Property Of Nano-silver Food Packaging Composites And Molecular Dynamics Simulation Of Silver Nanocluster In Polyethylene

Due to high antimicrobial activity of silver, nano-silver food packaging composites have a high application value. Although it gives the composite antimicrobial property, the migration of nano-silver in packaging composite is a food security risk. In this paper, the characterization and properties of nano-silver / low density polyethylene(LDPE) food packaging composites were tested. Molecular dynamics simulation method was used to study the movement behavior of silver clusters in polyethylene. Detailed studies are as follows:(1) Nano-silver/LDPE food packaging films were developed by melting-blending and extrus ion. Scanning electron microscope(SEM) and atomic force microscope(AFM) were used to test the characterization of films. Tensile mechanical properties, water vapor permeability, light transmittance and color of the films were tested. The results showed that the addition of nano-silver or plastic additives in the materials made the LDPE film much rougher, and decreased the light transmittance. The addition of nano-silver decreased the elongation at break and the transmittance of the materials increased the roughness and made the materials’ color dark and yellow. Plastic additives added in the material had no influence on the the color of materials, but decreasd the elongation at break of the materials.(2) Film covering method was used to test antimicrobial property of films. Results showed that with the increasing of the recruitment of nano-silver, antibacterial activity of the films became better. The packing effects of these films were evaluated by testing the total numbers of colonies, thawing loss rate and p H. The results showed that the larger the recruitment of nano-silver in film was, the better the film preservation effect was, and the less the p H changed. The recruitment of nano-silver had no influence on thawing loss rate. At the same time, K-B method was used to determine the antibacterial property of silver nitrate solution and nano-silver solution. When the concentration of nano-silver solution was 10 mg·m L-1, it had good antibacterial activity. When the concentration of silver nitrate solution was 20 mg·m L-1, it still had antibacterial activity. When contacted with S.aureus or E.coli, the inhibition zone diameter became bigger with the increas ing of solution concentration. The antimicrobial activity of nano-silver solution was better than that of silver nitrate solution.(3) The software which was used to study the molecular dynamics simulation and Monte Carlo method were described. The force fields, molecular ensemble, periodic boundary conditions, interface effects were discussed. The simulation conditions of nano-silver packaging composite were analyzed. For the model of silver nanocluster in PE, it was suitable to use the Universal forcefield. The cutoff distance was 15.5 ?. Anneal was under NPT ensemble.And molecular dynamics were under NVT ensemble。(4) Molecular dynamic method was used to establish the models. The behavior of silver clusters in polyethylene was analyzed to explain the diffusion law of nano-silver. The data of free volume showed that there was a little free volume for silver clusters to move. The figures of trajectory showed that the moving range at 343 K was larger than that at 293 K and 313 K. The diffusion constant of silver nanocluster in PE at different temperatures were as follows: D293 K,Ag=6.78×10- 9 cm2·s-1, D313 K,Ag =4.38×10-9 cm2·s-1,D343 K, Ag =2.02×10-8 cm2·s-1. The diffusion constant of silver nanocluster in PE at 343 K was the largest one。(5) The interface model was established by molecular dynamics method. The interface was formed by the contact of the polyethylene and water. The silver cluster was on the interface. The trajectorie of silver cluster was analyzed. In a 500 ps molecular dynamics simulation, the silver cluster directly moved towards water layer. The diffusion constant of silver nanocluster on the interface was 7.71×10- 5 cm2·s-1, which was larger than the diffusion constant of silver nanocluster in PE. It could be inferred that silver imigrated from package into food stimulants mostly came from silver on the surface of materials.