Recyclable-by-design mono-material flexible packaging with high barrier properties realized through graphene hybrid coatings

Due to the large production of plastic packaging, packaging mismanagement represents a significant problem for the environment and the related economic/social contexts. A new route towards sustainable recycling has been identified in the design of the plastic products together with their end-of-life recycling options. Following this approach, in this work, new recyclable-by-design mono-material flexible films with high barrier properties to gases and UV radiation have been developed by applying graphene oxide (GO) and graphene oxide/montmorillonite (GO/MMT) hybrid coatings on polyolefin substrates. The coatings induce a remarkable reduction of the UV transmittance (40-60%) and of the oxygen (94-99%) and water vapour (68-73%) permeability of the films, with very good stability after prolonged water immersion. Reprocessing tests demonstrate the easy recyclability of the coated films, whose commercial analogues are currently considered as non-recyclable. By extrusion and compression moulding, recycled films are obtained in which the nanostructured phases result well embedded in the polymer matrices. The mechanical properties of the samples obtained by reprocessing coated polyethylene and polypropylene films are comparable to those of the reprocessed pristine films. Moreover, no significant release of GO by water immersion for 24 h at room temperature is detected from the recycled samples. Overall, the results indicate that the application of thin GO/MMT coatings to realize mono-material barrier films for packaging applications is an effective strategy to realize high performance products able to be easily recycled. These mono-material flexible films represent a new sustainable end-of-life option with respect to current commercial multi-layer products.