Expandable polystyrene particle foam

The expandable polystyrene particles, based on suspension polymerization, are converted into foam in three steps pre-foaming, temporary storage and final... 

Expandable polystyrene with improved properties has been obtained by copolymerization, postreaction, additives, or by physical means. Improvements have been achieved particularly in resistance to premature fusion of particles during expansion, in reducing cell size, in self-extin-guishability, in attractive coloration, in resistance of foams to attack by gasoline and in dimensional stability of foams at elevated temperatures. 

Expanded polystyrene loose-fill is used in many markets today. The most common are dunnage (used to fill up space in a shipping box), cushioning (where the resilient qualities of the polystyrene foam are used), and texturizer, where it is ground into smaller particles and used in making textured ceilings in commercial and residential buildings. 

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... 

The production of molded articles made of particle foams such as expanded polypropylene (EPP) or expanded polystyrene (EPS, also known under the brand name Styropore) is carried out by welding individual foam particles together into a formed part or molding. In the conventional steam chest molding process the source of energy used is steam, which heats and welds the foam particles in the mold into a formed part (Fig. 15). 

Another cavity wall and foam technique is done by use of prefoamed EPS particles. The cavity between the two faces (walls) can be completely filled with the prefoamed expanded polystyrene (EPS) particles and then foamed by applying steam. 

Isotactic Polystyrene. The familiar steam molding of pre-expanded particles has so far not been applied successfully to isotactic polystyrene. However, the polymer has been foamed, according to three disclosed methods. For example, finely divided acetone-insoluble polymer, with a melting point in excess of 200°C., is blended with a liquid selected from methylene chloride, aromatic hydrocarbons, or halogenated aromatic hydrocarbons. This blend is then heated (84). A mixture of molten polymer and methyl chloride, propane, or butane is suddenly depressurized (8). Foam may also be generated in a continuous manner directly from a butyllithium-initiated polymerization conducted in the presence of a 4/1 blend of benzene and petroleum ether (15). 

Foams (cellular structures) made by expanding a material by growing bubbles in it [11]. A foam has at least two components. At a macroscopic scale, there are the solid and liquid phases. The solid phase can be a polymer, ceramic or metal. The fluid phase is a gas in most synthetic foams, and a liquid in most natural foams. At a microscopic scale, the solid phase may itself consist of several components. For example, the solid phase of an amorphous polystyrene foam has only one component. On the other hand, the solid phase of a polyethylene foam or a flexible polyurethane foam typically has two components. These components are the crystalline and amorphous phases in polyethylene foams, and the hard and soft phases formed by the phase separation of the hard and soft segment blocks in flexible polyurethane foams. The solid phase of a polyurethane foam may, in fact, have even more than two components, since additional reinforcing components such as styrene-acrylonitrile copolymer or polyurea particles are often incorporated [12,13]. The solid is always a continuous phase in a foam. Foams can generally be classified as follows, based on whether the fluid phase is co-continuous with the solid phase ... 

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