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What Are Factors Affecting Barrier Properties Of Polymers For Packaging?
In general you have polymer-based factors and molecule-based factors.
Polymer-based include temperature, plasticization, chain lenght, crystallinity, orientation and the presence (if any) of a reinforcing aggent (such asin nanocomposite films).
Molecule - based factors, meaning factors that are based on the nature of the diffusing species, include the size of the molecule (molar volume or molecular weight), the shape (linear or spherical?), the possibility of interactions with the polymer (as an example hydrogen bonding with a polyester or polyamide).
Of course you also have to think about other technical parameters like thickness or the presence of any microholes or defects in the polymer.
Polymer-based include temperature, plasticization, chain lenght, crystallinity, orientation and the presence (if any) of a reinforcing aggent (such asin nanocomposite films).
Molecule - based factors, meaning factors that are based on the nature of the diffusing species, include the size of the molecule (molar volume or molecular weight), the shape (linear or spherical?), the possibility of interactions with the polymer (as an example hydrogen bonding with a polyester or polyamide).
Of course you also have to think about other technical parameters like thickness or the presence of any microholes or defects in the polymer.
Barrier can be influenced by many factors including the type of material, thickness, orientation, humidity, defects, processing, and crystallinity. The barrier is directly proportional to thickness for typical film gauges. It is important to remember that coated films such as metallized PET are actually a composite structure. For metallized films, the thickness of the metal, expressed as optical density, is the determining factor. Thick foil is often used for its excellent barrier properties.
An increase in temperature will typically increase the permeation of a gas. Humidity can strongly effect barrier properties. For example, oxygen permeation through ethylene vinyl alcohol is strongly effected by moisture while high density polyethylene is not strongly effected by moisture. For metallized films, it is important that the metal not be damaged or attacked by the product.
Orientation has the same effect as increasing crystallinity. As a result, oriented PET has better barrier properties compared to unoriented PET. Thermoforming results in a thinner package and will reduce the barrier of the package. The orientation from thermoforming is not enough to compensate for the thinner film. The type of permeant will also change transmission rates. For example, carbon dioxide transmission rates are about 2-6 times higher than oxygen. Primarily, the polarity and size of the molecule and polarity of the resin determine this.
An increase in temperature will typically increase the permeation of a gas. Humidity can strongly effect barrier properties. For example, oxygen permeation through ethylene vinyl alcohol is strongly effected by moisture while high density polyethylene is not strongly effected by moisture. For metallized films, it is important that the metal not be damaged or attacked by the product.
Orientation has the same effect as increasing crystallinity. As a result, oriented PET has better barrier properties compared to unoriented PET. Thermoforming results in a thinner package and will reduce the barrier of the package. The orientation from thermoforming is not enough to compensate for the thinner film. The type of permeant will also change transmission rates. For example, carbon dioxide transmission rates are about 2-6 times higher than oxygen. Primarily, the polarity and size of the molecule and polarity of the resin determine this.