Expanded polyethylene

Expanded polyethylene (aka EPE foam) refers to foams made from polyethylene. Typically it is made from expanded pellets ('EPE bead') made with use of a blowing agent, followed by expansion into a mold in a steam chest - the process is similar to that used to make expanded polystyrene foam.

Polyethylene foam

Properties

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.[1] Typical densities are 29 to 120 kg/m3 (49 to 202 lb/cu yd) with the lower figure being common.[1] Densities as low as 14 kg/m3 (24 lb/cu yd) can be produced.[2]

Base polymer for EPE foams range from Low-density polyethylene (LDPE) to High-density polyethylene (HDPE).[2]

Co-polymers

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.[1]

Production

EPE foams were first manufactured in the 1970s.[2]

Production of the PE beads is usually by extrusion, followed by chopping, producing a 'pellet'.[3] Autoclave expansion is the most common route the bead foam.[4] 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.[3]

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.[5]

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.[6]

Uses

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.[4]

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.[7]

References
  1. Rosato, Rosato & Rosato 2004, p. 359.
  2. Spalding & Chatterjee 2017, p. 639.
  3. Spalding & Chatterjee 2017, Fig. 21.2 p.643; pp.650-652.
  4. Spalding & Chatterjee 2017, p. 640.
  5. Spalding & Chatterjee 2017, pp. 651–2.
  6. Spalding & Chatterjee 2017, pp. 645–6.
  7. Mills 2003, p. 34.

Sources
  • Mills, N.J. (2003), "(Report 167) Polyolefin Foams", Rapra Review Reports, iSmithers Rapra Publishing, vol. 14, no. 11, ISSN 0889-3144
  • Rosato, Dominick V.; Rosato, Donald V.; Rosato, Matthew V. (2004), Plastic Product Material and Process Selection Handbook, Elsevier
  • Spalding, Mark A.; Chatterjee, Ananda, eds. (2017), Handbook of Industrial Polyethylene and Technology: Definitive Guide to Manufacturing, Properties, Processing, Applications and Markets Set, Scrivener Publishing (Wiley)


This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.