While PET is one of the fastest growing sectors of the beverage bottling market, taking over from glass and cans as the container of choice, its use has been mainly limited to fizzy drinks and water.
However PET, and plastic in general, is not very good at keeping oxygen and other gasses from permeating the container and reducing the shelf life of such products as juices, teas and flavoured water. Oxygen has a degrading effect on flavour, colour and vitamin content for many beverages.
Now researchers at South Africa's Council for Scientific and Industrial Research (CSIR) say they have invented a barrier, called Oxyplete, that is 30 times better than ordinary PET, giving beverage makers a choice if they want to switch from glass or cans.
Oxyplete performs better than any other passive barrier currently available, the researchers claim The costs compare favourably and are competitive with other barrier technologies on the market.
"Oxyplete is suitable even for demanding applications such as hot or cold filling for beer and baby food packaging," the researchers stated.
The technology is based on a double-layered outside coating. Before it is applied, the surface of the plastic is activated, which is achieved through either an oxyfluorination process, corona discharge or plasma treatment, followed by conventional spray or dip coating and drying. The coating is aesthetically attractive and can be applied to different thermoplastics such as PET and PP, they stated.
"Because the barrier properties are situated in the thin coating, the properties of the base polymer become almost irrelevant," they stated. "This means more freedom in the selection of materials."
Since the coating is applied in a second, separate step, it is not necessary to have a dedicated production line for barrier packaging. A portion of normal production can be diverted for treatment. This is important for countries like South Africa, which has a relatively small market for barrier packaging, they stated.
"Oxyplete meets all the technical requirements for beverage packaging, including 100 per cent adhesion testing, scuffing, oxygen permeability and expansion testing with no adverse affects on recycling," they claimed.
PET is often used for such packaging as soft-drink bottles to prevent the loss of carbonation. Since PET has insufficient barrier properties for many oxygen-sensitive foods and beverage applications, fruit juices and beer are packaged in glass, cans or cardboard and foil laminates.
Many high barrier applications require multilayered packaging, combining PET with high barrier plastics such as ethylene vinyl-alcohol, Nylon 6 or Nylon MXD6 with concomitant recycling problems and expensive capital equipment, according to the researchers.
Recently FoodProductionDaily.com reported that Philadelphia-based Constar International had developed a material that when blended with monolayer PET, binds oxygen, thus preventing the degradation of products such as juices, teas and flavoured water.
The product, called DiamondClear, is currently being tested before being submitted for regulatory approval. Oxygen "scavengers" minimise the permeation of oxygen through the container by chemically binding the molecules.