July - 20218 MANUFACTURING TECHNOLOGY INSIGHTSIN MY OPINIONThermoplastic Foam Technology and Product UpdateBy Steven R. Sopher, Technical Director, JSPAs we become more environmentally conscious of the world around us, most of us are taking a renewed interest in understanding the origin and content of the products we use and interact with on a daily basis. Plastic foams have been in the news lately and have been the subject of much discussion and debate as to the necessity of these products, and end-of-life considerations for disposal, reuse and/or recyclability. Most people are familiar with the term `Styrofoam,' which was originally a Dow Chemical trademark for Expanded Polystyrene. However, Expanded Polystyrene comes in several forms, including Extruded Polystyrene (XPS) and Expanded Polystyrene (EPS). The former is produced as rigid extruded sheets (for thermoformed `clamshell' take-out containers, egg cartons, etc.) and boards used for building insulation (i.e., `Greenboard', `Pinkboard', etc.), while the latter is made as an expanded bead foam which can be shaped molded into a block (for fabricating sheets for packaging and used as `Geofoam' blocks in the construction industry) or specific molded shapes such as beverage cups, coolers, and other packaging containers. All of these products are made from Polystyrene and are foamed using a volatile blowing agent such as Butane or Pentane. Polystyrene can be recycled as a number 6 plastic (>6< recycling code). While it is difficult to argue against the long-term insulation benefits of Polystyrene Foam products used in the building industry, it is becoming increasingly difficult to support the use of Polystyrene Foam products as single-use items in the food and packaging industry. Aside from the disposal issues and volatile content of these single-use Polystyrene Foam products, one of the obvious negatives is the product durability and lack of resistance to chemicals for long-term use and reuse. Polystyrene Foam (XPS and EPS) is quite fragile and takes a permanent set when compressed or impacted.Polyolefin plastics such as Polypropylene and Polyethylene are much more durable than Polystyrene and are becoming more commonly used as foam plastics. Expanded Polypropylene (EPP) and Expanded Polyethylene (EPE) have been in use for over 60 years in the form of extruded foams (foamed boards and sheets) and for over 30 years in the form of expanded bead foam. The benefit of EPP is the ability to mold the product into a variety of shapes, sizes, and densities. EPP foam is available in bulk densities ranging from 8 to 250 kg/m3 (~0.5 to 250 lb/ft3) and can be molded to a finished density range of 16 to 300 kg/m3 (~1.0 to 19.0 lb/ft3). EPP foams have been widely used as safety foams for energy management impact protection in the automotive industry. While not commonly seen, these foams function as the backbone of many vehicle safety systems and offer occupant FIGURE 1
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