Acquiring an accurate measurement of water vapor permeability through porous materials, such as paper, plastic films, fiberboards, gypsum, plaster products, wood products, and plastics, is essential for compiling a methodical comprehension of materials desired for use. This is the primary interest of ASTM E96-22: Standard Test Methods for Gravimetric Determination of Water Vapor Transmission of Materials.
ASTM E96 Water Vapor Transmission Rate Test Methods
ASTM E96-22: Standard Test Methods for Gravimetric Determination of Water Vapor Transmission Rate of Materials addresses two testing procedures for determining the water vapor transmission rate (WVTR) of numerous materials, both of which can be incredibly useful for knowing the potential risks posed on the materials in different humidity levels. The standard’s testing methods are the Desiccant Method and the Water Method.
In the Desiccant Method, the test specimen is sealed to a test dish containing a desiccant, and the assembly is placed in a controlled atmosphere. Periodic weighings are used to assess rate of water vapor movement through the specimen into the desiccant. The Water Method is somewhat simpler, with the dish containing distilled water and periodic weighings being used to determine the rate of vapor movement through the specimen from the water.
ASTM E96 Explained
This process can be complicated, so NTA, Inc., a third-party code evaluation, product certification, and inspection agency, has created the following video to describe an overview of the two methods:
Please note that this video dates back to 2014, and the standard has been revised since. The exact specifications for the Desiccant Method and the Water Method are detailed in the ASTM E96-22 standard document.
If you’d like to learn a little more about this standard, please refer to our past post: ASTM E96-22: Water Vapor Transmission Standard Test Methods
ASTM E96-22: Standard Test Methods for Gravimetric Determination of Water Vapor Transmission Rate of Materials is available on the ANSI Webstore.
I need to understand the differences between Method A and Method B for this test.
How long does the each test method last?
What determines the result number?
Hi Jeff,
It really depends on a few factors. If you are doing this via humidity chambers (to be able to control the RH), the test could take a while – as in the order of weeks (keep in mind that these are mass diffusion type experiments and as such, they are slow). The amount of mass that you use will also play a role here, and of course, how well you can control temperature of the sample.
There are ways to speed things up. For instance, if you look up Dynamic Vapor Sorption (DVS) by Surface Measurement Systems, the instruments used employ a closed chamber where a very tiny version of the Payne cell can be used. The DVS is fully temperature controlled and has a controlled RH that can go from 0-98% and the weight change of the sample as water permeates is constantly monitored thanks to a microbalance, capable of reading weight changes of as little as 0.01 micrograms. Depending on the sample, running this test on a DVS can take a day or two at most.
If you need more information on this, please feel free to reach out to me at egutierrez@surfacemeasurementsystems.com