What Is Expanded Polystyrene (EPS)?

Everyone knows about large, lightweight materials (only 15kg per 1000 liter volume) that consist of foam beads of roughly the same size that stick together. How is such a thing made?

In the reactor, water and liquid styrene are broken up into uniform droplets by a stirrer. Surfactant, a rinse agent, is added to the water to keep the droplets stable. Styrene is premixed with catalyst and blowing agent. In the past, fluorinated or chlorinated blowing agents were often used, but today they are almost exclusively pentane. Mainly isopentane, n-pentane or a mixture of the two are used.

When styrene polymerizes, heat is released. This heat is easily absorbed by water. Otherwise the droplets will stick together. After the styrene was fully polymerized and cooled, the beads were washed, dried and sorted by size. They are then heated with steam and pre-foamed. This will soften the polystyrene and the pentane will evaporate slightly, but not completely.

Shelf life is limited because pentane keeps escaping even at room temperature. Therefore, the material must be completed quickly. These pre-expanded beads are placed in large heated molds for end users, such as insulation manufacturers. Pre-expanded beads are softer and the surface becomes sticky. The pentane evaporates completely and expands the material to its final size. Remove the foam block from the mold, allow it to cool, and use a hot wire to cut into sheets. These sheets are used in house walls for insulation purposes.