Expanded polyethylene (EPE foam) refers to foams made frompolyethylene. Typically it is made from expanded pellets ('EPE bead') made with use of ablowing agent, followed by expansion into a mold in a steam chest - the process is similar to that used to makeexpanded polystyrene foam.
EPE foams are low density, semi-rigid,closed cell foam that are generally somewhere instiffness/compliance betweenExpanded polystyrene andPolyurethane. 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 fromLow-density polyethylene (LDPE) toHigh-density polyethylene (HDPE).[2]
Expanded polyethylene copolymers (EPC) are also known - such as 50:50 (weight) materials withpolystyrene. 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]
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 ablowing agent (before 1992 CFCs may have been used). Depending on the specific process uses the beads may becross-linked either by electron beam irradiation (seeElectron beam processing), or by the addition of a chemical agent such asdicumyl peroxide.[3]
An alternate route (JSP Process) to the beads usescarbon 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 bysteam 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]
Polyethylene bead foams (including) EPE can be used to replace bothpolystyrene foam, and both rigid and flexiblepolyurethane. Uses include cushioning applications, and impact absorption applications including packaging.[4]
Consumption ofpolyethylene 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]
Gore-Tex uses EPE for a waterproof, windproof and breathable fabric forwinter clothing.
