2. Expansion (cellular foam)

The expansion (or foaming) process was first used with polymers in the 1930s for the manufacture of injected PS polystyrene parts. .

Then, in the 1950s, Dow patented a continuous extrusion process (using an extrusion screw) for foamed plate in PS .

Since then, this type of process has been widely developed and applied to all thermoplastics (see [AM 3 550] Foamed polymers. Presentation and properties). In general, amorphous polymers (such as PS) are easier to foam than semi-crystalline polymers. This is because the process has...