Thermoplastic Foam Technology and Product Update

Steven R. Sopher, VP of Technology

As 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) are 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 protection in the event of a vehicle crash. They are also being increasingly used in area such as seating, and trunk storage and stowage applications. As the automotive industry moves toward increasingly stringent efficiency standards, and as the industry transitions to electric vehicles, EPP foams are being used to achieve vehicle weight reduction, thus allowing OEM’s to achieve efficiency and range goals. EPP foam can be optimized to achieve specific weight reduction targets while maintaining product performance. Figure 1 illustrates various applications where EPP foams are used in vehicles.

Figure 1

A benefit of Polyolefin foams like EPP is their durability, chemical resistance, repetitive impact performance, and broad operating temperature range (-30°C to 110°C). EPP products are completely inert and produced without the use of VOC’s. They are also 100% recyclable. With more emphasis on End-Of-Life vehicle disposal and recycling, it is important to consider the selection of products being used for vehicle interiors. Single component materials like EPP facilitate ease of disassembly and recycling. EPP can be recycled as a number 5 plastic (>5< recycling code).

With the growing emphasis on recyclability, there is a growing concern with current plastic collection systems at the municipal level to cope with the number of different types and forms of plastics

Another growing field with a great potential for durable foamed products like EPP is the packaging and food service industries. With the growing emphasis on recyclability, there is a growing concern with current plastic collection systems at the municipal level to cope with the number of different types and forms of plastics. As such, there is a renewed interest in reusability. This is an area where EPP foam products offer great benefits. EPP foam products, due to the inherent durability and insulation properties can be reused multiple times, are resistant to chemicals, and can be cleaned and disinfected. Areas of opportunity include home delivery of appliances and groceries, on-site store pick-up of food items (perishable, hot, cold, etc.) with an emphasis of long term use and reuse with the ability to clean and disinfect between uses. EPP foam offers a lightweight solution to replace solid plastic containers with the added benefit of maintaining both hot and cold/frozen products in the same container for extended times, without secondary packaging or ice packs. This concept is also being used to transport assembly components for the automotive, appliance, and other manufacturing markets, whereby EPP is used for durable reusable transport totes. Figure 2 illustrates multiple designs and uses for EPP packaging.

Figure 2

An added benefit is the end-of-life (which can be up to 5 years or more) recyclability and established recycling networks that take back EPP foam containers. Once these EPP parts are returned to recycling centers, they can be ground up, pelletized and used to produce new EPP products. EPP products are currently available with recycled (PCR – Post Consumer Recyclate) content of 25% or more.

Polyolefin foam technology continues to innovate and adapt to a changing marketplace. While the market opportunities are growing, production methods are improving and manufacturing costs are being reduced. EPP (and EPE) foam products can be used to replace PU (polyurethane), and PS based foams while offering the combined benefits of cost reduction, weight reduction, chemical resistance, insulation properties, improved durability and longevity all while being fully recyclable and melt-processable back to the base resin level.