Retail outlets, from large supermarket chains to small corner shops, are becoming more and more like walk in/walk out restaurants, with convenience foods, sandwiches, and snacks providing a high proportion of turnover. There are many materials available for the plastic containers used in food packaging for these retail outlets, each with its own performance characteristics.
Explore this issueAugust/September 2008
Each plastics material available to the food packaging industry has its benefits. Many people influence the selection of packaging material and the final design, and it is important that each is committed to matching the proper material and design to the application. It takes more than dedication to the optimal solution; it takes a sound understanding of the duty the package is likely to see and the strengths of each candidate material.
In food processing, processors require ease of filling and of sealing or closing, depending on whether the end product is to be sealed or will have a snap closure. In these cases, amorphous polyethylene terephthalate (APET) has several qualities that make it useful. For clamshell packages, for example, APET’s mechanical traits ensure a package with clarity. In addition, its mechanical toughness protects products in transit. In comparison, while oriented polystyrene (OPS) has very good clarity, it has limits in terms of shock and vibration protection and is more prone to cracking.
APET is also available with polyethylene (PE) lamination, which allows for effective adhesion of lidding stock in applications like yogurt cups and sandwich wedges. APET can have a multi-layer structure with a thin layer of polyethylene terephthalate glycol (PETG), a heat-sealable form of PET, on at least one side. This option makes it suitable for many of the same applications as the PE/APET laminate, and it is ideal for consumer product clamshells, where extensive welding is the norm.
For food products that are to be microwaved or heated conventionally in the original package, or for hot liquids, polypropylene (PP) is still the best choice because of its ability to withstand most cooking temperatures. PP dominates this application and performs very well for a wide array of takeout foods, including whole precooked chicken and prepared dishes. Often, a PP bottom tray serves as the primary heat-tolerant container, while an APET dome serves as a clear lid that preserves the food’s freshness but allows the consumer to see the product inside. The lid is generally coated with an anti-fog agent and is removed prior to reheating.