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.
While PP is an excellent heat-resistant food packaging plastic, it does not have the rigidity of OPS or APET, so it is less suitable for stacking heavier items on table displays or in transit. While considered a clear rigid packaging plastic, its clarity is substantially inferior to that of OPS or APET.
To maximize the amount of saleable inventory on display, retailers often prefer to stack food products on store shelves or display tables. When this is the case, a plastic that is non-brittle but tough and rigid is needed.
APET and polyvinyl chloride (PVC) both provide the necessary mechanical strength, but because clarity is important for visual appeal, APET is the material best suited for this application. Additionally, its oxygen barrier properties help to extend shelf life, making it well suited for fresh foods, including dairy products. It is important to remember, however, that in cold display applications, an anti-fog coating on the inside of the package—no matter what the material—is essential.
In all situations, clarity is key. It is important for consumers to be able to see a food product inside the packaging, and if a combination of clarity and toughness is needed, APET will deliver high performance.
Waste Recovery Implications
Packagers and retailers also need to consider waste recovery implications when choosing packaging materials. PVC, OPS, and PP do not have a well-developed and readily available reuse stream. APET, on the other hand, can piggyback on the already well-established PET bottle recovery infrastructure.