Green and recyclable graphitic carbon nitride/chitosan/polyvinyl alcohol photocatalytic films with efficient antibacterial activity for fruit packaging

Chitosan (CS) is an excellent raw material for the preparation of food packaging films due to its good film-forming properties, non-toxicity, and biodegradability. However, pure chitosan films have drawbacks such as weak mechanical properties and limited antimicrobial activity. In this work, novel food packaging films containing chitosan, polyvinyl alcohol (PVA) and porous graphitic carbon nitride (g-C3N4) were successfully prepared. The PVA served to improve the mechanical properties of the chitosan-based films, whilst the porous g-C3N4 acted as a photocatalytically-active antibacterial agent. The tensile strength (TS) and elongation at break (EAB) of the g-C3N4/CS/PVA films both increased by ~4 times compared to the pristine CS/PVA films at the optimum g-C3N4 loading of ~10 wt%. The addition of g-C3N4 increase the water contact angle (WCA) of the films from 38° to 50°, whilst decreasing the water vapor permeability (WVP) from 160 × 10−12 to 135 × 10−12 g∙Pa−1 s−1 m−1. The shelf life of strawberries covered with g-C3N4/CS/PVA films at room temperature could be extended up to 96 h, compared to 48 h and 72 h for strawberries covered with polyethylene (PE) films or CS/PVA films, respectively. The g-C3N4/CS/PVA films offered good antibacterial properties against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Further, the composite films could be easily recycled with the regenerated films offering almost identical mechanical properties and activities as the original films. The prepared g-C3N4/CS/PVA films thus offer promise for low-cost antimicrobial packaging applications.