Barrier Films: Flexible Materials and Reliable Protection for Delicate Foodstuffs

Flexible packaging for the food sector is enjoying strong growth, not least thanks to the numerous design options and low weight and volume. Mondi Packaging offers a broad range of such materials, backed by in-depth technical know-how and leading-edge research and production systems. One of the four corners of Mondi Packaging’s Diamond for Growth strategy is the development of technically advanced packaging solutions, which help customers optimally market their products and provide the best possible protection.

TOTAL PROTECTION VERSUS CUSTOMERS’ NEEDS

Dangers to foodstuffs such as light or water vapour may appear harmless, but they impact even robust foods such as hard cheese and sauerkraut. A barrier film’s protective function may involve protecting against outside influences or alternatively keeping substances in, for example, to ensure packaged bread remains fresh. The question of how much protection is needed, or how much is desirable from a business standpoint, can sometimes be tricky: a complex combination of barriers may be required, and they may have to be tailored to the customer’s specific needs. Expenditure pays off if shelf life and visual appearance create a decisive competitive advantage at the POS.

THE GREAT ENEMY: OXYGEN

Though we rely on oxygen to survive, it adversely affects foodstuffs’ shelf life by helping sustain aerobic microbes such as moulds. Other undesirable effects include the oxidation of fatty acids (“turning rancid”); discolouration due to oxidation, eg of tomato sauce; and breakdown of vitamins and flavour.

Oxygen can be removed from the packaging by creating a vacuum or modified atmosphere, but which materials help prevent diffusion after that? While conventional solutions such as aluminium and metallised film offer a high level of protection, they are often unnecessarily heavy and expensive, unsuitable for microwaving, and non-transparent. Such factors are growing in importance as the market becomes increasingly geared to convenience food.

Among transparent films, PET 12 fym PVDC (2g/m2) and EVOH composites provide excellent barrier properties against oxygen. Frequently used inorganic barrier layers made of SiOx or AlOx involve a risk of (invisible) scratching during the pressurization or retort processes. Moreover, the packaging producer always has to create airtight seal seams and closures, to ensure the advantages of such barriers can be utilised.

WATER VAPOUR: NOT ALWAYS DESIRABLE

Moisture may be desirable for one type of foodstuff yet undesirable for others (no-one wants a soft piece of crispbread or a hard bread roll). In both cases, the packaging must provide a barrier against water vapour: if the food is to be protected against drying out (e.g. to prevent refrigerated vegetable products from wilting), it must keep moisture inside the packaging; alternatively it must keep water vapour out, so that potato crisps stay crunchy, cocoa remains lump-free, and candies don’t get sticky.

Polyolefins are an excellent barrier against water vapour. PE 100fym for example can create different kinds of barrier, depending on the specific density. Aluminium layers or metallised inorganic intermediate layers within a composite are the material of choice if a barrier against oxygen is also required.

TRANSPARENCY BUT NO LIGHT

Light does not have to be visible (wavelengths above 380 nm) to damage foodstuffs: saturated fatty acids, for example, can oxidise at 295 nm. Even the dim light in a refrigerated cabinet can cause unsightly changes in the colour of sausage or speed up the breakdown of vitamins and amino acids.

Consumer demand for transparent packaging in this area is a very special challenge, as classic solutions such as aluminium composites, printing across the entire surface of the packaging, or sealed films colourised using titanium oxide pigments may mean the consumer can’t see the product.

These days most consumers want to see what they’re buying. UV additives can provide a solution if the light wavelength damaging to the product is known.

ALL ABOUT THE CHEESE: OPTIMUM PACKAGING FOR EMMENTALER

Film packaging for cheese is a surprisingly complex business! Products such as Emmentaler continue to ripen in their film, creating carbon dioxide and propionic acid, which must be able to escape to keep the packaging from swelling. At the same time, oxygen in the packaging is undesirable, as it helps sustain mould. The film of choice is OPA, which at a strength of, for example, 15 fym provides a good balance between carbon dioxide permeability and oxygen barrier properties.

COLOURING ON THE MARCH

A problem frequently associated with transparent packaging is migration: fats and oils in particular have a tendency to migrate from the foodstuffs into the packaging. This is undesirable, as they often contain colouring which can cause unsightly discolouration of the sealed film and ruin the visual appearance of bright packaging. Tomatoes, curry and carrots present a very special challenge to producers wishing to create microwavable flexible packaging, due to the risk of discolouration. The challenge can be overcome provided food producer and packaging provider co-operate in applying the relevant know-how.

STRESS FACTOR: HEAT

High temperatures present a significant challenge to packaging, whether during sterilisation of the foodstuff by the producer, boiling in a flexible bag (eg rice), or warming in a microwave by the end consumer. The mechanical load must be taken into account, and the different expansion coefficients of composite films harmonised.

Very fatty products such as sauces also tend to create dents in the film following sterilisation. In all such cases, years of experience and extensive testing are required to ensure an optimum solution in terms of cost-effectiveness, protection and visual appearance.

Magic Fruits: innovative packaging for an innovative snack
Whenever a new product arrives to create a completely new market segment, there are significant challenges in terms of packaging. In particular, optimum protection for the product is a sine qua non. A recent case was the launch of Magic Fruits, when Mondi Packaging kept its client more than satisfied by meeting precisely those challenges.

The packaging for Magic Fruits, which are freeze-dried fruits (strawberry, apple, pineapple) positioned as a “beauty snack”, required several protective elements: a highly efficient moisture barrier, guaranteeing a shelf life of one year; antistatic properties, to keep the “fruit dust” from adhering to the packaging; preservation of the antioxidants and vitamins in the product; and the avoidance of additives capable of migration.

The design requirements were also tough: the selected material had to be transparent but not too thin, as the producer had opted for a stand-up pouch; and last but not least the packaging process involved gas flushing and a special closure mechanism. Mondi Packaging Korneuburg developed an elegant and novel film composite, consisting of PET AlOx, OPA and PE with antistatic properties, with a shimmering surface commensurate with the product’s high-quality appeal.

Magic Fruits are a good example of the Mondi Packaging team’s solution-oriented approach. Since the opening of R&D Centre last year, the team is ready to tackle tricky packaging assignments ranging from optimisations to newly developed solutions.

About Mondi Packaging Consumer Flexibles

Mondi Packaging Consumer Flexibles is an innovative supplier of active and convenient packaging for the pet food, food & non-food, confectionary & snacks as well as medical & pharmaceutical industries. These solutions comprise high quality polyethylene-coated and laminated papers, boards, films, stand-up pouches and plastic bags.

We provide flexible packaging solutions with a variety of features such as barrier properties, professional printing and end-user functionalities like easy opening, pourability and microwaveability. Our production sites are BRC/IoP and ISO 9000:2000 certified. Product development and innovation are key priorities of Mondi Packaging Consumer Flexibles, enabling us to offer tailor-made solutions to protect and promote our customers’ products.

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