Editing Polystyrene (section)

==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), commonly called "styrofoam", 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 |archive-date=12 November 2020 |access-date=8 April 2018 |archive-url=https://web.archive.org/web/20201112022306/https://www.thermalps.com.au/imagesDB/wysiwyg/TDS_Expanded_Polystyrene.pdf |url-status=dead }}</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 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]], a [[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|url-access=subscription}}</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), [[polyethylene terephthalate]] (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.