Flexible packaging films for food applications need to be mechanically stable to withstand compression forces and need to provide high barrier properties (oxygen, water vapour, aromas) to avoid spoilage.[1] Since virgin polymers lack especially in barrier properties, additional barrier materials are used in multi-material flexible films. These are usually more expensive than commodity polymers, but, in higher fractions, also make recycling more difficult. Current developments, therefore, aim at barrier layers that are as thin as possible and still retain the barrier properties. One approach to reach this, is to incorporate silicate platelets into these polymeric barrier layers.[2]

It has been shown that the incorporation of 30 vol% montmorillonite in polyvinyl alcohol lead to a barrier improvement from 1.3 to 0.12 cm³(STP)∙µm/(m²∙d∙bar) at 23°C and 50 %RH. This would allow a reduction in the barrier layer thickness by a factor of 12.[3] This improvement is due to the elongation in permeation path according to the tortuous path theory.[4]

It is possible to apply the developed barrier lacquer via both reverse gravure and slot-die coating on roll-to-roll lines at scale. The final mono-material structure with composite barrier lacquer is fully recyclable according to RecyClass protocol[5]. The films produced with the recyclates provide similar mechanical properties compared to virgin ones. The recyclability is additionally compared to other high barrier approaches, i.e. SiOx and aluminium by physical vapour deposition (PVD), which are applied at vacuum.

References
[1] C. Caner et al.; Packaging Technology and Science, 2004, 17, 139-153.
[2] P. Panda et al.; Food Packaging and Shelf Life, 2022, 33, 100904
[3] S. Schiessl et al.; Frontiers in Nutrition, 2022, 9, 790157.
[4] D. Mondal et al.; Progress in Natural Science: Materials International, 2013, 6, 579-587
[5] RecyClass; Sorting Evluation Protocol for Plastic Packaging, 2021, 1-18