Expanded polyethylene


Expanded polyethylene refers to foams made from polyethylene. Typically it is made from expanded pellets 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.

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. Typical densities are with the lower figure being common. Densities as low as can be produced.
Base polymer for EPE foams range from Low-density polyethylene to High-density polyethylene.

Co-polymers

Expanded polyethylene copolymers are also known - such as 50:50 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.

Production

EPE foams were first manufactured in the 1970s.
Production of the PE beads is usually by extrusion, followed by chopping, producing a 'pellet'. Autoclave expansion is the most common route the bead foam. Butane or pentane is often used as a blowing agent. Depending on the specific process uses the beads may be cross-linked either by electron beam irradiation, or by the addition of a chemical agent such as Dicumyl peroxide.
An alternate route 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 atmosphere to expand.
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.

Uses

Polyethylene bead foams 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.
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 fraction of demand. Use in protective packaging represented the largest use sector for such foams.