Enhanced Functional Properties for Packaging Applications Using Sodium Alginate/Starch Bilayer and Multilayer Films

This work developed bilayer and multilayer films from sodium alginate (SA) and starch (St) and systematically investigated their properties (thickness, moisture content, morphology, transparency, chemical interaction, film adhesion, tensile behavior, thermal transition, heat sealability, and gas permeability) to determine the potential use for flexible packaging. The SA/St bilayer and SA/St/St multilayer films were successfully developed by solution casting using layer-by-layer deposition and film drying on a hot plate. The SA/St and SA/St/St films were transparent and heat sealable. The interfacial fusion, adhesion, and hydrogen bonding between the SA and St layers promoted the mechanical properties (tensile strength, Young's modulus, and elongation at break) of the SA/St and SA/St/St films. The presence of SA layer enhanced the strength and rigidity of the starch film, while that of the starch layer improved the flexibility and heat sealability of the SA film. The seal strength increased with the thickness of the starch layer and the sealing temperature. The optimum seal strength was obtained from the SA/St/St films when heat sealed at 140–160 °C. In addition, the presence of SA layer provided the film structural integrity, preventing the deformation of starch layer during heat sealing. The obtained films had an excellent oxygen barrier. Thus, the SA/St and SA/St/St films could be promising alternatives for the oxygen barrier and single-use flexible packaging.