The air permeability of food packaging is not enough, it will cause food spoilage and even produce toxic substances. In order to prevent the above situation, it is necessary to test the gas permeability of food packaging to ensure the gas barrier performance of the packaging material. Divided from the testing principle, the permeability test method can be divided into two types: differential pressure method and electric quantity analysis sensor method.
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1. Test principle of differential pressure method
Use the film to be tested to divide the test chamber into two independent spaces, fill one side (high-pressure chamber) with test gas, and form a certain pressure difference between the two sides of the sample. The gas in the high-pressure chamber penetrates the low-pressure chamber through the film The gas permeability can be obtained by measuring the pressure or volume change of the low-pressure chamber.
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2. Electricity analysis sensor method test principle
The test chamber is divided into two independent airflow systems with the film to be tested, one side is the flowing gas to be tested (pure oxygen or oxygen-containing mixed gas can be used, and the relative humidity of the gas can be set), and the other side is the flow Of nitrogen. The pressure difference between the two sides of the sample is equal but the oxygen partial pressure is different. Under the effect of the concentration difference, the oxygen passing through the film is sent to the electricity analysis sensor under the load of the nitrogen flow, thereby calculating the oxygen permeability of the material.
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The test principle of the differential pressure method and the equal pressure method are different, the test conditions are different, and the unit of the test result is also different (the unit of the differential pressure method is cm3 / m2 • 24h • 0.1MPa, and the unit of the equal pressure method is cm3 / m2 • d) Therefore, the uncorrected raw data obtained by these two test methods is theoretically not comparable. However, by using standard membranes to calibrate the isobaric equipment and use the correction factor for the formal test, the results of the differential pressure method and the isobaric method can be compared.
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Due to the support of the membrane technology theory, the differential pressure method has always been used as a basic method in gas permeability testing, which is commonly used by scientific research and testing institutions. Its outstanding advantage is that it has no selectivity for test gas, and its versatility for different test gases is very good. With the advancement of vacuum gauge detection technology and the application of vacuum technology in equipment design, the detection accuracy of equipment and the repeatability of test data have been greatly improved.
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The sensor method emerges as the oxygen detector technology continues to mature. Since the sensor used is a consumable component, the correction factor obtained by device calibration is not long-term effective, and periodic device calibration needs to be performed according to the requirements. When the loss of the sensor reaches a certain level, it must be replaced.
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Through the above two methods, you can accurately measure the air permeability of food packaging, and check the quality of food packaging.
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