Carbon Dioxide (CO₂) Vapour Permeability Testing

Commercial measurement of Carbon Dioxide (CO₂) permeability rates is widespread, though it is particularly import for carbonated drinks containers, MAP packaging and corrosion.

Carbonated drinks bottles

These which are commonly made from polyethylene terephthalate (PET) as this material has good barrier properties against both oxygen and carbon dioxide. Versaperm can measure the CO₂ (and other gas) permeability of bottles or containers that are filled with fizzy drinks. It can also measure the permeability of the material in flat sample format. These two measurements are unlikely to be identical due to the thermoforming process, which can increase permeability by several hundred percent!

MAP food packaging

Controlling the flow or build-up of carbon dioxide can be critical if you are to avoid degradation in many fresh foods. MAP (Modified Atmosphere Packaging) technology can substantially reduce the rate of decay associated with processed fresh vegetable, fruits and other edible products. This leads to both a significant increase in both shelf-life and quality. Using films with the right CO2 (and oxygen etc) permeabilities controls, amongst other things, the respiration rate which is central to the MAP design. Unfortunately the complication of each food or vegetable type needs entirely different permeabilities and what is best for one product may actually speed decay in others. Hence the need for comprehensive testing.

The strength and effectiveness of a pack's seal can also play a part in this. For more information on this aspect click here.

Corrosion

To prevent excessive carbonation of steel, for example in concrete units, they need to be treated with a coating with a low CO2 vapour permeability (i.e. high resistance). A barrier against this CO2 is often needed to avoid carbonation, which leads to severe corrosion and is probably the most critical problem in the durability of concrete structures. At the same time there is also the need for a relatively high permeability (low resistance) for water vapour to allow any vapour to escape from the structure.

Testing vapour permeability

Typically a specimen is placed in the measurement chamber which separates the two sides of the material under test. One of these is exposed to a an inert atmosphere (e.g. a constant flow of nitrogen) while the other is exposed to CO₂. Once a steady state has been achieved the amount of oxygen in the nitrogen is measured with any one of a number of sensors (depending on the sensitivity required) and the permeability is simply read off the screen.

Click for a press release

Click here for a link to permeability on Wikipedia

Click here for a link to Carbon Dioxide on Wikipedia