Permeability is different, different gases on the same material to learn is to earn!

1, gas packaging packaging also calls the displacement gas packaging, packaging is called on the international MAP ( 即气调保鲜包装) , it is in a vacuum packing and filling nitrogen development on the basis of the improvement of a kind of modified atmosphere packaging, mainly used in food preservation. Gas packing the principle is to use modified atmosphere gases ( 2 - Four kinds of gas according to the characteristics of food mixing ratio) , to displacement of box or air bags, change boxes ( Bag) Food in the external environment, inhibit bacteria, Microbes) Growth, slowing the rate of metabolism of fresh fruits and vegetables, so as to extend the freshness and shelf life of food. Fresh-keeping, for example: fresh fruits and vegetables after harvest on respiration, consume oxygen carbon dioxide, gradually increase the amount of carbon dioxide in the environment and reduce the concentration of oxygen, high permeability of plastic film on the atmosphere in the gas exchange, supply the consumption of oxygen and carbon dioxide. When the gas velocity of membrane permeability and fruit and vegetable equals the respiration rate, concentration of gas to achieve a balance in the bag, can make to maintain a weak respiration rate and does not produce anaerobic respiration, in order to delay the mature of fruit and vegetable and fresh. By packaging can be achieved on the premise of not use preservatives, additives to ensure the food taste, nutrition and freshness. 2, different gas permeability of materials and aerosols packaging system design should consider the various factors, one of the most important factor is that the relative content of CO2 and O2 inside the packaging, this is mainly by gas concentration inside the packaging and gas permeability of packaging materials, is the ratio of modified atmosphere gas control precision and gas replacement rate of packaging materials. With vacuum packing or nitrogen inflator, gas packaging materials are mostly low blocking materials, has great gas permeability. Material permeability differences and macromolecule aggregation state ( Crystalline) , polymer structure on the diffusivity and solubility of the gas, the influence of using additives and other factors. But different gas is not the same on the permeability of the same material, for the same material, usually in N2 through minimum, O2 slightly bigger, the largest CO2, the size and the shape of the gas molecules with gas molecules. Molecular dynamics, the smaller the diameter of the easier diffusion in polymer, the larger the diffusion coefficient. But the size of gas molecule diameter is not the only factor of permeability, for permeability is related to the gas solubility in the polymer. Other molecules can also affect the shape of permeability, studies have shown that elongated molecule diffusion and penetration ability, the strongest permeability and molecular shape small changes can cause a lot of changes. 3, how to choose the suitable packaging material, no doubt, to package the products in a controlled atmosphere, we must pack the goods according to the characteristics of the product material permeability is the reasonable choice. Commonly used in gas packaging is a mixture of O2, CO2, N2, gas, or a mixture of O2, CO2, so when choosing gas packaging materials must be on the material of the permeability, the CO2 permeability of O2, N2 accurately testing permeability and must not discriminate between detection of various gases, or just detection materials of O2 transmittance again according to the proportion of experiences to convert, must conduct a comprehensive inspection. As you can imagine, if the target detection error, or without full testing packaging material selection is caused by gas, not only can cause huge economic losses to the enterprise, but also cause serious waste of resources. At present, the commonly used in the world of permeability test method with differential pressure and constant pressure method two kinds big. Pressure equipment such as a whole, the test object is a single, now can only detect material O2 through sex or CO2 permeability, there has not been company able to provide for detection of N2 through sex and other pressure equipment. For differential pressure method of equipment was completely different, because this method itself is no selectivity to test gas, can undertake the conventional gas such as O2, N2, CO2 test, the test of low cost, also can realize automatic test environment temperature. Also due to the support of the theory of membrane technology, using the method of vacuum differential pressure equipment can not only detect various common gas permeability of sample, can give at the same time test gas diffusion coefficient and the solubility coefficient of the sample. Differential pressure method, relative to the pressure equipment such as air permeability test equipment is more suitable for gas research institute of packaging materials and the use of manufacturers on the material to conduct a comprehensive testing and comprehensive analysis.