Polystyrene packaging applications

The largest outlet for polystyrene is in packaging applications. Specific uses include bottle caps, small jars and other injection moulded containers, blown containers (a somewhat recent development but which has found rapid acceptance for talcum powder), vacuum formed toughened polystyrene as liners for boxed goods and oriented polystyrene film for foodstuffs such as creamed... 

The production of foamed films and sheets from polypropylene and polystyrene is discussed, with particular reference to packaging applications. Advantages of foamed materials for this application are examined, and the chemical and physical foaming processes are described. Extrusion technology for film and sheet by chemical and physical foaming processes is discussed, and recent developments in the coextrusion of multilayer packaging trays for the food industry are considered. 

Packaging applications are the most extensive. Meat, poultry, and egg containers arc thermoformed from extruded foamed polystyrene sheet. The fast-food market also accounts for a substantial amount of polystyrene for takeout containers where the insulation value of a foamed container is an advantage. Containers, tubs, and trays formed from extruded impact polystyrene sheets are used for packaging a large variety of food. Biaxially oriented polystyrene film is thermoformed into blister packs, meat trays, container lids, and cookie, candy, pastiy, and other food packages where clarity is required. 

Selecting appropriate polystyrene packaging materials for specific packaging applications... 

Given the initial concentration of styrene residual monomer in the packaging material, the styrene threshold concentration in the product and the desired shelf life of the product one can estimate whether or not a given polystyrene material will cause taints in a given packaging application. 

ILSl Europe Report Series Packaging Materials 1. Polyethylene terephthalate (PET) for food packaging applications 2. Polystyrene for food packaging applications 3. Polypropylene for food packaging applications 4. Polyethylene for food packaging applications 5. Polyvinyl chloride (PVC) for food packaging applications. 

Polystyrene loose-fill packaging material used in US Federal Government applications must meet US Government Specification PPP-C-1683 (12/5/ 1988), Cushioning Material, Expanded Polystyrene Loose-Fill Bulk (for Packaging Application) . Compliance with eight properties is the basis for this... 

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. 

OPS is commercially available in 0.13-0.76 mm gauge. The tenter frame process for manufacturing OPS is the most common process used today. A typical tenter frame process is shown in Figure 11.1. Tentered OPS is distinguished from polystyrene blown films (which are also biaxially oriented) in that the tenter frame process can produce heavier gauge films than the blown-film process. Blown films (0.025-0.13 mm) are used primarily in window envelopes, lamination, and printed applications tentered OPS is typically used in thermoformed trays, lids, and containers for rigid food packaging applications. 

Oriented polystyrene (OPS) is widely used for many packaging applications, including deli and bakery packaging. The biaxial orientation of the crystal polystyrene provides a significant improvement in impact strength and makes a very rigid material. Even with the enhancement of impact resistance, usually some level of impact modifier is required. SBCs are an excellent modifier for OPS. They help maintain the excellent clarity while also improving impact and processability of the OPS. 

Some packaging applications may be particularly sensitive to styrene or other volatile components. SBC and crystal polystyrene blends, even with low residual monomer levels in the polystyrene, may be unacceptable for these applications. In this case one possible solution may be to co-extrude a thin food contact layer on the surface of the blended sheet. Studies have indicated that by co-extruding a thin layer of crystal polystyrene on the surface of an SBC and crystal polystyrene blend, the styrenic volatiles and the odor can be significantly reduced. However, the downside is that the added layer of crystal polystyrene can serve to make the blended part more brittle. Another option that could reduce odor, but not have a deleterious effect on impact, is a thin coextruded layer of PETG [20]. 

Thermoplastics may be further subdivided into two broad categories on the basis of their cost and suitable end uses. Commodity plastics are typified by high volume production, good properties, and low resin cost. The four major commodity plastics are polyethylene, polypropylene, poly(vinyl chloride), and polystyrene. Their adequate properties and low cost have led to the extensive use of these plastics in packaging applications where they are very competitive with paper, steel, and glass. They are also used for some less demanding applications as components of durable goods (Table 22.1). 

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

Phillips Petroleum Company now manufactures the K-Resin family of optically transparent impact polystyrene (35). These resins, made via anionic polymerization techniques, owe their transparency to the extremely small size of the dispersed rubber phase. The principal use of K-Resin is in packaging applications. 

Although the possible number of polymers is theoretically limitless, the economics of their production and processing, as well as the physical and chemical properties they have, restrict the number of commercial importance to a few dozen (see Fig. 2.2), and in packaging applications the number of polymers used is even smaller. The polymers most commonly used in packaging are polyolefins, specifically polyethylene and polypropylene. Polystyrene, polyvinyl chloride, and polyethylene terephthalate (PET) are also among the most commonly used packaging polymers. 

Polystyrene films and polyester (polyethylene terephthalate) films are only used in the biaxially stretched form, because unstretched films are very weak and brittle. To a lesser extent this is also true for polypropylene films. Roll-quenched flat film is used for many packaging applications, but below 0°C these films become brittle. Biaxially oriented polypropylene film, on the other hand, is not brittle at a temperature as low as — 50°C and is suitable for packaging frozen foods. 

---