| Flexible packages are applied more and more in food packages for the advantages of wide varieties, cheap price, light weight and easy to take. However, some problems which are occured during the process of heat sealing of flexible packages cannot be ignored. It’s easy to appear some sealing defect causing the channel leakage. The gas exchange through the channel can lead to physical or chemical changes of food and thus accelerate the food corruption, shorten the shelf life, etc. At present, there are less study on gas exchange through heat sealing micropore channel. Therefore, to establish a gas exchange model of flexible packages with heat sealing micropore channel is essential for determining the shelf life of products with sealing leakage.The gas exchange theory of heat sealing micropore channel was studied and summarized firstly in this paper. And the gas exchange model of flexible packages with heat sealing micropore channel was established and the influence of the channel characteristics parameters on gas exchange were studied at the same time. The shelf life prediction model of flexible packages with micropore channel was established by combining the products’ moisture absorption characteristics with water vapor exchange model. Finally, the models were applied to solve the packaging problems under actual working conditions. The main contents and results are as follows:(1) The gas exchange model of flexible packages with heat sealing micropore channel was established and verified. In this paper, the gas exchange model through heat sealing micropore channel was studied by contrasting four diffusion models, namely fick diffusion, viscous diffusion, knudsen diffusion and transition diffusion. The gas exchange model was established based on Hagen-Poiseuille law under the condition of micropore diameter ranging from 60 to 220μm. Heat sealing micropore channel mathematical model can be used to get the micropore radius estimated values. The gas exchange mathematical model based on Hagen-Poiseuille law was verified by the deviations within 5% comparing the estimated values and the actual values.(2) The influence of the channel characteristics parameters on gas exchange were studied. The influence on gas exchange were obtained by changing the channel characteristics parameters of micropore diameter, pore length, pressure difference, the number of pores and channel shapes. The results showed with the increase of micropore diameter, pressure difference and the number of pores, gas exchange increased and changed obviously. With the increase of pore length, gas exchange decreased. And after contrasting different channel shapes, the model was proved suitable for straight pore and inclined pore. It needs further discussion to see if it was suitable for channels with turning angle.(3) The products’ shelf life prediction model of flexible packages with heat sealing micropore channel was established and verified. The biscuits were tested by putting on the dynamic moisture adsorption instrument. And then the relationship between water activity and the equilibrium moisture content was obtained under the condition of 23℃ and 35℃. By comparing the four common moisture absorption models, GAB model turned out to be the most suitable one for the biscuits. The water vapor exchange model through heat sealing micropore channel was established based on Fick’s law. Considering permeability barrier film and permeability film, the biscuits’ shelf life prediction model of flexible packages with micropore channel was established combining water vapor exchange model with the biscuits’ isothermal moisture absorption model. The model was verified by the accelerated test.(4) The flexible packages with heat sealing micropore channel were applied under special working condition. Considering the special working condition, the flexible packages that were needed to transport to the plateau environment were added heat sealing tapes to assure the bags were not bulged. The existing flexible packages with sealing tapes were tested to get the equivalent cylindrical pore diameters. Through studying the influence of the heat seal parameters on gas exchange, it turned out the thickness was the decisive factor. Therefore, gas exchange could be changed by changing the thickness of sealing tapes in actual flexible packages. At the same time, the maximum radius of the micropore channel which satisfied the specific shelf life can be designed based on the shelf life prediction model. |
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