Developed by the American Society for Testing and Materials (ASTM),ASTM F1927 "Standard Test Method for Determination of Oxygen Gas Transmission Rate, Permeability, and Permeability at Controlled Relative Humidity Through Barrier Materials Using a Coulometric Detector" describes a test method for determining the transmission rate of oxygen gas through films, sheets, laminates, co-extrusions, or plastic-coated papers or fabrics at a specified temperature and relative humidity level under steady state.
This test method extends the common practice of using zero humidity, or at best, assumed humidity. Humidity plays a significant role in the oxygen gas transmission rate of many materials. This test method allows the determination of the oxygen gas transmission rate, the film's permeability to oxygen, the film's permeability to thickness, and the oxygen permeability coefficient for homogeneous materials at a specific temperature and relative humidity.
For the purposes of this standard, the following terms and definitions apply:
The oxygen gas transmission rate is determined after the sample reaches equilibrium at a specific temperature and humidity. 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 at a specific temperature and relative humidity, and the other chamber is purged with an oxygen stream, which may be at the same temperature as the nitrogen stream but at a different relative humidity. This more closely simulates actual shelf conditions. As oxygen gas diffuses from the film into the nitrogen carrier gas, it is transported to the coulometric detector, where it generates an electric current proportional to the amount of oxygen flowing to the detector per unit time.
The oxygen gas transmission rate at a given temperature and relative humidity is a significant determinant of the protection provided by barrier materials for packaging. However, it is not the sole determinant, and additional empirical testing should be used to correlate packaging performance with the oxygen gas transmission rate. It is suitable as an arbitrageur test method, provided the buyer and seller agree on sampling procedures, standardization procedures, test conditions, and acceptance criteria.
The presence of certain interfering substances in the carrier gas stream can lead to unwanted electrical outputs and error factors. Interfering substances include free chlorine and some strong oxidizing agents. Exposure to carbon dioxide should also be minimized to prevent damage to the sensor by reacting with the potassium hydroxide electrolyte.
The tests utilize an oxygen gas delivery device. Alternative systems need to be evaluated to ensure equivalent performance. The device has a diffusion cell consisting of two metal halves that, when closed over the test sample, will accurately define a circular area. Typical acceptable diffusion cell areas are 100 and 50 cm². The volume enclosed by each cell half when compressed is not critical: it should be small enough to allow rapid gas exchange, but not so small that a sagging or bulging unsupported film contacts the cell edges. The diffusion cell should be equipped with a temperature measuring and control facility and a means of measuring and controlling relative humidity. Temperature control is critical because relative humidity can vary by as much as 5 percent RH/degree Celsius in certain temperature zones. A compact design of the diffusion cell structure, along with associated controls, allows for better temperature control. Temperature should be controlled to plus/minus 0,5 degrees Celsius or better.
A coulometric detector is a type of analytical detector used in chemical analysis, most commonly in gas chromatography (GC), that measures substances based on the total electrical charge required to carry out a chemical reaction involving an analyte. The detector uses an electrochemical cell in which the target compound undergoes oxidation or reduction. The reaction produces or consumes electrons, and the amount of electrical current (or total charge) required is measured. Because the electrical current is directly proportional to the amount of analyte, this allows for highly accurate quantification. A coulometric titrator determines the water content in samples by measuring the charge required to produce iodine, which will react with water.
The coulometric detector provides very accurate results, especially when properly calibrated and used under optimal conditions. It is a highly sensitive and precise method, particularly for trace analysis.
Our organization, which has been supporting businesses across all sectors for years through a wide range of testing, measurement, analysis, and evaluation activities, boasts a strong team of employees who closely follow global developments in science and technology and are constantly improving themselves. In this context, we also provide testing services in accordance with the "ASTM F1927 Standard Test Method for Determining Oxygen Gas Transmission Rate, Permeability, and Permeability Through Barrier Materials at Controlled Relative Humidity Using a Coulometric Detector."
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