The demand for recyclable packaging is increasing worldwide. Many manufacturers are focusing on mono-material packaging, i.e. packaging that consists of just one basic raw material and is therefore easier to recycle. However, manufacturers face a number of pitfalls on the road to mono-material packaging. After all, mono-material packaging not only has to meet recycling requirements, but also comply with the technical specifications of the packaging industry.
For example, multi-layer barrier films, such as those used for thermoforming film and vacuum skin packaging, should be easy to form and transparent. Until now, manufacturers have not been able to meet this requirement optimally with packaging made from monostructures: Compared to multi-layer packaging with different raw materials, the easily recyclable alternatives were previously less transparent and could only be thermoformed moderately well.
Moldable mono-material packaging: product example shows feasibility
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However, there are technical solutions that can be used to combine the requirements for recyclability and the properties of the packaging. In cooperation with the raw material manufacturer ExxonMobil and the packaging machine manufacturer Multivac, Reifenhäuser has developed a product solution for moldable mono-material packaging and tested its feasibility. The result is a fully recyclable and thermoformable packaging with 95% polyethylene (PE) by weight, whose film properties are comparable to a thermoformed film containing polyamide (PA).
The packaging consists of a bottom film and a top film made from various PE raw materials from ExxonMobil, which offer high puncture resistance and formability. These are supplemented by an EVOH raw material specially developed by ExxonMobil for thermoforming: It combines low thickness with high barrier properties - but does not affect the recycling of the film because it only makes up a small proportion of the overall product.
Water-cooled film for better formability of the mono-material packaging
The films were produced on a 9-layer blown film line from Reifenhäuser with shock water cooling, called EVO Aqua Cool. "Our technology is able to cool plastic melts extremely quickly," says Abdelali Rouhi, Area Sales Manager at Reifenhäuser. The rapid cooling of the melt inhibits or even prevents crystallization. As a result, the barrier film remains transparent and glossy, has greater puncture and tear resistance and excellent forming properties. "Water cooling creates film properties that are ideal for thermoforming films, lidding films, vacuum skin packaging and vacuum bag packaging," emphasizes Rouhi.
The pack was produced as a test on a MULTIVAC machine under standard industry process conditions - after all, it must be possible to process the mono-material laminate in a stable process without any loss of productivity.
Impressive result in comparative test
The properties of the film and packaging produced were then tested using standard methods. It was shown that the combination of different PE raw materials in conjunction with a water-cooled blown film line produces outstanding packaging integrity: The PE monofilm has a comparable film stiffness and puncture resistance to a PA-containing thermoforming film and also has corresponding barrier functions and appearance.
"The feasibility test proves that the combination of high-performance raw materials with our EVO Aqua Cool technology enables the production of 95% by weight PE-based thermoformed packaging - without compromising on packaging properties, appearance or processability," says Abdelali Rouhi. "Nevertheless, there are numerous aspects that manufacturers should consider when switching from a material mix to a mono-material composite. The requirements for the film are crucial."
Different extrusion technologies for mono-material packaging film
In some areas of application, the required film properties of a mono-material packaging film can also be achieved using technologies other than water cooling. For example, blown film and cast film are given different mechanical properties through stretching, such as greater stability, which is required for stand-up pouches. In other cases, coatings are the best solution for mono-material composites.
