Chitosan–Poly(vinyl alcohol)–Tea Tree Essential Oil Composite Films: Fabrication, Physicochemical Properties, and Inhibitory Effects on Representative Bacterial Strains and Application for Blueberry Preservation

Conventional polyethylene (PE) wrap has poor degradability and causes environmental pollution. Meanwhile, pure chitosan (CS) films exhibit weak mechanical strength, and CS–polyvinyl alcohol (PVA) blend films show limited inhibitory performance. To address these limitations, a biodegradable bio-based preservation film was fabricated by incorporating tea tree essential oil (TTEO) into a CS–PVA matrix via a solvent-casting method. The formulation was optimized using single-factor and orthogonal experiments. The films were characterized using SEM, FTIR, XRD, and TGA; their optical, swelling, mechanical, and inhibitory properties were evaluated. Blueberries were coated with the composite film and stored at ambient temperature for 10 days. The optimal formulation consisted of 3.0 wt% CS, 0.5 wt% TTEO, and 1.5 wt% PVA, with good inter-component compatibility driven by hydrogen-bond interactions. The optimized composite film achieved a light transmittance of 88.30% at 600 nm and exhibited inhibition-zone diameters of 1.18 cm and 1.14 cm against Staphylococcus aureus and Escherichia coli, respectively. Compared with the pure CS film, the composite film obtained higher elongation at break (141.36%) and stress at break (0.42 MPa). The composite-film-coated blueberries showed suppressed MDA accumulation and reduced water loss under ambient storage conditions. This composite film exhibited superior comprehensive performance compared with the pure CS film and provides a promising degradable active-packaging candidate for fruit and vegetable preservation.