Fifty years ago, most perishable items such as meat, cheese, or vegetables were packaged in glass or metal containers. Even soda was packaged exclusively in glass containers. Today, many perishable items are packaged in flexible, plastic containers. Plastic containers are lighter and more convenient than metal or glass containers, reducing shipping costs, and providing ergonomic advantages to consumers. Plastic containers don’t shatter or dent and are in many ways safer than glass or metal containers. Marketers also prefer plastic containers because they are amenable to printing and molding, making them aesthetically pleasing surfaces for promoting their contents. Flexible packaging materials are not without drawbacks, however. First generation plastic packaging for potato chips, for example, kept the chips fresh for only a few days, after which time they became stale and inedible. Even today, the shelf life of some products is longer in metal containers than in plastic containers and some products that require rigorous processing such as extreme heating during packaging are still packaged in metal containers. However, flexible barrier packaging solutions continue to evolve and are widely used in stringent applications such as retort packaging and even for containing fish or other aromatic foods. Market needs in flexible barrier packaging include cost reduction, longer shelf life, lighter packaging, improved environmental footprint, reduction in processing steps and improved consumer appeal. Below we discuss how Selvol Ultiloc polymers can help our customers meet these requirements.
Compared to metal or glass, plastic materials are permeable to gases, such as oxygen, that can cause contents to decompose and become unusable. In order to overcome this, plastic barrier packaging generally consists of many layers, each layer imparting different attributes to the layered structure such as improved gas barrier properties, increased mechanical strength, puncture resistance, chemical resistance, good printability, and transparency. A typical multilayer structure is illustrated in the drawing below.
By combining multiple materials in such a layered structure, it is possible to make a flexible barrier package that imparts shelf life stability similar to that of a metal or glass container, while achieving the other attributes mentioned above. Aluminum foil provides excellent gas barrier properties and has been used in flexible packaging for many years. Aluminum is impermeable to gases, but it must be applied in relatively thick layers (> 25 µm) to give excellent barrier properties, adding to product cost and weight. Furthermore, aluminum cannot be microwaved and is not recyclable. Polyvinylidene chloride (PVdC) is an excellent gas barrier polymer, but is being phased out of many packaging applications because of environmental concerns. Selvol Ultiloc polymers are environmentally benign and offer an excellent alternative to PVdC and aluminum in many barrier packaging applications. Selvol Ultiloc copolymers have a surface energy greater than about 55 dynes/cm. This high surface energy allows the Selvol Ultiloc polymer to serve several functions in addition to having excellent gas barrier at low humidity. The high surface energy allows the Ultiloc film to function as a nucleation layer for efficient metal vapor deposition while also eliminating the need for tie layers in some multilayer structures. In order to demonstrate this, we recently produced a prototype multilayer film using Selvol Ultiloc 5003 as shown below.
The prototype film was coated with a thin layer of aluminum. Even with such a thin metal layer, the barrier properties were good even at high humidity, as shown in the plot below.
This illustrates the possibility of using Selvol Ultiloc polymers in flexible barrier packaging systems as an environmentally acceptable replacement to aluminum foil and PVDC. With further optimization, we expect that lighter, essentially transparent barrier films can be produced with fewer converting steps and layers than existing multilayer barrier structures. This will reduce packaging and transportation costs and result in a more functional and sustainable product for the consumer.
To find out which grade will best enhance your products or processes, contact a Selvol polymers specialist at our Houston Technology Center.
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