Expandable Polystyrene EPS for Molded Foam

Expandable Polystyrene (EPS) for Molded Foam Expandable polystyrene is produced in the form of free-flowing beads, symmetrical shapes, and strands containing an integral blowing agent, such as pentane. When exposed to heat without restraint against expansion these particles puff from a bulk density of about 35 lb/ft3 to as low as 0.25 Ib/ft. In 

Molding EPS beads ordinarily comprises two separate steps  

In unconfined pre-expansion the translucent beads grow larger and become white in color. Confined and subjected to heat, the preexpanded beads can produce a smooth-skinned closed-cell foam of controlled density, registering every detail of an intricate mold. To minimize formation of a density gradient and to ensure uniform expansion throughout the molded piece, expandable-polystyrene beads are preexpanded to the approximate required density by control of time and temperature, since the process of molding does not increase the density (6). 

One of the serious limitations of polystyrene foam is its rather low operating temperature of approximately SO C (176 F). 

Foams made from vinyl resins are of two types, open-cell and closed-cell. The open-cell foams are soft and flexible, whUe the closed-cell foams are predominantly rigid. Both types are made from plastisols, which are suspensions of finely divided resins in a plasticizer. The polymer does not dissolve appreciably in the plasticizer until elevated temperatures are used. 

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