Extruded Polystyrene Foam

FOAAffiD PLASTICS] (Vol 11) Extruded polystyrene foam sheet... 

Property ASTM Test Phenolics Foamedin Syntactic Place Castable Polyvinyl Chloride Rigid Closed Cell Phenylene Oxide Foamable Resin Polycarbonate Polystyrene Medium-Density Foam Polystyrene Molded Extruded Polyurethane Rigid Closed Cell... 

Extruded polystyrene foam sheet is primarily produced in a single screw tandem extrusion line. Primary application of foam sheet is as a packaging material in items such as disposable dishes and food containers, trays for meal, poultry and produce products, and egg canons. 

Housewares is another large segment of the use of polystyrenes. Refrigerator door liners and furniture panels are typical thermo formed impact polystyrene applications. Extruded profiles of solid or foamed impact polystyrene are used for mirror or picture frames, and moldings for construction applications. 

In an effort to make homes and other buildings more energy efficient, the use of polystyrenes in extruded foam board with flame-retardant additives for walls and under slabs has experienced exceptional growth in recent years. Used as a sheeting material, extruded foam board complies with the requirements of the major building codes as well as federal and military spedfiea lions,... 

While unaffected by water, styrofoam is dissolved by many organic solvents and is unsuitable for high-temperature applications because its heat-distortion temperature is around 77°C. Molded styrofoam objects are produced commercially from expandable polystyrene beads, but this process does not appear attractive for laboratory applications because polyurethane foams are much easier to foam in place. However, extruded polystyrene foam is available in slabs and boards which may be sawed, carved, or sanded into desired shapes and may be cemented. It is generally undesirable to join expanded polystyrene parts with cements that contain solvents which will dissolve the plastic and thus cause collapse of the cellular structure. This excludes from use a large number of cements which contain volatile aromatic hydrocarbons, ketones, or esters. Some suitable cements are room-temperature-vulcanizing silicone rubber (see below) and solvent-free epoxy cements. When a strong bond is not necessary, polyvinyl-acetate emulsion (Elmer s Glue-All) will work. 

Tn 1967 the total sales of polystyrene foam in the United States were about 193 million pounds (78). Foams molded or extruded from expandable polystyrene amounted to 145 million pounds. The recent growth rate of polystyrene foam in the United States is depicted in Figure 1. The lower section represents expandable polystyrene. 

Mixed Polymers. A mixture of 5 parts of polyethylene and 95 parts of expandable polystyrene is extruded and converted to quenched pellets. The pellets are expanded and converted into molded foams with improved resistance to solvents and water vapor transmission (29). There is a polyethylene skin on the surface. 

Other styrenic polymer foams were developed in the mid-1950s through the early 1960s. Examples are molded expanded polystyrene foam (MEPS), extruded polystyrene foam sheet, and expanded polystyrene loose-fill packaging material. 

Table 10.1 Physical properties of commercial extruded polystyrene foams ASTM C578 - Standard for Rigid, Cellular Polystyrene Thermal Insulation... 

Figure 10.1 Compressive strength at yield vs density for extruded polystyrene foam. Unpublished data of J. M. Corbett. To convert kg/m3 to Ib/ft3, multiply by 0.0624...

Owens Corning manufactures a similar extruded polystyrene foam under the trade name FoamulaR. A single-screw tandem extrusion line is used to produce foam boardstock in a vacuum chamber connected to a barometric leg that acts as a vacuum seal [78]. Owens Corning also licenses their process to a number of international parties. 

Low-density polystyrene foam sheet was first produced by the extrusion of expandable polystyrene beads or pellets containing pentane as blowing agent [81,82]. Currently, polystyrene foam is extruded in a single-screw tandem line or in a twin-screw extruder. 

In foundation insulation, rigid plastic foams are widely used. A covering over the foam provides protection against ultraviolet light and physical damage. The properties of extruded polystyrene foam make it a desirable insulation for foundation applications. 

Polystyrene foam sheet can be made by a variety of extrusion processes (single screw, twin screw) but is most commonly made using a tandem extrusion process as shown in Figure 11.6. This process uses two extruders in series, which effectively optimize the melting, mixing, and cooling unit operations. The diameters of the extruders currently used in this process are usually 115 mm for the primary extruder and 150 mm for the secondary extruder, with an output capability of 400 kg/h. 

Figure 11.6 A tandem extrusion process for the manufacture of polystyrene foam sheet. (1) Primary extruder (2) blowing agent addition system (3) screen changer (4) secondary extruder (5) annular die (6) cooling mandrel (7) S-wrap (8) winders...

The cost of manufacturing thermoformed, polystyrene foam sheet parts is less dependent on raw material cost than other extrusion processes. This is largely due to the combined effects of additional energy costs required to operate two extruders, heat removal requirements in the secondary extruder, cost of pelletizing (densifying) regrind and the relatively low output of the process for the equipment scale and cost. Typical cost factors for the manufacture of thermoformed polystyrene foam sheet products include raw materials 35%, labor 27%, sales and administration 16%, depreciation 8%, utilities 7% and other 7%. 

Polystyrene (PS) Structural polystyrene foams are molded by injection and expansion-casting methods. They have a strong continuous skin and a foam cote. Their densities are quite high, ranging from 20 to 40 lb/ft3, in contrast to the 1 to 5 Ibs/ft range of the steam-molded and extruded polystyrene foams discussed below (11). Compared to other structural foams, however, the densities are relatively low (see Table 3-1). 

This type of foam is available in two forms, extruded-polystyrene foam and expanded polystyrene for molded foams. Polystyrene foams are light, closed-cell foams with low thermal conductivities and excellent water resistance. They meet the requirements for low-temperature insulation and buoyancy media (6). 

Extruded-Polystyrene Foam This material has been produced for over 40 years and is manufactured as billets and boards. It is made by extruding molten polystyrene containing a blowing agent, under elevated temperature and pressure, into the atmosphere, where the mass expands. The billets and boards can be used directly or can be cut into many different forms. Common tools for fabrication are bandsaws, hotwire cutters, planers and routers. Boards may have a cut or planed surface, or may have an integrally extruded skin of extremely small cells. Many sizes are available in extruded cellular polystyrene. BUlets can be... 

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