it-into-tiny-diamonds/ |journal=New Scientist}}</ref>
 
===Other applications===
Line 146 ⟶ 149:
* 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 |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 |issn=1517-7076|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 |language=en |volume=17 |issue=7 |pages=e0270328 |doi=10.1371/journal.pone.0270328 |issn=1932-6203 |pmc=9286293 |pmid=35839177 |bibcode=2022PLoSO..1770328B |doi-access=free }}</ref> to 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 |language=en |volume=14 |issue=13 |pages=2564 |doi=10.3390/polym14132564 |issn=2073-4360 |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 light-emitting diode 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 |language=en |volume=12 |issue=15 |pages=2499 |doi=10.3390/ma12152499 |issn=1996-1944 |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 |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 |pmid=33254837 |bibcode=2021JHzM..40224070G |s2cid=224894411 |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 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 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>
* It is used to make specific types of [[Kippah]], or Yarmulke, popular with rabbinical teachers at [[Yeshiva]].
 
<gallery mode=packed>
Line 170 ⟶ 172:
==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 non-crystalline ([[Amorphous solid|amorphous]]) or crystalline articles. Its amenability to [[Drawing (manufacturing)|drawing]] in manufacturing makes PET useful in fibre and film applications. Like most [[Aromaticity|aromatic polymers]], it has better barrier properties{{Clarification needed|reason=What are these?|date=June 2024}} than [[Aliphatic compound|aliphatic polymers]]. It is strong and [[toughness|impact-resistant]]. PET is [[hygroscopic]] and absorbs water.<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.{{Clarification needed|reason=Polyester fibers of PET or other polymers?|date=June 2024}} Transparent products can be produced by rapidly cooling molten polymer below T<sub>g</sub>the [[glass transition temperature]] (T<sub>g</sub>) to form ana 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> 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. AtWhile at room temperature the molecules are frozen in place, but, if enough heat energy is put back into them afterward by heating the material above T<sub>g</sub>, they can begin to move again, allowing crystals to [[nucleation|nucleate]] and grow. This procedure is known as solid-state crystallization.{{Citation needed|date=June 2024}} Amorphous PET also crystallizes and becomes opaque when exposed to [[Solvent|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>
 
WhenA allowedmore tocrystalline coolproduct slowly,can be produced by allowing the molten polymer formsto acool moreslowly. crystallineRather material.than Thisforming one large single crystal, this material has a number of [[Spherulite (polymer physics)|spherulites]] (crystallized areas) each containing many small [[crystallite]]s when crystallized from an amorphous solid, rather than forming one large single crystal(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.{{Citation needed|date=June 2024}} Orientation also renders polymers more transparent.{{Clarification needed|reason=Orientation of what?|date=June 2024}} This is why [[BoPET|BOPET]] film and bottles are both crystalline, to a degree, and transparent.{{Citation needed|date=June 2024}}
 
=== Flavor absorption ===
Orientation also renders polymers more transparent. This is why BOPET film and bottles are both crystalline to a degree and transparent.
PET has an affinity for [[Hydrophobe|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}} While heavy gauge PET bottles 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 returned bottles to avoid cross-contamination of flavors.<ref name="Ashurst-2009"/>{{Rp|page=115}}
 
Amorphous PET crystallizes and becomes opaque when exposed to 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>
 
PET is stoichiometrically a mixture of carbon and {{chem2|H2O}}, and therefore has been used in an experiment involving laser-driven shock compression which created [[nanodiamond]]s and [[superionic water]]. This could be a possible way of producing nanodiamonds commercially.<ref>{{cite journal|url=https://www.science.org/doi/10.1126/sciadv.abo0617|display-authors=etal |last1=He |first1=Jhiyu |title=Diamond formation kinetics in shock-compressed C─H─O samples recorded by small-angle x-ray scattering and x-ray diffraction |journal=Science Advances |date=Sep 2, 2022 |volume=8 |issue=35 |pages=eabo0617 |doi=10.1126/sciadv.abo0617|pmid=36054354 |bibcode=2022SciA....8O.617H |s2cid=252046278 |hdl=10852/101445 |hdl-access=free }}</ref><ref>{{cite journal |last1=Leah Crane |title=Blasting plastic with powerful lasers turns it into tiny diamonds |journal=New Scientist |date=Sep 10, 2022 |url=https://www.newscientist.com/article/2336362-blasting-plastic-with-powerful-lasers-turns-it-into-tiny-diamonds/}}</ref>
 
=== Absorption/scalping ===
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}} Heavy gauge PET bottles are sometimes returnable for re-use as is practiced in some EU countries, however the propensity of PET to absorb flavors makes it necessary to conduct a "sniffer" test on 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 mass|molecular weight]] of PET is measured by solution viscosity.{{Clarification needed|reason=How is this true?|date=June 2024}} 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 ==
IV is a dimensionless measurement. It is found by extrapolating the relative viscosity (measured in (dℓ/g)) to zero concentration.
{{Unreferenced|section|date=June 2024}}[[File:Phthalic acid isomers.PNG|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]].]]PET is often copolymerized with other diols or diacids to optimize the properties for particular applications. For example, [[cyclohexanedimethanol]] (CHDM) can be added to the polymer backbone in place of [[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. Another common modifier is [[isophthalic acid]], replacing some of the 1,4-(''para-'') linked [[Terephthalic acid|terephthalate]] units. The 1,2-(''ortho-'') or 1,3-(''[[Arene substitution patterns|meta]]''-) linkage produces an angle in the chain, which also disturbs crystallinity.
 
Shown below are the IV ranges for the main 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>
 
; Fibers
:* 0.40–0.70: textile
:* 0.72–0.98: technical eg [[tire]] cord
; Films
:* 0.60–0.70: [[BoPET|biaxially oriented PET film]]
:* 0.70–1.00: [[wikt:sheet|sheet]] grade for [[thermoforming]]
; Bottles
:* 0.70–0.78: general purpose bottles
:* 0.78–0.85: bottles for carbonated drinks
; Monofilaments, [[engineering plastic]]s:
:* 1.00–2.00
 
==Copolymers==
PET is copolymerized with other diols or diacids to optimize the properties for particular applications.
 
For example, [[cyclohexanedimethanol]] (CHDM) can be added to the polymer backbone in place of [[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.
 
[[File:Phthalic acid isomers.PNG|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 [[Terephthalic acid|terephthalate]] units. The 1,2-(''ortho-'') or 1,3-(''[[Arene substitution patterns|meta]]''-) linkage produces an angle in the chain, which also disturbs crystallinity.
 
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 [[ethyleneterephthalic glycolacid]] (usuallyPTA), referredas towell inas theto tradea aslesser "MEG",extent forfrom monoethylene[[ethylene glycol|(mono-)ethylene and [[dimethyl terephthalateglycol]] (DMTMEG) (C<sub>6</sub>H<sub>4</sub>(CO<sub>2</sub>CH<sub>3</sub>)<sub>2</sub>) but mostlyand [[terephthalicdimethyl acidterephthalate]] (known in the trade as "PTA", for purified terephthalic acidDMT).<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|p-xylene]] made from [[crude oil]]. Typically an [[antimony]] or [[titanium]] compound is used as a catalyst, a [[Phosphite anion|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=2002 |volume=51 |issue=10 |pages=923–930 |doi=10.1002/pi.917 }}</ref>
 
=== Processes ===
 
==== Dimethyl terephthalate (DMT) process ====
[[File:PET by Transesterification V1.svg|thumb|Polyesterification reaction in the production of PET]]
In the [[dimethyl terephthalate]] (DMT) process, DMT and excess ethylene glycol (MEG) are [[Transesterification|transesterified]] in the melt at 150–200&nbsp;°C with a [[base (chemistry)|basic catalyst]]. [[Methanol]] (CH<sub>3</sub>OH) 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&nbsp;°C, with continuous distillation of MEG as well.<ref name=polyesters/>
 
The reactions can be summarized as follows:
Line 230 ⟶ 232:
: ''n'' C<sub>6</sub>H<sub>4</sub>(CO<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>OH)<sub>2</sub> → [(CO)C<sub>6</sub>H<sub>4</sub>(CO<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>O)]<sub>n</sub> + ''n'' HOCH<sub>2</sub>CH<sub>2</sub>OH
 
==== Terephthalic acid (PTA) process ====
[[File:PET by Polycondensation V1.svg|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&nbsp;°C). Water is eliminated in the reaction, and it is also continuously removed by [[distillation]]:<ref name = polyesters/>
 
: ''n'' C<sub>6</sub>H<sub>4</sub>(CO<sub>2</sub>H)<sub>2</sub> + ''n'' HOCH<sub>2</sub>CH<sub>2</sub>OH → [(CO)C<sub>6</sub>H<sub>4</sub>(CO<sub>2</sub>CH<sub>2</sub>CH<sub>2</sub>O)]<sub>n</sub> + 2''n'' H<sub>2</sub>O
 
==== Bio-PET ====
'''Bio-PET''' is the [[Drop-in bioplastic|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 |pages=10 |doi=10.1021/cen-09546-notw6 |url=https://pubs.acs.org/doi/10.1021/cen-09546-notw6 |access-date=4 March 2022|last1=Alex Tullo }}</ref> and it is also technically possible to make PTA from readily available biobasedbio-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 |pages=8249 |doi=10.1038/srep08249 |pmid=25648201 |pmc=4316194 |bibcode=2015NatSR...5E8249T |language=en |issn=2045-2322}}</ref>
 
=== Bottle processing equipment ===
===Degradation===
{{Unreferenced|section|date=June 2024}}[[File:Plastic bottle.jpg|thumb|upright|A finished PET drink bottle compared to the preform from which it is made]]
PET is subject to [[polymer degradation|degradation]] during processing. If the moisture level is too high, hydrolysis will reduce the molecular weight by chain [[Bond cleavage|scission]], resulting in brittleness.
 
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]].
If the residence time and/or melt temperature are too high, then thermal degradation or thermooxidative degradation will occur resulting in:
 
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.
*discoloration
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.
*reduced molecular weight
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}}
*formation of [[acetaldehyde]],
*[[cross-link]]ing ("gel" or "fish-eye" formation).
 
===Degradation===
Mitigation measures include
PET is subject to [[polymer degradation|degradation]] during processing. If the moisture level is too high, [[hydrolysis]] will reduce the [[Molar mass|molecular weight]] by chain [[Bond cleavage|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 reduced molecular weight, as well as the formation of [[acetaldehyde]], and the formation "gel" or "fish-eye" formations through [[cross-link]]ing. Mitigation measures include [[copolymer]]isation with other monomers like [[Cyclohexanedimethanol|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=3446175717 |page=92 |edition=4th }}</ref>
*[[copolymer]]isation. Comonomers such as CHDM or [[isophthalic acid]] lower the melting point and thus the melt temperature of the resin ([[#Copolymers|copolymers]], above).
*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>
 
====Acetaldehyde====
[[Acetaldehyde]], which can form by degradation of PET after mishandling of the material, is a colorless, volatile substance with a fruity smell. Although it forms naturally in some fruit, it can cause an off-taste in bottled water. AcetaldehydeAs formswell byas degradation of PET through the mishandling of the material. Highhigh temperatures (PET decomposes above 300&nbsp;°C or 570&nbsp;°F) and long barrel residence times, high pressures, and high extruder speeds (excessivewhich cause shear flowraising raisesthe temperature), andcan long barrel residence times allalso contribute to the production of acetaldehyde. [[Photo-oxidation of polymers|Photo-oxidation]] can also cause the gradual formation acetaldehyde over the object's lifespan. This 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>
[[File:Poly(ethylene_terephthalate)_-_Type_II_Norrish_to_acetaldehyde.png|600px|center]]
 
When acetaldehyde is produced, some of it remains dissolved in the walls of a container and then [[diffusion|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>
 
===Biodegradation===
 
At least one species of bacterium in the genus ''[[Nocardia]]'' can degrade PET with an [[esterase]] enzyme.<ref name="Samak-2020">{{cite journal |last1=Samak |first1=Nadia A. |last2=Jia |first2=Yunpu |last3=Sharshar |first3=Moustafa M. |last4=Mu |first4=Tingzhen |last5=Yang |first5=Maohua |last6=Peh |first6=Sumit |last7=Xing |first7=Jianmin |title=Recent advances in biocatalysts engineering for polyethylene terephthalate plastic waste green recycling |journal=Environment International |date=December 2020 |volume=145 |pages=106144 |doi=10.1016/j.envint.2020.106144 |pmid=32987219 |s2cid=222156984|doi-access=free }}</ref> Esterases are enzymes able to cleave the ester bond.<ref name="Samak-2020" /> Also, the initial degradation of PET can be esterases expressed by ''Bacillus'' and ''Nocardia''.<ref>{{cite journal |last1=Smith |first1=Matthew R. |last2=Cooper |first2=Sharon J. |last3=Winter |first3=Derek J. |last4=Everall |first4=Neil |title=Detailed mapping of biaxial orientation in polyethylene terephthalate bottles using polarised attenuated total reflection FTIR spectroscopy |journal=Polymer |date=July 2006 |volume=47 |issue=15 |pages=5691–5700 |doi=10.1016/j.polymer.2005.07.112}}</ref>
 
Japanese scientists have isolated a bacterium ''[[Ideonella sakaiensis]]'' that possesses two enzymes which can break down the PET into smaller pieces that the bacterium can digest. A colony of ''I. sakaiensis'' can disintegrate a plastic film in about six weeks.<ref>{{cite journal |title=A bacterium that degrades and assimilates poly(ethylene terephthalate) |doi=10.1126/science.aad6359 |pmid=26965627 |date=11 March 2016 |journal=Science |volume=351 |issue=6278 |pages=1196–9 |last1=Yoshida |first1=S. |last2=Hiraga |first2=K. |last3=Takehana |first3=T. |last4=Taniguchi |first4=I. |last5=Yamaji |first5=H. |last6=Maeda |first6=Y. |last7=Toyohara |first7=K. |last8=Miyamoto |first8=K. |last9=Kimura |first9=Y. |last10=Oda |first10=K. |bibcode=2016Sci...351.1196Y |s2cid=31146235}}</ref><ref>{{cite news |title=Could a new plastic-eating bacteria help combat this pollution scourge? |url=https://www.theguardian.com/environment/2016/mar/10/could-a-new-plastic-eating-bacteria-help-combat-this-pollution-scourge |date=10 March 2016 |work=The Guardian |access-date=11 March 2016}}</ref>
 
French researchers report developing an improved PET hydrolase that can depolymerize at least 90 percent of PET in 10 hours, breaking it down into monomers.<ref name="Ong">{{cite journal |last1=Ong |first1=Sandy |title=The living things that feast on plastic |journal=Knowable Magazine {{!}} Annual Reviews |date=24 August 2023 |doi=10.1146/knowable-082423-1|doi-access=free |url=https://knowablemagazine.org/article/food-environment/2023/how-to-recycle-plastic-with-enzymes}}</ref><ref name="Tournier">{{cite journal |last1=Tournier |first1=V. |last2=Topham |first2=C. M. |last3=Gilles |first3=A. |last4=David |first4=B. |last5=Folgoas |first5=C. |last6=Moya-Leclair |first6=E. |last7=Kamionka |first7=E. |last8=Desrousseaux |first8=M.-L. |last9=Texier |first9=H. |last10=Gavalda |first10=S. |last11=Cot |first11=M. |last12=Guémard |first12=E. |last13=Dalibey |first13=M. |last14=Nomme |first14=J. |last15=Cioci |first15=G. |last16=Barbe |first16=S. |last17=Chateau |first17=M. |last18=André |first18=I. |last19=Duquesne |first19=S. |last20=Marty |first20=A. |title=An engineered PET depolymerase to break down and recycle plastic bottles |journal=Nature |date=April 2020 |volume=580 |issue=7802 |pages=216–219 |doi=10.1038/s41586-020-2149-4 |pmid=32269349 |bibcode=2020Natur.580..216T |s2cid=215411815 |url=https://www.nature.com/articles/s41586-020-2149-4 |language=en |issn=1476-4687}}</ref><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=14 March 2023 |volume=123 |issue=9 |pages=5612–5701 |doi=10.1021/acs.chemrev.2c00644 |pmid=36916764 |s2cid=257506291 |url=https://pubs.acs.org/doi/10.1021/acs.chemrev.2c00644 |issn=0009-2665}}</ref>
 
An enzyme based on a natural PET-ase was designed with the help of a machine learning algorithm to be able to tolerate pH and temperature changes by the [[University of Texas at Austin]]. The PET-ase was found to able to degrade various products and could break them down as fast as 24 hours.<ref>{{cite web |title=Scientists Engineer New Plastic-Eating Enzyme {{!}} Sci-News.com |url=http://www.sci-news.com/biology/fast-petase-10752.html |website=Breaking Science News {{!}} Sci-News.com |date=28 April 2022 |access-date=2 June 2022}}</ref><ref>{{cite journal |last1=Lu |first1=Hongyuan |last2=Diaz |first2=Daniel J. |last3=Czarnecki |first3=Natalie J. |last4=Zhu |first4=Congzhi |last5=Kim |first5=Wantae |last6=Shroff |first6=Raghav |last7=Acosta |first7=Daniel J. |last8=Alexander |first8=Bradley R. |last9=Cole |first9=Hannah O. |last10=Zhang |first10=Yan |last11=Lynd |first11=Nathaniel A. |last12=Ellington |first12=Andrew D. |last13=Alper |first13=Hal S. |title=Machine learning-aided engineering of hydrolases for PET depolymerization |journal=Nature |date=April 2022 |volume=604 |issue=7907 |pages=662–667 |doi=10.1038/s41586-022-04599-z |pmid=35478237 |bibcode=2022Natur.604..662L |s2cid=248414531 |url=https://www.nature.com/articles/s41586-022-04599-z |language=en |issn=1476-4687}}</ref>
 
==Environmental concerns==
 
===Resource depletion===
Compared to the use of petroleum as fuel, however, the amount of crude oil processed into PET is very small. The total production capacity of PET is around 30 million tons,<ref>{{Cite web|url=https://www.statista.com/statistics/242764/global-polyethylene-terephthalate-production-capacity/|title = PET production capacity worldwide 2024}}</ref> compared to 4.2 billion tons of crude oil production,<ref>{{Cite web|url=https://www.statista.com/statistics/265229/global-oil-production-in-million-metric-tons/#:~:text=In%202020%2C%20global%20crude%20oil,where%20this%20is%20recovered%20separately)|title = Global oil production in million metric tons 2020}}</ref> thus around 0.7% of crude oil is processed into PET.
 
===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 |doi-access=free }}</ref>
 
====Littering====
Nevertheless, [[litter]]ing has become a prominent issue in public opinion, and PET bottles are a visible part of that.
 
====Dumping of apparel====
A substantial amount of post consumer waste from the textile industry ends up in landfills in developing countries such as Chile<ref>{{cite web |title=Chile's desert dumping ground for fast fashion leftovers |url=https://www.france24.com/en/live-news/20211108-chile-s-desert-dumping-ground-for-fast-fashion-leftovers |website=France 24 |access-date=5 March 2022 |language=en |date=8 November 2021}}</ref> and in countries in West Africa such as Ghana.<ref>{{cite news |title=Fast fashion in the U.S. is fueling an environmental disaster in Ghana |work=CBS News |url=https://www.cbsnews.com/news/ghana-fast-fashion-environmental-disaster/ |access-date=19 December 2022}}</ref> PET being a substantial component of apparel, this waste in landfills contains much PET.
 
====Microfibres from apparel and microplastics====
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. [[Scientific Advice Mechanism|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 |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 |title=Degradation Rates of Plastics in the Environment |journal=ACS Sustainable Chemistry & Engineering |date=9 March 2020 |volume=8 |issue=9 |pages=3494–3511 |doi=10.1021/acssuschemeng.9b06635 |s2cid=212404939 |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. |title=The degradation potential of PET bottles in the marine environment: An ATR-FTIR based approach |journal=Scientific Reports |date=22 March 2016 |volume=6 |pages=23501 |doi=10.1038/srep23501 |pmid=27000994 |pmc=4802224 |bibcode=2016NatSR...623501I }}</ref>
 
==Safety and environmental concerns==
Commentary published in ''[[Environmental Health Perspectives]]'' in April 2010 suggested that PET might yield [[endocrine disruptor]]s 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}}</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&nbsp;°C (140&nbsp;°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|author=Tukur, Aminu |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|year=2012|volume=14|issue=4|doi=10.1039/C2EM10917D|pmid=22402759|pages=1236–1246}}</ref>
Line 299 ⟶ 267:
[[Antimony]] (Sb) is a [[metalloid]] element that is used as a [[catalyst]] in the form of compounds such as [[antimony trioxide]] (Sb<sub>2</sub>O<sub>3</sub>) 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|pmid=20309737|year=2010|author=Cheng, X. |pages=1323–30|issue=7|volume=17|title=Assessment of metal contaminations leaching out from recycling plastic bottles upon treatments|doi=10.1007/s11356-010-0312-4|journal=Environmental Science and Pollution Research International|bibcode=2010ESPR...17.1323C |s2cid=20462253|display-authors=etal}}</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 [[World Health Organization|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&nbsp;μg/L of antimony, well above the EU limits for [[tap water]] of 5&nbsp;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 ===
==Bottle processing equipment==
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. [[Scientific Advice Mechanism|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 |url=https://allea.org/sapea-report-microplastics/ |access-date=5 March 2022}}</ref>
[[File:Plastic bottle.jpg|thumb|upright|A finished PET drink bottle compared to the preform from which it is made]]
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 |s2cid=212404939 |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 |pages=23501 |bibcode=2016NatSR...623501I |doi=10.1038/srep23501 |pmc=4802224 |pmid=27000994}}</ref>
 
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.
 
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}}
 
==Polyester recycling==
{{main|PET bottle recycling}}
 
{{More citations needed section|date=April 2011}}
 
Line 320 ⟶ 284:
[[File:Symbol Resin Code 01 PET.svg|thumb|upright=.5|Alternate 2]]
 
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="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 |issn=0972-656X |s2cid=99732501}}</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. |date=April 2013 |title=Manganese-, cobalt-, and zinc-based mixed-oxide spinels as novel catalysts for the chemical recycling of poly(ethylene terephthalate) via glycolysis |url=https://linkinghub.elsevier.com/retrieve/pii/S0141391013000220 |journal=Polymer Degradation and Stability |language=en |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="link.springer.com" /> 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 |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 |bibcode=2005EurPJ..41.1453A |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>
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>
 
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 |date=2023-01-03 |title=Chemical Recycling of Used PET by Glycolysis Using Niobia-Based Catalysts |journal=ACS Engineering Au |language=en |volume=3 |issue=1 |pages=37–44 |doi=10.1021/acsengineeringau.2c00029 |issn=2694-2488 |pmc=9936547 |pmid=36820227 |s2cid=255634660}}</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 |issn=1759-9962 |s2cid=106033120 |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 |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 |s2cid=99621770}}</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 name="link.springer.com"/><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. |date=April 2013 |title=Manganese-, cobalt-, and zinc-based mixed-oxide spinels as novel catalysts for the chemical recycling of poly(ethylene terephthalate) via glycolysis |url=https://linkinghub.elsevier.com/retrieve/pii/S0141391013000220 |journal=Polymer Degradation and Stability |language=en |volume=98 |issue=4 |pages=904–915 |doi=10.1016/j.polymdegradstab.2013.01.007}}</ref> The prime uses for recycled PET are polyester [[Synthetic fiber|fiber]], strapping, and non-food containers.
 
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>
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.
 
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 |date=December 2020 |title=Chemical recycling of PET : A stepping-stone toward sustainability |url=https://onlinelibrary.wiley.com/doi/10.1002/pat.5023 |journal=Polymers for Advanced Technologies |language=en |volume=31 |issue=12 |pages=2912–2938 |doi=10.1002/pat.5023 |issn=1042-7147 |s2cid=225374393}}</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).
 
PET is also 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 |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 |pages=2 |doi=10.1186/s12302-020-00447-x |issn=2190-4715 |pmc=7787125 |pmid=33432280 |doi-access=free}}</ref>
When recycling polyethylene terephthalate or PET or polyester, in general three ways have to be differentiated:
 
===Biodegradation===
#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 |journal=ACS Engineering Au |volume=3 |issue=1 |language=en |pages=37–44 |doi=10.1021/acsengineeringau.2c00029 |pmid=36820227 |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 |s2cid=99621770 |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.
 
Mechanical recycling or direct circulation of PET in the polymeric state is operated in most diverse variants today. These kinds of processes are typical of small and medium-size industry. Cost-efficiency can already be achieved with plant capacities within a range of 5000–20,000 tons/year. In this case, nearly all kinds of recycled-material feedback into the material circulation are possible today. These diverse recycling processes are being discussed hereafter in detail.
 
Besides chemical contaminants and [[Chemical decomposition|degradation]] products generated during first processing and usage, mechanical impurities are representing the main part of quality depreciating impurities in the recycling stream. Recycled materials are increasingly introduced into manufacturing processes, which were originally designed for new materials only. Therefore, efficient sorting, separation and cleaning processes become most important for high quality recycled polyester.
 
When talking about polyester recycling industry, we are concentrating mainly on recycling of PET bottles, which are meanwhile used for all kinds of liquid packaging like water, carbonated soft drinks, juices, beer, sauces, detergents, household chemicals and so on. Bottles are easy to distinguish because of shape and consistency and separate from waste plastic streams either by automatic or by hand-sorting processes. The established polyester recycling industry consists of three major sections:
 
* PET bottle collection and waste separation: waste logistics
* Production of clean bottle flakes: flake production
* Conversion of PET flakes to final products: flake processing
 
Intermediate product from the first section is baled bottle waste with a PET content greater than 90%. Most common trading form is the bale but also bricked or even loose, pre-cut bottles are common in the market. In the second section, the collected bottles are converted to clean PET bottle flakes. This step can be more or less complex and complicated depending on required final flake quality. During the third step, PET bottle flakes are processed to any kind of products like film, bottles, fiber, filament, strapping or intermediates like pellets for further processing and engineering plastics.
 
Besides this external (post-consumer) polyester bottle recycling, numbers of internal (pre-consumer) recycling processes exist, where the wasted polymer material does not exit the production site to the free market, and instead is reused in the same production circuit. In this way, fiber waste is directly reused to produce fiber, preform waste is directly reused to produce preforms, and film waste is directly reused to produce film.
 
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>
 
===PET bottle recycling===
{{main|PET bottle recycling}}
 
The only form of PET that is widely recycled in 2022 is the bottle. These are recycled by 'mechanical recycling' increasingly to bottles but still to other forms such as film or fibre. Other forms of polyester are not (as of 2022) collected in significant quantities.
 
At least one species of bacterium in the genus ''[[Nocardia]]'' can degrade PET with an esterase enzyme.<ref name="Samak-2020">{{cite journal |last1=Samak |first1=Nadia A. |last2=Jia |first2=Yunpu |last3=Sharshar |first3=Moustafa M. |last4=Mu |first4=Tingzhen |last5=Yang |first5=Maohua |last6=Peh |first6=Sumit |last7=Xing |first7=Jianmin |date=December 2020 |title=Recent advances in biocatalysts engineering for polyethylene terephthalate plastic waste green recycling |journal=Environment International |volume=145 |pages=106144 |bibcode=2020EnInt.14506144S |doi=10.1016/j.envint.2020.106144 |pmid=32987219 |s2cid=222156984 |doi-access=free}}</ref> [[Esterase|Esterases]] are enzymes able to cleave the [[ester bond]] between two oxygens that links subunits of PET.<ref name="Samak-2020" /> The initial degradation of PET can also be achieved esterases expressed by ''[[Bacillus]]'', as well as ''Nocardia''.<ref>{{cite journal |last1=Smith |first1=Matthew R. |last2=Cooper |first2=Sharon J. |last3=Winter |first3=Derek J. |last4=Everall |first4=Neil |date=July 2006 |title=Detailed mapping of biaxial orientation in polyethylene terephthalate bottles using polarised attenuated total reflection FTIR spectroscopy |journal=Polymer |volume=47 |issue=15 |pages=5691–5700 |doi=10.1016/j.polymer.2005.07.112}}</ref> Japanese scientists have isolated another bacterium, ''[[Ideonella sakaiensis]]'', that possesses two enzymes which can break down the PET into smaller pieces digestible by the bacteria. A colony of ''I. sakaiensis'' can disintegrate a plastic film in about six weeks.<ref>{{cite journal |last1=Yoshida |first1=S. |last2=Hiraga |first2=K. |last3=Takehana |first3=T. |last4=Taniguchi |first4=I. |last5=Yamaji |first5=H. |last6=Maeda |first6=Y. |last7=Toyohara |first7=K. |last8=Miyamoto |first8=K. |last9=Kimura |first9=Y. |last10=Oda |first10=K. |date=11 March 2016 |title=A bacterium that degrades and assimilates poly(ethylene terephthalate) |journal=Science |volume=351 |issue=6278 |pages=1196–9 |bibcode=2016Sci...351.1196Y |doi=10.1126/science.aad6359 |pmid=26965627 |s2cid=31146235}}</ref><ref>{{cite news |date=10 March 2016 |title=Could a new plastic-eating bacteria help combat this pollution scourge? |url=https://www.theguardian.com/environment/2016/mar/10/could-a-new-plastic-eating-bacteria-help-combat-this-pollution-scourge |access-date=11 March 2016 |work=The Guardian}}</ref> French researchers report developing an improved PET [[hydrolase]] that can [[Depolymerization|depolymerize]] (break apart) at least 90 percent of PET in 10 hours, breaking it down into individual [[Monomer|monomers]].<ref name="Ong">{{cite journal |last1=Ong |first1=Sandy |date=24 August 2023 |title=The living things that feast on plastic |url=https://knowablemagazine.org/article/food-environment/2023/how-to-recycle-plastic-with-enzymes |journal=Knowable Magazine {{!}} Annual Reviews |doi=10.1146/knowable-082423-1 |doi-access=free}}</ref><ref name="Tournier">{{cite journal |last1=Tournier |first1=V. |last2=Topham |first2=C. M. |last3=Gilles |first3=A. |last4=David |first4=B. |last5=Folgoas |first5=C. |last6=Moya-Leclair |first6=E. |last7=Kamionka |first7=E. |last8=Desrousseaux |first8=M.-L. |last9=Texier |first9=H. |last10=Gavalda |first10=S. |last11=Cot |first11=M. |last12=Guémard |first12=E. |last13=Dalibey |first13=M. |last14=Nomme |first14=J. |last15=Cioci |first15=G. |date=April 2020 |title=An engineered PET depolymerase to break down and recycle plastic bottles |url=https://www.nature.com/articles/s41586-020-2149-4 |journal=Nature |language=en |volume=580 |issue=7802 |pages=216–219 |bibcode=2020Natur.580..216T |doi=10.1038/s41586-020-2149-4 |issn=1476-4687 |pmid=32269349 |s2cid=215411815 |last16=Barbe |first16=S. |last17=Chateau |first17=M. |last18=André |first18=I. |last19=Duquesne |first19=S. |last20=Marty |first20=A.}}</ref><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 |date=14 March 2023 |title=Enzymes' Power for Plastics Degradation |url=https://pubs.acs.org/doi/10.1021/acs.chemrev.2c00644 |journal=Chemical Reviews |volume=123 |issue=9 |pages=5612–5701 |doi=10.1021/acs.chemrev.2c00644 |issn=0009-2665 |pmid=36916764 |s2cid=257506291}}</ref> Also, an enzyme based on a natural PET-ase was designed with the help of a machine learning algorithm to be able to tolerate pH and temperature changes by the [[University of Texas at Austin]]. The PET-ase was found to able to degrade various products and could break them down as fast as 24 hours.<ref>{{cite web |date=28 April 2022 |title=Scientists Engineer New Plastic-Eating Enzyme {{!}} Sci-News.com |url=http://www.sci-news.com/biology/fast-petase-10752.html |access-date=2 June 2022 |website=Breaking Science News {{!}} Sci-News.com}}</ref><ref>{{cite journal |last1=Lu |first1=Hongyuan |last2=Diaz |first2=Daniel J. |last3=Czarnecki |first3=Natalie J. |last4=Zhu |first4=Congzhi |last5=Kim |first5=Wantae |last6=Shroff |first6=Raghav |last7=Acosta |first7=Daniel J. |last8=Alexander |first8=Bradley R. |last9=Cole |first9=Hannah O. |last10=Zhang |first10=Yan |last11=Lynd |first11=Nathaniel A. |last12=Ellington |first12=Andrew D. |last13=Alper |first13=Hal S. |date=April 2022 |title=Machine learning-aided engineering of hydrolases for PET depolymerization |url=https://www.nature.com/articles/s41586-022-04599-z |journal=Nature |language=en |volume=604 |issue=7907 |pages=662–667 |bibcode=2022Natur.604..662L |doi=10.1038/s41586-022-04599-z |issn=1476-4687 |pmid=35478237 |s2cid=248414531}}</ref>
Significant investments were announced in 2021 and 2022 for chemical recycling of PET by glycolysis, methanolysis,<ref>{{cite news |last1=Laird |first1=Karen |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 |date=18 January 2022 |language=en}}</ref><ref>{{cite news |last1=Toto |first1=Deanne |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 |date=1 Feb 2021 |language=en}}</ref> and enzymatic recycling<ref>{{cite news |last1=Page Bailey |first1=mary |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 |date=24 February 2022 |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 |date=December 2020 |title=Chemical recycling of PET : A stepping‐stone toward sustainability |url=https://onlinelibrary.wiley.com/doi/10.1002/pat.5023 |journal=Polymers for Advanced Technologies |language=en |volume=31 |issue=12 |pages=2912–2938 |doi=10.1002/pat.5023 |s2cid=225374393 |issn=1042-7147}}</ref>
 
==See also==
Line 394 ⟶ 333:
[[Category:Thermoplastics]]
[[Category:Transparent materials]]
[[Category:Food packaging| ]]
Retrieved from "https://en.wikipedia.org/wiki/Polyethylene_terephthalate"