Method and Apparatus for Online and Selective Measurement of Gas Permeation Through Polymer Films

The invention is a method and a test system for measuring gas transmission rates through barrier materials, not only in single gases but also for gas mixtures. The test system consists of a continuous flow permeation cell, a mass spectrometer with electron multiplier, gas supplies, flow controls and software for online data acquisition. The temperature and relative humidity of the gases are also controlled. A quadrupole mass spectrometer is used as the versatile detector for monitoring the permeation of up to 10 (small molecule) gas species simultaneously.

The gas permeability of polymer films is important in various packaging applications. For example, for many foods and beverages, the package’s resistance to oxygen and water intrusion is the limiting factor determining product shelf life. New and more stringent packaging standards have triggered a new wave of development of novel gas barrier films. At the same time, the demand for fast, accurate and versatile gas permeation test systems is also on the rise. There are no gas permeation test systems on the market that can measure mixed gas permeation or single gas permeation of critical organic compounds responsible for odors.

The test methods as described in ASTM 1434-82 are limited in their application range for not being rate-measurement methods and for the lack of selectivity in gas measurements. Commercial gas permeation measurement devices currently on the market also lack the selectivity in gas measurement as they are limited in the sensor type for detecting a specific gas. For example, a coulometric sensor is needed for sensing oxygen and an IR detector is needed for water vapor. Therefore, three different test systems will be required if one wants to test oxygen, water vapor and carbon dioxide permeation. This certainly adds to the total cost.