Designing bilayered composite films by direct agar/chitosan and citric acid-crosslinked PVA/agar layer-by-layer casting for packaging applications

Packaging is a crucial tool for reducing food waste and enhancing product competitiveness. Fossil fuel-based plastics, mostly used for food packaging, account for nearly 40% of global plastic waste. To address this issue, this study developed a layer-by-layer casting technique to create novel bilayered plastic composites with distinct agar/chitosan and PVA/agar layers. Film's properties, such as thickness, plasticity, and tensile strength, were affected by adjusting the volume of the layers. The elongation at break was positively related to the presence of citric acid (up to 30 wt%) as a crosslinker. The chitosan-rich first layer provided better UV-light blocking potential and opacity, which were beneficial in the prevention of lipid oxidation. Increasing the second layer by 40–60% substantially reduced the light absorption, while the colors were proportional to the citric acid content. The FT-IR band at 1713 cm−1 indicated an increase in C=O ester groups with crosslinker content. The hydrophobicity of the films was enhanced by the chitosan-rich layer. XRD supported intramolecular and intermolecular hydrogen bonding, whereas the micrographs revealed tightly bound structure between layers. The results corroborated that the inclusion of agar in the formulations increased the stability of the film, making it ideal for various packaging applications.