Jan 06

Multi-layer materials

Posted by Wallentin in Uncategorized

This is why we need multi-layer materials and packages that weigh as little as possible

By combining different materials, it is possible to create “customised” protective packaging with the least possible material consumption, above all for foodstuffs. The most common combination is paper, plastic and aluminium foil. These materials are all good on their own, but the combination is even better. The composite materials are lighter and less resource-consuming than one single material with the same properties. Thus, the amount of waste is reduced. This is of course even more valid for flexible plastic packaging.

In general, many different properties are demanded from a package. The classical description of the main demands on a package says that it shall contain, protect and preserve, facilitate handling and use, inform and sell.

In practice, it is exceptional to find one single packaging material whose properties meet all these demands. This is the reason why much of our present-day packaging consists of multi-layer materials in the form of laminates, e.g. materials that are composed and combined in different ways.

By combining two or more materials, it is possible to build several properties into the package and to have the composite material fulfil many functions. Each separate material layer can represent one or more properties. The combination of many thin layers of different materials gives a package that provides the product the best possible protection, using the least amount of material. Compare with the “multi-layer parinciple” recommended when dressing for bad weather. You should have one windbreaking layer, one for warmth, one against moisture, etc.

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The foundation for modern distribution

It is a fact that composite packaging materials have been of vital importance to our modern way of distributing goods. Cardboard and paper were used originally without being combined with other materials, e.g. wrapping paper, shoe boxes, cake cartons, flour bags and sweet papers, for purposes with simple functional demands.

The development of composite materials began when we learnt how to coat paper or cardboard with plastic. Now quick and reliable heat sealing (welding) could be substituted for paste and glue. The technique suddenly made it possible to pack liquids in paper! It became possible to develop different cardboard and paper based packaging solutions for new products, e.g. deep-frozen food. This also created new opportunities for rational production and distribution of food.

The self-service system and an increasing variety of products created a demand for packaging with even better protection for the products. This meant fast development towards more and more “customised” multi-layer packaging. Not only were different types of materials combined (e.g. paper, aluminium and plastic), but different plastics were also combined into materials with very advanced properties.

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For a given product, there are often several effective packaging solutions able to perform the required functions. But some solutions are more resource efficient than others in that they use less resources.

Today, resource efficiency is a critical objective, given the Earth’s limited resources and, more generally, the World’s environmental challenges. It is at the core of the flagship initiative for a resource-efficient Europe under the Europe 2020 strategy, seeking to transform Europe’s economy into a sustainable one by 2050.

What does ‘resource efficiency’ mean exactly for packaging? This has to do with the minimal use of material and energy resources throughout its lifecycle and also the minimised amount of material leaving the cycle (i.e. not recycled).

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The general perception is that a pack, serving the same consumption purpose with a high recycling rate, is better than a pack with zero recycling. This is not necessarily true as the packaging weight must be taken into  account.

Compare, for example a non-flexible pack weighing 50g with a recycling rate of 80% and a flexible packaging weighing 5g with the same functionality, but with zero recycling. Which pack is the more resource efficient? The flexible packaging of course! Even after recycling, the net material loss of the non-flexible packaging is 10g – twice as much as the 5g flexible pack.

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New methods created

New materials made it possible to develop an entirely new technique for maintaining freshness and quality in foodstuffs and to facilitate cooking in microwave ovens. New improved plastics opened new possibilities. The number of layers could be increased. New techniques for the lamination of material layers made production cheap and the method of co-extruding plastics (one single work operation to combine different molten plastics) revolutionised the production of multi-layer materials. It has been established that if one single material is used instead of a laminate (= multi-layer material), the material consumption would be at least quadrupled in some cases. Also, more energy would be consumed in production and distribution and the amount of waste would increase considerably.

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Recovery – a challenge

As can be understood, the use of multi-layer materials is highly motivated. But new demands for material recovery from household packaging waste cause an undeniable problem. Therefore, the development of new techniques for the manufacture of multi-layer materials suitable for material recovery has now become high-priority for the packaging industry. Some problems are well on the way to being solved. For example, there exists a functioning method for the separation of the polyethylene, aluminium and paper in milk and juice cartons.

It is also highly likely that it will be possible to material-recover plastic laminates. This will be enabled by the developmet of super-thin layers of newly developed barrier materials (barrier materials = materials that are impervious to gases, aromas and light). One such material is silicon oxide (in principle = glass) which is used as coating on plastic film in such thin layers that they can be disregarded when the packaging material is recovered.

If the recovery of multi-layer materials is aimed instead at energy recovery by incineration of the material in ovens where the generated heat is recovered, the multi-layer materials are an interesting resource, as they generally make splendid fuels with high energy content.

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Alternatives on the way?

At present, interesting experiments are being conducted with multi-layer materials where one and the same plastic – but with different properties – is found in all layers. Such “mono-laminates” are easily re-cycled because, despite their many layers, they basically consist of one and the same kind of material. A good example is micro-flute corrugated board.

Other exciting trends concern wood fibre based barrier materials, similar to greaseproof paper which, in some cases, make it possible to substitute the aluminium foil in, for instance, dairy packages. Since both the basic cardboard and the barrier layer are made from cellulose, the material recovery is considerably simplified. Long-term, one can also see some development of plastic “alloys”, i.e. compounds of polymers instead of layers of different materials. Each such plastic alloy can be given desired characteristics and then be recovered as a specific material for a specific purpose. (Compare with the metal industry recovery of different metal alloys.)

There are many ideas about how problems with recovery can be solved technically. In Germany, for instance, chemical recovery to oil is one alternative.

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Information obtained from Flexible Packaging Europe, as well as the aluminium and paper/pulp industries.

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The 3 illustrations are randomly chosen for the following reasons:

  1. Danish Cookies: gold metal for long shelf life and to look precious, cardboard for easy handling, stockability/merchandising and appetite appeal;
  2. Fresh meat: wood for being a natural material, paper label for branding, appetite appeal, etc.
  3. Irish pork: rigid black plastic as the main tray sealed with a plastic film to be airtight for longer shelf life and cardboard wraparound label for branding and origin, as even the farmer is pictured.

LW/December 2017

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