Effect of Temperature and Humidity on Water Vapor Transmission Rate of Packaging Materials

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According to different uses, materials barrier properties of oxygen, water vapor, nitrogen, carbon dioxide, air and other gases are tested and expressed by the transmittance of the corresponding gas. Temperature and humidity are two important test parameters in the test of barrier performance. The change of temperature and humidity will affect the internal structure of materials and the movement ability of gas molecules, especially for water vapor permeability test, humidity is the drive for water vapor permeation on both sides of the packaging materials. Therefore, different temperature and humidity conditions lead to different gas transmission rates in packaging materials. The study on how temperature and humidity affect material barrier performance can provide reference for packaging materials in different storage environments

The test specimens are Black & White Film for milk packaging; they are tested under conditions of 23℃、90%RH，38℃、70%RH and 38℃、90%RH for Water Vapor Transmission Rate.

Cup method, infrared sensor method, electrolytic sensor method and humidity sensor method are widely used for testing film Water Vapor Transmission Rate. The test described in this article used cup method which conforms to ASTM E96, Standard Test Methods for Water Vapor Transmission of Materials

The testing instrument is C360M Water Vapor Transmission Rate Test System manufactured by Labthink Instruments Co., Ltd.

Cup method also known as gravimetric method, it refers to the method used to test a specimen Water Vapor Transmission Rate by measuring the weight change of the test dish over time. Cup method is subdivided into dry cup method and wet cup method. Seal the test dish with the specimen to form separate environment inside and outside the test dish. Dry cup method uses test dish filled with desiccant while wet cup method uses test dish filled with distilled water. Control the humidity in the test chamber in order to create humidity difference between the two sides of the specimen, water vapor permeate from the high humidity side through the specimen to the low humidity side, the weight of the test dish increase when dry cup method is used, in wet cup method test, the weight of the test dish decreases. Monitor the weight change over time and calculate and analyze the Water Vapor Transmission Rate.

Cut 3 pieces of specimens with diameter of 74mm from the Black & White Film for milk packaging.

Add certain amount of desiccant into the 3 test dishes. Clamp the specimens on the dishes with sealing rings and screw the lids tightly, be sure that the specimen does not touch the desiccant. Put the dishes in the test chamber of the instrument and close the cover.

Select “dry cup method” mode in equipment operation software, set the parameter information such as sample name, test temperature (23 C), humidity (90% RH), click “test” to start the test. The equipment automatically weighs intermittently according to the set parameters and displays the test results when the test is complete.

Follow the above steps to test the specimens under conditions of 38 ~C, 70% RH and 38 ~C, 90% RH.

Take the arithmetic mean values of the test results of three specimens under each test condition as the water vapor transmission rate. The water vapor transmission rates of the black-white film specimens measured in this test were 1.5674 g /(m2 24h), 2.6073 g /(m2 24h) and 4.1037 g /(m2 24h), respectively at 23 C, 90% RH, 38 C, 70% RH and 38 C, and 90% RH.

By using the testing instrument, the test process was highly automated, and the testing condition was accurately controlled, the test result is reliable. The result shows that, under the same temperature, the specimen in 90%RH has higher Water Vapor Transmission Rate; under same humidity, the specimen in 38℃ environment has higher Water Vapor Transmission Rate. Therefore it can be concluded that specimens’ water vapor barrier performance degrades under high temperature and high humidity.