Plastic recycling

Although plastics were discovered before the 20th century, large-scale production was not realised until World War II. Nylon replaced silk in parachutes, while Perspex was a light-weight alternative to glass in aeroplanes. After the war these materials were commercialized. The plastic age began around 1950, part of the post-war economic boom.

Global environmental movements in the 1960s and 1970s led to the formation of environmental agencies in the US (EPA, 1970), EU (DG ENV, 1973) Australia (EPA, 1971) and Japan (JEA 1971). Environmental awareness put plastic waste under scrutiny.{{cite book |last1=Huffman |first1=George L. |last2=Keller |first2=Daniel J. |title=Polymers and Ecological Problems |chapter=The Plastics Issue |date=1973 |pages=155–167 |doi=10.1007/978-1-4684-0871-3_10|isbn=978-1-4684-0873-7 }} The earliest effort to abate plastic pollution was arguably the 1973 and 1978 MARPOL agreements, whose Annex V banned dumping plastics in the oceans.

File:KEEP AMERICA BEAUTIFUL DAY. GIRL SCOUTS REMOVING LITTER FROM SALINAS - NARA - 543177.jpg cleanup in 1970. The Keep American Beautiful campaign was a greenwashing campaign by the plastics and other polluting industries founded in the 1970s to try to displace responsibility of plastic pollution and other disposable packing trash onto consumers as "littering".{{Cite news|title=The Litter Myth : Throughline|url=https://www.npr.org/2019/09/04/757539617/the-litter-myth|access-date=15 June 2021|website=NPR.org|language=en}}]]

As regulations expanded, the plastics industry responded with lobbying to preserve their business interests. In the U.S., the 1970 Resource Recovery Act directed the nation towards recycling and energy recovery. More than a thousand attempts to pass legislation to ban or tax packaging, including plastics, came by 1976.{{Cite journal |last=Jaeger |first=Andrew Boardman |date=April 8, 2017 |title=Forging Hegemony: How Recycling Became a Popular but Inadequate Response to Accumulating Waste |journal=Social Problems |volume=65 |issue=3 |pages=395–415 |doi=10.1093/socpro/spx001 |issn=0037-7791}} The plastics industry responded by lobbying for plastic to be recycled. A $50 million per year campaign was run by organisations such as Keep America Beautiful with the message that plastic could and would be recycled, as well as lobbying for the establishment of curbside recycling.{{cite journal |last1=Elmore |first1=Bartow J. |title=The American Beverage Industry and the Development of Curbside Recycling Programs, 1950–2000 |journal=Business History Review |date=2012 |volume=86 |issue=3 |pages=477–501 |doi=10.1017/S0007680512000785 |jstor=41720628 |url=https://www.jstor.org/stable/41720628}}

However, plastic could not be economically recycled using the technology of the time. For example, an April 1973 report written by industry scientists stated that, "There is no recovery from obsolete products" and that, "A degradation of resin properties and performance occurs during the initial fabrication, through aging, and in any reclamation process." The report concluded that sorting the plastic is "infeasible". Contemporary scientific reports highlighted numerous technical barriers.{{cite journal |last1=Paul |first1=D. R. |last2=Vinson |first2=C. E. |last3=Locke |first3=C. E. |title=The potential for reuse of plastics recovered from solid wastes |journal=Polymer Engineering and Science |date=May 1972 |volume=12 |issue=3 |pages=157–166 |doi=10.1002/pen.760120302}}{{cite journal |last1=Sperber |first1=R. J. |last2=Rosen |first2=S. L. |title=Reuse of Polymer Waste |journal=Polymer-Plastics Technology and Engineering |date=January 1974 |volume=3 |issue=2 |pages=215–239 |doi=10.1080/03602557408545028}}{{cite journal |last1=Scott |first1=Gerald |title=Some chemical problems in the recycling of plastics |journal=Resource Recovery and Conservation |date=June 1976 |volume=1 |issue=4 |pages=381–395 |doi=10.1016/0304-3967(76)90027-5}}{{cite journal |last1=Buekens |first1=A.G. |title=Some observations on the recycling of plastics and rubber |journal=Conservation & Recycling |date=January 1977 |volume=1 |issue=3–4 |pages=247–271 |doi=10.1016/0361-3658(77)90014-5}}{{cite journal |last1=Leidner |first1=J. |title=Recovery of the Value from Postconsumer Plastics Waste |journal=Polymer-Plastics Technology and Engineering |date=January 1978 |volume=10 |issue=2 |pages=199–215 |doi=10.1080/03602557809409228}}

Globally, plastic waste was almost entirely disposed of via landfill until the 1980s when rates of incineration increased. Although better technology was known,{{cite journal |last1=Poller |first1=Robert C. |title=Reclamation of waste plastics and rubber: Recovery of materials and energy |journal=Journal of Chemical Technology and Biotechnology |date=30 December 1979|volume=30 |issue=1 |pages=152–160 |doi=10.1002/jctb.503300120}} these early incinerators often lacked advanced combustors or emission-control systems, leading to the release of dioxins and dioxin-like compounds.{{cite journal |last1=Victorin |first1=K |last2=Stahlberg |first2=M |last3=Ahlborg |first3=U |title=Emission of mutagenic substances from waste incineration plants |journal=Waste Management & Research |date=June 1988 |volume=6 |issue=2 |pages=149–161 |doi=10.1016/0734-242X(88)90059-6|bibcode=1988WMR.....6..149V }}

In the late 1980s plastic recycling began in earnest. In 1988 the U.S. Society of the Plastics Industry created the Council for Solid Waste Solutions as a trade association to promote the idea of plastic recycling to the public.{{cite journal |last1=Liesemer |first1=Ronald |title=A perspective of the plastics waste issue in the United States |journal=Makromolekulare Chemie. Macromolecular Symposia |date=May 1992 |volume=57 |issue=1 |pages=1–13 |doi=10.1002/masy.19920570103}} The association lobbied American municipalities to launch or expand plastic waste collection programmes and lobbied U.S. states to require the labelling of plastic containers and products with recycling symbols.

The industry introduced resin identification codes in 1988, which provided a standard system for the identification of various polymer types at materials recovery facilities.

Globalisation during the 1990s included the export of plastic waste from advanced economies to developing and middle-income ones, where it could be sorted and recycled less expensively. The annual trade in plastic waste increased rapidly from 1993 onwards as part of the global waste trade.{{cite journal |last1=Brooks |first1=Amy L. |last2=Wang |first2=Shunli |last3=Jambeck |first3=Jenna R. |author-link=Jenna Jambeck |title=The Chinese import ban and its impact on global plastic waste trade |journal=Science Advances |date=June 2018 |volume=4 |issue=6 |pages=eaat0131 |doi=10.1126/sciadv.aat0131|pmid=29938223 |pmc=6010324 |bibcode=2018SciA....4..131B }}

Many governments count items as recycled if they have been exported for that purpose, regardless of the actual outcome. The practice has been labeled environmental dumping, as environmental laws and enforcement are generally weaker in less developed economies.{{cite web |title=Trashed: how the UK is still dumping plastic waste on the rest of the world |url=https://www.greenpeace.org.uk/resources/trashed-plastic-report/ |website=Greenpeace UK |date=16 May 2021 |access-date=20 May 2021 |language=en}}{{cite journal |last1=Bishop |first1=George |last2=Styles |first2=David |last3=Lens |first3=Piet N.L. |title=Recycling of European plastic is a pathway for plastic debris in the ocean |journal=Environment International |date=September 2020 |volume=142 |pages=105893 |doi=10.1016/j.envint.2020.105893 |pmid=32603969 |doi-access=free|bibcode=2020EnInt.14205893B |hdl=10344/9217 |hdl-access=free }} By 2016 about 14 Mt of plastic waste was exported, with China taking 7.35 Mt. Much of this was low quality mixed plastic that ended up in landfills. However, recycled plastic is used extensively in manufacturing in China, and imported plastic waste was predominantly processed using low-technology processing. High-income countries such as Germany, Japan, the United Kingdom and the United States were the top exporters.{{Cite web |last=Environment |first=U. N. |date=2021-10-21 |title=Drowning in Plastics – Marine Litter and Plastic Waste Vital Graphics |url=http://www.unep.org/resources/report/drowning-plastics-marine-litter-and-plastic-waste-vital-graphics |access-date=2022-03-23 |website=UNEP - UN Environment Programme |language=en}}

In 2017, China began restricting waste plastics imports via Operation National Sword. Exporters eventually exported to other countries mostly in Southeast Asia, such as Vietnam and Malaysia, but also Turkey and India.{{cite journal |last1=Wang |first1=Chao |last2=Zhao |first2=Longfeng |last3=Lim |first3=Ming K |last4=Chen |first4=Wei-Qiang |last5=Sutherland |first5=John W. |title=Structure of the global plastic waste trade network and the impact of China's import Ban |journal=Resources, Conservation and Recycling |date=February 2020 |volume=153 |pages=104591 |doi=10.1016/j.resconrec.2019.104591|bibcode=2020RCR...15304591W |s2cid=214271589 |url=https://pureportal.coventry.ac.uk/en/publications/structure-of-the-global-plastic-waste-trade-network-and-the-impact-of-chinas-import-ban(399872a7-4c4a-45ab-9c5f-cd01133bcd42).html }}{{Cite web|title=Piling Up: How China's Ban on Importing Waste Has Stalled Global Recycling|url=https://e360.yale.edu/features/piling-up-how-chinas-ban-on-importing-waste-has-stalled-global-recycling|access-date=12 October 2020|website=Yale E360|language=en-US}} Indonesia, Malaysia, and Thailand reacted to illegal plastic waste imports by reinforcing border controls. Illegally imported containers were repatriated or refused entry. Consequently, plastic waste containers accumulated in ports.

Given limited export options, attention turned to local solutions. Proposed extended producer responsibility would tax plastic producers to subsidise recyclers.{{cite journal |last1=Leal Filho |first1=Walter |last2=Saari |first2=Ulla |last3=Fedoruk |first3=Mariia |last4=Iital |first4=Arvo |last5=Moora |first5=Harri |last6=Klöga |first6=Marija |last7=Voronova |first7=Viktoria |date=March 2019 |title=An overview of the problems posed by plastic products and the role of extended producer responsibility in Europe |journal=Journal of Cleaner Production |volume=214 |pages=550–558 |doi=10.1016/j.jclepro.2018.12.256|bibcode=2019JCPro.214..550L |s2cid=158295219 |url=https://e-space.mmu.ac.uk/622465/1/Plastics.Paper.Final.pdf }}

In 2019, international trade in plastic waste became regulated under the Basel Convention. Under the convention, any Party can decide to prohibit imports of hazardous plastic waste and, since 1 January 2021, of some mixed plastic wastes. Parties to the convention are required to ensure environmentally sound management of their refuse either through alternative importers or by increasing capacity.

The COVID-19 pandemic temporarily reduced trade in plastic waste, due in part to reduced activity at waste management facilities, shipping disruptions, and low oil prices that reduced the cost of virgin plastic and made recycling less profitable.

The European Commission's "Action Plan" for a circular economy, adopted in December 2015, saw plastics as a strategic priority for developing circular economy actions. In 2017, the Commission further adopted a focus on plastic production and use, targeting the achievement of all plastic packaging being recyclable by 2030. The Commission then issued a strategic document in January 2018 which set out an "ambitious vision" and an opportunity for global action on plastic recycling.

File:Global production and fate of plastics.png

The total amount of plastic ever produced worldwide, until 2015, is estimated to be 8.3 billion tonnes (Bt). Approximately 6.3 Bt of this was discarded as waste, of which around 79% accumulated in landfills or the natural environment, 12% was incinerated, and 9% was recycled - only ~1% of all plastic has been recycled more than once. More recently, as of 2017, still only 9% of the 9 Bt of plastic produced was recycled.{{Cite web |title=What Percentage of Plastic is Recycled Globally? |url=https://bren.ucsb.edu/news/international-statistic-year-91-plastic-has-never-been-recycled |access-date=2024-01-22 |website=UCSB Bren School of Environmental Science & Management |date=18 December 2018 |language=en-US}}{{Cite journal |last1=Nikiema |first1=Josiane |last2=Asiedu |first2=Zipporah |date=April 2022 |title=A review of the cost and effectiveness of solutions to address plastic pollution |journal=Environmental Science and Pollution Research |language=en |volume=29 |issue=17 |pages=24547–24573 |doi=10.1007/s11356-021-18038-5 |issn=0944-1344 |pmc=8783770 |pmid=35066854|bibcode=2022ESPR...2924547N }}

By 2015 global production had reached some 381 million tonnes (Mt) per year.{{cite journal |last1=Geyer |first1=Roland |last2=Jambeck |first2=Jenna R. |author-link2=Jenna Jambeck |last3=Law |first3=Kara Lavender |title=Production, use, and fate of all plastics ever made |journal=Science Advances |date=July 2017 |volume=3 |issue=7 |pages=e1700782 |doi=10.1126/sciadv.1700782 |pmid=28776036 |pmc=5517107 |bibcode=2017SciA....3E0782G |doi-access=free}} The recycling rate that year was 19.5%, while 25.5% was incinerated and the remaining 55% disposed of, largely to landfill. These rates lag behind those of other recyclables, such as paper, metal and glass. Although the percentage of recycled or incinerated material is increasing each year, the tonnage of waste left-over also continues to rise. Production could reach ~800 Mt per year by 2040, although implementing all feasible interventions could reduce plastic pollution by 40% from 2016 rates.{{cite journal |last1=Lau |first1=Winnie W. Y. |last2=Shiran |first2=Yonathan |last3=Bailey |first3=Richard M. |last4=Cook |first4=Ed |last5=Stuchtey |first5=Martin R. |last6=Koskella |first6=Julia |last7=Velis |first7=Costas A. |last8=Godfrey |first8=Linda |last9=Boucher |first9=Julien |last10=Murphy |first10=Margaret B. |last11=Thompson |first11=Richard C. |last12=Jankowska |first12=Emilia |last13=Castillo Castillo |first13=Arturo |last14=Pilditch |first14=Toby D. |last15=Dixon |first15=Ben |last16=Koerselman |first16=Laura |last17=Kosior |first17=Edward |last18=Favoino |first18=Enzo |last19=Gutberlet |first19=Jutta |last20=Baulch |first20=Sarah |last21=Atreya |first21=Meera E. |last22=Fischer |first22=David |last23=He |first23=Kevin K. |last24=Petit |first24=Milan M. |last25=Sumaila |first25=U. Rashid |last26=Neil |first26=Emily |last27=Bernhofen |first27=Mark V. |last28=Lawrence |first28=Keith |last29=Palardy |first29=James E. |title=Evaluating scenarios toward zero plastic pollution |journal=Science |date=2020-09-18 |volume=369 |issue=6510 |pages=1455–1461 |doi=10.1126/science.aba9475|pmid=32703909 |bibcode=2020Sci...369.1455L |hdl=10026.1/16767 |s2cid=221767531 |url=http://arodes.hes-so.ch/record/5725 |hdl-access=free }}

Recycling rates vary among types of plastic. Several types are in common use, each with distinct chemical and physical properties. This affects sorting and reprocessing costs; which affects the value and market size for recovered materials.{{cite news |title=Why plastic recycling is so confusing |url=https://www.bbc.co.uk/news/science-environment-45496884 |access-date=6 August 2021 |work=BBC News |date=18 December 2018}} PET and HDPE have the highest recycling rates, whereas polystyrene and polyurethane are rarely recycled.{{cite web |title=Advancing Sustainable Materials Management: 2018 Tables and Figures |url=https://www.epa.gov/sites/default/files/2021-01/documents/2018_tables_and_figures_dec_2020_fnl_508.pdf |publisher=US_EPA |access-date=9 November 2021}}

One of the reasons for low levels of plastic recycling is weak demand, given the materials' poor/inconsistent properties.{{CELEX|52018DC0028|format=HTML|text=Communication from the Commission to the European Parliament, the Council, the European Economic and Social Committee and the Committee of the Regions – A European Strategy for Plastics in a Circular Economy, COM(2018) 28 final, 6 January 2018}} The percentage of plastic that can be fully recycled, rather than downcycled or go to waste, can be increased when manufacturers minimise mixing of packaging materials and eliminate contaminants. The Association of Plastics Recyclers has issued a "Design Guide for Recyclability".{{Cite web |title=The Association of Plastics Recyclers {{!}} APR Design® Guide |url=https://plasticsrecycling.org/apr-design-guide |access-date=2023-02-24 |website=The Association of Plastic Recyclers |language=en-gb}}

The most commonly produced plastic consumer products include packaging made from LDPE (e.g. bags, containers, food packaging film), containers made from HDPE (e.g. milk bottles, shampoo bottles, ice cream tubs), and PET (e.g. bottles for water and other drinks). Together these products account for around 36% of plastic production. The use of plastics in building and construction, textiles, transportation and electrical equipment accounts for another substantial share of the plastics market.{{Cite web |last=Environment |first=U. N. |date=2021-10-21 |title=Drowning in Plastics – Marine Litter and Plastic Waste Vital Graphics |url=http://www.unep.org/resources/report/drowning-plastics-marine-litter-and-plastic-waste-vital-graphics |access-date=2022-03-21 |website=UNEP - UN Environment Programme |language=en}}

Plastic consumption differs among countries and communities, although it is found almost everywhere. As of 2022 North American countries (NAFTA) accounted for 21% of global plastic consumption, closely followed by China (20%) and Western Europe (18%). In North America and Europe per capita plastic consumption was 94 kg and 85 kg/capita/year, respectively. China reached 58 kg/capita/year.

In 2012, 25.2 Mt of post-consumer plastic waste was collected in the European Union. Of this, more than 60% (15.6 Mt) was recovered and 40% (9.6 Mt) was disposed of as municipal solid waste (MSW). Of the 15.6 Mt of recovered plastic waste, about 6.6 Mt was recycled, while the remainder was likely used as refuse-derived fuel (RDF) or incinerated in MSW incinerators with energy recovery (about 9 Mt). Europe leads in plastics recycling, reusing about 26%.{{Citation |last1=Shen |first1=Li |title=Plastic Recycling |date=2014 |url=https://linkinghub.elsevier.com/retrieve/pii/B9780123964595000131 |work=Handbook of Recycling |pages=179–190 |publisher=Elsevier |language=en |doi=10.1016/b978-0-12-396459-5.00013-1 |isbn=978-0-12-396459-5 |access-date=2022-11-13 |last2=Worrell |first2=Ernst}}

The recycling activities of the largest producers of plastic waste have the greatest effect on global averages. These are a mix of advanced economies and large developing nations. Some publish official statistics on their plastic recycling rates. Others may release partial data, usually limited to population centres. This makes it difficult to draw accurate comparisons, especially as the published recycling rates vary.

* Although not formally a country, legislation affecting recycling is often made at the EU level

File:Primary plastic waste generation by polymer, OWID.svg

{{main|Resin identification code}}

Many plastic items bear symbols identifying the type of polymer from which they are made. These resin identification codes (RIC), are used internationally.{{cite web|title=Standard Practice for Coding Plastic Manufactured Articles for Resin Identification|url=http://www.astm.org/Standards/D7611.htm|website=Standard Practice for Coding Plastic Manufactured Articles for Resin Identification|publisher=ASTM International|access-date=21 January 2016}} They were developed in 1988 by the Society of the Plastics Industry (now the Plastics Industry Association) in the United States, but since 2008 have been administered by standards organisation ASTM International.

RICs are not mandatory in all countries, but many producers voluntarily mark their products. More than half of U.S. states have enacted laws that require plastic products be identifiable.{{cite book|title=Holt Chemistry|publisher=Holt, Rinehart, and Winston|year=2006|isbn=978-0-03-039114-9|chapter=19|page=702|quote=More than half the states in the United States have enacted laws that require plastic products to be labelled with numerical codes that identify the type of plastic used in them.|title-link=Florida|edition=Florida}} The seven codes include six for the most common commodity plastics and one as a catch-all. The EU maintains a similar nine-code list that also includes ABS and polyamides.Official Journal of the EC; [http://eur-lex.europa.eu/legal-content/EN/ALL/?uri=CELEX:31997D0129 Commission Decision (97/129/EC)] establishing the ID system for packaging materials pursuant to European Parliament & Council Directive 94/62/EC RICs are based on the recycling symbol, but have drawn criticism, as they imply that marked items are always recyclable when this may not be true.{{Cite web|last=Petsko|first=Emily|title=Recycling Myth of the Month: Those numbered symbols on single-use plastics do not mean 'you can recycle me'|url=https://oceana.org/blog/recycling-myth-month-those-numbered-symbols-single-use-plastics-do-not-mean-you-can-recycle-me|access-date=12 October 2020|website=Oceana|date=11 March 2020|language=en}}

RICs are not particularly important for single-stream recycling, as these operations are increasingly automated. However, in some countries citizens are required to separate their plastic waste according to polymer type before collection. For instance, in Japan PET bottles are collected separately for recycling.

{{clear}}

Plastic waste consists of various polymer types.{{cite book |last1=Geyer |first1=Roland |title=Plastic waste and recycling : environmental impact, societal issues, prevention, and solutions |date=2020 |publisher=Academic Press |location=Amsterdam |isbn=978-0-12-817880-5 |page=22}} Polyolefins make up nearly 50% of all plastic waste and more than 90% of waste is made of thermosoftening polymers, which can be remelted

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File:Bales of PET bottles.jpg (blues, clear and greens) Olomouc, the Czech Republic.]]

File:Recycling Video.webm

File:Bales of PET bottles closeup.jpg

Recycling begins with the collection and sorting of waste. Curbside collection operates in many countries. Waste is sent to a materials recovery facility or MBT plant where the plastic is separated, cleaned and sorted for sale. Unsuitable materials are sent to a landfill or incinerator. These operations account for a large proportion of the financial and energy costs associated with recycling.

Sorting plastic is more complicated than other recyclable materials because it comes in a greater range of forms. For example, glass is separated into three streams (clear, green and amber), metals are usually either steel or aluminum and can be separated using magnets or eddy current separators, and paper is usually sorted into a single stream.

Six types of commodity polymer account for about 75% of plastics waste, with the rest comprising a myriad of polymer types, including polyurethanes and synthetic fibers with a range of chemical structures. Items made from the same type of polymer may be incompatible with each other depending on the additives they contain. Additives are compounds blended into plastics to enhance performance and include stabilisers, fillers and, most significantly, dyes.{{cite journal |last1=Hahladakis |first1=John N. |last2=Velis |first2=Costas A. |last3=Weber |first3=Roland |last4=Iacovidou |first4=Eleni |last5=Purnell |first5=Phil |title=An overview of chemical additives present in plastics: Migration, release, fate and environmental impact during their use, disposal and recycling |journal=Journal of Hazardous Materials |date=February 2018 |volume=344 |pages=179–199 |doi=10.1016/j.jhazmat.2017.10.014|pmid=29035713 |doi-access=free|bibcode=2018JHzM..344..179H }} Clear plastics hold the highest value as they may be dyed after recycling, while black or strongly coloured plastic is much less valuable, because they affect the color of the downstream product. Thus, plastic is typically sorted by both polymer type and colour.

Various sorting approaches and technologies have been developed. They can be combined in various ways.{{cite journal |last1=Cimpan |first1=Ciprian |last2=Maul |first2=Anja |last3=Wenzel |first3=Henrik |last4=Pretz |first4=Thomas |title=Techno-economic assessment of central sorting at material recovery facilities – the case of lightweight packaging waste |journal=Journal of Cleaner Production |date=January 2016 |volume=112 |pages=4387–4397 |doi=10.1016/j.jclepro.2015.09.011|bibcode=2016JCPro.112.4387C }} In practice no approach is 100% effective.{{cite journal |last1=Faraca |first1=Giorgia |last2=Astrup |first2=Thomas |title=Plastic waste from recycling centres: Characterisation and evaluation of plastic recyclability |journal=Waste Management |date=July 2019 |volume=95 |pages=388–398 |doi=10.1016/j.wasman.2019.06.038|pmid=31351625 |bibcode=2019WaMan..95..388F |s2cid=198331405 }}{{cite journal |last1=Antonopoulos |first1=Ioannis |last2=Faraca |first2=Giorgia |last3=Tonini |first3=Davide |title=Recycling of post-consumer plastic packaging waste in the EU: Recovery rates, material flows, and barriers |journal=Waste Management |date=May 2021 |volume=126 |pages=694–705 |doi=10.1016/j.wasman.2021.04.002|pmid=33887695 |pmc=8162419 |bibcode=2021WaMan.126..694A |doi-access=free}} Sorting accuracy varies between recyclers, producing a market where products are poorly standardised. This inconsistency is another barrier to recycling.

Sorting by hand is the oldest and simplest method. In developing countries this may be done by waste pickers, while in a recycling center, workers pick items off a conveyor-belt. It requires low levels of technology and investment, but has high labor costs. Although many plastic items have identification codes workers rarely have time to look for them, so leaving problems of inefficiency and inconsistency. Even advanced facilities retain manual pickers to troubleshoot and correct sorting errors. Working conditions can be unsanitary.{{cite journal |last1=Poulsen |first1=Otto M. |last2=Breum |first2=Niels O. |last3=Ebbehøj |first3=Niels |last4=Hansen |first4=Åse Marie |last5=Ivens |first5=Ulla I. |last6=van Lelieveld |first6=Duco |last7=Malmros |first7=Per |last8=Matthiasen |first8=Leo |last9=Nielsen |first9=Birgitte H. |last10=Nielsen |first10=Eva Møller |last11=Schibye |first11=Bente |last12=Skov |first12=Torsten |last13=Stenbaek |first13=Eva I. |last14=Wilkins |first14=Ken C. |title=Sorting and recycling of domestic waste. Review of occupational health problems and their possible causes |journal=Science of the Total Environment |date=May 1995 |volume=168 |issue=1 |pages=33–56 |doi=10.1016/0048-9697(95)04521-2|pmid=7610383 |bibcode=1995ScTEn.168...33P }}

Plastics can be separated by exploiting differences in their densities. In this approach the plastic is first ground into flakes of a similar size, washed and subjected to gravity separation.{{cite journal |last1=Ragaert |first1=Kim |last2=Delva |first2=Laurens |last3=Van Geem |first3=Kevin |title=Mechanical and chemical recycling of solid plastic waste |journal=Waste Management |date=November 2017 |volume=69 |pages=24–58 |doi=10.1016/j.wasman.2017.07.044|pmid=28823699 |bibcode=2017WaMan..69...24R }} This can be achieved using either an air classifier or hydrocyclone, or via wet float-sink method.{{cite journal |last1=Bauer |first1=Markus |last2=Lehner |first2=Markus |last3=Schwabl |first3=Daniel |last4=Flachberger |first4=Helmut |last5=Kranzinger |first5=Lukas |last6=Pomberger |first6=Roland |last7=Hofer |first7=Wolfgang |title=Sink–float density separation of post-consumer plastics for feedstock recycling |journal=Journal of Material Cycles and Waste Management |date=July 2018 |volume=20 |issue=3 |pages=1781–1791 |doi=10.1007/s10163-018-0748-z |doi-access=free|bibcode=2018JMCWM..20.1781B }} These approaches provide partial sorting, as some polymers have similar density. Polypropylene (PP) and polyethylene (PE) are similar as are polyethylene terephthalate (PET), polystyrene (PS), and PVC. In addition, if the plastic contains fillers, this may affect its density.{{cite journal |last1=Bonifazi |first1=Giuseppe |last2=Di Maio |first2=Francesco |last3=Potenza |first3=Fabio |last4=Serranti |first4=Silvia |title=FT-IR Analysis and Hyperspectral Imaging Applied to Postconsumer Plastics Packaging Characterization and Sorting |journal=IEEE Sensors Journal |date=May 2016 |volume=16 |issue=10 |pages=3428–3434 |doi=10.1109/JSEN.2015.2449867|bibcode=2016ISenJ..16.3428B |s2cid=6670818 }} The lighter PP and PE fraction is known as mixed polyolefin (MPO) and can be sold as a low-value product,{{cite journal |last1=Hubo |first1=Sara |last2=Delva |first2=Laurens |last3=Van Damme |first3=Nicolas |last4=Ragaert |first4=Kim |title=Blending of recycled mixed polyolefins with recycled polypropylene: Effect on physical and mechanical properties |series=AIP Conference Proceedings |date=2016 |volume=1779 |pages=140006 |doi=10.1063/1.4965586|doi-access=free }} the heavier mixed plastics fraction is usually unrecyclable.

{{main|electrostatic separator}}

In electrostatic separators, the triboelectric effect is used to charge plastic particles electrically; with different polymers charged to different extents. They are then blown through an electric field, which deflects them depending on their charge, directing them into appropriate collectors. As with density separation, the particles need to be dry, be uniform in size and shape.{{cite journal |last1=Wu |first1=Guiqing |last2=Li |first2=Jia |last3=Xu |first3=Zhenming |title=Triboelectrostatic separation for granular plastic waste recycling: A review |journal=Waste Management |date=March 2013 |volume=33 |issue=3 |pages=585–597 |doi=10.1016/j.wasman.2012.10.014|pmid=23199793 |bibcode=2013WaMan..33..585W |s2cid=12323746 }} Electrostatic separation can be complementary to density separation, allowing full separation of polymers,{{cite journal |last1=Dodbiba |first1=G. |last2=Sadaki |first2=J. |last3=Okaya |first3=K. |last4=Shibayama |first4=A. |last5=Fujita |first5=T. |title=The use of air tabling and triboelectric separation for separating a mixture of three plastics |journal=Minerals Engineering |date=December 2005 |volume=18 |issue=15 |pages=1350–1360 |doi=10.1016/j.mineng.2005.02.015|bibcode=2005MiEng..18.1350D }} albeit of mixed colours.

File:STEINERT UniSort PR.jpg

{{main|Sensor-based sorting}}

This approach is largely automated and involves various sensors linked to a computer, which analyses items and directs them into appropriate chutes or belts.{{cite journal |last1=Gundupalli |first1=Sathish Paulraj |last2=Hait |first2=Subrata |last3=Thakur |first3=Atul |title=A review on automated sorting of source-separated municipal solid waste for recycling |journal=Waste Management |date=February 2017 |volume=60 |pages=56–74 |doi=10.1016/j.wasman.2016.09.015|pmid=27663707 |bibcode=2017WaMan..60...56G }} Near-infrared spectroscopy can be used to distinguish polymer types,{{cite book |last1=Hollstein |first1=Frank |last2=Wohllebe |first2=Markus |last3=Arnaiz |first3=Sixto |title=Near Infrared Spectroscopy: Proceedings of the International Conference |chapter=Identification and Sorting of Plastics Film Waste by NIR-Hyperspectral-Imaging |date=24 October 2015 |doi=10.17648/NIR-2015-34127}} although black/strongly-coloured plastics, as well as composite materials like plastic-coated paper and multilayered packaging, which can give misleading readings. Optical sorting such as colour sorters or hyperspectral imaging can then split by colour. Sensor based separation is more expensive to install but has the best recovery rates and produces more high-quality products.

Plastic waste is either industrial scrap (sometimes referred to as post industrial resin) or consumer waste. Scrap is generated during production and is usually handled differently.{{cite journal |last1=Kleinhans |first1=Kerstin |last2=Demets |first2=Ruben |last3=Dewulf |first3=Jo |last4=Ragaert |first4=Kim |last5=De Meester |first5=Steven |title=Non-household end-use plastics: the 'forgotten' plastics for the circular economy |journal=Current Opinion in Chemical Engineering |date=June 2021 |volume=32 |pages=100680 |doi=10.1016/j.coche.2021.100680|issn=2211-3398 |doi-access=free|hdl=1854/LU-8710264 |hdl-access=free }} It can include flashings, trimmings, sprues and rejects. As it is collected at the point of manufacture it is clean, and of a known type and grade, and is valuable. As scrap is mostly privately traded, it is often not included in official statistics.

File:Polymer compatibilization.png

The majority of plastic waste is made of thermosoftening polymers, which can be re-melted and reformed into new items via mechanical recycling. Globally, this is by far the most common form of recycling and in many countries it is the only type practised. It is the simplest and most economical technique. It has a lower carbon footprint than other processes.{{cite journal |last1=Schyns |first1=Zoé O. G. |last2=Shaver |first2=Michael P. |title=Mechanical Recycling of Packaging Plastics: A Review |journal=Macromolecular Rapid Communications |date=February 2021 |volume=42 |issue=3 |pages=2000415 |doi=10.1002/marc.202000415|pmid=33000883 |doi-access=free }} However, several factors can reduce output quality, which limits its applicability.

Plastics are melted at anywhere between {{Convert|150-320|C|F|round=5}}, depending on polymer type. This is sufficient to cause unwanted chemical reactions that degrade the output.{{cite journal |last1=Yin |first1=Shi |last2=Tuladhar |first2=Rabin |last3=Shi |first3=Feng |last4=Shanks |first4=Robert A. |last5=Combe |first5=Mark |last6=Collister |first6=Tony |title=Mechanical reprocessing of polyolefin waste: A review |journal=Polymer Engineering & Science |date=December 2015 |volume=55 |issue=12 |pages=2899–2909 |doi=10.1002/pen.24182}} This can produce volatile, low-molecular weight compounds, which may impart undesirable taste or odour, as well as discolouration. Additives can accelerate this degradation. For instance, oxo-biodegradable additives, intended to improve the biodegradability of plastic, also increase the degree of thermal degradation.{{cite journal |last1=Babetto |first1=Alex S. |last2=Antunes |first2=Marcela C. |last3=Bettini |first3=Sílvia H. P. |last4=Bonse |first4=Baltus C. |title=A Recycling-Focused Assessment of the Oxidative Thermomechanical Degradation of HDPE Melt Containing Pro-oxidant |journal=Journal of Polymers and the Environment |date=February 2020 |volume=28 |issue=2 |pages=699–712 |doi=10.1007/s10924-019-01641-6|bibcode=2020JPEnv..28..699B |s2cid=209432804 |url=https://repositorio.fei.edu.br/handle/FEI/3410 }}{{cite journal |last1=Aldas |first1=Miguel |last2=Paladines |first2=Andrea |last3=Valle |first3=Vladimir |last4=Pazmiño |first4=Miguel |last5=Quiroz |first5=Francisco |title=Effect of the Prodegradant-Additive Plastics Incorporated on the Polyethylene Recycling |journal=International Journal of Polymer Science |date=2018 |volume=2018 |pages=1–10 |doi=10.1155/2018/2474176|doi-access=free }} Flame retardants can similarly have unwanted effects.{{cite journal |last1=Delva |first1=Laurens |last2=Hubo |first2=Sara |last3=Cardon |first3=Ludwig |last4=Ragaert |first4=Kim |title=On the role of flame retardants in mechanical recycling of solid plastic waste |journal=Waste Management |date=December 2018 |volume=82 |pages=198–206 |doi=10.1016/j.wasman.2018.10.030|pmid=30509582 |bibcode=2018WaMan..82..198D |s2cid=54487823 }} Product quality also depends strongly on how well the plastic was sorted. Many polymers are immiscible with each other when molten and phase separate (like oil and water) during reprocessing. Products made from such blends contain boundaries between the different polymers with weak cohesion across these boundaries, compromising mechanical properties. In more extreme cases the polymers may degrade each other, particularly with PVC, as it can generate hydrogen chloride which strongly affects condensation polymers such as PET.{{cite journal |last1=Paci |first1=M |last2=La Mantia |first2=F.P |title=Influence of small amounts of polyvinylchloride on the recycling of polyethyleneterephthalate |journal=Polymer Degradation and Stability |date=January 1999 |volume=63 |issue=1 |pages=11–14 |doi=10.1016/S0141-3910(98)00053-6}}

Many of these problems have technological solutions, though they bear a financial cost. Advanced polymer stabilisers and can be used to protect plastics from the stress of thermal reprocessing.{{cite journal |last1=Pfaendner |first1=R. |last2=Herbst |first2=H. |last3=Hoffmann |first3=K. |last4=Sitek |first4=F. |title=Recycling and restabilization of polymers for high quality applications. An Overview |journal=Angewandte Makromolekulare Chemie |date=October 1995 |volume=232 |issue=1 |pages=193–227 |doi=10.1002/apmc.1995.052320113}}{{cite journal |last1=Pfaendner |first1=Rudolf |title=Restabilization – 30 years of research for quality improvement of recycled plastics Review |journal=Polymer Degradation and Stability |date=July 2022 |volume=203 |pages=110082 |doi=10.1016/j.polymdegradstab.2022.110082|doi-access=free}} Volatile degradation products can be removed by a range of devolatilisation techniques. Flame retardants can be removed by chemical treatment,{{cite journal |last1=Zhang |first1=Cong-Cong |last2=Zhang |first2=Fu-Shen |title=Removal of brominated flame retardant from electrical and electronic waste plastic by solvothermal technique |journal=Journal of Hazardous Materials |date=June 2012 |volume=221-222 |pages=193–198 |doi=10.1016/j.jhazmat.2012.04.033|pmid=22575175 |bibcode=2012JHzM..221..193Z |url=http://ir.rcees.ac.cn/handle/311016/7942 }} while damaging metallic additives can be rendered inert with deactivators. Finally, the properties of mixed plastics can be improved by using compatibilisers.{{cite journal |last1=Koning |first1=C |title=Strategies for compatibilization of polymer blends |journal=Progress in Polymer Science |date=1998 |volume=23 |issue=4 |pages=707–757 |doi=10.1016/S0079-6700(97)00054-3|hdl=2268/4370 |hdl-access=free }}{{cite journal |last1=Vilaplana |first1=Francisco |last2=Karlsson |first2=Sigbritt |title=Quality Concepts for the Improved Use of Recycled Polymeric Materials: A Review |journal=Macromolecular Materials and Engineering |date=14 April 2008 |volume=293 |issue=4 |pages=274–297 |doi=10.1002/mame.200700393|doi-access=free }} These are compounds that improve miscibility between polymer types to give a more homogeneous product, with better internal cohesion and improved mechanical properties. They are small-molecules possessing two chemical regions, each of which is compatible with a certain polymer. This allows them to act like molecular-nails or screws, anchoring the polymers to one another. As a result, compatibilisers are normally limited to systems dominated by two particular types of plastic and are not cost-effective for heterogeneous mixtures. No compatibiliser solves all plastic combinations. Even with these technologies, it is particularly challenging to recycle plastic so that it can meet food contact standards.

In closed-loop, or primary recycling, used plastic is endlessly recycled back into new items of the same quality and type. For instance, turning drinks bottles back into drinks bottles. It can be considered an example of a circular economy. The continual mechanical recycling of plastic without reduction in quality is challenging due to cumulative polymer degradation{{cite journal |last1=Eriksen |first1=M.K. |last2=Christiansen |first2=J.D. |last3=Daugaard |first3=A.E. |last4=Astrup |first4=T.F. |title=Closing the loop for PET, PE and PP waste from households: Influence of material properties and product design for plastic recycling |journal=Waste Management |date=August 2019 |volume=96 |pages=75–85 |doi=10.1016/j.wasman.2019.07.005|pmid=31376972 |bibcode=2019WaMan..96...75E |s2cid=199067235 |url=https://backend.orbit.dtu.dk/ws/files/186061805/Eriksen_et_al._2019_ORBIT.pdf }} and risk of contaminant build-up. In 2013 only 2% of plastic packaging was recycled in a closed loop.{{cite web |title=The New Plastics Economy: Rethinking the future of plastics & catalysing action |url=https://www.ellenmacarthurfoundation.org/publications/the-new-plastics-economy-rethinking-the-future-of-plastics-catalysing-action |website=www.ellenmacarthurfoundation.org |date=January 2017 |access-date=28 May 2021}} Although closed-loop recycling has been investigated for many polymers, to-date the only industrial success is with PET bottle recycling.{{cite journal |last1=Welle |first1=Frank |title=Twenty years of PET bottle to bottle recycling—An overview |journal=Resources, Conservation and Recycling |date=September 2011 |volume=55 |issue=11 |pages=865–875 |doi=10.1016/j.resconrec.2011.04.009|bibcode=2011RCR....55..865W }} This is because polymer degradation in PET is often repairable. PET's polymer chains tend to cleave at their ester groups and the alcohol and carboxyl groups left by this can be joined back together by the use of chemical agents called chain extenders.{{cite journal |last1=Schyns |first1=Zoé O. G. |last2=Shaver |first2=Michael P. |title=Mechanical Recycling of Packaging Plastics: A Review |journal=Macromolecular Rapid Communications |date=February 2021 |volume=42 |issue=3 |pages=2000415 |doi=10.1002/marc.202000415|pmid=33000883 |doi-access=free }} Pyromellitic dianhydride is one such compound.

File:Miss Etam recycled re-usable shopping bag, Oude Pekela (2020) 08.jpg

In open-loop recycling, also known as secondary recycling, or downcycling, the quality of the plastic is reduced each time it is recycled, so that the material eventually becomes unrecyclable. It is the most common type. Recycling PET bottles into fleece or other fibres is a common example, and accounts for the majority of PET recycling.{{cite journal |last1=Shen |first1=Li |last2=Worrell |first2=Ernst |last3=Patel |first3=Martin K. |title=Open-loop recycling: A LCA case study of PET bottle-to-fibre recycling |journal=Resources, Conservation and Recycling |date=November 2010 |volume=55 |issue=1 |pages=34–52 |doi=10.1016/j.resconrec.2010.06.014|bibcode=2010RCR....55...34S }} Life-cycle assessment shows it to be of ecological benefit.{{cite journal |last1=Huysman |first1=Sofie |last2=Debaveye |first2=Sam |last3=Schaubroeck |first3=Thomas |last4=Meester |first4=Steven De |last5=Ardente |first5=Fulvio |last6=Mathieux |first6=Fabrice |last7=Dewulf |first7=Jo |title=The recyclability benefit rate of closed-loop and open-loop systems: A case study on plastic recycling in Flanders |journal=Resources, Conservation and Recycling |date=August 2015 |volume=101 |pages=53–60 |doi=10.1016/j.resconrec.2015.05.014|bibcode=2015RCR...101...53H |hdl=1854/LU-6851927 |hdl-access=free }}{{cite journal |last1=Lazarevic |first1=David |last2=Aoustin |first2=Emmanuelle |last3=Buclet |first3=Nicolas |last4=Brandt |first4=Nils |title=Plastic waste management in the context of a European recycling society: Comparing results and uncertainties in a life cycle perspective |journal=Resources, Conservation and Recycling |date=December 2010 |volume=55 |issue=2 |pages=246–259 |doi=10.1016/j.resconrec.2010.09.014|bibcode=2010RCR....55..246L }} Recycling can displace demand for fresh plastic.{{cite journal |last1=Geyer |first1=Roland |last2=Kuczenski |first2=Brandon |last3=Zink |first3=Trevor |last4=Henderson |first4=Ashley |title=Common Misconceptions about Recycling |journal=Journal of Industrial Ecology |date=October 2016 |volume=20 |issue=5 |pages=1010–1017 |doi=10.1111/jiec.12355|bibcode=2016JInEc..20.1010G |s2cid=153936564 }} However, if it is used to produce items that would not otherwise have been made, then it is not displacing production and is of little or no benefit to the environment.

The reduction in polymer quality can be offset by mixing recycled and new materials. Compatibilised plastics can be used as a replacement for virgin material, as it is possible to produce them with the right melt flow index needed for good results.{{cite journal |last1=Gupta |first1=Arvind |last2=Misra |first2=Manjusri |last3=Mohanty |first3=Amar K. |title=Novel sustainable materials from waste plastics: compatibilized blend from discarded bale wrap and plastic bottles |journal=RSC Advances |date=2021 |volume=11 |issue=15 |pages=8594–8605 |doi=10.1039/D1RA00254F |pmid=35423365 |pmc=8695198 |bibcode=2021RSCAd..11.8594G |doi-access=free}} Low quality mixed plastics can be recycled in an open-loop, although demand for such products is limited. When these are mixed during reprocessing the result is usually an unappealing dark-brown. These blends find use as outdoor furniture or plastic lumber. As the material is weak, but of low cost it is produced in thick planks to provide material strength.

Although thermoset polymers do not melt, technologies have been developed for their mechanical recycling. This usually involves breaking the material down to small particles (crumbs), which can then be mixed with a binding agent to form a composite material. For instance, polyurethanes can be recycled as reconstituted crumb foam.{{cite journal |last1=Yang |first1=Wenqing |last2=Dong |first2=Qingyin |last3=Liu |first3=Shili |last4=Xie |first4=Henghua |last5=Liu |first5=Lili |last6=Li |first6=Jinhui |title=Recycling and Disposal Methods for Polyurethane Foam Wastes |journal=Procedia Environmental Sciences |date=2012 |volume=16 |pages=167–175 |doi=10.1016/j.proenv.2012.10.023|doi-access=free |bibcode=2012PrEnS..16..167Y }}{{cite journal |last1=Zia |first1=Khalid Mahmood |last2=Bhatti |first2=Haq Nawaz |last3=Ahmad Bhatti |first3=Ijaz |title=Methods for polyurethane and polyurethane composites, recycling and recovery: A review |journal=Reactive and Functional Polymers |date=August 2007 |volume=67 |issue=8 |pages=675–692 |doi=10.1016/j.reactfunctpolym.2007.05.004|bibcode=2007RFPol..67..675Z }}

In feedstock recycling, also called chemical recycling or tertiary recycling, polymers are reduced to their chemical building-blocks (monomers), which can then be polymerised back into fresh plastics.{{cite journal |last1=Lee |first1=Alicia |last2=Liew |first2=Mei Shan |title=Tertiary recycling of plastics waste: an analysis of feedstock, chemical and biological degradation methods |journal=Journal of Material Cycles and Waste Management |date=January 2021 |volume=23 |issue=1 |pages=32–43 |doi=10.1007/s10163-020-01106-2|bibcode=2021JMCWM..23...32L |s2cid=225247645 }}{{cite journal |last1=Rahimi |first1=AliReza |last2=García |first2=Jeannette M. |title=Chemical recycling of waste plastics for new materials production |journal=Nature Reviews Chemistry |date=June 2017 |volume=1 |issue=6 |pages=0046 |doi=10.1038/s41570-017-0046}}{{cite journal |last1=Coates |first1=Geoffrey W. |last2=Getzler |first2=Yutan D. Y. L. |title=Chemical recycling to monomer for an ideal, circular polymer economy |journal=Nature Reviews Materials |date=July 2020 |volume=5 |issue=7 |pages=501–516 |doi=10.1038/s41578-020-0190-4|bibcode=2020NatRM...5..501C |s2cid=215760966 }} In theory, this allows for near infinite recycling; as impurities, additives, dyes and chemical defects are completely removed with each cycle.{{cite journal |last1=Vollmer |first1=Ina |last2=Jenks |first2=Michael J. F. |last3=Roelands |first3=Mark C. P. |last4=White |first4=Robin J. |last5=Harmelen |first5=Toon |last6=Wild |first6=Paul |last7=Laan |first7=Gerard P. |last8=Meirer |first8=Florian |last9=Keurentjes |first9=Jos T. F. |last10=Weckhuysen |first10=Bert M. |title=Beyond Mechanical Recycling: Giving New Life to Plastic Waste |journal=Angewandte Chemie International Edition |date=September 2020 |volume=59 |issue=36 |pages=15402–15423 |doi=10.1002/anie.201915651 |pmid=32160372 |pmc=7497176 |doi-access=free}}{{cite journal |last1=Thiounn |first1=Timmy |last2=Smith |first2=Rhett C. |title=Advances and approaches for chemical recycling of plastic waste |journal=Journal of Polymer Science |date=15 May 2020 |volume=58 |issue=10 |pages=1347–1364 |doi=10.1002/pol.20190261|doi-access=free}} In practice, chemical recycling is far less common than mechanical recycling. Implementation is limited because technologies do not yet exist to reliably depolymerise all polymers on an industrial scale and also because the equipment and operating costs are much higher. In 2018 Japan had one of the highest rates in the world at ~4%, compared to 23% mechanical recycling,{{cite journal |last1=Kumagai |first1=Shogo |last2=Nakatani |first2=Jun |last3=Saito |first3=Yuko |last4=Fukushima |first4=Yasuhiro |last5=Yoshioka |first5=Toshiaki |title=Latest Trends and Challenges in Feedstock Recycling of Polyolefinic Plastics |journal=Journal of the Japan Petroleum Institute |date=1 November 2020 |volume=63 |issue=6 |pages=345–364 |doi=10.1627/jpi.63.345|doi-access=free }} in the same period Germany, another major recycler, reported a feedstock recycling rate of 0.2%.{{cite web |title=Plastics - the Facts 2020 |url=https://www.plasticseurope.org/application/files/8016/1125/2189/AF_Plastics_the_facts-WEB-2020-ING_FINAL.pdf |website=PlasticsEurope |access-date=1 September 2021}} Depolymerising, purifying and re-polymerising the plastic can also be energy intensive, leading to the carbon footprint of feedstock recycling normally being higher than that of mechanical recycling. PET, PU and PS are depolymerised commercially to varying extents, but the feedstock recycling of polyolefins, which make-up nearly half of all plastics, is much more limited.

Certain polymers like PTFE, polystyrene, nylon 6, and polymethylmethacrylate (PMMA) undergo thermal depolymerisation when heated to sufficiently high temperatures.{{cite journal |last1=Kaminsky |first1=W |last2=Predel |first2=M |last3=Sadiki |first3=A |title=Feedstock recycling of polymers by pyrolysis in a fluidised bed |journal=Polymer Degradation and Stability |date=September 2004 |volume=85 |issue=3 |pages=1045–1050 |doi=10.1016/j.polymdegradstab.2003.05.002}} The reactions are sensitive to impurities and require clean and well sorted waste to produce a good product. Even then, not all depolymerisation reactions are completely efficient and some competitive pyrolysis is often observed; the monomers, therefore, require purification before reuse. The feedstock recycling of polystyrene has been commercialised, but global capacity remains fairly limited.

Condensation polymers bearing cleavable groups such as esters and amides can be completely depolymerised by hydrolysis or solvolysis. This can be a purely chemical process but may also be promoted by enzymes such as PETase.{{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.|date=April 2020|title=An engineered PET depolymerase to break down and recycle plastic bottles|url=http://www.nature.com/articles/s41586-020-2149-4|journal=Nature|language=en|volume=580|issue=7802|pages=216–219|doi=10.1038/s41586-020-2149-4|pmid=32269349|bibcode=2020Natur.580..216T|s2cid=215411815|issn=0028-0836}}{{cite journal |last1=Wei |first1=Ren |last2=Zimmermann |first2=Wolfgang |title=Microbial enzymes for the recycling of recalcitrant petroleum-based plastics: how far are we? |journal=Microbial Biotechnology |date=November 2017 |volume=10 |issue=6 |pages=1308–1322 |doi=10.1111/1751-7915.12710|pmid=28371373 |pmc=5658625 }} Such technologies have lower energy costs than thermal depolymerisation but are not available for all polymers. Polyethylene terephthalate has been the most heavily studied polymer,{{cite journal |last1=Geyer |first1=B. |last2=Lorenz |first2=G. |last3=Kandelbauer |first3=A. |title=Recycling of poly(ethylene terephthalate) – A review focusing on chemical methods |journal=Express Polymer Letters |date=2016 |volume=10 |issue=7 |pages=559–586 |doi=10.3144/expresspolymlett.2016.53|doi-access=free }} and has reached commercial scale.

File:Koh Tao Island, Trash Collecter and Incinerator.JPG, Thailand. Well regulated incinerators reduce harmful toxins released during the burning process, but not all plastic is burned in proper facilities.]]

Energy recovery, also called energy recycling or quaternary recycling, involves burning waste plastic in place of fossil fuels for energy production.{{cite journal |last1=Singh |first1=Narinder |last2=Hui |first2=David |last3=Singh |first3=Rupinder |last4=Ahuja |first4=I.P.S. |last5=Feo |first5=Luciano |last6=Fraternali |first6=Fernando |title=Recycling of plastic solid waste: A state of art review and future applications |journal=Composites Part B: Engineering |date=April 2017 |volume=115 |pages=409–422 |doi=10.1016/j.compositesb.2016.09.013}} It is included in the recycling data reported by many countries,{{cite web |title=An Introduction to Plastic Recycling in Japan 2019 |url=https://www.pwmi.or.jp/ei/plastic_recycling_2019.pdf |publisher=Plastic Waste Management Institute |access-date=19 May 2021}}{{cite web |last1=US EPA |first1=OLEM |title=Plastics: Material-Specific Data |url=https://www.epa.gov/facts-and-figures-about-materials-waste-and-recycling/plastics-material-specific-data |website=US EPA |language=en |date=2017-09-12}} although it is not considered recycling by the EU.{{Cite web|date=2008 |location=Paragraph 15a|title=Directive 2008/98/EC of the European Parliament and of the Council. Article 3: Definitions|url=https://www.legislation.gov.uk/eudr/2008/98/article/3|access-date=August 4, 2021|website=Legislation.gov.uk}} It is distinct from incineration without energy recovery, which is historically more common, but which does not reduce either plastic production or fossil fuel use.

Energy recovery is often the waste management method of last resort, a position previously held by landfill. In urban areas a lack of suitable sites for new landfills can drive this,{{cite journal |title=A review on municipal solid waste-to-energy trends in the USA |journal=Renewable and Sustainable Energy Reviews |date=1 March 2020 |volume=119 |pages=109512 |doi=10.1016/j.rser.2019.109512|last1=Mukherjee |first1=C. |last2=Denney |first2=J. |last3=Mbonimpa |first3=E.G. |last4=Slagley |first4=J. |last5=Bhowmik |first5=R. |s2cid=209798113 |doi-access=free |bibcode=2020RSERv.11909512M }} but it is also driven by regulation, such as the EU's Landfill Directive or other landfill diversion policies. Compared to the other recycling options, its appeal is largely economic. If the correct technologies are used, then the plastics do not need to be separated, or from other municipal solid waste (garbage), which reduces costs. Compared to the sometimes variable market for recyclables, demand for electricity is universal and better understood, reducing the perceived financial risk. As a means of waste management, it is highly effective, reducing the volume of waste by about 90%, with the residues sent to landfill or used to make cinder block. Although its CO₂ emissions are high, comparing its overall ecological desirability to other recycling technologies is difficult. For instance, while recycling greatly reduces greenhouse gas emissions compared to incineration, it is an expensive way of achieving these reductions when compared to investing in renewable energy.{{cite journal |last1=Gradus |first1=Raymond H.J.M. |last2=Nillesen |first2=Paul H.L. |last3=Dijkgraaf |first3=Elbert |last4=van Koppen |first4=Rick J. |title=A Cost-effectiveness Analysis for Incineration or Recycling of Dutch Household Plastic Waste |journal=Ecological Economics |date=May 2017 |volume=135 |pages=22–28 |doi=10.1016/j.ecolecon.2016.12.021|bibcode=2017EcoEc.135...22G |hdl=1871.1/390ebc9d-5968-479b-bd72-23ffe7c85c43 |s2cid=21744131 |url=https://research.vu.nl/en/publications/390ebc9d-5968-479b-bd72-23ffe7c85c43 |hdl-access=free }}

Plastic waste may be burnt as refuse-derived fuel (RDF), or it may be chemically converted to a synthetic fuel first. In either approach PVC must be excluded or compensated for by installing dechlorination technologies, as it generates large amounts of hydrogen chloride (HCl) when burnt. This can corrode equipment and cause undesirable chlorination of fuel products.{{cite journal |last1=Fukushima |first1=Masaaki |last2=Wu |first2=Beili |last3=Ibe |first3=Hidetoshi |last4=Wakai |first4=Keiji |last5=Sugiyama |first5=Eiichi |last6=Abe |first6=Hironobu |last7=Kitagawa |first7=Kiyohiko |last8=Tsuruga |first8=Shigenori |last9=Shimura |first9=Katsumi |last10=Ono |first10=Eiichi |title=Study on dechlorination technology for municipal waste plastics containing polyvinyl chloride and polyethylene terephthalate |journal=Journal of Material Cycles and Waste Management |date=June 2010 |volume=12 |issue=2 |pages=108–122 |doi=10.1007/s10163-010-0279-8|bibcode=2010JMCWM..12..108F |s2cid=94190060 }} Burning has long been associated with the release of harmful dioxins and dioxin-like compounds, however these hazards can be abated by the use of advanced combustors and emission control systems. Incineration with energy recovery remains the most common method, with more advanced waste-to-fuel technologies such as pyrolysis hindered by technical and cost hurdles.{{cite journal |last1=Fernández-González |first1=J.M. |last2=Grindlay |first2=A.L. |last3=Serrano-Bernardo |first3=F. |last4=Rodríguez-Rojas |first4=M.I. |last5=Zamorano |first5=M. |title=Economic and environmental review of Waste-to-Energy systems for municipal solid waste management in medium and small municipalities |journal=Waste Management |date=September 2017 |volume=67 |pages=360–374 |doi=10.1016/j.wasman.2017.05.003|pmid=28501263 |bibcode=2017WaMan..67..360F }}

{{See also|Waste-to-energy}}

Mixed plastic waste can be depolymerised to give a synthetic fuel. This has a higher heating value than the starting plastic and can be burnt more efficiently, although it remains less efficient than fossil fuels.{{cite conference |last1=Nugroho |first1=Arif Setyo |last2=Chamim |first2=Moch. |last3=Hidayah |first3=Fatimah N. |title=Plastic waste as an alternative energy |conference=Human-Dedicated Sustainable Product and Process Design: Materials |series=AIP Conference Proceedings |date=2018 |volume=1977 |issue=1 |pages=060010 |doi=10.1063/1.5043022|bibcode=2018AIPC.1977f0010N |doi-access=free }} Various conversion technologies have been investigated, of which pyrolysis is the most common.{{cite journal |last1=Butler |first1=E. |last2=Devlin |first2=G. |last3=McDonnell |first3=K. |title=Waste Polyolefins to Liquid Fuels via Pyrolysis: Review of Commercial State-of-the-Art and Recent Laboratory Research |journal=Waste and Biomass Valorization |date=1 August 2011 |volume=2 |issue=3 |pages=227–255 |doi=10.1007/s12649-011-9067-5|bibcode=2011WBioV...2..227B |hdl=10197/6103 |s2cid=98550187 |hdl-access=free }}{{cite journal |last1=Anuar Sharuddin |first1=Shafferina Dayana |last2=Abnisa |first2=Faisal |last3=Wan Daud |first3=Wan Mohd Ashri |last4=Aroua |first4=Mohamed Kheireddine |title=A review on pyrolysis of plastic wastes |journal=Energy Conversion and Management |date=May 2016 |volume=115 |pages=308–326 |doi=10.1016/j.enconman.2016.02.037|bibcode=2016ECM...115..308A }} Conversion can take place as part of incineration in an IGC cycle, but often the aim is to collect the fuel to sell it. Pyrolysis of mixed plastics can give a fairly broad mix of chemical products (between 1 and 15 carbon atoms) including gases and aromatic liquids.{{cite journal |last1=Kaminsky |first1=W. |last2=Schlesselmann |first2=B. |last3=Simon |first3=C.M. |title=Thermal degradation of mixed plastic waste to aromatics and gas |journal=Polymer Degradation and Stability |date=August 1996 |volume=53 |issue=2 |pages=189–197 |doi=10.1016/0141-3910(96)00087-0}}{{Cite journal|last1=Quesada|first1=L.|last2=Calero|first2=M.|last3=Martín-Lara|first3=M. A.|last4=Pérez|first4=A.|last5=Blázquez|first5=G.|date=2019-11-01|title=Characterization of fuel produced by pyrolysis of plastic film obtained of municipal solid waste|url=http://www.sciencedirect.com/science/article/pii/S0360544219315464|journal=Energy|language=en|volume=186|pages=115874|doi=10.1016/j.energy.2019.115874|bibcode=2019Ene...18615874Q |s2cid=201243993|issn=0360-5442}}{{cite journal |last1=Kumagai |first1=Shogo |last2=Yoshioka |first2=Toshiaki |title=Feedstock Recycling via Waste Plastic Pyrolysis |journal=Journal of the Japan Petroleum Institute |date=1 November 2016 |volume=59 |issue=6 |pages=243–253 |doi=10.1627/jpi.59.243 |url=https://www.jstage.jst.go.jp/article/jpi/59/6/59_243/_article/-char/en|doi-access=free }} Catalysts can give a better-defined product with a higher value.{{cite journal |last1=Aguado |first1=J. |last2=Serrano |first2=D. P. |last3=Escola |first3=J. M. |title=Fuels from Waste Plastics by Thermal and Catalytic Processes: A Review |journal=Industrial & Engineering Chemistry Research |date=5 November 2008 |volume=47 |issue=21 |pages=7982–7992 |doi=10.1021/ie800393w}}{{cite journal |last1=Miandad |first1=R. |last2=Barakat |first2=M. A. |last3=Aburiazaiza |first3=Asad S. |last4=Rehan |first4=M. |last5=Nizami |first5=A. S. |title=Catalytic pyrolysis of plastic waste: A review |journal=Process Safety and Environmental Protection |date=1 July 2016 |volume=102 |pages=822–838 |doi=10.1016/j.psep.2016.06.022 |bibcode=2016PSEP..102..822M }}{{cite journal |last1=Rehan |first1=M. |last2=Miandad |first2=R. |last3=Barakat |first3=M. A. |last4=Ismail |first4=I. M. I. |last5=Almeelbi |first5=T. |last6=Gardy |first6=J. |last7=Hassanpour |first7=A. |last8=Khan |first8=M. Z. |last9=Demirbas |first9=A. |last10=Nizami |first10=A. S. |title=Effect of zeolite catalysts on pyrolysis liquid oil |journal=International Biodeterioration & Biodegradation |date=1 April 2017 |volume=119 |pages=162–175 |doi=10.1016/j.ibiod.2016.11.015 |bibcode=2017IBiBi.119..162R |url=http://eprints.whiterose.ac.uk/109930/7/Revised%20Manuscript%20%28R1%29.pdf }} Liquid products can be used as synthetic diesel fuel,{{cite journal |last1=Bukkarapu |first1=Kiran Raj |last2=Gangadhar |first2=D. Siva |last3=Jyothi |first3=Y. |last4=Kanasani |first4=Prasad |title=Management, conversion, and use of waste plastic as a source of sustainable energy to run automotive: a review |journal=Energy Sources, Part A: Recovery, Utilization, and Environmental Effects |date=18 July 2018 |volume=40 |issue=14 |pages=1681–1692 |doi=10.1080/15567036.2018.1486898|s2cid=103779086 }} with commercial production in several countries.{{cite journal |last1=Oasmaa |first1=Anja |title=Pyrolysis of plastic waste: opportunities and challenges |url=https://dc.engconfintl.org/pyroliq_2019/39 |journal=Pyroliq 2019: Pyrolysis and Liquefaction of Biomass and Wastes |publisher=ECI Digital Archives |access-date=10 June 2021 |date=2019-06-17|volume=152 |doi=10.1016/j.jaap.2020.104804 |bibcode=2020JAAP..15204804Q }} Life-cycle analysis shows that plastic-to-fuel can displace fossil fuels and lower net greenhouse gas emissions (~15% reduction).{{cite journal |last1=Benavides |first1=Pahola Thathiana |last2=Sun |first2=Pingping |last3=Han |first3=Jeongwoo |last4=Dunn |first4=Jennifer B. |last5=Wang |first5=Michael |title=Life-cycle analysis of fuels from post-use non-recycled plastics |journal=Fuel |date=September 2017 |volume=203 |pages=11–22 |doi=10.1016/j.fuel.2017.04.070|osti=1353191 |doi-access=free |bibcode=2017Fuel..203...11B }}

Compared to the widespread practise of incineration, plastic-to-fuel technologies have struggled to become economically viable.{{cite journal |last1=Rollinson |first1=Andrew Neil |last2=Oladejo |first2=Jumoke Mojisola |title='Patented blunderings', efficiency awareness, and self-sustainability claims in the pyrolysis energy from waste sector |journal=Resources, Conservation and Recycling |date=February 2019 |volume=141 |pages=233–242 |doi=10.1016/j.resconrec.2018.10.038|bibcode=2019RCR...141..233R |s2cid=115296275 }}

Many kinds of plastic can be used as a carbon source (in place of coke) in scrap steel recycling,{{Cite web |url=http://www.cnn.com/2005/TECH/08/10/plastic.steel.reut/index.html |title=Scientists use plastic to make steel|website=CNN.com|access-date=10 August 2005 |archive-url=https://web.archive.org/web/20050812011212/http://www.cnn.com/2005/TECH/08/10/plastic.steel.reut/index.html |archive-date=12 August 2005 |url-status=dead |df=dmy-all }} with roughly 200,000 tonnes of waste plastics processed each year in Japan.{{cite journal |last1=Nomura |first1=Seiji |title=Use of Waste Plastics in Coke Oven: A Review |journal=Journal of Sustainable Metallurgy |date=March 2015 |volume=1 |issue=1 |pages=85–93 |doi=10.1007/s40831-014-0001-5|s2cid=137233367 |doi-access=free |bibcode=2015JSusM...1...85N }}

The use of recovered plastics in engineering materials is gaining ground.{{Cite journal |last1=Khan |first1=Kaffayatullah |last2=Jalal |first2=Fazal E. |last3=Iqbal |first3=Mudassir |last4=Khan |first4=Muhammad Imran |last5=Amin |first5=Muhammad Nasir |last6=Al-Faiad |first6=Majdi Adel |date=2022-04-23 |title=Predictive Modeling of Compression Strength of Waste PET/SCM Blended Cementitious Grout Using Gene Expression Programming |journal=Materials |language=en |volume=15 |issue=9 |pages=3077 |doi=10.3390/ma15093077 |issn=1996-1944 |pmc=9102582 |pmid=35591409|bibcode=2022Mate...15.3077K |doi-access=free }} Ground plastic may be used as a construction aggregate or filler material in certain applications.{{Cite journal |last1=Reis |first1=J. M. L. |last2=Carneiro |first2=E. P. |date=2012-02-01 |title=Evaluation of PET waste aggregates in polymer mortars |url=https://www.sciencedirect.com/science/article/pii/S0950061811004521 |journal=Construction and Building Materials |language=en |volume=27 |issue=1 |pages=107–111 |doi=10.1016/j.conbuildmat.2011.08.020 |issn=0950-0618}}{{Cite journal |last1=Gavela |first1=Stamatia |last2=Rakanta |first2=Eleni |last3=Ntziouni |first3=Afroditi |last4=Kasselouri-Rigopoulou |first4=Vasilia |date=2022-10-24 |title=Eleven-Year Follow-Up on the Effect of Thermoplastic Aggregates' Addition to Reinforced Concrete |journal=Buildings |volume=12 |issue=11 |pages=1779 |doi=10.3390/buildings12111779 |doi-access=free |issn=2075-5309}} While generally unsuitable in structural concrete, plastic's inclusion in asphalt concrete, (forming rubberised asphalt), subbase and recycled insulation can be beneficial.{{cite journal |last1=Awoyera |first1=P.O. |last2=Adesina |first2=A. |title=Plastic wastes to construction products: Status, limitations and future perspective |journal=Case Studies in Construction Materials |date=June 2020 |volume=12 |pages=e00330 |doi=10.1016/j.cscm.2020.e00330|s2cid=212815459 |doi-access=free }} An example of this is the construction of plastic roads. These may be made entirely of plastic or can incorporate significant amounts of plastic. The practice is popular in India, which by 2021 had constructed some 700 km (435 miles) of highways.{{cite news|url=https://pib.gov.in/PressReleseDetailm.aspx?PRID=1740262|title=Use of Plastic Waste in Road Construction}} It may allow the leaching of plastic additives into the environment.{{cite journal |last1=Conlon |first1=Katie |title=Plastic roads: not all they're paved up to be |journal=International Journal of Sustainable Development & World Ecology |date=18 April 2021 |volume=29 |pages=80–83 |doi=10.1080/13504509.2021.1915406|s2cid=234834344 |url=https://pdxscholar.library.pdx.edu/cgi/viewcontent.cgi?article=1314&context=usp_fac }} Research is ongoing to use plastics in various forms in cementitious materials such as concrete. Densifying plastic materials such as PET and plastic bags and then using them to partially replace aggregate and depolymerizing PET to use as a polymeric binder to enhance concrete are under study.{{Cite journal |last1=Dębska |first1=Bernardeta |last2=Brigolini Silva |first2=Guilherme Jorge |date=January 2021 |title=Mechanical Properties and Microstructure of Epoxy Mortars Made with Polyethylene and Poly(Ethylene Terephthalate) Waste |journal=Materials |language=en |volume=14 |issue=9 |pages=2203 |doi=10.3390/ma14092203 |issn=1996-1944 |pmc=8123358 |pmid=33923013|bibcode=2021Mate...14.2203D |doi-access=free }}{{Cite journal |last1=Thorneycroft |first1=J. |last2=Orr |first2=J. |last3=Savoikar |first3=P. |last4=Ball |first4=R. J. |date=2018-02-10 |title=Performance of structural concrete with recycled plastic waste as a partial replacement for sand |url=https://www.sciencedirect.com/science/article/pii/S0950061817323474 |journal=Construction and Building Materials |language=en |volume=161 |pages=63–69 |doi=10.1016/j.conbuildmat.2017.11.127 |issn=0950-0618}}{{Cite journal |last1=Bahij |first1=Sifatullah |last2=Omary |first2=Safiullah |last3=Feugeas |first3=Francoise |last4=Faqiri |first4=Amanullah |date=2020-07-15 |title=Fresh and hardened properties of concrete containing different forms of plastic waste – A review |url=https://www.sciencedirect.com/science/article/pii/S0956053X20302981 |journal=Waste Management |language=en |volume=113 |pages=157–175 |doi=10.1016/j.wasman.2020.05.048 |pmid=32534235 |bibcode=2020WaMan.113..157B |s2cid=219637371 |issn=0956-053X}}

{{Commons category|Plastic recycling}}

{{Portal|Environment}}

• Economics of plastics processing
• Electronic waste
• Microplastics
• Mobro 4000
• Phase-out of lightweight plastic bags
• Plastics 2020 Challenge

{{Free-content attribution

| title = Drowning in Plastics – Marine Litter and Plastic Waste Vital Graphics

| publisher = United Nations Environment Programme

| documentURL = https://www.unep.org/resources/report/drowning-plastics-marine-litter-and-plastic-waste-vital-graphics

| license statement URL = https://commons.wikimedia.org/wiki/File:United_Nations_Environment_Programme_Drowning_in_Plastics_%E2%80%93_Marine_Litter_and_Plastic_Waste_Vital_Graphics.pdf

| license = Cc BY-SA 3.0 IGO

}}

{{reflist}}

• ISF's Plastics Recovery Manual

{{Recycling}}

{{Plastics}}

Category:Recycling by material

Category:Energy conservation