How Expanded Polystyrene Are Processed

How Expanded Polystyrene Are Processed

Expanded polystyrene are processed (EPS foam) from styrene monomer (single chain), a liquid hydrocarbon. Before it was discovered accidentally from a storax balsam, in a tree known as Oriental Sweet Gum, nowadays EPS are made from styrene monomer that are fully synthetic for efficient polymerization process.

How Expanded Polystyrene Are Processed?

Made from a polymerization process (combining a number of monomer into a long chain via chemical process) that produces spherical beads, and used to expand and molded into desired shape, for various applications and uses.

how expanded polystyrene are processed

A Three Stage Process In Producing EPS

Before making the polystyrene itself, the monomer styrene is created from a two-fold reaction of ethylene and benzene, with aluminum chloride as catalyst. The process produces uniform styrene droplets and are transferered for the next polymerization stage.

A polymerization activator is added for the monomers to start attached to each other, forming long chain polystyrene molecules.

The whole process is stopped once a certain chain length is achieved (too long would lengthen the molding process while too short chains will make them brittle and unusable). the beads are then cooled, washed and dried thoroughly. Depending on the end results needed, an extra step of letting uniform sized beads may be done through a filter.


Polystrene beads starts to boil in a vessel, with the help of foaming agent, usually up to 50x of their original dimension. Since expanded beads becomes lighter, it ‘flies’ out of the vessel cavity and is collected.


These beads are then ‘aged’ (usually a day) to allow air into the beads, cooling them to reach a certain pressure.


These beads are placed in a mold, and heated with a steam at low pressure. This causes the beads to expand even further and fill up the mold, fusing each bead together.

Once done, the molded shape is then cut and processed into desired shape and size (for example, either into a block shapes for packaging and construction applications, through a coating process, or a customized molded shape to cover products).

Source: 1,2,3

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