Expanded polyethylene (aka EPE foam) refers to foams made from

polyethylene Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including bo ...

. Typically it is made from expanded pellets ('EPE bead') made with use of a

blowing agent A blowing agent is a substance which is capable of producing a cellular structure via a foaming process in a variety of materials that undergo hardening or phase transition, such as polymers, plastics, and metals. They are typically applied when ...

, followed by expansion into a mold in a steam chest - the process is similar to that used to make

expanded polystyrene foam Polystyrene (PS) is a synthetic polymer made from monomers of the Aromatic hydrocarbon, aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin pe ...

Properties

EPE foams are low density, semi-rigid, closed cell foam that are generally somewhere in

stiffness Stiffness is the extent to which an object resists deformation in response to an applied force. The complementary concept is flexibility or pliability: the more flexible an object is, the less stiff it is. Calculations The stiffness, k, of a b ...

/compliance between

Expanded polystyrene Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is a ...

and

Polyurethane Polyurethane (; often abbreviated PUR and PU) refers to a class of polymers composed of organic chemistry, organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethan ...

. 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 Low-density polyethylene (LDPE) is a thermoplastic made from the monomer ethylene. It was the first grade of polyethylene, produced in 1933 by Imperial Chemical Industries (ICI) using a high pressure process via free radical polymerization. Its ...

(LDPE) to

High-density polyethylene High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a thermoplastic polymer produced from the monomer ethylene. It is sometimes called "alkathene" or "polythene" when used for HDPE pipes. With a high strength-to-density ratio, ...

(HDPE).

Co-polymers

Expanded polyethylene copolymers (EPC) are also known - such as 50:50 (weight) materials with

polystyrene Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is a ...

. 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 An autoclave is a machine used to carry out industrial and scientific processes requiring elevated temperature and pressure in relation to ambient pressure and/or temperature. Autoclaves are used before surgical procedures to perform sterilizat ...

expansion is the most common route the bead foam. Butane or pentane is often used as a

(before 1992 CFCs may have been used). Depending on the specific process uses the beads may be

cross-linked In chemistry and biology a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...

either by electron beam irradiation (see

Electron beam processing Electron-beam processing or electron irradiation (EBI) is a process that involves using electrons, usually of high energy, to treat an object for a variety of purposes. This may take place under elevated temperatures and nitrogen atmosphere. Poss ...

), or by the addition of a chemical agent such as

Dicumyl peroxide Dicumyl peroxide is an organic compound with the formula (Me = CH3). Classified as a dialky peroxide, it is produced on a large scale industrially for use as an initiator for the production of low density polyethylene. Production It is synth ...

. An alternate route (JSP Process) to the beads uses

carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...

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. 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 (including) EPE can be used to replace both

polystyrene foam Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is a ...

, and both rigid and flexible

polyurethane Polyurethane (; often abbreviated PUR and PU) refers to a class of polymers composed of organic chemistry, organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethan ...

. Uses include cushioning applications, and impact absorption applications including packaging. Consumption of

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.

References

Sources

* * * Packaging materials Polyolefins Foams {{material-stub