View source for Polystyrene

{{short description|Polymer resin widely used in packaging}}
{{Other uses}}
{{Use dmy dates|date=October 2021}}
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| ImageFile = Polystyrene.svg
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| ImageName = Repeating unit of PS polymer chain
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| ImageFile1 = Polystyrene-chain-from-xtal-3D-bs-17.png
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| ImageFile2 = Polystyrene-chain-from-xtal-3D-sf.png
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| IUPACName = Poly(1-phenylethylene) 
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| OtherNames = Thermocol
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| Abbreviations = PS
| CASNo = 9003-53-6
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|Section2={{Chembox Properties
| Formula = (C<sub>8</sub>H<sub>8</sub>)<sub>n</sub>
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| Density = 0.96–1.05&nbsp;g/cm<sup>3</sup>
| MeltingPt= ~
| MeltingPtC = 240
| MeltingPt_ref = <ref name="Wunsch2000">{{cite book|author=Wunsch, J.R. |title=Polystyrene – Synthesis, Production and Applications|url=https://books.google.com/books?id=9Oal8DG_7GAC&pg=PA15|access-date=25 July 2012|year=2000|publisher=iSmithers Rapra Publishing|isbn=978-1-85957-191-0|page=15}}</ref>
| MeltingPt_notes = for isotactic polystyrene
| ThermalConductivity = 0.033 W/(m·K) (foam, ρ 0.05 g/cm<sup>3</sup>){{sfn|Haynes|2011|p={{page needed|date=November 2017}}}}
| BoilingPtC = 430
| BoilingPt_notes = and depolymerizes
| Solubility = Insoluble
| SolubleOther = Soluble in benzene, carbon disulfide, chlorinated aliphatic hydrocarbons, chloroform, cyclohexanone, dioxane, ethyl acetate, ethylbenzene, MEK, NMP, THF<ref>{{cite book |doi=10.1016/B978-1-895198-47-8.50162-4 |chapter=PS polystyrene |title=Handbook of Polymers |pages=541–7 |year=2012 |last1=Wypych |first1=George |isbn=978-1-895198-47-8 }}</ref>
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| RefractIndex = 1.6; [[dielectric constant]] 2.6 (1 kHz – 1 GHz){{sfn|Haynes|2011|pp=13–17}}
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|Section8={{Chembox Related
| OtherCompounds = [[Styrene]] (monomer)
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[[File:Expanded polystyrene foam dunnage.jpg|thumb|Expanded polystyrene packaging]]
[[File:Envase de yogur.jpg|thumb|A polystyrene yogurt container]]
[[File:Ps6cup.jpg|thumb|Bottom of a [[vacuum forming|vacuum-formed]] cup; fine details such as the glass and fork [[food contact materials]] symbol and the [[resin identification code]] symbol are easily molded]]

'''Polystyrene''' ('''PS''') {{IPAc-en|ˌ|p|ɒ|l|i|ˈ|s|t|aɪ|r|iː|n}} is a synthetic [[polymer]] made from monomers of the [[Aromatic hydrocarbon|aromatic]] hydrocarbon [[styrene]].<ref>{{cite book|author1=John Scheirs|author2=Duane Priddy|title=Modern Styrenic Polymers: Polystyrenes and Styrenic Copolymers|url=https://books.google.com/books?id=FRGoFxKels4C&pg=PA3|date=28 March 2003|publisher=John Wiley & Sons|isbn=978-0-471-49752-3|page=3}}</ref> Polystyrene can be solid or [[foam|foamed]]. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is a poor barrier to air and water vapor and has a relatively low melting point.<ref name="acc">{{cite web|title=Common Plastic Resins Used in Packaging|url=http://plastics.americanchemistry.com/Education-Resources/Hands-on-Plastics/Introduction-to-Plastics-Science-Teaching-Resources/History-of-Polymers-Plastics-for-Teachers.html|website=Introduction to Plastics Science Teaching Resources|publisher=American Chemistry Council, Inc.|access-date=24 December 2012}}</ref> Polystyrene is one of the most widely used [[plastic]]s, with the scale of its production being several million tonnes per year.<ref name=Ullmann/> Polystyrene is naturally [[Transparency (optics)|transparent]], but can be colored with colorants. Uses include protective packaging (such as [[Foam peanut|packing peanuts]] and in the [[Optical disc packaging#Jewel case|jewel cases]] used for storage of optical discs such as [[CD]]s and occasionally [[DVD]]s), containers, lids, bottles, trays, tumblers, [[disposable]] [[cutlery]],<ref name="acc"/> in the making of models, and as an alternative material for [[phonograph record]]s.<ref>{{cite web |title=Polystyrene phonograph record and process of manufacture |url=https://patents.google.com/patent/US2681323A/en |access-date=22 September 2021 |language=en |date=22 March 1949}}</ref>

As a [[thermoplastic]] polymer, polystyrene is in a solid (glassy) state at room temperature but flows if heated above about 100&nbsp;°C, its [[glass transition temperature]].  It becomes rigid again when cooled. This temperature behaviour is exploited for [[extrusion]] (as in [[Styrofoam]]) and also for [[Molding (process)|molding]] and [[vacuum forming]], since it can be cast into molds with fine detail.  The temperatures behavior can be controlled by photocrosslinking.<ref>{{Cite journal |last1=Carroll |first1=Gregory T. |last2=Sojka |first2=Melissa E. |last3=Lei |first3=Xuegong |last4=Turro |first4=Nicholas J. |last5=Koberstein |first5=Jeffrey T. |date=2006-08-01 |title=Photoactive Additives for Cross-Linking Polymer Films: Inhibition of Dewetting in Thin Polymer Films |url=https://pubs.acs.org/doi/10.1021/la0611099 |journal=Langmuir |language=en |volume=22 |issue=18 |pages=7748–7754 |doi=10.1021/la0611099 |pmid=16922559 |issn=0743-7463}}</ref>

Under [[ASTM]] standards, polystyrene is regarded as not [[biodegradable]]. It is accumulating as a form of [[litter]] in the outside [[environment (biophysical)|environment]], particularly along shores and waterways, especially in its foam form, and in the Pacific Ocean.<ref>{{cite journal | vauthors = Kwon BG, Saido K, Koizumi K, Sato H, Ogawa N, Chung SY, Kusui T, Kodera Y, Kogure K | title = Regional distribution of styrene analogues generated from polystyrene degradation along the coastlines of the North-East Pacific Ocean and Hawaii | journal = Environmental Pollution | volume = 188 | pages = 45–9 | date = May 2014 | pmid = 24553245 | doi = 10.1016/j.envpol.2014.01.019 | bibcode = 2014EPoll.188...45K | display-authors = etal }}</ref>

==History==
Polystyrene was discovered in 1839 by [[Eduard Simon]], an [[apothecary]] from Berlin.<ref>Simon, E. (1839) [https://babel.hathitrust.org/cgi/pt?id=uva.x002457910;view=1up;seq=277 "Ueber den flüssigen Storax (''Styrax liquidus'')"] [On liquid storax (''Styrax liquidus'')], ''Annalen der Chemie'', '''31''' :  265–277.</ref> From [[storax]], the resin of the Oriental sweetgum tree ''[[Liquidambar orientalis]]'', he distilled an oily substance, that he named styrol, now called [[styrene]]. Several days later, Simon found that it had thickened into a jelly, now known to have been a [[polymer]], that he dubbed styrol oxide ("Styroloxyd") because he presumed that it had resulted from oxidation ([[styrene oxide]] is a distinct compound). By 1845 Jamaican-born chemist [[John Buddle Blyth]] and German chemist [[August Wilhelm von Hofmann]] showed that the same transformation of styrol took place in the absence of oxygen.<ref>Blyth, John, and Hofmann, Aug. Wilh. (1845). [https://books.google.com/books?id=A8MwAAAAYAAJ&pg=PA289 "Ueber das Stryol und einige seiner Zersetzungsproducte"] ("On styrol and some of its decomposition products"), ''Annalen der Chemie und Pharmacie'', '''53'''(3): 289–329.</ref> They called the product "meta styrol"; analysis showed that it was chemically identical to Simon's Styroloxyd.<ref>Blyth and Hofmann, 1845, p. 312.  From p. 312: "Analysis, as well as synthesis, have equally demonstrated, that styrol and the solid, glassy material, for which we suggest the name 'meta styrol', possess the same percentage composition."</ref> In 1866 [[Marcellin Berthelot]] correctly identified the formation of meta styrol/Styroloxyd from styrol as a [[polymerisation]] process.<ref>Berthelot, M. (1866) [https://archive.org/stream/bulletin27frangoog#page/n295/mode/2up "Sur Les caractères de la benzine et du styrolène, comparés avec ceux des Autres carburetors d'hydrogène"] ("On the characters of benzene and styrene, compared with those of other hydrocarbons"), ''Bulletin de la Société Chimique de Paris'', 2nd series, '''6''':  289–298. From p. 294:  "On sait que le stryolène chauffé en vase scellé à 200°, pendant Quelques heures, se change en un polymère résineux (métastyrol), et que ce polymère, distillé brusquement, reproduit le styrolène." ("One knows that styrene [when] heated in a sealed vessel at 200&nbsp;°C, for several hours, is changed into a resinous polymer (polystyrene), and that this polymer, [when] distilled abruptly, reproduces styrene.")</ref> About 80 years later it was realized that heating of styrol starts a chain reaction that produces [[macromolecule]]s, following the thesis of German organic chemist [[Hermann Staudinger]] (1881–1965). This eventually led to the substance receiving its present name, polystyrene.{{Citation needed|date=January 2021}}

The company [[IG Farben|I. G. Farben]] began manufacturing polystyrene in [[Ludwigshafen]], about 1931, hoping it would be a suitable replacement for die-cast [[zinc]] in many applications. Success was achieved when they developed a reactor vessel that extruded polystyrene through a heated tube and cutter, producing polystyrene in pellet form.<ref>{{Cite news |date=2007-09-21 |title=Business Gives Styrofoam a Rare Redemption |url=http://www.recordnet.com/apps/pbcs.dll/article?AID=/20070921/A_NEWS/709210329 |access-date=2022-06-18}}</ref>

[[Ray McIntire]] (1918–1996), a chemical engineer of Dow Chemical, rediscovered a process first patented in early 1930s by Swedish inventor [[Carl Munters]].<ref>{{cite web | url = https://www.invent.org/inductees/otis-ray-mcintire | title = Otis Ray McIntire | date = 16 August 2023 | publisher = National Inventor's Hall of Fame }}</ref> According to the Science History Institute, "Dow bought the rights to Munters's method and began producing a lightweight, water-resistant, and buoyant material that seemed perfectly suited for building docks and watercraft and for insulating homes, offices, and chicken sheds."<ref>{{Cite web | url = https://www.sciencehistory.org/distillations/styrofoam-a-practical-and-problematic-creation | title = Styrofoam, a Practical and Problematic Creation | publisher = Science History Institute | date = 31 July 2018}}</ref> In 1944, [[Styrofoam]] was patented.<ref>{{Cite web |title=NIHF Inductee Otis Ray McIntire Invented STYROFOAM Brand Foam |url=https://www.invent.org/inductees/otis-ray-mcintire |access-date=2022-06-18 |publisher=www.invent.org |language=en}}</ref>

Before 1949, chemical engineer Fritz Stastny (1908–1985) developed pre-expanded PS beads by incorporating aliphatic hydrocarbons, such as pentane. These beads are the raw material for molding parts or extruding sheets. [[BASF]] and Stastny applied for a patent that was issued in 1949. The molding process was demonstrated at the Kunststoff Messe 1952 in Düsseldorf. Products were named Styropor.<ref>{{Cite web |last=Vidco |title=PAGEV |url=https://pagev.org/polystyrene |access-date=2022-06-18 |website=PAGEV |language=en}}</ref>

The crystal structure of isotactic polystyrene was reported by [[Giulio Natta]].<ref>{{Cite journal | doi = 10.1007/BF02731861| title = Crystal structure of isotactic polystyrene| journal = Il Nuovo Cimento| volume = 15| pages = 68–82| year = 1960| last1 = Natta | first1 = G.| last2 = Corradini | first2 = P.| last3 = Bassi | first3 = I. W.| issue = S1| bibcode = 1960NCim...15S..68N| s2cid = 119808547}}</ref>

In 1954, the [[Koppers|Koppers Company]] in [[Pittsburgh]], Pennsylvania, developed [[expanded polystyrene]] (EPS) foam under the trade name Dylite.<ref>Ferrigno, T.H. (1967). ''Rigid Plastics Foams'', 2nd edition. p. 207.</ref> In 1960, [[Dart Container]], the largest manufacturer of foam cups, shipped their first order.<ref>{{cite web|title=Celebrating 50 Years of Excellence in People and Products|url=http://www.dartcontainer.com/web/products.nsf/pages/celebrating50timeline.html|publisher=Dart Container Corporation|access-date=23 December 2012|url-status=dead|archive-url=https://archive.today/20100604022321/http://www.dartcontainer.com/web/products.nsf/pages/celebrating50timeline.html|archive-date=4 June 2010}}</ref>

== Structure and production ==
[[File:Poliestireno.JPG|thumb|right|Polystyrene is [[fire|flammable]], and releases large amounts of [[soot|black smoke]] upon burning.]]
[[File:201904 Man carrying polystyrene boxes in Guiyang, China.jpg|thumb|Expanded polystyrene is lightweight. This is a man in [[Guiyang]], China carrying a lot of expanded polystyrene packaging.]]
In [[chemistry|chemical]] terms, polystyrene is a long chain hydrocarbon wherein alternating carbon centers are attached to [[phenyl group]]s (a derivative of [[benzene]]). Polystyrene's chemical formula is {{chem|(C|8|H|8|)|n}}; it contains the [[chemical elements]] [[carbon]] and [[hydrogen]].{{Citation needed|date=May 2024}}

The material's properties are determined by short-range [[Van der Waals force|van der Waals]] attractions between polymer chains. Since the molecules consist of thousands of atoms, the cumulative attractive force between the molecules is large.  When heated (or deformed at a rapid rate, due to a combination of viscoelastic and thermal insulation properties), the chains can take on a higher degree of confirmation and slide past each other. This [[intermolecular]] weakness (versus the high ''[[Intramolecular force|intramolecular]]'' strength due to the hydrocarbon backbone) confers flexibility and elasticity.  The ability of the system to be readily deformed above its glass transition temperature allows polystyrene (and thermoplastic polymers in general) to be readily softened and molded upon heating. Extruded polystyrene is about as strong as an unalloyed [[aluminium]] but much more flexible and much less dense (1.05 g/cm<sup>3</sup> for polystyrene vs. 2.70 g/cm<sup>3</sup> for aluminium).<ref>{{Cite patent|number=US9738739B2|title=Method of fixing radioactive tritiated water in a stable tritiated polystyrene product|gdate=2017-08-22|invent1=Digenis|invent2=Digenis|inventor1-first=George A.|inventor2-first=Alexander G.|url=https://patents.google.com/patent/US9738739/en}}</ref>

=== Production ===
Polystyrene is an [[addition polymer]] that results when styrene [[monomer]]s [[polymerization|polymerize]] (interconnect). In the polymerization, the carbon-carbon [[pi bond|π bond]] of the [[vinyl group]] is broken and a new carbon-carbon [[sigma bond|σ bond]] is formed, attaching to the carbon of another styrene monomer to the chain. Since only one kind of monomer is used in its preparation, it is a homopolymer. The newly formed σ bond is stronger than the π bond that was broken, thus it is difficult to depolymerize polystyrene. About a few thousand monomers typically comprise a chain of polystyrene, giving a [[Molar mass distribution#Number average molar mass|molar mass]] of 100,000–400,000&nbsp;g/mol.{{Citation needed|date=January 2021}}

[[File:Polystyrene formation.PNG|center]]

Each carbon of the backbone has [[tetrahedral geometry]], and those carbons that have a [[phenyl group]] (benzene ring) attached are [[chirality (chemistry)|stereogenic]]. If the backbone were to be laid as a flat elongated zig-zag chain, each phenyl group would be tilted forward or backward compared to the plane of the chain.{{Citation needed|date=January 2021}}

The relative [[stereochemical]] relationship of consecutive phenyl groups determines the [[tacticity]], which affects various physical properties of the material.<ref>{{Cite web |date=2013-10-02 |title=The Phenyl Group |url=https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Organic_Chemistry)/Arenes/Properties_of_Arenes/The_Phenyl_Group |access-date=2022-06-18 |website=Chemistry LibreTexts |language=en}}</ref>

===Tacticity===

In polystyrene, [[tacticity]] describes the extent to which the phenyl group is uniformly aligned (arranged at one side) in the polymer chain. Tacticity has a strong effect on the properties of the plastic. Standard polystyrene is atactic. The [[diastereomer]] where all of the phenyl groups are on the same side is called ''isotactic'' polystyrene, which is not produced commercially.{{Citation needed|date=January 2021}}

[[File:Polystyrene tacticity en.svg]]

====Atactic polystyrene====
The only commercially important form of polystyrene is ''atactic'', in which the phenyl groups are [[randomness|randomly]] distributed on both sides of the polymer chain. This random positioning prevents the chains from aligning with sufficient regularity to achieve any [[crystallinity]]. The plastic has a glass transition temperature ''T''<sub>g</sub> of ~90&nbsp;°C.  Polymerization is initiated with [[free radical]]s.<ref name=Ullmann>Maul, J.; Frushour, B. G.; Kontoff, J. R.; Eichenauer, H.; Ott, K.-H. and Schade, C. (2007) "Polystyrene and Styrene Copolymers" in ''Ullmann's Encyclopedia of Industrial Chemistry'', Wiley-VCH, Weinheim, {{doi|10.1002/14356007.a21_615.pub2}}</ref>

==== Syndiotactic polystyrene ====
[[Ziegler–Natta catalyst|Ziegler–Natta polymerization]] can produce an ordered ''syndiotactic'' polystyrene with the phenyl groups positioned on alternating sides of the hydrocarbon backbone. This form is highly crystalline with a ''T''<sub>m</sub> (melting point) of {{convert|270|C|F|abbr=on}}.  Syndiotactic polystyrene resin is currently produced under the trade name XAREC by Idemitsu corporation, who use a metallocene catalyst for the polymerisation reaction.<ref>{{cite web|title = XAREC Syndiotactic Polystyrene – Petrochemicals – Idemitsu Kosan Global|url = http://www.idemitsu.com/products/petrochemicals/engineering/polystyrene.html|website = www.idemitsu.com|access-date = 2016-01-01}}</ref>

==Degradation==
Polystyrene is relatively chemically inert. While it is waterproof and resistant to breakdown by many acids and bases, it is easily attacked by many organic solvents (e.g. it dissolves quickly when exposed to [[acetone]]), chlorinated solvents, and aromatic hydrocarbon solvents. Because of its resilience and inertness, it is used for fabricating many objects of commerce. Like other organic compounds, polystyrene burns to give [[carbon dioxide]] and [[water|water vapor]], in addition to other thermal degradation by-products. Polystyrene, being an [[aromatic hydrocarbon]], typically [[Charring|combusts incompletely]] as indicated by the [[soot]]y flame.{{Citation needed|date=January 2021}}

The process of [[Depolymerization|depolymerizing]] polystyrene into its [[monomer]], [[styrene]], is called [[pyrolysis]]. This involves using high heat and pressure to break down the chemical bonds between each styrene compound. Pyrolysis usually goes up to 430&nbsp;°C.<ref>{{Cite web |url=https://www.azocleantech.com/article.aspx?ArticleID=336 |title=What is Pyrolysis? |date=2012-12-29 |website=AZoCleantech.com |language=en |access-date=2019-08-15}}</ref> The high energy cost of doing this has made commercial recycling of polystyrene back into styrene monomer difficult.{{Citation needed|date=January 2021}}

===Organisms===
Polystyrene is generally considered to be non-biodegradable. However, certain organisms are able to degrade it, albeit very slowly.<ref>{{cite journal |last1=Ho |first1=Ba Thanh |last2=Roberts |first2=Timothy K. |last3=Lucas |first3=Steven |title=An overview on biodegradation of polystyrene and modified polystyrene: the microbial approach |journal=Critical Reviews in Biotechnology |date=August 2017 |volume=38 |issue=2 |pages=308–320 |doi=10.1080/07388551.2017.1355293|pmid=28764575 |s2cid=13417812 }}</ref>

In 2015, researchers discovered that [[mealworm]]s, the larvae form of the darkling beetle ''Tenebrio molitor'', could digest and subsist healthily on a diet of EPS.<ref name="news.stanford.edu">{{cite web |title=Plastic-eating worms may offer solution to mounting waste, Stanford researchers discover |author=Jordan, R. |date=29 September 2015 |url=http://news.stanford.edu/pr/2015/pr-worms-digest-plastics-092915.html |website=Stanford News Service |publisher=Stanford University |access-date=4 January 2017 |archive-date=8 January 2021 |archive-url=https://web.archive.org/web/20210108134659/https://news.stanford.edu/pr/2015/pr-worms-digest-plastics-092915.html |url-status=dead }}</ref><ref name="mealworms">{{cite journal |vauthors = Yang Y, Yang J, Wu WM, Zhao J, Song Y, Gao L, Yang R, Jiang L |title = Biodegradation and Mineralization of Polystyrene by Plastic-Eating Mealworms: Part 1. Chemical and Physical Characterization and Isotopic Tests |journal = Environmental Science & Technology |volume = 49 |issue = 20 |pages = 12080–6 |date = October 2015 |pmid = 26390034 |doi = 10.1021/acs.est.5b02661 |bibcode = 2015EnST...4912080Y }}</ref> About 100 mealworms could consume between 34 and 39 milligrams of this white foam in a day. The droppings of mealworm were found to be safe for use as soil for crops.<ref name="news.stanford.edu"/>

In 2016, it was also reported that superworms (''[[Zophobas morio]]'') may eat expanded polystyrene (EPS).<ref>{{cite web |title=Think you can't compost styrofoam? Mealworms are the answer! |url=http://livingearthsystems.com/mealworms-compost-styrofoam/ |publisher=Living Earth Systems |website=Blog |date= 2016-10-08|access-date=4 January 2017}}</ref> A group of high school students in [[Ateneo de Manila University]] found that compared to ''Tenebrio molitor'' larvae, ''Zophobas morio'' larvae may consume greater amounts of EPS over longer periods of time.<ref>{{cite web |last1=Aumentado |first1=Dominic |title=A Comparative Study of the Efficacy of ''Tenebrio molitor'' Larvae and ''Zophobas morio'' Larvae as Degradation Agents of Expanded Polystyrene Foam |website=Academia |url=https://www.academia.edu/43122081}}{{psc|date=September 2020}}</ref> 

In 2022 scientists identified several bacterial genera, including ''[[Pseudomonas]]'', ''[[Rhodococcus]]'' and ''[[Corynebacterium]]'',  in the gut of superworms that contain encoded enzymes associated with the degradation of polystyrene and the breakdown product styrene.<ref name="Sun et al. 2022">{{cite journal |last1=Sun |first1=Jiarui |last2=Prabhu |first2=Apoorva |last3=Aroney |first3=Samuel T. N. |last4=Christian |first4=Rinke |title=Insights into plastic biodegradation: community composition and functional capabilities of the superworm (Zophobas morio) microbiome in styrofoam feeding trials |journal=Microbial Genomics |date=2022 |volume=8 |issue=6 |pages=1–19 |doi=10.1099/mgen.0.000842 |doi-access=free |pmid=35678705 |pmc=9455710 }}</ref>

The bacterium ''[[Pseudomonas putida]]'' is capable of converting [[styrene]] oil into the [[biodegradable plastic]] [[Polyhydroxyalkanoates|PHA]].<ref>{{cite web |last=Roy |first=Robert |url=http://www.livescience.com/technology/060307_styrofoam_cup.html |title=Immortal Polystyrene Foam Meets its Enemy |publisher=LiveScience |date=2006-03-07 |access-date=2019-01-17}}</ref><ref>{{cite journal |vauthors = Ward PG, Goff M, Donner M, Kaminsky W, O'Connor KE |title = A two step chemo-biotechnological conversion of polystyrene to a biodegradable thermoplastic |journal = Environmental Science & Technology |volume = 40 |issue = 7 |pages = 2433–7 |date = April 2006 | pmid = 16649270 |doi = 10.1021/es0517668 |bibcode = 2006EnST...40.2433W }}</ref><ref>{{cite journal |last1=Biello |first1=David |title=Bacteria Turn Styrofoam into Biodegradable Plastic |journal=Scientific American |date=27 February 2006 |url=http://www.scientificamerican.com/article/bacteria-turn-styrofoam-i/}}</ref> This may someday be of use in the effective disposing of polystyrene foam. It is worthy to note the polystyrene must undergo pyrolysis to turn into styrene oil.{{Citation needed|date=January 2021}}

==Forms produced==
{| class="wikitable floatright" style="margin: 20px 20px 0px 20px;"
|-
! colspan=2|Properties
|-
| Density of EPS
| 16–640&nbsp;kg/m<sup>3</sup><ref name=pse1>{{cite journal|journal=New Scientist |date=22 June 1961|url=https://books.google.com/books?id=d_XOKdeyXrYC&pg=PA706|page=706|volume=240|title=Making and using an expanded plastic|author=Goodier, K. }}</ref>
|-
| [[Young's modulus]] (''E'')
| 3000–3600 [[Pascal (unit)|MPa]]
|-
| [[Tensile strength]] (''s''<sub>t</sub>)
| 46–60 MPa
|-
| Elongation at break
| 3–4%
|-
| [[Charpy impact test]]
| 2–5 [[kilojoules|kJ]]/m<sup>2</sup>
|-
| Glass transition temperature
| 100&nbsp;°C<ref>Mark, James E. (2009). ''Polymer Data Handbook'' (2nd Edition). Oxford University Press. {{ISBN|978-0-19-518101-2}}</ref>
|-
| [[Vicat softening point]]
| 90&nbsp;°C<ref>van der Vegt, A.K. and Govaert, L.E. (2003) ''Polymeren, van keten tot kunstof'', DUP Blue Print, {{ISBN|90-407-2388-5}}</ref>
|-
| [[Coefficient of thermal expansion]]
| 8×10<sup>−5</sup> /[[Kelvin|K]]
|-
| [[Specific heat capacity]] (''c'')
| 1.3 kJ/(kg·K)
|-
| [[Absorption (chemistry)|Water absorption]] (ASTM)
| 0.03–0.1
|-
| [[Decomposition]]
| X years, still decaying
|}

Polystyrene is commonly [[injection molding|injection molded]], [[vacuum forming|vacuum formed]], or extruded, while expanded polystyrene is either extruded or molded in a special process.
Polystyrene [[copolymers]] are also produced; these contain one or more other monomers in addition to styrene. In recent years the expanded polystyrene composites with cellulose<ref>{{cite journal |doi=10.1177/0892705704035405 |title=Expanded Wood Fiber Polystyrene Composites: Processing–Structure–Mechanical Properties Relationships |journal=Journal of Thermoplastic Composite Materials |volume=17 |pages=13–30 |year=2016 |last1=Doroudiani |first1=Saeed |last2=Kortschot |first2=Mark T. |s2cid=138224146 }}</ref><ref>{{cite journal |doi=10.1002/polb.10129 |title=Sorption and diffusion of carbon dioxide in wood-fiber/polystyrene composites |journal=Journal of Polymer Science Part B: Polymer Physics |volume=40 |issue=8 |pages=723–735 |year=2002 |last1=Doroudiani |first1=Saeed |last2=Chaffey |first2=Charles E. |last3=Kortschot |first3=Mark T. |bibcode=2002JPoSB..40..723D }}</ref> and starch<ref>{{cite journal |doi=10.1177/0021955X07076532 |title=Foaming of Polystyrene/ Thermoplastic Starch Blends |journal=Journal of Cellular Plastics |volume=43 |issue=3 |pages=215–236 |year=2016 |last1=Mihai |first1=Mihaela |last2=Huneault |first2=Michel A. |last3=Favis |first3=Basil D. |s2cid=135968555 |url=https://nrc-publications.canada.ca/eng/view/accepted/?id=43335b28-49c7-4640-877c-1d79813ff029 }}</ref> have also been produced. Polystyrene is used in some [[polymer-bonded explosive]]s (PBX).{{Citation needed|date=January 2021}}

===Sheet or molded polystyrene===
[[File:Caja de CD.jpg|thumb|left|upright|CD case made from general purpose polystyrene (GPPS) and high impact polystyrene (HIPS)]]
[[File:Maquinilla de afeitar desechable.JPG|thumb|left|Disposable polystyrene razor]]
Polystyrene (PS) is used for producing disposable plastic [[cutlery]] and [[dinnerware]], [[CD and DVD packaging|CD "jewel" cases]], [[smoke detector]] housings, [[license plate]] frames, [[plastic model]] assembly kits, and many other objects where a rigid, economical plastic is desired. Production methods include [[thermoforming]] ([[vacuum forming]]) and [[injection molding]].

Polystyrene [[Petri dish]]es and other [[laboratory]] containers such as [[test tubes]] and [[microplate]]s play an important role in biomedical research and science. For these uses, articles are almost always made by injection molding, and often sterilized post-molding, either by irradiation or by treatment with [[ethylene oxide]]. Post-mold surface modification, usually with [[oxygen]]-rich [[Plasma (physics)|plasma]]s, is often done to introduce polar groups. Much of modern biomedical research relies on the use of such products; they, therefore, play a critical role in pharmaceutical research.<ref>{{cite web|author=Norton, Jed |title=Blue Foam, Pink Foam and Foam Board|publisher=Antenociti's Workshop|url=http://www.barrule.com/workshop/images/info/foams/index.htm|access-date=29 January 2008 |archive-url = https://web.archive.org/web/20080226152632/http://barrule.com/workshop/images/info/foams/index.htm |archive-date = 26 February 2008}}</ref>

Thin sheets of polystyrene are used in polystyrene [[film capacitor]]s as it forms a very stable [[dielectric]], but has largely fallen out of use in favor of [[polyester]].

===Foams===
[[File:Polistirolo.JPG|thumb|Closeup of expanded polystyrene packaging]]
Polystyrene foams are 95–98% air.<ref>{{cite web|title=Polystyrene|url=https://www.chemicalsafetyfacts.org/polystyrene-post/|website=ChemicalSafetyFacts.org|publisher=American Chemistry Council|date=May 2014|access-date=11 December 2017|archive-date=8 March 2018|archive-url=https://web.archive.org/web/20180308035110/https://www.chemicalsafetyfacts.org/polystyrene-post/|url-status=dead}}</ref><ref>{{cite web|title=Recycle Your EPS|url=http://www.epspackaging.org/index.php?option=com_content&view=article&id=8&Itemid=4|publisher=EPS Industry Alliance|access-date=11 December 2017}}</ref> Polystyrene foams are good thermal insulators and are therefore often used as building insulation materials, such as in [[insulating concrete forms]] and structural insulated panel building systems. Grey polystyrene foam, incorporating [[graphite]], has superior insulation properties.<ref>{{cite web|website=Neotherm Ltd.|url=http://www.neotherm.ie/neographite_031_graphite_enhanced_polystyrene.html|title=Products: graphite enhanced polystyrene|access-date=26 December 2018|archive-url=https://web.archive.org/web/20180311052238/http://neotherm.ie/neographite_031_graphite_enhanced_polystyrene.html|archive-date=11 March 2018|url-status=dead}}</ref>

[[Carl Munters]] and John Gudbrand Tandberg of Sweden received a US patent for polystyrene foam as an insulation product in 1935 (USA patent number 2,023,204).<ref>{{US patent|02023204}}</ref>

PS foams also exhibit good damping properties, therefore it is used widely in packaging. The [[trademark]] [[Styrofoam]] by [[Dow Chemical Company]] is informally used (mainly US & Canada) for all foamed polystyrene products, although strictly it should only be used for "extruded closed-cell" polystyrene foams made by Dow Chemicals.

Foams are also used for non-weight-bearing architectural structures (such as ornamental [[column|pillars]]).

====Expanded polystyrene (EPS)====
[[File: Thermocol blocks.jpg|thumb|Thermocol slabs made of expanded polystyrene (EPS) beads. The one on the left is from a packing box. The one on the right is used for crafts. It has a corky, papery texture and is used for stage decoration, exhibition models, and sometimes as a cheap alternative to shola (''[[Aeschynomene aspera]]'') stems for artwork.]]

[[File:Microscopic Section of Thermocol block (Under light-microscope, bright-field, Objective 10 X, Eyepiece 10 X).jpg|thumb|Section of a block of thermocol under a [[Optical microscope|light microscope]] ([[Bright-field microscopy|bright-field]], objective = 10×, eyepiece = 15×). The larger spheres are expanded polystyrene beads which were compressed and fused. The bright, star-shaped hole at the center of the image is an air-gap between the beads where the bead margins have not completely fused. Each bead is made of thin-walled, air-filled bubbles of polystyrene.]]

Expanded polystyrene (EPS) is a rigid and tough, closed-cell [[foam]] with a normal density range of 11 to 32&nbsp;kg/m<sup>3</sup>.<ref>{{Cite book |url=http://www.thermalps.com.au/imagesDB/wysiwyg/TDS_Expanded_Polystyrene.pdf |title=Expanded Polystyrene (EPS) Technical Data |publisher=Australian Urethane & Styrene |year=2010 |location=Australia}}</ref> It is usually white and made of pre-expanded polystyrene beads. The manufacturing process for EPS conventionally begins with the creation of small polystyrene beads. Styrene monomers (and potentially other additives) are suspended in water, where they undergo free-radical addition polymerization. The polystyrene beads formed by this mechanism may have an average diameter of around 200&nbsp;μm. The beads are then permeated with a "blowing agent", a material that enables the beads to be expanded. [[Pentane]] is commonly used as the blowing agent. The beads are added to a continuously agitated reactor with the blowing agent, among other additives, and the blowing agent seeps into pores within each bead. The beads are then expanded using steam.<ref>{{Cite journal |last=Howard |first=Kevin A. |date=8 June 1993 |title=Method for manufacturing expanded polystyrene foam components from used polystyrene materials |url=https://patentimages.storage.googleapis.com/38/74/c0/e31dc824c43b22/US5217660.pdf |journal=United States Patent}}</ref>

EPS is used for [[foam food container|food containers]], molded sheets for [[building insulation]], and packing material either as solid blocks formed to accommodate the item being protected or as loose-fill [[foam peanut|"peanuts"]] [[cushioning]] fragile items inside boxes. EPS also has been widely used in automotive and road safety applications such as [[motorcycle helmet]]s and [[SAFER barrier|road barriers on automobile race tracks]].<ref>{{Cite report |last1=Faller |first1=Ronald |last2=Bielenberg |first2=Robert |last3=Sicking |first3=Dean |last4=Rohde |first4=John |last5=Reid |first5=John |date=2006-12-05 |title=Development and Testing of the SAFER Barrier – Version 2, SAFER Barrier Gate, and Alternative Backup Structure |website=SAE Mobilus |series=SAE Technical Paper Series |volume=1 |doi=10.4271/2006-01-3612}}</ref><ref>{{Cite conference |last1=Bielenberg |first1=Robert W. |last2=Rohde |first2=John D. |last3=Reid |first3=John D. |date=2005-01-01 |title=Design of the SAFER Emergency Gate Using LS-DYNA |conference=Engineering/Technology Management |pages=345–352 |publisher=ASMEDC |doi=10.1115/imece2005-81078 |isbn=0-7918-4230-4}}</ref><ref>{{Cite journal |last1=Mills |first1=N.J. |last2=Wilkes |first2=S. |last3=Derler |first3=S. |last4=Flisch |first4=A. |date=July 2009 |title=FEA of oblique impact tests on a motorcycle helmet |journal=International Journal of Impact Engineering |volume=36 |issue=7 |pages=913–925 |doi=10.1016/j.ijimpeng.2008.12.011|bibcode=2009IJIE...36..913M |s2cid=138180148 |issn=0734-743X|url=https://hal.science/hal-00574810 }}</ref>

A significant portion of all EPS products are manufactured through injection molding. Mold tools tend to be manufactured from steels (which can be hardened and plated), and aluminum alloys. The molds are controlled through a split via a channel system of gates and runners.<ref>{{Cite web |url=http://www.bpf.co.uk/plastipedia/processes/moulding_eps.aspx |title=Moulding Expanded Polystyrene (EPS)}}</ref> EPS is colloquially called "styrofoam" in the [[Core Anglosphere|Anglosphere]], an [[Generic trademark|genericization]] of Dow Chemical's [[Styrofoam|brand of extruded polystyrene]].<ref name="what-is-styrofoam">{{cite web |url=http://building.dow.com/styrofoam/what.htm |archive-url=https://web.archive.org/web/20080324134328/http://building.dow.com/styrofoam/what.htm |url-status=dead |archive-date=2008-03-24 |title=Dow Chemical Company Styrofoam page |access-date=2019-01-17}}</ref>

====EPS in building construction====
Sheets of EPS are commonly packaged as [[rigid panel]]s (common in Europe is a size of 100&nbsp;cm x 50&nbsp;cm, usually depending on an intended type of connection and glue techniques, it is, in fact, 99.5&nbsp;cm x 49.5&nbsp;cm or 98&nbsp;cm x 48&nbsp;cm; less common is 120 x 60&nbsp;cm; size {{cvt|4|by|8|ft}} or {{cvt|2|by|8|ft}} in the United States). Common thicknesses are from 10&nbsp;mm to 500&nbsp;mm. Many customizations, additives, and thin additional external layers on one or both sides are often added to help with various properties. An example of this is  [[ThermaSAVE|lamination with cement board]] to form a [[structural insulated panel]].

[[Thermal conductivity]] is measured according to EN 12667. Typical values range from 0.032 to 0.038&nbsp;W/(m⋅K) depending on the density of the EPS board. The value of 0.038&nbsp;W/(m⋅K) was obtained at 15&nbsp;kg/m<sup>3</sup> while the value of 0.032&nbsp;W/(m⋅K) was obtained at 40&nbsp;kg/m<sup>3</sup> according to the datasheet of K-710 from StyroChem Finland. Adding fillers (graphites, aluminum, or carbons) has recently allowed the thermal conductivity of EPS to reach around 0.030–0.034&nbsp;W/(m⋅K) (as low as 0.029&nbsp;W/(m⋅K)) and as such has a grey/black color which distinguishes it from standard EPS. Several EPS producers have produced a variety of these increased thermal resistance EPS usage for this product in the UK and EU.

Water vapor [[diffusion resistance]] (''μ'') of EPS is around 30–70.

ICC-ES ([[International Code Council]] Evaluation Service) requires EPS boards used in building construction meet ASTM C578 requirements. One of these requirements is that the [[limiting oxygen index]] of EPS as measured by ASTM D2863 be greater than 24 volume %. Typical EPS has an oxygen index of around 18 volume %; thus, a flame retardant is added to styrene or polystyrene during the formation of EPS.

The boards containing a flame retardant when tested in a tunnel using test method UL 723 or ASTM E84 will have a flame spread index of less than 25 and a smoke-developed index of less than 450. ICC-ES requires the use of a 15-minute thermal barrier when EPS boards are used inside of a building.

According to the EPS-IA ICF organization, the typical density of EPS used for insulated concrete forms ([[expanded polystyrene concrete]]) is {{convert|1.35|to|1.80|lb/ft3|kg/m3}}. This is either Type II or Type IX EPS according to ASTM C578. EPS blocks or boards used in building construction are commonly cut using hot wires.<ref>''[http://www.ceresana.com/en/insight/products/plastics/expandable-polystyrene/ Expandable Polystyrene]'', Insight database from Ceresana Research</ref>

==== Extruded polystyrene (XPS) ====
[[File:Foam Board.jpg|thumb|upright=1.7|Extruded polystyrene has a smooth texture, and can be cut into sharp-edged shapes without crumbling]]
{{anchor|Extruded polystyrene foam}}
Extruded polystyrene foam (XPS) consists of closed cells. It offers improved surface roughness, higher stiffness and reduced thermal conductivity. The density range is about 28–34&nbsp;kg/m<sup>3</sup>.<ref>{{Cite journal|last=Al-Ajlan|first=Saleh A.|date=2006-12-01|title=Measurements of thermal properties of insulation materials by using transient plane source technique|url=https://www.sciencedirect.com/science/article/pii/S1359431106001256|journal=Applied Thermal Engineering|language=en|volume=26|issue=17|pages=2184–2191|doi=10.1016/j.applthermaleng.2006.04.006|bibcode=2006AppTE..26.2184A |issn=1359-4311}}</ref><ref>{{Cite web |title=National Commercial Corporation |url=https://www.nathanibiz.com/ti-xps.php |access-date=2022-06-18 |website=www.nathanibiz.com}}</ref>

Extruded polystyrene material is also used in [[craft]]s and [[Physical model|model]] building, in particular [[Architecture|architectural]] models. Because of the extrusion manufacturing process, XPS does not require facers to maintain its thermal or physical property performance. Thus, it makes a more uniform substitute for [[corrugated cardboard]]. Thermal conductivity varies between 0.029 and 0.039 W/(m·K) depending on bearing strength/density and the average value is ~0.035 W/(m·K).

Water vapor diffusion resistance (μ) of XPS is around 80–250.

Commonly extruded polystyrene foam materials include:
* [[Styrofoam]], also known as Blue Board, produced by [[DuPont]]
* Depron, a thin insulation sheet also used for model building<ref>{{cite web |title=Technical details |url=http://www.depron.co.uk/technical.htm |website=Depron foam |access-date=17 June 2020}}</ref>

==== Water absorption of polystyrene foams ====
Although it is a closed-cell foam, both expanded and extruded polystyrene are not entirely waterproof or vapor proof.<ref>Gnip, Ivan et al. (2007) [http://leidykla.vgtu.lt/conferences/MBM_2007/1pdf/Gnip_Kersulis.pdf LONG-TERM WATER ABSORPTION OF EXPANDED POLYSTYRENE BOARDS] {{Webarchive|url=https://web.archive.org/web/20180128002027/http://leidykla.vgtu.lt/conferences/MBM_2007/1pdf/Gnip_Kersulis.pdf |date=28 January 2018 }}. Institute of Thermal Insulation of Vilnius Gediminas Technical University</ref> In expanded polystyrene there are interstitial gaps between the expanded closed-cell pellets that form an open network of channels between the bonded pellets, and this network of gaps can become filled with liquid water. If the water freezes into ice, it expands and can cause polystyrene pellets to break off from the foam. Extruded polystyrene is also permeable by water molecules and can not be considered a vapor barrier.<ref>[http://www.foamular.com/assets/0/144/172/174/e45fe07d-5cc9-4e4b-866a-5e35d75090ec.pdf Owens Corning FOAMULAR Extruded Polystrene Insulation: Resisting Water Absorption, the Key for High-Performance Foam Plastic Rigid Insulation], ''Technical Bulletin'', Pub. No. 10011642-A, September 2011,</ref>

Water-logging commonly occurs over a long period in polystyrene foams that are constantly exposed to high humidity or are continuously immersed in water, such as in hot tub covers, in floating docks, as supplemental flotation under boat seats, and for below-grade exterior building insulation constantly exposed to groundwater.<ref>[http://epsindustry.org/sites/default/files/EPS%20Below%20Grade%20105.pdf "XPS Insulation Extracted After Field Exposure Confirms High Water Absorption & Diminished R‐Value"] {{Webarchive|url=https://web.archive.org/web/20150206100709/http://epsindustry.org/sites/default/files/EPS%20Below%20Grade%20105.pdf |date=6 February 2015 }}, EPS Below Grade Series 105, March 2014, Technical Bulletin, EPS Industry Alliance.</ref> Typically an exterior vapor barrier such as impermeable plastic sheeting or a sprayed-on coating is necessary to prevent saturation.

===Oriented polystyrene===
Oriented polystyrene (OPS) is produced by stretching extruded PS film, improving visibility through the material by reducing haziness and increasing stiffness.  This is often used in packaging where the manufacturer would like the consumer to see the enclosed product.  Some benefits to OPS are that it is less expensive to produce than other clear plastics such as [[polypropylene]] (PP), (PET), and high-impact polystyrene (HIPS), and it is less hazy than HIPS or PP. The main disadvantage of OPS is that it is brittle, and will crack or tear easily.

==Co-polymers==
Ordinary ([[homopolymeric]]) polystyrene has an excellent property profile about transparency, surface quality and stiffness. Its range of applications is further extended by [[copolymerization]] and other modifications ([[Polymer blend|blends]] e.g. with [[Polycarbonate|PC]] and syndiotactic polystyrene).<ref>[[Wilhelm Keim|W. Keim]]: ''Kunststoffe: Synthese, Herstellungsverfahren, Apparaturen'', 379 Seiten, Verlag Wiley-VCH Verlag GmbH & Co. KGaA, 1. Auflage (2006) {{ISBN|3-527-31582-9}}</ref>{{rp|102–104}} Several copolymers are used based on [[styrene]]: The [[brittleness]] of homopolymeric polystyrene is overcome by elastomer-modified styrene-butadiene copolymers. Copolymers of styrene and acrylonitrile ([[Styrene-acrylonitrile resin|SAN]]) are more resistant to thermal stress, heat and chemicals than homopolymers and are also transparent. Copolymers called [[Acrylonitrile butadiene styrene|ABS]] have similar properties and can be used at low temperatures, but they are [[Opacity (optics)|opaque]].

=== Styrene-butane co-polymers ===
Styrene-butane co-polymers can be produced with a low [[1-Butene|butene]] content. Styrene-butane co-polymers include PS-I and SBC (see below), both co-polymers are [[Impact resistance|impact resistant]]. PS-I is prepared by [[Graft polymerization|graft co-polymerization]], SBC by anionic block co-polymerization, which makes it [[Transparency and translucency|transparent]] in case of appropriate block size.<ref>{{cite web|title=Übersicht Polystyrol auf chemgapedia.de|url=http://www.chemgapedia.de/vsengine/vlu/vsc/de/ch/9/mac/werkstoff_polystyren/sorten/sorten.vlu/Page/vsc/de/ch/9/mac/werkstoff_polystyren/sorten/copolymere/uebersicht.vscml.html}}</ref>

If styrene-butane co-polymer has a high butylene content, [[styrene-butadiene rubber]] (SBR) is formed.

The impact strength of styrene-butadiene co-polymers is based on phase separation, polystyrene and poly-butane are not soluble in each other (see [[Flory–Huggins solution theory]]). Co-polymerization creates a boundary layer without complete mixing. The butadiene fractions (the "rubber phase") assemble to form particles embedded in a polystyrene matrix. A decisive factor for the improved impact strength of styrene-butadiene copolymers is their higher absorption capacity for deformation work. Without applied force, the rubber phase initially behaves like a [[Filler (materials)|filler]]. Under tensile stress, [[Crazing|crazes]] (microcracks) are formed, which spread to the rubber particles. The energy of the propagating crack is then transferred to the rubber particles along its path. A large number of cracks give the originally rigid material a laminated structure. The formation of each lamella contributes to the consumption of energy and thus to an increase in elongation at break. Polystyrene homo-polymers deform when a force is applied until they break. Styrene-butane co-polymers do not break at this point, but begin to flow, solidify to tensile strength and only break at much higher elongation.<ref name="Domininghaus-2012">{{Cite book|title=Kunststoffe: Eigenschaften und Anwendungen|last=Domininghaus, Hans.|date=2012|publisher=Springer|others=Elsner, Peter., Eyerer, Peter., Hirth, Thomas.|isbn=9783642161735|edition=8., neu bearbeitete und erweiterte Auflage|location=Heidelberg|oclc=834590709}}</ref>{{rp|426}}

With a high proportion of polybutadiene, the effect of the two phases is reversed. Styrene-butadiene rubber behaves like an elastomer but can be processed like a thermoplastic.

==== Impact-resistant polystyrene (PS-I) ====
PS-I ('''''<u>i</u>'''mpact resistant '''<u>p</u>'''oly'''<u>s</u>'''tyrene'') consists of a continuous polystyrene matrix and a rubber phase dispersed therein. It is produced by polymerization of styrene in the presence of polybutadiene dissolved (in styrene). Polymerization takes place simultaneously in two ways:<ref>{{cite web|title=Schlagzähes PS auf chemgapedia.de|url=http://www.chemgapedia.de/vsengine/vlu/vsc/de/ch/10/styrol_polymerisation/schlagzaehes_ps/schlagzaehes_ps.vlu.html}}</ref>

* [[Graft polymerization|Graft copolymerization]]: The growing polystyrene chain reacts with a [[double bond]] of the [[polybutadiene]]. As a result, several polystyrene chains are attached to one polybutadiene. 
** <span style="color:#F46C2C">S</span> represents in the figure the styrene [[repeat unit]]
** <span style="color:#00AAC5">B</span> the butadiene repeat unit. However, the middle block often does not consist of such depicted butane homo-polymer but of a styrene-butadiene co-polymer:

:::<span style="color:#F46C2C">SSSSSS&shy;SSSSSSS&shy;SSSSSS</span><span style="color:#00AAC5">BB</span><span style="color:#F46C2C">S</span><span style="color:#00AAC5">BB</span><span style="color:#F46C2C">S</span><span style="color:#00AAC5">B</span>&shy;<span style="color:#F46C2C">S</span><span style="color:#00AAC5">BBBB</span><span style="color:#F46C2C">S</span><span style="color:#00AAC5">B</span>&shy;<span style="color:#F46C2C">SS</span><span style="color:#00AAC5">BBB</span><span style="color:#F46C2C">S</span><span style="color:#00AAC5">B</span><span style="color:#F46C2C">SSSSSSS&shy;SSSSSSS&shy;SSSSSSSSSSSSSSS</span><span style="color:#F46C2C">S</span>

By using a statistical copolymer at this position, the polymer becomes less susceptible to [[Cross linking|cross-linking]] and [[Melt flow index|flows]] better in the melt. For the production of SBS, the first styrene is homopolymerized via anionic copolymerization. Typically, an organometallic compound such as butyllithium is used as a catalyst. Butadiene is then added and after styrene again its polymerization. The catalyst remains active during the whole process (for which the used chemicals must be of high purity). The [[molecular weight distribution]] of the polymers is very low ([[polydispersity]] in the range of 1.05, the individual chains have thus very similar lengths). The length of the individual blocks can be adjusted by the ratio of catalyst to monomer. The size of the rubber sections, in turn, depends on the block length. The production of small structures (smaller than the wavelength of the light) ensure transparency. In contrast to PS-I, however, the block copolymer does not form any particles but has a lamellar structure.

==== Styrene-butadiene rubber ====
{{main article|Styrene-butadiene}}

Styrene-butadiene rubber (SBR) is produced like PS-I by graft copolymerization, but with a lower styrene content. Styrene-butadiene rubber thus consists of a rubber matrix with a polystyrene phase dispersed therein.<ref name="Pfropfcopolymere">{{cite web|title=PS-Pfropfcopolymere auf chemgapedia.de|url=http://www.chemgapedia.de/vsengine/vlu/vsc/de/ch/9/mac/werkstoff_polystyren/sorten/sorten.vlu/Page/vsc/de/ch/9/mac/werkstoff_polystyren/sorten/copolymere/sb/pfropfcopolymere.vscml.html}}</ref> Unlike PS-I and SBC, it is not a [[thermoplastic]], but an [[elastomer]]. Within the rubber phase, the polystyrene phase is assembled into domains. This causes physical cross-linking on a microscopic level. When the material is heated above the glass transition point, the domains disintegrate, the cross-linking is temporarily suspended and the material can be processed like a thermoplastic.<ref>{{cite web|title=styrenic block copolymers – IISRP|url=https://iisrp.com/wp-content/uploads/08SBC16Aug2012.pdf}}</ref>

=== Acrylonitrile butadiene styrene ===
{{main article|Acrylonitrile butadiene styrene}}
Acrylonitrile butadiene styrene (ABS) is a material that is stronger than pure polystyrene.

===Others===
[[styrene maleic anhydride|SMA]] is a copolymer with [[maleic anhydride]]. Styrene can be copolymerized with other monomers; for example, [[divinylbenzene]] can be used for cross-linking the polystyrene chains to give the polymer used in [[solid phase peptide synthesis]]. [[Styrene-acrylonitrile resin]] (SAN) has a greater thermal resistance than pure styrene.

==Environmental issues==

===Production===
Polystyrene foams are produced using blowing agents that form bubbles and expand the foam. In expanded polystyrene, these are usually hydrocarbons such as [[pentane]], which may pose a flammability hazard in manufacturing or storage of newly manufactured material, but have relatively mild environmental impact.{{citation needed|date=June 2015}} Extruded polystyrene is usually made with [[hydrofluorocarbon]]s ([[HFC-134a]]),<ref>[http://www.earthresource.org/campaigns/capp/capp-styrofoam.html Polystyrene Foam Report] {{webarchive|url=https://web.archive.org/web/20130325091953/http://www.earthresource.org/campaigns/capp/capp-styrofoam.html |date=25 March 2013 }}. Earth Resource Foundation.</ref> which have global warming potentials of approximately 1000–1300 times that of carbon dioxide.<ref>[http://www.epa.gov/ozone/geninfo/gwps.html Global Warming Potentials of ODS Substitutes]. EPA.gov</ref> Packaging, particularly expanded polystyrene, is a contributor of [[microplastics]] from both land and maritime activities.<ref>{{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}}</ref>

===Environmental degradation===
Polystyrene is not [[biodegradeable]] but it is susceptible to [[Photo-oxidation of polymers|photo-oxidation]].<ref>{{cite journal |last1=Yousif |first1=Emad |last2=Haddad |first2=Raghad |title=Photodegradation and photostabilization of polymers, especially polystyrene: review |journal=SpringerPlus |date=December 2013 |volume=2 |issue=1 |pages=398 |doi=10.1186/2193-1801-2-398 |pmid=25674392 |pmc=4320144 |doi-access=free}}</ref> For this reason commercial products contain [[Polymer stabilizers|light stabilizers]].

===Litter===
[[File:Physical weathering styrofoam cup Lake MIchigan.jpg|thumb|Discarded polystyrene cup on the shore of [[Lake Michigan]]]]
Animals do not recognize polystyrene foam as an artificial material and may even mistake it for food.<ref name="Hofer 2008 59">{{cite book|last=Hofer|first=Tobias N.|title=Marine pollution: new research|year=2008|publisher=Nova Science Publishers|location=New York|isbn=978-1-60456-242-2|page=59}}</ref>
Polystyrene foam blows in the wind and floats on water due to its low specific gravity.  It can have serious effects on the health of birds and marine animals that swallow significant quantities.<ref name="Hofer 2008 59"/> Juvenile rainbow trout exposed to polystyrene fragments show toxic effects in the form of substantial histomorphometrical changes.<ref>{{cite journal |last1=Karbalaei |first1=Samaneh |last2=Hanachi |first2=Parichehr |last3=Rafiee |first3=Gholamreza |last4=Seifori |first4=Parvaneh |last5=Walker |first5=Tony R. |title=Toxicity of polystyrene microplastics on juvenile Oncorhynchus mykiss (rainbow trout) after individual and combined exposure with chlorpyrifos |journal=Journal of Hazardous Materials |date=September 2020 |volume=403 |pages=123980 |doi=10.1016/j.jhazmat.2020.123980 |pmid=33265019 |s2cid=224995527 |url=https://zenodo.org/record/4588238 }}</ref>

===Reducing===
{{Main|Phase-out of polystyrene foam}}
Restricting the use of foamed polystyrene takeout food packaging is a priority of many solid waste [[environmental organisation]]s.<ref>{{cite journal |doi=10.1016/j.marpolbul.2018.10.001 |pmid=30503422 |title=Reducing marine pollution from single-use plastics (SUPs): A review |journal=Marine Pollution Bulletin |volume=137 |pages=157–171 |year=2018 |last1=Schnurr |first1=Riley E.J. |last2=Alboiu |first2=Vanessa |last3=Chaudhary |first3=Meenakshi |last4=Corbett |first4=Roan A. |last5=Quanz |first5=Meaghan E. |last6=Sankar |first6=Karthikeshwar |last7=Srain |first7=Harveer S. |last8=Thavarajah |first8=Venukasan |last9=Xanthos |first9=Dirk |last10=Walker |first10=Tony R. |bibcode=2018MarPB.137..157S |s2cid=54522420 }}</ref> Efforts have been made to find alternatives to polystyrene, especially foam in restaurant settings. The original impetus was to eliminate [[chlorofluorocarbon]]s (CFC), which was a former component of foam.

====United States====
In 1987, [[Berkeley, California]], banned CFC food containers.<ref>{{cite news|title=Berkeley Barring Use of a Food Container|url=https://www.nytimes.com/1987/09/24/us/berkeley-barring-use-of-a-food-container.html?src=pm|access-date=23 December 2012|newspaper=[[The New York Times]]|date=24 September 1987|agency=[[Associated Press]]}}</ref> The following year, [[Suffolk County, New York]], became the first U.S. jurisdiction to ban polystyrene in general.<ref>{{cite news|title=Suffolk Votes A Bill to Ban Plastic Bags|url=https://www.nytimes.com/1988/03/30/nyregion/suffolk-votes-a-bill-to-ban-plastic-bags.html|access-date=23 December 2012|newspaper=The New York Times|date=30 March 1988}}</ref> However, legal challenges by the [[Society of the Plastics Industry]]<ref>{{cite news|last=Hevesi|first=Dennis|title=Ban on Plastics in Suffolk Is Overturned|url=https://www.nytimes.com/1990/03/04/nyregion/ban-on-plastics-in-suffolk-is-overturned.html?src=pm|access-date=23 December 2012|newspaper=The New York Times|date=4 March 1990}}</ref> kept the ban from going into effect until at last it was delayed when the Republican and Conservative parties gained the majority of the county legislature.<ref>{{cite news|last=Barbanel|first=Josh|title=Vote Blocks Plastics Ban For Suffolk|url=https://www.nytimes.com/1992/03/04/nyregion/vote-blocks-plastics-ban-for-suffolk.html|access-date=23 December 2012|newspaper=The New York Times|date=4 March 1992}}</ref> In the meantime, Berkeley became the first city to ban all foam food containers.<ref name="berkeley-1988"/> As of 2006, about one hundred localities in the United States, including [[Portland, Oregon]], and [[San Francisco]] had some sort of ban on polystyrene foam in restaurants. For instance, in 2007 [[Oakland, California]], required restaurants to switch to disposable food containers that would biodegrade if added to food compost.<ref>{{cite news|title=Styrofoam food packaging banned in Oakland|url=http://www.sfgate.com/news/article/Styrofoam-food-packaging-banned-in-Oakland-2516522.php|access-date=23 December 2012|newspaper=[[San Francisco Chronicle]]|date=28 June 2006|author=Herron Zamora, Jim }}</ref> In 2013, [[San Jose, California|San Jose]] became reportedly the largest city in the country to ban polystyrene foam food containers.<ref>{{cite web|last=Sanchez|first=Kris|title=San Jose Approves Styrofoam Ban|url=http://www.nbcbayarea.com/news/local/San-Jose-Set-to-Ban-Styrofoam-221354051.html|publisher=[[NBC]]|access-date=30 August 2013|date=27 August 2013}}</ref> Some communities have implemented wide polystyrene bans, such as [[Freeport, Maine]], which did so in 1990.<ref>{{cite web|title=CHAPTER 33 STYROFOAM ORDINANCE|url=http://www.freeportmaine.com/inc/scripts/file.php?file_id=1060|website=Ordinances|publisher=Town of Freeport, Maine|access-date=23 December 2012|archive-date=29 March 2014|archive-url=https://web.archive.org/web/20140329123453/http://freeportmaine.com/inc/scripts/file.php?file_id=1060|url-status=dead}}</ref> In 1988, the first U.S. ban of general polystyrene foam was enacted in Berkeley, California.<ref name="berkeley-1988">{{cite news|title=Berkeley Widens Ban on Foam Food Containers|url=https://www.latimes.com/archives/la-xpm-1988-06-16-mn-6881-story.html|access-date=23 December 2012|newspaper=The Los Angeles Times|date=16 June 1988}}</ref>

On 1 July 2015, [[New York City]] became the largest city in the United States to attempt to prohibit the sale, possession, and distribution of [[disposable product|single-use]] polystyrene foam (the initial decision was overturned on appeal).<ref>{{cite web|author=Tony Dokoupil |url=http://www.msnbc.com/new-york-city-foam-ban-overturned |title=msnbc.com |publisher=msnbc.com |date=2015-09-22 |access-date=2019-01-17}}</ref> In San Francisco, supervisors approved the toughest ban on "Styrofoam" (EPS) in the US which went into effect 1 January 2017. The city's Department of the Environment can make exceptions for certain uses like shipping medicines at prescribed temperatures.<ref>{{cite web| url=http://www.sfchronicle.com/bayarea/article/City-OKs-ban-on-Styrofoam-Jane-Kim-wants-to-play-8332796.php| title=S.F. supervisors OK toughest ban on foam packaging in U.S|access-date=2016-06-30| date=2016-06-30}}</ref>

The U.S. [[Green Restaurant Association]] does not allow polystyrene foam to be used as part of its certification standard.<ref>{{cite web | url=http://www.dinegreen.com/disposables-standard | title=Disposables Standard | publisher=Green Restaurant Association | access-date=14 December 2016}}</ref> Several green leaders, including the [[Ministry of the Environment|Dutch Ministry of the Environment]], advise people to reduce their environmental harm by using reusable coffee cups.<ref>{{cite news|author=Dineen, Shauna|title=The Throwaway Generation: 25 Billion Styrofoam Cups a Year|publisher=E-The Environmental Magazine|date=Nov–Dec 2005|url=http://www.emagazine.com/view/?2933|archive-url=https://web.archive.org/web/20061112142759/http://www.emagazine.com/view/?2933|url-status=dead|archive-date=2006-11-12}}</ref>

In March 2019, Maryland banned polystyrene foam food containers and became the first state in the country to pass a food container foam ban through the state legislature. Maine was the first state to officially get a foam food container ban onto the books.  In May 2019, Maryland Governor Hogan allowed the foam ban (House Bill 109) to become law without a signature making Maryland the second state to have a food container foam ban on the books, but is the first one to take effect on 1 July 2020.<ref>{{Cite web|url=https://news.bloombergenvironment.com/environment-and-energy/maryland-foam-packaging-ban-energy-bills-to-become-law|title=Maryland Foam Packaging Ban, Energy Bills to Become Law|last=Andrew M. Ballard|website=news.bloombergenvironment.com|language=en|access-date=2019-06-20}}</ref><ref>{{Cite web|url=https://environmentamerica.org/news/ame/statement-maryland-becomes-second-state-ban-plastic-foam-containers|title=Statement: Maryland becomes the second state to ban plastic foam containers|website=environmentamerica.org|language=en|access-date=2019-06-20}}</ref><ref>{{Cite web|url=https://www.baltimoresun.com/politics/bs-md-hogan-bill-list-20190524-story.html|title=Maryland's new laws: banning foam food containers, raising tobacco-buying age, reforming UMMS board|last=The Sun|first=Baltimore|website=baltimoresun.com|date=24 May 2019 |language=en-US|access-date=2019-06-20}}</ref><ref>{{Cite web|url=http://www.mdlcv.org/2019-foam-ban|title=2019 Foam Ban|date=2019-05-30|website=Maryland League of Conservation Voters|language=en|access-date=2019-06-20|archive-date=20 June 2019|archive-url=https://web.archive.org/web/20190620002002/http://www.mdlcv.org/2019-foam-ban|url-status=dead}}</ref>

In September 2020, the New Jersey state legislature voted to ban disposable [[foam food container]]s and cups made of polystyrene foam.<ref>{{cite news |last1=Zaveri |first1=Mihir |title=Even Paper Bags Will Be Banned From N.J. Supermarkets |url=https://www.nytimes.com/2020/09/25/nyregion/nj-paper-plastic-bag-ban.html |access-date=22 November 2020 |work=[[The New York Times]] |date=25 September 2020}}</ref>

====Outside the United States====
[[File:火気厳禁 禁煙 (3715967341).jpg|thumb|Expanded polystyrene waste in Japan]]
[[China]] banned expanded polystyrene takeout/takeaway containers and tableware around 1999. However, compliance has been a problem and, in 2013, the Chinese plastics industry was lobbying for the ban's repeal.<ref>{{cite web|author1=Ying Sun, Nina  |author2=Toloken, Steve  |name-list-style=amp |title=China moves to end its 'ban' on PS food packaging|url=http://www.plasticsnews.com/article/20130321/NEWS/130329979/china-moves-to-end-its-ban-on-ps-food-packaging|website=Plastics News|access-date=10 June 2013|date=21 March 2013}}</ref>

[[India]] and [[Taiwan]] also banned polystyrene-foam food-service ware before 2007.<ref>{{cite web|last=Quan|first=Jean|title=letter to Public Works Committee|url=http://clerkwebsvr1.oaklandnet.com/attachments/13659.pdf|archive-url=https://web.archive.org/web/20061023152054/http://clerkwebsvr1.oaklandnet.com/attachments/13659.pdf|url-status=dead|archive-date=23 October 2006|access-date=26 January 2014|date=13 June 2006}}</ref>

The government of [[Zimbabwe]], through its Environmental Management Agency (EMA), banned polystyrene containers (popularly called 'kaylite' in the country), under Statutory Instrument 84 of 2012 (Plastic Packaging and Plastic Bottles) (Amendment) Regulations, 2012 (No 1.)
<ref>{{cite web|title=Government bans kaylite packaging|url=http://www.herald.co.zw/government-bans-kaylite-packaging-%e2%80%a2health-considerations-cited-%e2%80%a2defiant-citizens-face-prosecution/|work=The Herald|date=13 July 2017 |access-date=13 July 2017}}</ref>
<ref>{{cite web|title=Expanded polystyrene (kaylite): What are its impacts?|url=http://www.herald.co.zw/expanded-polystyrene-kaylite-what-are-its-impacts/|work=The Herald|date=12 July 2017 |access-date=13 July 2017}}</ref>

The city of [[Vancouver]], Canada, has announced its Zero Waste 2040 plan in 2018. The city will introduce bylaw amendments to prohibit business license holders from serving prepared food in polystyrene foam cups and take-out containers, beginning 1 June 2019.<ref>''[http://vancouver.ca/green-vancouver/single-use-items.aspx Single-Use Item Reduction Strategy, Zero Waste 2040]'' City of Vancouver, 2018</ref>

In 2019, the European Union voted to ban expanded polystyrene food packaging and cups, with the law officially going into effect in 2021.<ref>{{cite news |last1=Pyzyk |first1=Katie |title=European Parliament approves 2021 single-use plastics ban |url=https://www.wastedive.com/news/european-parliament-approves-2021-single-use-plastics-ban/551552/ |access-date=6 January 2022 |work=Waste Dive |date=March 29, 2019}}</ref><ref>{{cite web |title=Directive (EU) 2019/904 |url=https://eur-lex.europa.eu/legal-content/EN/TXT/HTML/?uri=CELEX:32019L0904&from=EN |website=Official Journal of the European Union |access-date=6 January 2022}}</ref>

[[Fiji]] passed the Environmental Management Bill in December 2020. Imports of polystyrene products were banned in January 2021.<ref>{{Cite web|title=Grace period for polystyrene products|url=https://www.fbcnews.com.fj/news/grace-period-for-polystyrene-products/|access-date=2020-12-12|website=Fiji Broadcasting Corporation}}</ref>

===Recycling===
[[File:Symbol_Resin_Code_6_PS.svg|thumb|90px|The [[resin identification code]] symbol for polystyrene<!--The [[Unicode]] character is U+2678, which will appear here if you have a suitable font installed: <span style="font-size:250%;">♸</span>.-->]]

In general, polystyrene is not accepted in [[curbside collection]] recycling programs and is not separated and recycled where it is accepted. In Germany, polystyrene is collected as a consequence of the packaging law (Verpackungsverordnung) that requires manufacturers to take responsibility for recycling or disposing of any packaging material they sell.

Most polystyrene products are currently not recycled due to the lack of incentive to invest in the compactors and logistical systems required. Due to the low density of polystyrene foam, it is not economical to collect. However, if the waste material goes through an initial compaction process, the material changes density from typically 30&nbsp;kg/m<sup>3</sup> to 330&nbsp;kg/m<sup>3</sup> and becomes a recyclable commodity of high value for producers of recycled plastic pellets. Expanded polystyrene scrap can be easily added to products such as EPS insulation sheets and other EPS materials for construction applications; many manufacturers cannot obtain sufficient scrap because of collection issues. When it is not used to make more EPS, foam scrap can be turned into products such as clothes hangers, park benches, flower pots, toys, rulers, stapler bodies, seedling containers, picture frames, and architectural molding from recycled PS.<ref>https://expandedpoly.co.uk/environment/ Polystyrene recycling. Retrieved 17 October 2019.</ref> As of 2016, around 100 tonnes of EPS are recycled every month in the UK.<ref>[http://ecclestons.com/expanded-polystyrene-recycling.htm EPS recycling.] {{Webarchive|url=https://web.archive.org/web/20201122023542/https://ecclestons.com/index.php?page=expanded-polystyrene-recycling.htm |date=22 November 2020 }} Eccleston & Hart Polystrene. Retrieved 21 July 2016.</ref>

Recycled EPS is also used in many metal casting operations. [[Rastra]] is made from EPS that is combined with cement to be used as an insulating amendment in the making of concrete foundations and walls. American manufacturers have produced insulating concrete forms made with approximately 80% recycled EPS since 1993.

=== Upcycling ===
A March 2022 joint study by scientists Sewon Oh and Erin Stache at Cornell University in Ithaca, New York found a new processing method of upcycling polystyrene to [[benzoic acid]]. The process involved irradiation of polystyrene with iron chloride and acetone under white light and oxygen for 20 hours.<ref name="refup">{{Cite journal |last1=Oh |first1=Sewon |last2=Stache |first2=Erin E. |date=2022-04-06 |title=Chemical Upcycling of Commercial Polystyrene via Catalyst-Controlled Photooxidation |url=https://pubs.acs.org/doi/10.1021/jacs.2c01411 |journal=Journal of the American Chemical Society |language=en |volume=144 |issue=13 |pages=5745–5749 |doi=10.1021/jacs.2c01411| pmid=35319868 |s2cid=247629479 |issn=0002-7863}}</ref> The scientists also demonstrated a similar scalable commercial process of upcycling polystyrene into valuable small-molecules (like benzoic acid) taking just a few hours.<ref name="refup"/>

===Incineration===
If polystyrene is properly incinerated at high temperatures (up to 1000&nbsp;°C<ref name="basfti2810d">BASF Technische Information TI 0/2-810d 81677 Juni 1989, Verwertungs- und Beseitigungsverfaren gebrauchter Schaumstoff-Verpackungen aus Styropor®</ref>) and with plenty of air<ref name="basfti2810d" /> (14 m<sup>3</sup>/kg{{Citation needed|date=July 2013}}), the chemicals generated are water, carbon dioxide, and possibly small amounts of residual halogen-compounds from flame-retardants.<ref name="basfti2810d"/> If only incomplete incineration is done, there will also be leftover carbon soot and a complex mixture of volatile compounds.<ref name=burning>[http://www.newton.dep.anl.gov/askasci/chem00/chem00053.htm Polystyrene Foam Burning Danger] {{Webarchive|url=https://web.archive.org/web/20150226223555/http://newton.dep.anl.gov/askasci/chem00/chem00053.htm |date=26 February 2015 }}. Newton.dep.anl.gov. Retrieved 25 December 2011.  Q and A page with an partially incorrect information.</ref>{{better source needed|reason=Q and A page with an incorrect information included|date=July 2013}} According to the [[American Chemistry Council]], when polystyrene is incinerated in modern facilities, the final volume is 1% of the starting volume; most of the polystyrene is converted into carbon dioxide, water vapor, and heat. Because of the amount of heat released, it is sometimes used as a power source for [[steam]] or [[electricity generation]].<ref name="basfti2810d"/><ref>{{Cite news|title = Ease of Disposal|url = http://www.americanchemistry.com/s_plastics/sec_pfpg.asp?CID=1434&did=5226|access-date = 25 June 2009|url-status = dead|archive-url = https://web.archive.org/web/20090607023527/http://americanchemistry.com/s_plastics/sec_pfpg.asp?CID=1434&DID=5226|archive-date = 7 June 2009}}</ref>

When polystyrene was burned at temperatures of 800–900&nbsp;°C (the typical range of a modern incinerator), the products of combustion consisted of "a complex mixture of [[polycyclic aromatic hydrocarbon]]s (PAHs) from alkyl benzenes to benzoperylene. Over 90 different compounds were identified in combustion effluents from polystyrene."<ref>{{cite journal |doi=10.1016/S0021-9673(01)90737-X |title=Products obtained during combustion of polymers under simulated incinerator conditions |journal=Journal of Chromatography A |volume=315 |pages=201–210 |year=1984 |last1=Hawley-Fedder |first1=R.A. |last2=Parsons |first2=M.L. |last3=Karasek |first3=F.W. }}  Quoted from a campaign site giving no details of the original source and experiment conditions.</ref>{{better source needed|reason=Quoted from a campaign site giving no details of the original source and experiment conditions, experiment may have been flawed or the campaign site may be misquoting|date=July 2013}} The American National Bureau of Standards Center for Fire Research found 57 chemical by-products released during the combustion of expanded polystyrene (EPS) foam.<ref>{{cite journal |last1=Gurman |first1=Joshua L. |title=Polystyrenes: A Review of the Literature on the Products of Thermal Decomposition and Toxicity |journal=Fire and Materials |date=1987 |volume=11 |issue=3 |pages=109–130 |url=https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=101741 |access-date=18 February 2021 |publisher=NIST|doi=10.1002/fam.810110302 }}</ref>

==Safety==

===Health===
The [[American Chemistry Council]], formerly known as the Chemical Manufacturers' Association, writes:
{{blockquote|Based on scientific tests over five decades, government safety agencies have determined that polystyrene is safe for use in foodservice products.  For example, polystyrene meets the stringent standards of the U.S. Food and Drug Administration and the European Commission/European Food Safety Authority for use in packaging to store and serve food.  The Hong Kong Food and Environmental Hygiene Department recently reviewed the safety of serving various foods in polystyrene foodservice products and reached the same conclusion as the U.S. FDA.<ref>{{cite web |title=Q & A on the Safety of Polystyrene Foodservice Products |date=2010–2011 |url=http://plasticfoodservicefacts.com/main/Safety/Californias-Proposition-65/Q-A-on-the-Safety-of-Polystyrene-Foodservice-Products.GMEditor.html |publisher=[[American Chemistry Council]] |access-date=2011-06-14 |url-status=dead |archive-url=https://web.archive.org/web/20110824143749/http://plasticfoodservicefacts.com/main/Safety/Californias-Proposition-65/Q-A-on-the-Safety-of-Polystyrene-Foodservice-Products.GMEditor.html |archive-date=24 August 2011 }}</ref>}}

From 1999 to 2002, a comprehensive review of the potential health risks associated with exposure to styrene was conducted by a 12-member international expert panel selected by the Harvard Center for Risk Assessment. The scientists had expertise in toxicology, epidemiology, medicine, risk analysis, pharmacokinetics, and exposure assessment. The Harvard study reported that styrene is naturally present in trace quantities in foods such as strawberries, beef, and spices, and is naturally produced in the processing of foods such as wine and cheese. The study also reviewed all the published data on the quantity of styrene contributing to the diet due to migration of food packaging and disposable food contact articles, and concluded that risk to the general public from exposure to styrene from foods or food-contact applications (such as polystyrene packaging and foodservice containers) was at levels too low to produce adverse effects.<ref>{{cite journal | author1 = Cohen JT |author2 = Carlson G |author3 = Charnley G | author4 = Coggon D | author5 = Delzell E | author6 = Graham JD | author7 = Greim H | author8 = Krewski D | author9 = Medinsky M | author10 = Monson R | author11 = Paustenbach D | author12 = Petersen B | author13 = Rappaport S | author14 = Rhomberg L | author15 = Ryan PB | author16 = Thompson K | title = A comprehensive evaluation of the potential health risks associated with occupational and environmental exposure to styrene | journal = Journal of Toxicology and Environmental Health Part B: Critical Reviews | volume = 5 | issue = 1–2 | pages = 1–265 | year = 2011 | doi = 10.1080/10937400252972162 |pmid = 12012775 |s2cid = 5547163}}
*{{cite web |title=A Comprehensive Evaluation of the Potential Health Risks Associated with Occupational and Environmental Exposure to Styrene |website=The McLaughlin Centre for Population Health Risk Assessment |url=http://www.mclaughlincentre.ca/publications/styrene.shtml}}</ref>

Polystyrene is commonly used in containers for food and drinks. The styrene monomer (from which polystyrene is made) is a cancer suspect agent.<ref name="12Report2011">{{cite web |author=National Toxicology Program |title=12th Report on Carcinogens |date=10 June 2011 |publisher=[[National Toxicology Program]] |url=https://ntp.niehs.nih.gov/go/roc12 |access-date=2011-06-11 |url-status=dead |archive-url=https://web.archive.org/web/20110612024850/http://ntp.niehs.nih.gov/index.cfm?objectid=72016262-BDB7-CEBA-FA60E922B18C2540 |archive-date=12 June 2011 |author-link=National Toxicology Program }}</ref> Styrene is "generally found in such low levels in consumer products that risks aren't substantial".<ref name="Harris">{{cite news |last1=Harris |first1=Gardiner |title=Government Says 2 Common Materials Pose Risk of Cancer |date=10 June 2011 |url=https://www.nytimes.com/2011/06/11/health/11cancer.html |newspaper=The New York Times |access-date=11 June 2011 }}</ref> Polystyrene which is used for food contact may not contain more than 1% (0.5% for fatty foods) of styrene by weight.<ref>{{cite web|title=Sec. 177.1640 Polystyrene and rubber-modified polystyrene|url=http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/cfrsearch.cfm?fr=177.1640|website=Code of Federal Regulations, Title 21—Food and Drugs, Subchapter B—Food for Human Consumption|publisher=U.S. Food and Drug Administration|access-date=4 April 2014}}</ref> Styrene oligomers in polystyrene containers used for food packaging have been found to migrate into the food.<ref>{{cite journal |doi=10.3358/shokueishi.41.200 |title=使い捨て弁当容器から溶出するスチレンダイマー及びトリマーの定量 |trans-title=Quantitative Analysis of Styrene Dimer and Trimers Migrated from Disposable Lunch Boxes |language=ja |journal=Journal of the Food Hygienic Society of Japan |volume=41 |issue=3 |pages=200–205 |year=2000 |last1=Sakamoto |first1=Hiromi |last2=Matsuzaka |first2=Ayako |last3=Itoh |first3=Rimiko |last4=Tohyama |first4=Yuko |doi-access=free }}</ref> Another Japanese study conducted on wild-type and [[Aryl hydrocarbon receptor|AhR]]-null mice found that the styrene trimer, which the authors detected in cooked polystyrene container-packed instant foods, may increase thyroid hormone levels.<ref>{{cite journal | vauthors = Yanagiba Y, Ito Y, Yamanoshita O, Zhang SY, Watanabe G, Taya K, Li CM, Inotsume Y, Kamijima M, Gonzalez FJ, Nakajima T | title = Styrene trimer may increase thyroid hormone levels via down-regulation of the aryl hydrocarbon receptor (AhR) target gene UDP-glucuronosyltransferase | journal = Environmental Health Perspectives | volume = 116 | issue = 6 | pages = 740–5 | date = June 2008 | pmid = 18560529 | pmc = 2430229 | doi = 10.1289/ehp.10724 }}</ref>

Whether polystyrene can be microwaved with food is controversial. Some containers may be safely used in a microwave, but only if labeled as such.<ref>{{cite web |url=https://www.health.harvard.edu/staying-healthy/microwaving-food-in-plastic-dangerous-or-not |title=Microwaving food in plastic: Dangerous or not? |date=20 September 2017 |publisher=Harvard Health }}</ref> Some sources suggest that foods containing carotene (vitamin A) or cooking oils must be avoided.<ref>{{cite web|title=Polystyrene & Health Homepage|url=http://www.ejnet.org/plastics/polystyrene/health.html|publisher=Energy Justice Network|access-date=9 December 2013}}</ref>

Because of the pervasive use of polystyrene, these serious health related issues remain topical.<ref>{{cite web |last=Entine |first=Jon |title=Styrene in the Crosshairs: Competing Standards Confuse Public, Regulators |url=http://www.aei.org/publication/styrene-in-the-crosshairs-competeing-standards-confuse-public-regulators/ |publisher=[[American Enterprise Institute]] |date=2011-09-14 }}{{Dead link|date=February 2022 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>{{unreliable source?|date=October 2018}}

===Fire hazards===
Like other [[organic compound]]s, polystyrene is flammable. Polystyrene is classified according to [[DIN4102 A1|DIN4102]] as a "B3" product, meaning highly flammable or "Easily Ignited". As a consequence, although it is an efficient insulator at low temperatures, its use is prohibited in any exposed installations in [[building construction]] if the material is not [[flame retardant|flame-retardant]].{{citation needed|date=June 2011}} It must be concealed behind [[drywall]], sheet metal, or concrete.<ref>{{cite book |oclc=166313665 |url=https://ir.canterbury.ac.nz/bitstream/handle/10092/14390/RNelligan06.pdf |type=MS Thesis |title=Guidelines for the use of expanded foam polystyrene panel systems in industrial buildings to minimize the risk of fire |first=R.J. |last=Nelligan |year=2006 }}</ref> Foamed polystyrene plastic materials have been accidentally ignited and caused huge fires and losses of life, for example at the [[Düsseldorf Airport fire|Düsseldorf International Airport]] and in the [[1996 Channel Tunnel fire|Channel Tunnel]] (where polystyrene was inside a railway carriage that caught fire).<ref>{{cite news|title=Foul Play Considered in Channel Tunnel Fire Inquiry |date=28 November 1996 |url=https://www.irishtimes.com/news/foul-play-considered-in-chunnel-fire-inquiry-1.110786 |newspaper=The Irish Times |access-date=14 January 2018}}</ref>

== See also ==
* [[Styrofoam]]
* [[Foam food container]]
* [[Bioplastic]]
* [[Geofoam]]
* [[Structural insulated panel]]
* [[Polystyrene sulfonate]]
* [[Shrinky Dinks]]
* [[Insulating concrete form]]
* [[Foamcore]]

== References ==
{{reflist}}

== Sources ==
{{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
}}

==Bibliography==
* {{cite book | editor1-last = Haynes |editor1-first=William M. | year = 2011 | title = CRC Handbook of Chemistry and Physics | edition = 92nd | publisher = [[CRC Press]] | isbn = 978-1439855119 | title-link = CRC Handbook of Chemistry and Physics }}

== External links ==
{{commons|Polystyrene}}
*[http://www.pslc.ws/mactest/styrene.htm Polystyrene Composition] – The University of Southern Mississippi
*[https://web.archive.org/web/20160306155212/http://plasticsindustry.org/aboutplastics/content.cfm?itemnumber=825&navitemnumber=1124 SPI resin identification code] – Society of the Plastics Industry
*[http://www.cawrecycles.org/polystyrene-local-ordinances Polystyrene: Local Ordinances] – Californians Against Waste
*[http://plastics.americanchemistry.com/Education-Resources/Publications/Brochure-Take-a-Closer-Look-at-Todays-Polystyrene-PackagingSafe-Affordable-and-Environmentally-R.pdf Take a Closer Look at Today's Polystyrene Packaging] (brochure by the industry group [[American Chemistry Council]], arguing that the material is "safe, affordable and environmentally responsible")
* {{cite journal | vauthors = Lettieri TR, Hartman AW, Hembree GG, Marx E | title = Certification of SRM1960: Nominal 10 μm Diameter Polystyrene Spheres ("Space Beads") | journal = Journal of Research of the National Institute of Standards and Technology | volume = 96 | issue = 6 | pages = 669–691 | year = 1991 | pmid = 28184141 | pmc = 4915770 | doi = 10.6028/jres.096.044 }}

{{HealthIssuesOfPlastics}}
{{Plastics}}

{{Authority control}}

[[Category:Insulators]]
[[Category:Building insulation materials]]
[[Category:Organic polymers]]
[[Category:Packaging materials]]
[[Category:Food packaging]]
[[Category:Thermoplastics]]
[[Category:Commodity chemicals]]
[[Category:Vinyl polymers]]