Phase Separation Drives the Spatial Distribution of Waxes in Agar/Maltodextrin Emulsified Films: Relationships Between Structure and Performance

Phase separation-induced bilayer construction offers a one-step strategy to reduce the moisture susceptibility of polysaccharide edible films, yet the spatial distribution mechanism of the hydrophobic phase remains unclear. Herein, agar/maltodextrin (AM) films incorporated with five distinct waxes (soy wax, paraffin wax, beeswax, candelilla wax, and carnauba wax) were fabricated to investigate how the intrinsic melting behaviors of lipids regulate phase separation, microstructural evolution, and film properties. ATR-FTIR analysis indicated that the upward migration and aggregation of waxes weakened the molecular interactions within the upper AM matrix. SEM and AFM observations confirmed that the formation of a wax-enriched surface layer is strongly dependent on the relationship between the wax melting point and the film-drying temperature. The AM-candelilla wax (AM-CW) film exhibited the most distinct phase separation, forming a pseudo-bilayer structure that yielded the lowest water vapor permeability (3.82 × 10−13 g·m−1·s−1·Pa−1). Conversely, carnauba wax (CRW), possessing a melting point higher than the drying temperature, underwent premature crystallization before the matrix fully dried. This hindered full stratification and resulted in a random wax distribution within the AM network, compromising the moisture barrier. Furthermore, DSC, XRD, and Raman spectroscopy showed that higher wax melting temperatures induced greater crystalline ordering. This highly ordered structure provided the AM-CRW film with the highest tensile strength (22.57 MPa) and Young’s modulus (867.99 MPa), but at the expense of a significantly reduced elongation at break (3.59%). These findings demonstrate that matching lipid melting properties with processing temperatures is critical for tailoring phase separation and optimizing the barrier performance of biopolymer-based food packaging.