In situ synthesis and characterization of antibacterial sodium alginate–silver nanocomposite films incorporated with eucalyptus oil for food packaging applications

This study reports the synthesis of sodium alginate (SA)-based nanocomposite films developed through a simple in situ method, incorporating silver nanoparticles (Ag NPs) and eucalyptus essential oil (EO) for use in food packaging and biomedical materials. Characterization using FTIR, XRD, TEM, and FESEM confirmed the successful incorporation of Ag NPs (up to 90 nm) within the SA matrix. Mechanical tests showed that Ag NPs improved tensile strength and Young’s modulus, with the SA-0.3Ag formulation reaching the highest tensile strength at 16.18 MPa. Conversely, EO addition increased flexibility but slightly reduced mechanical strength. Water contact angle measurements demonstrated decreased hydrophilicity with higher Ag NPs and EO content, suggesting improved moisture resistance for packaging applications. Antibacterial tests revealed that pure SA and SA-Gly films lacked antibacterial activity, while Ag NP-loaded films showed noticeable inhibitory zones against Staphylococcus aureus and Escherichia coli , with better results against Gram-positive bacteria. The combination of Ag NPs and EO produced a synergistic antibacterial effect, with the SA-0.3Ag-0.75EO sample showing the largest zones of inhibition (18.48 ± 0.92 mm for S. aureus and 13.14 ± 0.65 mm for E. coli ). These results highlight the potential of these nanocomposite films, which offer improved structural strength, water resistance, and antibacterial activity. • Sodium alginate–silver nanocomposite films were prepared via a simple in situ synthesis route. • Silver nanoparticles were uniformly generated within the alginate matrix without external stabilizers. • Incorporation of eucalyptus essential oil enhanced the performance of the films. • The composite films exhibited improved mechanical and water-resistant properties. • The developed films show potential for antimicrobial food-packaging applications.