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Imballaggio lattiero-caseario
Industry knowledge 丨 Raw material barrier
  • 2019-06-18 08:47:04
In many food packaging, there are high requirements for barrier properties, which directly affect the shelf life of food.
Barrier property can be achieved by barrier materials, usually in the standard state (23 degrees Celsius, 65% relative humidity), 25 micron membrane oxygen permeability below 5ml / (m2.d), and moisture permeability in 2g / ( M2.d) The following materials.
1. Orientation degree: high degree of orientation and high barrier property;
2, the rigidity of the polymer chain: the polymer has a high glass transition temperature, strong rigidity, and thus good barrier properties;
3. The gap between the polymers: as small as possible, the packing degree of the polymer chain is dense;
4. Cohesive energy density: high polarity polymer (containing -OH, -CN) has high binding force and gas diffusion is difficult;
5. Sensitivity to water vapor: plasticization after absorption of water vapor, weakening of bonding force, and easy passage of gas.
The speed of the whole infiltration process is determined by two factors, one is the speed of penetration and dissolution in the polymer, which is represented by the solubility parameter; the other is the speed at which the permeate is moved in the polymer molecule, expressed by the diffusion coefficient.

From the mechanism by which the gas permeates the film, it is known that the gas is first adsorbed on the surface of the film and then diffused through the film. For the film polymer with high gas barrier properties, the basic laws of gas permeation mechanism and polymer properties are as follows:
1. Orientation degree: high degree of orientation and high barrier property;
2. the rigidity of the polymer chain: the polymer has a high glass transition temperature, strong rigidity, and thus good barrier properties;
3. The gap between the polymers: as small as possible, the packing degree of the polymer chain is dense;
4. Cohesive energy density: high polarity polymer (containing -OH, -CN) has high binding force and gas diffusion is difficult;
5. Sensitivity to water vapor: plasticization after absorption of water vapor, weakening of bonding force, and easy passage of gas.
Different infiltration objects have different permeation processes for the same material. Generally, the barrier properties of materials are classified into the barrier properties of materials to inorganic gases according to the nature of the infiltrated objects (that is, the so-called gas permeability, and can be further divided into Oxygen permeability, nitrogen permeability, carbon dioxide permeability, etc.), barrier properties against water vapor, and barrier properties to organic substances. The principle of penetration of materials by these three types of materials is different, and the infiltration process varies greatly due to the difference in the permeating substances.

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