Fabrication of polylactic acid bilayer composite films using polyvinyl alcohol based coatings containing functionalized carbon dots and layered clay for active food packaging

Abstract

To enhance the inadequate active function and gas barrier properties of fully biodegradable polylactic acid (PLA) film within the active packaging field, the application potential of PLA material was improved by introducing polyvinyl alcohol (PVA) based coatings with excellent active functions. In this work, PVA based active coatings were developed using nitrogen-doped carbon dots (NCDs) that exhibit antioxidant and antibacterial properties, in conjunction with anthocyanin functionalized layered clay (AF-LDHs) that possess natural barrier properties and secondary active function. Due to the excellent active function of NCDs, original PLA film only coated with NCDs/PVA coatings could also exhibit good active function. Upon the addition of AF-LDHs reaching 3 %, antioxidant activity (ABTS method), antibacterial activity (against Escherichia coli), and UV barrier (280 nm) of PLA bilayer films were enhanced by 76.1 %, 70.3 %, and 53.0 % compared with original PLA film. Antibacterial and antioxidant assays indicated that the incorporation of AF-LDHs at a threshold of 3 % or above could supplement the release of NCDs as a secondary active agent, ensuring a more sustained release of active components. The experiment on preserving the freshness of fresh-cut apples demonstrated that PVA based active coatings can effectively delay the browning process by providing antioxidant and oxygen barrier properties, thereby maintaining the freshness of fresh-cut fruits. These results indicate that combining the active and barrier properties of NCDs and AF-LDHs in PVA based coatings offers great application potential for active food packaging.