expanded polyethylene

EPE foams are low density, semi-rigid, closed cell foam that are generally somewhere in stiffness/compliance between Expanded polystyrene and Polyurethane. Production of EPE foams is similar to that of expanded polystyrene, but starting with PE beads.{{sfn|Rosato|Rosato|Rosato|2004|p=359}} Typical densities are {{convert|29|to|120|kg/m3|abbr=on}} with the lower figure being common.{{sfn|Rosato|Rosato|Rosato|2004|p=359}} Densities as low as {{convert|14|kg/m3|abbr=on}} can be produced.{{sfn|Spalding|Chatterjee|2017|p=639}}

Base polymer for EPE foams range from Low-density polyethylene (LDPE) to High-density polyethylene (HDPE).{{sfn|Spalding|Chatterjee|2017|p=639}}

Expanded polyethylene copolymers (EPC) are also known - such as 50:50 (weight) materials with polystyrene. Though other properties are intermediate between the two bases, toughness for the copolymer exceeds either, with good tensile and puncture resistance. It is particularly applicable for re-usable products.{{sfn|Rosato|Rosato|Rosato|2004|p=359}}

EPE foams were first manufactured in the 1970s.{{sfn|Spalding|Chatterjee|2017|p=639}}

Production of the PE beads is usually by extrusion, followed by chopping, producing a 'pellet'.{{sfn|Spalding|Chatterjee|2017|loc=Fig. 21.2 p.643; pp.650-652}} Autoclave expansion is the most common route the bead foam.{{sfn|Spalding|Chatterjee|2017|p=640}} Butane or pentane is often used as a blowing agent (before 1992 CFCs may have been used). Depending on the specific process uses the beads may be cross-linked either by electron beam irradiation (see Electron beam processing), or by the addition of a chemical agent such as dicumyl peroxide.{{sfn|Spalding|Chatterjee|2017|loc=Fig. 21.2 p.643; pp.650-652}}

An alternate route (JSP Process) to the beads uses carbon dioxide as a blowing agent which is impregnated into the pellets in an autoclave at a temperature close to the plastic's crystalline melting point. The pellets are foamed by "flashing" into the (lower pressure) atmosphere to expand.{{sfn|Spalding|Chatterjee|2017|pp=651-2}}

Finally molding is done by steam chest compression molding; usually the low pressure variant of the process is used, though the high pressure variant may be used for HDPE based EPE foams.{{sfn|Spalding|Chatterjee|2017|pp=645-6}}

Polyethylene bead foams (including) EPE can be used to replace both polystyrene foam, and both rigid and flexible polyurethane. Uses include cushioning applications, and impact absorption applications including packaging.{{sfn|Spalding|Chatterjee|2017|p=640}}

Consumption of polyethylene for PE foam was estimated at 114x10⁶ kg in 2001. The majority was used for non-crosslinked foams, but crosslinked PE foams represented a significant (~ one third) fraction of demand. Use in protective packaging represented the largest use sector for such foams.{{sfn|Mills|2003|p=34}}

Gore-Tex uses EPE for a waterproof, windproof and breathable fabric for winter clothing.

• Waterproof fabric

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• {{citation|title = (Report 167) Polyolefin Foams| volume =14| number = 11| publisher = iSmithers Rapra Publishing | year = 2003 | first = N.J.| last = Mills| work = Rapra Review Reports |issn = 0889-3144 }}
• {{citation| title = Plastic Product Material and Process Selection Handbook | first = Dominick V. | last = Rosato | first2= Donald V. | last2= Rosato | first3= Matthew V.| last3= Rosato | publisher = Elsevier | year = 2004 }}
• {{citation| title =Handbook of Industrial Polyethylene and Technology: Definitive Guide to Manufacturing, Properties, Processing, Applications and Markets Set | editor-first = Mark A. | editor-last = Spalding | editor-first2= Ananda |editor-last2 = Chatterjee | publisher = Scrivener Publishing (Wiley) | year = 2017 }}

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Category:Packaging materials

Category:Polyolefins

Category:Foams

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