Expandable polystyrene steam expansion

Steam-Chest Expansion. In steam-chest expansion the resin beads in which gas is already present are poured into molds into which steam is injected. The steam increases the temperature close to the melting point and expands within the stmcture to create beads with food cushioning and insulating properties. Expanded polystyrene is widely used in this process for thermal insulation of frozen food packaging. 

One alternative approach to the two-stage steam moulding process is that in which impregnated beads are fed directly to an injection moulding machine or extruder so that expansion and consolidation occur simultaneously. This approach has been used to produce expanded polystyrene sheet and paper by a tubular process reminiscent of that used with polyethylene. Bubble nucleating... 

The Polymer. Amorphous Polystyrene. All of the expandable polystyrene referred to above is the amorphous type that is obtained by free radical initiation. This polymer is completely noncrystalline, and in the absence of impurities such as monomer and blowing agent it exhibits a glass-transition temperature of about 100°C. Both the rate of expansion and the extent of expansion are enhanced by reducing molecular weight, but the foam becomes less resistant to collapse on further steaming (63). Other polymeric modifications are discussed below. 

On the other hand, thermoplastic-based hollow microspheres can be prepared by heating thermoplastics containing low-boiling-point solvents. One example is polystyrene hollow microspheres. In the first stage, expandable polystyrene powder is prepared, e.g., polystyrene powder containing propane, butane or pentane is prepared by emulsion polymerization. The powder is then exposed to steam for expansion to form hollow microspheres. 

Close temperature control is required to obtain reproducible results, because the expansion of the polystyrene is a function of temperature. The polystyrene microspheres may be pre-expanded by steam or radiant heat and then added to the mold, heated in advance to a convenient temperature, such as 60°C. The mixed epoxy resin is then poured over the pre-expanded beads and allowed to cure. In this case, a limited amount of further expansion will occur as a result of exotherm or cure temperature to permit complete mold fill (10). A typical formulation is shown below ... 

Expanded polystyrene foam (EPS) has different applications, because of its physical form (beads) and properties (higher permeability to water and less effective adhesion to facing materials than polyurethane). The expansion gases, pentane and steam, escape fairly rapidly from the foam, so the thermal conductivity of the foam filled with air is about twice that of the best polyurethane foam—a 50 mm thick slab of foam has a U-value of 0.5-0.6 Wm K . EPS mouldings can be used as shutters (formwork) for pouring concrete in a composite wall. The two EPS layers are connected at intervals to fix the thickness of the concrete. Extruded polystyrene foam (XPS) is used in plank form for insulation imder the concrete floor of houses, and in roofing panels. 

Expansion/molding/extrusion PS Expanded polystyrene products, hot beverage cups, floats, insulating tiles. Meat trays, snack boxes for fast food Steam expansion/molding Steam expansion/extrusion... 

Expanded polystyrene (EPS) foam widely used in the food service industry is made by steam expansion of PS beads containing pentane or other blowing agents. The foam is... 

Expandable polystyrene is the usual name for the beads used to make molded polystyrene foam parts. Parts made with these beads are usually made in a two-step process. The first step consists of pre-expansion of the beads by heat. After this step, the beads are stored for 6-12 h to allow them to reach equilibrium. The beads are then conveyed to the mold, where they expand to the final dimensions. Steam is the preferred mode of heating, either by introducing live steam through perforations in the mold or by the means of steam probes, which are withdrawn as the beads are expanding. Expandable polystyrene foam can be distinguished from expanded polystyrene foam by the round bead outlines on the surface of the part. The expanded foam has a smooth surface. 

Expanded polystyrene (EPS) headboard insulation is produced with expandable polystyrene beads. These beads are produced by impregnating with 5-8% pentane and sometimes with flame retardants such as hexabromocyclododecane or pentabromomonochlorohexane. The beads are preexpanded by fabricators with steam or vacuum and then allowed to age. The preexpanded beads are fed to the steam-heated block molds where further expansion and fusion of beads take place. The molded blocks are then sliced into various sizes needed for specific applications after curing. Block densities range from 13 to 48 kg/m (0.8-3 Ib/ft ), with 24 kg/m (1.5 Ib/ft ) most common for cushion packaging and 16 kg/m (1.0 Ib/ft ) for insulation applications. 

Expandable grades of polystyrene are manufactured by steeping volatile polystyrene granules in a low boiling hydrocarbon solvent until the polymer becomes saturated with the solvent. When the granules are put in a mould and are treated with steam, they imdergo an expansion to many times their original volume and the expanded... 

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