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Like any other type of plastic, expandable polystyrene ultimately derived from petroleum. The diagram below shows the components and the different stages from the distillation of petroleum to the collection of expandable polystyrene.

This raw material is in the form of small beads of polystyrene containing an agent inside expandente evenly distributed allowing its expansion during the transformation process. The agent expandente is a hydrocarbon of low boiling point (usually pentane). In the manufacture of polystyrene foam is not used or never used gas expandentes family of CFCs, HCFCs, HFCs or agents responsible for the degradation of the Ozone Layer.

The expandable polystyrene beads are spherical in shape with a diameter ranging 0.2-3.0 mm in the interval and treated with various additives to influence the material properties expanded.
Manufacturing Process

Polymerization .- The polymerization consists in obtaining long macromolecular chains based on the basic unit or monomer. In the case of polystyrene is styrene monomer. The polymerization is carried out through suspension in water of styrene in a reactor equipped with agitator mechanisms that produce the division of styrene droplets suspended in the water. The reactors are covered by a jacket of cooling / heating to regulate the temperature inside the reactor.

During this process additives are also used for the purpose of:

-Stabilization of the suspension and regulation of the diameter of the pearls.
-Catalysts to initiate the polymerization reaction.
-Addition of flame retardant agents (for raw materials that require this feature.)
-The polymerization reaction is exothermic and takes place following a defined temperature program and when you reach a certain conversion rate, which varies according to different processes, the expansion agent is introduced under pressure.
Upon completing this stage you get a mixture of polystyrene beads and water that is sent to a homogenization tank.

Drying and Finishing .- At this stage the mixture is dried by air and by centrifugation and transferred to a certain height for subsequent screening at different particle sizes because there is always some dispersion in the diameter of the pearls obtained. Different additive sieve, usually with stearates, to improve further processing.

After an intermediate storage in silos produced the raw material is packaged primarily in coated cardboard containers inside a plastic film can also be used although metal containers. The product to be stored at moderate temperatures (below 20 º C) to prevent volatilization of the blowing agent.

Parameters characterizing

Particle size: the finest products, with diameters ranging from 0.2 to 1.0 mm are mainly in the manufacture of packaging. The thicker products (1.0 to 3.0 mm.) Are used for the production of thermal insulation boards.

Potential for expansion: the nature of the polymer content in expandente agent and the presence of certain additives to obtain products with a more accurate final density.

Cadence molding: additives and surface treatments allow the production of products whose cycle molding / demolding can be shortened.

Flame retardant agents: when the application requires (eg construction), this raw material can be treated with flame retardants that significantly improve its reaction to fire.

Low-pentane: the usual content of pentane in expandable polystyrene is around 6-7%. In recent years there have been raw materials with low-pentane (4%) which is well suited for the manufacture of parts and blocks of medium-high density and that reductions are achieved at the time of stabilization and cycles molding / demolding.

The polymer industry is continually researching new developments and thus have occurred in recent years insulation products with better performance or better behavior with respect to water absorption.