Advanced antioxidant bilayer films based on polylactic acid and chitosan: Structural, functional, and application...

Polylactic acid (PLA) is a promising alternative to petroleum-derived polymers, but its inherent poor plasticity and barrier properties hinder its application in packaging. For overcoming this disadvantage, an efficient surface-modification strategy was employed to deposit a chitosan (CS) layer onto PLA file, developing bilayer films with markedly improved mechanical and barrier attributes. Systematic variation on the PLA:CS mass ration (100:0, 75:25, 50:50, 25:75, 0:100) revealed that the incorporation of CS improved the plasticity of the PLA film and reduced the elongation at break from 374.55 % to 70.04-52.19 % for the bilayers; the oxygen permeability also reduced from 30.67 cm³·m^-2·d^-1·0.1 MPa^-1 to 25.82-3.67 cm³·m^-2·d^-1·0.1 MPa^-1. The film with a 50:50 mass ratio exhibited the best tensile strength (37.47 MPa) and oxygen barrier (3.67 cm³·m^-2·d^-1·0.1 MPa^-1). The antioxidant bilayer films were further prepared by adding antioxidants [tea polyphenols (TP), bamboo leaf antioxidant (AOB), and phytic acid (PA)] to the CS matrix. All antioxidant bilayer films displayed strong antioxidant properties (free radical scavenging rate of about 80 %) and excellent packaging performance. The antioxidant bilayer films exhibited anti-permeability against walnut oil and the TP-reinforced film effectively retarded the lipid oxidation of walnut oil during storage at 60 °C for 18 days, outperforming commercial PP film. The resultant PLA/CS-antioxidant bilayers thus provide a sustainable, high-performance packaging solution that circumvents the intrinsic limitations of PLA and extends the shelf life of oxygen-sensitive edible oils.