The sense of multilayer films for packaging

Everyone knows potato chips and has tasted them before. One likes them more, the other less. The main point is that they are fresh and crispy if you want to consume them. If you open a pack of chips, they become soft relatively quickly. After about one or two days, the chips are no longer as crispy as when the packaging was opened because they have absorbed moisture. Thus, it is important for manufacturers to use packaging that keeps the potato chips fresh and crunchy.

Did you know that an ordinary package for chips is in fact made of many (ultra thin) different layers of plastics?

So called ‘multilayer films’ are used for this purpose, because each layer has a different function. The requirements placed on films for food packaging include strength, flexibility and barrier properties to aromas. However, these different properties can only be achieved if different plastics are bonded together.

Summarized, the materials used are:

  • Polyethylene (PE) (depending on the density, different types of polyethylene are used)
    • polyethylene-low density (LDPE)
    • polyethylene high density (HDPE)
    • ultra high molecular weight polyethylene (UHMWPE)
  • Polypropylene (PP)
  • Polyamide (PA)
  • Ethylene vinyl alcohol copolymer (EVOH)
  • Tie layer

The main components of multi-layer films are polyethylene (PE) and polypropylene (PP). Both materials have

  • very good flexibility,
  • barrier effect against water vapour and 
  • are sealable.

Combined with polyamide (PA), the potato chips packaging have very good properties, while PA supplements PE and PP with its flexibility, stability, good strength at higher temperatures and very good sliding and wear properties. In addition, PA has good resistance to chemicals and is an effective barrier against oxygen.

Furthermore, ethylene-vinyl alcohol (EVOH) is used as a barrier and adhesion promoter between these layers in multilayer films.

This multilayer films can be produced in a coextrusion process, where each extruder melts one material and extrudes one film, before the get bond together. Alternatively, a more complex extrusion tool combines more of the molten plastic to extrude a thin film. The film is then further stretched on rollers and wound up.

As you can see in the video below the process isn’t simple at all, thus we call a potato chips package a “high-tech product”.

multilayer film production

Such great products shouldn’t be thrown away carelessly, nor are they easy to dispose of, but there are

Recycling solutions for multilayer films:

Nowadays it is important to handle resources consciously and carefully. Therefore, the recycling of waste is extremely important, especially for non-consumable goods such as packaging. Composite materials pose a major challenge. The question arises as to how thin multi-layer plastic films can be separated again according to type.

There are solutions for this on the market that include a mechanical and a chemical-physical preparation process.

Recycling sounds easier as it is:

Using a multilayer film made of polyethylene/polyamide (PE/PA) as an example, the films are crushed into flakes. The flakes are then fed into a solvent container and the PE is dissolved. This does not break up to the monomer but the chain floats in the solvent and is therefore not destroyed. The PA does not dissolve and remains as a solid phase.

The liquid phase is then separated from the solid phase in a centrifuge. The solids flow then enters the extrusion process.  The solvent is removed by degassing and PA is granulated.

From the liquid phase, the solvent is reduced to a certain percentage via various stages and also fed into an extrusion process. The remaining solvent is removed by degassing and the PE is granulated.

Hopefully we were able to give you some new inputs. Don’t hesitate to share your thoughts and join the hubbub.

Peter & Herwig

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