Lightfastness, surface and interfacial properties of colour-printed paper substrates coated with PCL/ZnO and PCL/TiO2 nanocomposites

Packaging production often includes varnishing to increase printed information durability. In addition, as some materials cannot be recycled (which could be the case in food packaging), the use of biobased materials enables waste to be composted. This paper proposes biopolymer-based nanocomposite coating which could be applied onto the printed paper substrate to protect it and increase its barrier properties to the water vapour. For the purpose of the research, two sets of the nanocomposite coatings were prepared by mixing polycaprolactone (PCL) base with ZnO or TiO2 nanoparticles in different weight concentrations. The prepared nanocomposites were applied onto the printed samples and artificially aged. The prepared samples were characterized by SEM imaging and EDS analysis, by calculation of adhesion parameters, evaluation of the water vapour transmission rate and colour stability during the ageing process. Results of the research showed that preparing of the nanocomposite coatings did not result with agglomerates of nanoparticles on the substrates. The adhesion of the coatings is adequate before and after the artificial ageing process. The application of coatings did not cause significant change in original colour. Both types of nanocomposites have diminished colour fading and water vapour transfer rate due to the artificial ageing process. To conclude, all proposed nanocomposite coatings are suitable for use in the cardboard packaging production. Nevertheless, due to a better protection in the artificial ageing, nanocomposite coatings with ZnO proved to be a better choice.