DEVELOPMENT OF HIGH PERFORMANCE BIOPOLYMER COATINGS FOR FOOD PACKAGING APPLICATIONS

This PhD project aims to the optimization of the food packaging materials currently available on the market. The purpose is to develop high performance coatings able to improve the original characteristics of the plastic substrate beneath, as a consequence of the coating deposition. In particular, to fulfil the increasing request for replacing synthetic polymers already used in the nowadays packaging applications as well as to reduce the overall amount of plastics, biomacromolecules, possibly combined with inorganic compounds, will be used to generate a new class of “bio-nanocomposite-hybrid-coatings”. This will lead to a “greener” packaging structure with the same overall performances of the conventional ones. Some films properties will be considered, in particular the oxygen barrier performances at high relative humidity values, the surface properties and the optical properties. The overall project has been divided in three parts. In the first part, selected bio-macromolecules have been used as individual coatings onto polyethylene terephthalate (PET) and polylactid acid (PLA) films and the changes induced by the coating application were investigated by different techniques. Rising from the contact angle investigation, a new potential antifog coating has been disclosed, while the barrier analysis allowed highlighting the great potential of pullulan as oxygen barrier coating even at high relative humidity values. A comparison with some commercial synthetic coatings has also been performed. Ensuing from the obtained results, the second part of the project focused on the coating barrier performance, with special focus on the nanotechnology approach adopted. Specifically, both a bottom-up and a top-down approach were used. With regards to the former, a metal alkoxides was properly treated and combined with a biopolymer (pullulan) to design a final bio-nanostructure to be applied on PET, and the barrier performance was analyzed; concerning the latter, an inorganic clay was exfoliated through an ultrasonication process and mixed with pullulan; the Design of Experiment technique was then used to optimize the formulation in terms of permeability coefficient (P’O2) at the following condition: 23°C and 70% of relative humidity. The best coating formulation allowed decreasing P’O2 of ~84% with respect to the bare substrate (PET), and of ~77% with respect to the film composed by PET coated with pure pullulan (i.e without clays). In addition, microscopy analyses revealed some features of these bionanocomposites and supported the indication about a good exfoliation process. The third and last part of the PhD project, that is still an ongoing project, concerns the simultaneous combination of the aforementioned approaches (i.e. bottom-up and top-down). In principle, this would allow exploiting benefits arising from each individual approach, as well as exploiting any potential synergism.