ASTM F2476-20 Standard Test Method for Determining Carbon Dioxide Gas Transmission Rate (CO2TR) Through Barrier Materials Using an Infrared Detector

The standard "ASTM F2476-20 Standard test method for determining the transmission rate of carbon dioxide gas (CO2TR) through barrier materials using an infrared detector" developed by the American Society for Testing and Materials (ASTM) describes a procedure for determining the steady-state transmission rate of carbon dioxide gas through plastics in the form of films, sheets, laminates, coextruded or plastic-coated papers or fabrics. In the case of homogeneous materials, it allows the determination of:

• Carbon dioxide gas transmission rate (CO2TR)
• Permeability of the film to carbon dioxide gas (PCO2)
• Carbon dioxide permeability coefficient (P'CO2)

For the purposes of this standard, the following terms and definitions apply:

• The carbon dioxide permeability coefficient (P'CO2) is the product of permeability and film thickness. Permeability is only meaningful for homogeneous materials, in which case it is a property of the bulk material. This quantity should not be used unless the relationship between thickness and permeability has been confirmed by tests using several different thicknesses of the material.
• Carbon dioxide permeability (PCO2) is the ratio of TR to the difference in partial pressure of carbon dioxide on the two sides of the film.
• Carbon dioxide transmission rate (CO2TR) is the amount of carbon dioxide gas passing through unit area of ​​parallel surfaces of a plastic film per unit time under test conditions. Test conditions, including temperature and partial pressure of carbon dioxide on both sides of the film, shall be specified.

The carbon dioxide gas transmission rate is determined after the sample has reached equilibrium in the dry test environment. In this context, a dry environment is considered to be one in which the relative humidity is less than 1 percent. The sample is mounted as a sealed semi-barrier between two chambers at ambient atmospheric pressure. One chamber is slowly purged with a nitrogen stream, the other chamber with carbon dioxide. As the carbon dioxide gas diffuses through the film into the nitrogen carrier gas, it is carried to an infrared detector where an electrical output is produced whose magnitude is proportional to the amount of carbon dioxide flowing into the detector per unit time.

Carbon dioxide gas transmission rate (CO2TR) is an important determinant of the packaging protection provided by barrier materials. However, it is not the sole determinant and additional testing based on experience should be used to relate packaging performance to CO2TR. It is suitable as an arbitration test method provided that the buyer and seller agree on sampling procedures, standardization procedures, test conditions and acceptance criteria.

Temperature is a critical parameter affecting CO2TR measurement. Careful temperature control will help minimize changes due to temperature fluctuations. Temperature should be maintained within plus/minus 0,1 degrees during testing. The average temperature and temperature range found during a test should be reported. Accurate temperature control is more easily achieved if the instrument is placed in a temperature-controlled environment.

The sensor will need time to settle into a low reading characteristic of a good carbon dioxide barrier after being used to test a high transmission barrier. Therefore, materials with comparable gas transmission qualities should be tested together. Calibration should be performed with an appropriate amount of carbon dioxide comparable to the CO2TR of the tested samples.

The sampling units used to determine CO2TR should be representative of the amount of product for which data is required. Care should be taken to ensure that the samples are representative of conditions across the width and length of a roll of film.

Test specimens shall be representative of the materials being tested and free from defects including wrinkles, folds and pinholes (unless these are a characteristic of the material being tested). If required, the average thickness shall be determined to the nearest 2,5 µm using a digital micrometer (or equivalent) at at least five points distributed over the entire test area. The maximum, minimum and average values ​​shall be recorded.

If a sample is brittle (such as a thin coating or unprotected metallization), measuring the material may compromise or scratch the barrier layer. For such samples, it may be preferable to analyze the material thickness after the transmission rate test. If the test sample has an asymmetric (multilayered) structure, the two surfaces should be marked with appropriate distinguishing marks and the orientation of the test sample in the diffusion cell should be reported.

If a special conditioning procedure is used, this should be included in the report.

Our organization, which has been trying to support businesses from every sector with its testing, measurement, analysis and evaluation studies carried out in a wide range for years, has a strong staff that closely follows the developments in the world in the field of science and technology and constantly improves itself. In this context, testing services are also provided to businesses in accordance with the standard "ASTM F2476-20 Standard test method for determining the carbon dioxide gas transmission rate (CO2TR) through barrier materials using an infrared detector".