Simulation And Analysis Of Air And Moisture Permeability Of High Barrier Film

This paper simulated permeation of oxygen,carbon dioxide and water in the high barrier film PET and EVOH using molecular simulation software Material Studio6.1 and caculated correlation coefficient and discussed the effects of temperature,the degree of polymerization and molecular chain configuration on the permeation.The main research includes:(1)This paper simulated permeation of oxygen,carbon dioxide and water in PET at 283K?288K?293K?298K?303K and 100 kPa.The results show that diffusion coefficient of oxygen,carbon dioxide and water decreases in turn in PET while the solubility coefficient and permeability coefficient increase in turn at the same temperature,which indicates that the permeability of the three kinds of small molecules depends on solubility.The solubility coefficient of the same molecule gradually decreases,and the diffusion and permeability coefficient increase with the increase of temperature,which indicates that the effect of temperature on the permeation process of small molecules depends on the diffusion process.(2)This paper simulated permeation of oxygen,carbon dioxide and water in EVOH at 298 K and 100 kPa.The results show that the arrangement of three small molecules in size of its corresponding coefficient is consistent in EVOH and PET for the same coefficient at 298 K and 100 kPa.Compared with PET,EVOH has lower air permeability and higher moisture permeability due to its extremely low oxygen and carbon dioxide solubility coefficient and higher water solubility coefficient.In addition,for the oxygen barrier performance that will be mostly cared in food packaging,this paper simulated the permeation process of oxygen in EVOH owned different chain structure.The results show that the syndiotactic EVOH has better oxygen barrier performance compared with the isotactic EVOH due to its smaller free volume fraction and higher molecular chain activity.The effect of polymerization on molecular chain activity is greater than its effect on free volume,so the EVOH with high degree of polymerization has better oxygen barrier performance.(3)Through the simulation of permeation of oxygen,carbon dioxide and water in the high barrier film PET and EVOH,the small molecular diffusion trajectory indicates that its diffusion in the polymer is a combination of small vibrations within the cavity for a long time and momentary jump between the cavities in a long distance transition.The density field profile shows that the dissolution of the three small molecules in the polymer is not evenly distributed,mainly concentrated in the place which has larger free volume.The larger the free volume fraction is,the greater the diffusion coefficient and the solubility coefficient are for the same kind of gas and the same polymer film through the calculation of free volume fraction.The research work in this paper can provide effective theoretical basis and guidance to the engineering application of high barrier film in food,fruit and vegetable packaging and preservation.