Nanostructured Al-doped ZnO coatings on PLA films for food packaging applications

Food quality and safety are key issues when dealing with materials for food packaging applications. Polylactic acid (PLA) is widely used in food packaging, since it is considered safe for contact with food and it is flexible and optically highly transparent. Further improvements can be achieved through functionalization of the PLA surface with suitable materials. For example, coatings based on zinc oxide (ZnO) have been reported to show significant antimicrobial effects. With this aim, PLA films were extruded starting from commercial pellets and then functionalized by thin coatings made of nanostructured aluminum-doped zinc oxide (AZO). A set of AZO coatings was deposited at different sputtering power, and analyzed by scanning electron microscopy (SEM) inspection. X-ray diffraction was used to evaluate the structural properties of the AZO coatings. Optical transmission measurements revealed high transparency of the AZO-coated PLA films, with transmittance values around 80-90% in the visible range. Preliminary release tests were conducted by putting the coated films in contact with a fixed volume of a physiological saline solution and the amount of released AZO particles was evaluated by spectrophotometric measurements.