EPS is produced from styrene monomers; low levels of styrene occur naturally in many plants, fruits, vegetables, nuts and meat. EPS is a derivative of ethylene and benzene and is made using a polymerisation process which produces translucent spherical beads of polystyrene, approximately the size of sugar granules. During this process a low boiling point hydrocarbon, usually pentane gas is added to the material to assist expansion during the subsequent processes.
Three stages of EPS production is as follows:
Pre-expansion; upon contact with steam the pre-foaming agent found within the polystyrene beads (usually a hydrocarbon such as pentane) starts to boil and the beads are expanded to between 40 to 50 times their original volumes.
Conditioning; after expansion the beads undergo a maturing period in order to reach an equilibrium temperature and pressure.
Moulding; the beads are placed within a mould and reheated again with steam. The pre-foamed beads expand further, completely fill the mould cavity and fuse together. The beads are moulded to form blocks or customised products. When moulded, 98% of the EPS’s volume is air. There are two moulding processes for EPS:
Block moulding produces large blocks of EPS that can be cut into shapes or sheets for use in both packaging and building/construction applications.
Shape moulding produces parts that have custom designed specifications. Shape moulded EPS is used extensively in electronic product packaging.