Preparation And Application Of Polyoxometallates/Polyvinyl Alcohol Active Composite Films

Polyoxometalates?POMs?are a kind of sub-nanometer metal oxide clusters with well-defined structure.Due to their clear structure-activity relationship,POMs have promising value in the field of antibacterial.In this study,several representative POMs were selected,and the application of POMs-polyvinyl alcohol?PVA?composite material was studied in the field of food packaging.?1?As a biocompatible material,Nb plays an important role in surgical care,and it has potential value for food preservation.POMs,K₇HNb₆O₁₉(Nb₆O₁₉),was synthesized by using Nb₂O₅ as precursor.The preservation effect of the PVA active film,which incorporated with Nb₆O₁₉ at level of 0.5%,1%,3%?w/w?,on fresh pork stored at 25? were carried out by testing the weight loss rate,pH and total number of bacteria.The results of the preservation experiment showed that the pH value and the total number of bacteria of the pork wrapped with the active film containing 3%?w/w?Nb₆O₁₉ were lower than the blank control,and the shelf life of one day could be extended under the harsh experiment conditions.?2?A silver-containing polyoxometalates K₁₃Na[AgP₅W₃₀O₁₁₀](AgP₅W₃₀)are explored to control the release of silver with activation mechanism,and nuclear magnetic resonance was used to monitor the release behavior of Ag⁺in the experiment.AgP₅W₃₀ is stable in aqueous solution with the presence of transferrin and common metal ions that are rich in biological fluids,but releases Ag⁺based on the ions exchange between Ag⁺and Na⁺.The release rate of Ag⁺is close to 100%when the molar ratio of Na⁺to AgP₅W₃₀ exceeds 14:1.AgP₅W₃₀ also showed good anti-resistance for both Escherichia coli and Staphylococcus aureus,and the minimum inhibitory concentrations remained unchanged for 20 incubation cycles.In addition,the AgP₅W₃₀-PVA composite packaging films were prepared by the solution casting method and the properties of the films were characterized.When the amount of AgP₅W₃₀ was 3%?w/w?,the tensile strength of the composite film increased by 26.14%,and the elongation at break decreased by 6.59%,without significant change in thermal stability and surface morphology.In the test of inhibition zone,the composite packaging films also showed good bacteriostatic effects for both both Escherichia coli and Staphylococcus aureus.Application of silver-containing polyoxometalates provides an effective method on controlled release of silver ions to fight against bacterial resistance,which has potential value for food package.?3?H₃PW₁₂O₄₀(PW₁₂)contained PVA film was prepared by solution casting method,and the ultraviolet blocking property was evaluated by ultraviolet-visible spectrum and UV-sensitive samples.PVA-PW₁₂ active packaging film has a close to 100%UVB-blocking rate with approximately 90%visible light transmission.In the evaluation of UV blocking property through UV-sensitive samples,the PVA film contained 10%PW₁₂ could protect the UV sensitive samples from color-changing.POMs have the potential to be used in the protection of UV sensitive food components with good transparent in visible region,great UV blocking rate and safety in food contact materials.