ASTM F2622 - Standard Test Method for Oxygen Gas Transmission Rate Through Plastic Film and Sheeting Using Various Sensors:
The ASTM F2622 test method is based on the principle that a stream of nitrogen gas is continuously passed over one side of the test specimen in a chamber at a controlled temperature and humidity, while oxygen is passed over the other side of the specimen. The permeating oxygen is carried by the nitrogen into an oxygen sensor where it is measured.
For most packaging applications, the critical property of a packaging material is the permeation of oxygen. Oxygen transmission rate (OTR) is a measurement of the amount of oxygen gas that passes through a substance over a given period.
There are several methods that could be used to determine OTR:
- Manometric or Pressure Differential: In this technique, the barrier film to be tested is sealed between two chambers, with the higher pressure on one side. The decrease in pressure on the higher pressure side is measured over time, and the rate of gas transmission is calculated.
- Coulometric detection: In this method, oxygen passing through the specimen is detected electrochemically. Oxygen molecules are reduced at a cathode and, for each molecule, a certain number of electrons are generated and measured.
- Constant Volume Variable Pressure: This technique uses a test chamber and a precisely controlled pressure regulating system. The barrier film separates the test chamber into two halves. One half of the chamber is slowly pressurized with a test gas, while the pressure in the other half is monitored.
It is important to note that the precision and bias of each design need to be individually established to determine the applicability of the instrument or method to meet the needs of the user.
It's important to understand that this method is not meant to be the definitive test for oxygen gas transmission. Other methods may be more appropriate depending on the specific requirements of a project.
The accuracy and precision of the measurement are highly dependent on the correct use of the equipment, including calibration and operation. In addition, the test result is also affected by the sample uniformity, thickness, and surface quality.
Furthermore, the testing conditions, such as temperature and humidity, also influence the result and should be controlled.