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Standard: |
TAPPI |
Method: |
TAPPI T 448 |
Title: |
Water vapor transmission rate of paper and paperboard at 23°C and 50% RH |
TAPPI T 448 provides for the gravimetric determination of the water vapor transmission rate (WVTR) of sheet materials at 23°C with an atmosphere of 50% RH on one side and a desiccant on the other. It is generally suitable for materials up to 3 mm thick (1/8 inch), although it may be used with caution for thicker materials if the edges of the specimen are completely sealed. For testing at other conditions, see TAPPI T 464 “Gravimetric Determination of Water Vapor Transmission Rate of Sheet Materials at High Temperature and Humidity” for 37.8°C (100°F) and 90% RH. This test can be used for both creased and uncreased specimens.
This method provides a means for measuring the ability of a material to protect contents that are enclosed within the material from undesirable changes due to the transmission of water vapor to or from the surrounding environment. The influence of temperature and humidity on the water vapor transmission rate of sheet materials is seldom linear, so test results obtained at higher or lower temperatures and humidities cannot safely be extrapolated to apply to these conditions. If sheet materials are not homogeneous, there may be a considerable difference in the transmission rate depending on which side faces the high humidity. The test is usually made to simulate use conditions; for example, a material for enclosing a dry product would be tested by exposing to the dry atmosphere that surface which would face the product in the package.
Three sheets of material are needed for the test. IPS will test for 5 days with readings taken twice a day, unless the customer specifies an alternate time frame. The customer must specify which surface is exposed to the humidity.
SGS-IPS cannot sell or otherwise provide standards, specifications, or test procedures to third parties.