Editing Polystyrene (section)

====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>