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

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.

Test Specimen

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.

Test Standards

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

Testing Instrument

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

4.1 Test Principle

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.

C360M Water Vapor Transmission Rate Test System

4.2 Instrument Features

C360M Water Vapor Transmission Rate Test System supports dry cup method and wet cup method. The test range of dry cup method is 0.01 ~ 1,200 g/(m2·24h). The test range of wet cup method is 0.01 ~ 10,000 g/(m2·24h). Six specimens can be tested simultaneously, which improves the testing efficiency. The test temperature of the test chamber can be controlled within the range of 15~55℃ ± 0.2℃. The instrument is equipped with high efficiency and mist-free automatic humidity regulator which can precisely control the humidity within the range of10%~90%± 1%RH. The desiccator has a long service life up to 20000 hours, meets the requirements for long-term continuous tests. The specimen size is Φ74 mm and the test area is 33 cm2. Air velocity in the test chamber is monitored and regulated in real time. Patented test chamber and test dishes with advanced fluid dynamics and thermodynamic designs ensure the uniform flow rate over the specimen surface, stable temperature and humidity, create a uniform and stable testing environment. As a result, the test duration is shortened and the test results are more accurate. Unique, optional, DataShieldTM system, meets the requirements for centralized management of user data. It supports a variety of formats of exported data. Reliable security algorithms are used to prevent data leakage. It supports universal wired and wireless LAN, optional private wireless network, and supports third-party software.

4.3 Application Scope

(1) The instrument is applicable to determination of water vapor transmission rate of film, sheeting, paper and paperboard, textile and non-woven fabrics, etc. Films include plastic film, paper plastic composite film, geomembrane, co-extruded film, waterproof breathable film, aluminum coated film, aluminum foil and aluminum plastic composite film. Sheeting includes various engineering plastic, rubber, building material, insulation material, such as PP, PVC, PVDC and nylon sheeting. The instrument can also be used to test the water vapor transmission rate of building material, aseptic wound protection films and medical plasters, etc.

(2) The instrument conforms to multiple standards including ISO 2528, ASTM E96, ASTM D1653, TAPPI T464 and DIN 53122-1, GB 1037,GB/T 16928, YBB00092003

Test Process

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

b)        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.

c)         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.

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

e)         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.

7. Conclusion

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.

Labthink Instruments Co., Ltd is one high-tech enterprise specialized in research & development and manufacturing of packaging testing instruments as well as packaging testing services. The new Labthink C series instruments adopted Infrared, Coulometer, Electrolysis and Cup Method, are equipped with Labthink’s self-developed sensors with greatly improved reliability, accuracy, efficiency and repeatability.

For more details, please visit www.labthink.com.