Measures of permeability (O2, H2O)

Applications

• Measure of permeability to oxygen and water steam of films, of corks, of plastic bottles, of polymer films
• Evolution of permeability according to humidity and temperature

Operational principle

Different setups allow to measure the passage of a gas through a film. They have in common a splited (in two) cell by the sample to be tested. Any passage of gas from a compartment to an other can only happen through the sample. In every setups the compartment above contain the gas which we want to test the rate of passage at a certain pressure. Differences are at the below compartment level in which we measure the quantity of gas that went through the sample. There are two major types of setups:

1. After we make it empty, the upstream pressure in the compartment is measured. This pressure going up allows to determinate permeability. Advantage : the measure can be done whatever the gas tested. Disadvantage : samples to test (polymer film for instance) have to be solid enough to resist to the difference of pressure between both compartements (above and below).
2. The two compartments have the same pressure but, in the compartment below, we have a pure carrier gas which does not contain permeant molecule (O₂, H₂O). Disadvantage : the permeant captor is much more complex than a simple pressure captor (mass spectrometer, coulometric captor). Advantage : a better precision and samples do not need to be mechanically resistant.