Gas Permeability

Question:

 

In the context of a project with a customer, we are looking for a breathable film. It must also be possible for nitrogen to diffuse through the film. Please advise us of thickness of your films.

 

Answer:

 

High pressure polyethylene (LDPE - Low Density Polyethylene) is gas and steam permeable, as are all plastics. This permeability plays an significant role, particularly with packaging materials. With films, it is generally permeability q which is specified without reducing the values to units of thickness, rather than P - the coefficient of permeability. Below, the permeability of a 100 my thick LDPE film (thickness density 0.918 g/cm³) for various gases and steams at 23°C:

Gas or Steam Permeability cm³/m² x d x bar (DIN 53 380)
Nitrogen 700
Qxygen 2.000
Helium 5.000
Hydrogen 8.000
Carbon Dioxide 10.000
Sulphur Dioxide 40.000
Ethylen Dioxide 100.000
Methyl Bromide 300.000
   
Steam 1g/m² x d (DIN 53122)

The permeability is dependant on the density and thickness of the film. We produce LDPE films from a strength of approx. 20 my to almost 500 my, HDPE (density approx. 0.95 g/cm³) in strengths from 7 my to approx. 150 my.

 

As well as film thickness and density, the chemical nature of the contents, the storage temperature and the storage time also have an effect on the permeability.

 
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