Preparation of composite films composed of polyvinyl alcohol, shellac and carboxymethyl chitosan-CuO nanoparticles and their application in food preservation

This study aimed to develop a bilayer film prepared by layer-by-layer solution casting method from polyvinyl alcohol (PVA) and shellac (sh). And the degradable antibacterial films (PVA@CMCS-CuO/Sh) were prepared with carboxymethyl chitosan-copper oxide nanoparticles (CMCS-CuO NPs) as the antibacterial agent in the PVA matrix. The chemical composition, morphological structure, mechanical properties, water resistance, antimicrobial property, and biodegradability of the composite films were also investigated. With the addition of CMCS-CuO NPs at 1, 2.5, and 5%, the water resistance of the films increased significantly, and the elongation at break (EAB) and tensile strength (TS) increased first and then decreased, and at 2.5% of CMCS-CuO NPs, the films had better mechanical properties and UV-blocking properties, and the inhibition rate of E. coli and S. aureus reached over 90%. Freshness tests on cherry tomatoes showed that PVA/Sh and PVA@CMCS-CuO/Sh films had a certain freshness retention effect, maintaining higher hardness and lower weight loss rate within two weeks. Degradation experiments showed a higher soil biodegradation rate of the bilayer films within 30 days. Compared with PVA films, PVA/Sh and PVA@CMCS-CuO/Sh films have superior antimicrobial activity and freshness preservation performance and have higher potential for food preservation applications.