Preparation of chitosan/nano-copper sulfide/carrageenan bilayer film and its application in strawberry preservation

Abstract This study developed a bilayer film (CS-xCuS/CA) for food packaging, using chitosan (CS), nano-copper sulfide (CuS NP) and carrageenan (CA) through a casting method and a layer-by-layer approach. The structure of CS-xCuS/CA was analyzed by Fourier transform infrared spectroscopy and X-ray diffraction. The mechanical properties, swelling degree, water vapor permeability, water contact angle, and optical properties of the film were evaluated. At 0 % humidity, tensile strength of the film increased with concentration of CuS NP. Conversely, at 25 % and 50 % humidity, tensile strength initially increased and then decreased with rising CuS NP concentration, a behavior attributed to hydrogen bonding. Furthermore, the incorporation of CuS NP enhanced the hydrophobicity of the film, achieving a contact angle of 118.88° at a CuS NP mass fraction of 0.75 wt%. Additionally, CuS NP significantly improved the UV resistance of the composite film. In tests for strawberry preservation, the efficacy of CS-xCuS/CA increased with the concentration of CuS NP. This film holds promise for applications in fruit packaging and food preservation industry.