Polystyrene foam packaging

The clean, durable, nondust-forrning character of polyethylene foam has led to its acceptance in packaging missile parts (230). Polyethylene foam sheet has also displaced polystyrene foam sheet for packaging glass bottles and containers because of its greater resUiency and tear resistance. 

There are five basic types of polystyrene foams produced in a wide range of densities and employed in a wide variety of apphcations (/) extmded polystyrene board (2) extmded polystyrene sheet (2) expanded bead mol ding (4) injection molded stmctural foam and (5) expanded polystyrene loose-fiU packaging. 

The most important use of polystyrene is in packaging. Molded polystyrene is used in items such as automobile interior parts, furniture, and home appliances. Packaging uses plus specialized food uses such as containers for carryout food are growth areas. Expanded polystyrene foams, which are produced by polymerizing styrene with a volatile solvent such as pentane, have low densities. They are used extensively in insulation and flotation (lifejackets). 

It was possible to cover additional applications with these new types. In 1951 BASF found it was possible to impregnate polystyrene direct with expanding agents in the suspension process. This opened up great new possibilities for polystyrene foam (STYR0P0R, BASF, 33), for example in the packaging and building fields. 

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. 

Polystyrene A polymer of styrene, used primarily in the production of polystyrene foam for use in packaging. 

Fully halogenated CFCs were eliminated in polystyrene foam food packaging and containers. Substitute blowing agents used are either no threat to the ozone or are a 95% improvement over fully halogenated CFCs. Action has been taken such as where PS foam cups now are 100% CFC-free, etc. 

Figure 1.10 Polystyrene foam rapidly became the packaging material of choice for everything from medical instruments to engines (courtesy of BASF, Ludwigs-hafen)...

The Dow Chemical Company first entered the loose-fill packaging market in 1962 with a material that resembled spaghetti strands. Eventually the shape evolved to the S shape that characterized the product from the early 1970s to the present. Other competitors in the polystyrene foam loose-fill market include Flo-Pak, manufactured by Free-Flow Packaging, Inter-Pac, manufactured by Inter-Pac, WingPac and C-Pac, manufactured by Rapac, and Alta-Pak, manufactured by Storopack. In 1993, Dow sold the trademark rights to the S shape and Pelaspan-Pac to Storopack. The information about foamed polystyrene loose-fill that follows is an overview specific to materials that are formed in hard resin strands, cut to length, boxed and shipped to and later expanded for customer use at a convertor (expander) location. 

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. 

More recently Pactiv, formerly Tenneco Packaging, has manufactured foamed polystyrene sheet and boardstock. A tandem extrusion line is used to produce polystyrene foam insulation products. 

Polystyrene Packaging Applications Foam Sheet and Oriented Sheet... 

Two of the most important food packaging materials using polystyrene resins are oriented polystyrene sheet (OPS) and polystyrene foam sheet. Together, OPS and polystyrene foam sheet packaging account for nearly 40 % of the polystyrene resins used in food packaging applications in North America. 

Figure 11.11 Various polystyrene foam sheet food packaging applications...

The use of polystyrene foam sheet has grown significantly since its introduction in the mid-1960s. In 1998, approximately 338000 metric tons of polystyrene foam sheet were produced (Table 11.1). Most of the current use is in disposable thermoformed food packaging such as egg cartons, meat, poultry and produce trays, fast food containers, dinnerware (bowls and plates) and bottle labels (Figure 11.11). 

Apparently, AMSd is also useful in the reduction of the molecular weight of waste polymer.491 Heating polystyrene foam pieces recycled from food packaging materials at 160 °C for 1 h in the presence of AMSd reduced the Mn from approximately 70 000 to 10 000. The mode of action is unknown, but it is presumed that AMS radicals are generated and abstract hydrogen atoms from the polystyrene backbone, resulting in chain cleavage. 

M.B. Hocking, Relative Merits of Polystyrene Foam and Paper in Hot Drink Cups Implications for Packaging. Environ. Manage. 15(6), 731-747 (1991). 

Special collection systems are generally provided for large-scale or commercial postconsumer applications such as for agricultural films, chemical containers, automotive parts, carpets, and polystyrene foam packaging. Since most of the plastic is collected as multimaterial or in commingled forms, the collected plastic waste has to be sorted, separated, and cleaned, and most of this is done at material recovery facilities (MRFs). 

Any television, computer, or other fragile item you have purchased in recent years has probably come packaged in polystyrene foam (Styrofoam ) for protection. The same foam is likely to be serving as insulation in the cooler you take along on a picnic. It is a stiff, low-density, non-heat-conducting solid produced by blowing gas into polystyrene liquid as it solidifies. Over 700 million pounds were manufactured in 1995. 

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). 

Polystyrene, as mentioned, is the most common packaging foam. Polystyrene foam is the material of choice if it can perform acceptably, since it is typically the least expensive packaging foam available. It is used extensively for containers as well as for cushioning material, in molded shapes and in extruded form. Molded shapes are commonly termed expanded polystyrene foam (EPS), while the extruded material is called simply extruded PS foam. The term styrofoam is often incorrectly used for these materials, but Styrofoam is a Dow Chemical Company trade-marked extruded polystyrene foam used primarily for building insulation and not found in packaging. 

A 1 kg product that must be kept at a temperature of 0°C is packaged with 2 kg of ice in a 1.5 cm thick expanded polystyrene container, with inside dimensions measuring 0.4 m x 0.4 m x 0.6 m. How long will the product be protected The thermal conductivity of the polystyrene foam is 0.030 w/m K. The outside temperature is constant at 25°C. 

Expanded polystyrene products have widely increased the market for polystyrene resin (see the section on polystyrene foams in Chapter 2). With as light a weight as 2 Ib/ft (0.032 g/cm ), the thermal conductivity of expanded polystyrene is very low, and its cushioning value is high. It is an ideal insulation and packaging material. Common applications include ice buckets, water coolers, wall panels, and general thermal insulation applications. 

---