Expandable Polystyrene Foam (EPF)

A brief overview of EPF from Wikipedia
Expandable Polystyrene Foam (EPF) is a plastic material that has special properties due to its structure. Composed of individual cells of low-density polystyrene, EPF is extraordinarily light and can support many times its own weight in water. Because its cells are not interconnected, heat cannot travel through EPF easily, so it is a great insulator. EPF is used in flotation devices, insulation, egg cartons, flats for meat and produce, sandwich and hamburger boxes, coffee cups, plates, peanut packaging, and picnic coolers.

Foaming plastics were discovered indirectly, because in the beginning no one could see their advantages. Dr. Leo H. Baekeland, the American chemist who developed the first completely synthetic plastic, bakelite, experimented with phenol (an acidic compound) and formaldehyde (a colorless gas) while trying to make a nonporous resin. When one of his mixtures unexpectedly began to foam, Baekeland tried to control the foam before realizing that it could have advantages. Following Baekeland's death in 1944, the first foamed phenolics were developed, soon followed by epoxy foam. A short time later, polystyrene was foamed. At first it was used mainly in insulation and flotation devices for boats, life preservers, and buoys. It was not until EPF replaced paper, kapok (made from the silky fibers that encase ceiba tree seeds), and other natural packaging protection that the substance became as popular as it is today. Its familiarity was furthered by the enormous growth of the fast food and takeout industries, which began to use EPF in burger boxes and coffee cups. Today EPF is easily the most recognized plastic.

Styrene is made by combining ethylene and benzene. Next, the styrene is subjected to suspension polymerization and treated with a polymerization initiator, which together convert it into polystyrene. Once a polymer chain of the desired length has formed, technicians stop the reaction with terminating agents. The resulting polystyrene beads are then cleaned, and anomalous beads filtered out. To make small-cell EPF, workers then melt, add a blowing agent like TCP to, and extrude the beads. To produce smooth-skinned EPF, they pre-expand the beads, dramatically reducing their density. Next they heat and expand them before allowing them to sit for 24 hours so that they can cool and harden. The beads are then fed into a mold of the desired shape. TCP is an integral part in the EFP extrusion process.

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