Silkworm Pupae-Derived Chitosan/Poly(vinyl alcohol) Films with Silver Nitrate: Structure, Properties, and Antibacterial Activity Against Gram-Negative and Gram-Positive Bacteria

Chitosan-based films are attracting attention as renewable antibacterial materials for food packaging, but chitosan from crustacean sources remains costly, and insect-derived alternatives are hardly explored. This study examined how the polymer ratio and silver nitrate (AgNO3) incorporation govern the properties of films prepared from chitosan (CS) extracted from mulberry silkworm (Bombyx mori) pupae, an abundant by-product of the sericulture industry in Uzbekistan. Films were cast from CS and poly(vinyl alcohol) (PVA) solutions at volume ratios of 75:25, 60:40, and 50:50, with and without AgNO3, and characterized by infrared spectroscopy, X-ray diffraction, scanning electron microscopy with elemental analysis, and thermal analysis, together with mechanical, swelling, acid-stability, and water vapor transmission measurements. Antibacterial activity was assessed by agar diffusion against ten reference and clinical bacterial strains. The characteristic bands of both polymers were retained at essentially unchanged positions in all compositions, and the degree of structural order followed the PVA content. The CS/PVA 50:50 film reached the highest tensile strength (60.7 ± 7.8 MPa) and the lowest thickness-normalized water vapor permeability among the binary films, and AgNO3 increased the residual mass on heating, reduced swelling, and extended the antibacterial spectrum to nine of the ten strains, including two Staphylococcus aureus isolates and Acinetobacter baumannii, whereas no film inhibited Enterococcus faecalis. Film properties can therefore be tuned through composition, supporting the development of silkworm-derived chitosan films as antibacterial polymeric materials for packaging and related non-contact applications.

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