Extruded Polystyrene Foam Sheet

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%. 

Because the majority of foam sheet produced is thermoformed into containers for food packaging, all raw materials must meet applicable governmental 

Sweeting, O. J., The Science and Technology of Polymer Films, Wiley-Interscience, New York, 1971, pp. 290-291. 

Simmons, R. S., Polymer films process, structure and performance, presented at Polymer Technology Symposia, Industrial Materials Institute, National Research Council, Boucherville, Quebec, November 6-7, 2000. 

Benning, C. J. Plastic Films for Packaging, Technomic, Lancaster, PA, 1983, p. 34. 

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

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. 

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. 

Effective nucleating agents for extruding polystyrene foam sheet include the following (47) ... 

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. 

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...

Low density polyethylene foam products (thin sheets, planks, rounds, tubes) in the range of 32-160 kg/m (2-10 Ib/ft ) have been prepared by an extrusion technique using various gaseous fluorocarbon blowing agents (97,98). The techniques are similar to those described earlier for producing extruded polystyrene foam planks and foam sheets. 

Foams Wave by Mater-Bi, foamed sheet packaging is a biodegradable alternative to conventional protective foam packaging such as polystyrene, polyurethane and polyethylene. Wave by Mater-Bi is starch-based, and is expanded using water, extruded into sheets and then assembled into blocks that can be cut into any shape. The foams have a robust and resilient closed-cell structure. 

Very few studies have been performed investigating the effect of branching on the extensional rheological properties of polystyrenes. Such investigations can be valuable because many of the fabrication operations associated with commercial applications of polystyrene include operations in which the polystyrene melt undergoes an extensional deformation. Some examples are extruded foam sheet, blown film, oriented (tentered) sheet, and thermoforming. The types of deformations associated with these processing operations are best described as... 

The book also has a six-page article on Cushioning Design, with excellent illustrations, and a one-page article on Foam, Extruded Polystyrene (sheet). 

Polystyrene (PS) is another resin widely used in food packaging and other cushion packaging applications. These include extruded foam sheets such as meat trays. 

Major applications for styrene plastics are summarized in Table III (23). The packaging and serviceware (disposables) markets predominate, and account for approximately 50% of the total. One of the most rapidly growing portions of these markets is in low-density (usually 1-10 Ib/ft ) polystyrene foams, either in the form of extruded foam sheet or expanded polystyrene beads (EPS). Projections indicate that production of these foams will be greater than 2000 metric tons (24). 

Foams are available as rigid sheets or slabs (which are used in the majority of roofing systems), as beads and granules (used in cavity wall insulation), and also as spray and pour-in applications. The market is dominated by polyurethane (PU) foams, in particular polyisocyanurate products, expanded polystyrene (PS), and extruded polystyrene. 

Flame-retardance of expanded polystyrene beads can be brought about by the application of the additive (e.g. pentabromophenyl allyl ether), dispersed in fine quartz flour, to the surface of beads before expansion. For the flame-retardance of extruded foam sheets, the agent should be admixed with the polystyrene granules. 

Polystyrene. There are five basic types of polystyrene foams produced in a wide range of densities and employed in a wide variety of applications (1) extruded polystyrene board (2) extruded polystyrene sheet (3) expanded bead molding (4) injection-molded structural foam and (5) expanded polystyrene loose-fill packaging. 

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