Determination of how water vapor passes through some porous materials is covered by ASTM E96-22: Standard Test Methods For Gravimetric Determination Of Water Vapor Transmission Rate Of Materials.
Why Water Vapor Transmission Rate is Tested
While the majority of the water on Earth is found in the ocean and other bodies of water, there is still 12,900 cubic kilometers (3,095 cubic miles) located in the atmosphere. Water in general has an association with nothingness, as a clear liquid that will not stain clothing and is offered free at restaurants. While water vapor generally cannot harm humans, since it is just water in a different state of matter, it can be troublesome for many materials used for different purposes.
Determining the water vapor transmission rate (WVTR) of a multitude of materials through ASTM E96-22 testing procedures is essential for moisture control. Knowing this can forecast how the materials will resist water damage, and it can help prevent other situations in which the presence of moisture could contribute to detrimental conditions. For example, these tests can help to understand the increased humidity in a heated dry building during a rainstorm.
ASTM E96-22: Two Test Methods
ASTM E96-22 describes two test methods that determine the water vapor transmission rate of materials through which the passage of water vapor could damage the material or be of some importance.
The processes identified in this standard can be used to test many different kinds of materials, including paper, plastic films, other sheet materials, fiberboards, gypsum and plaster products, wood products, and plastics, among others.
The two basic methods covered in ASTM E96-22 are the Desiccant Method and the Water Method.
The Desiccant Method
In the Desiccant Method, the test specimen, which can be any one of the materials covered by the scope of the standard, is sealed to the open mouth of the test dish containing a desiccant, and the assembly is placed in a controlled atmosphere with a set temperature and humidity. The desiccant used must be anhydrous calcium chloride in the form of small lumps that have been dried at 200°C (400°F). For some time after this assembly is constructed, periodic weighings of the desiccant will determine the rate of water vapor from the air that travels through the specimen into the desiccant.
The Water Method
In the Water Method, a test dish is simply filled with water 19 mm (0.75 in) from the specimen, with a margin of error of 6 mm (0.25 in). The test dish used in both the Water Method and the Desiccant Method should be as large as practical, at least 3000 sq mm (4.65 sq in). The weighings in the Water Method determine the rate of vapor movement into the sample from the water in the controlled atmosphere. This method creates an environment with much more humidity than that of the Desiccant Method.
Completion of either one of these methods should result in a test report, which compiles information on the test method used and the temperature and humidity of the test chamber.
You can learn more about these testing methods in our post ASTM E96: Explaining Water Vapor Transmission Rate Testing.
About ASTM E96-22
ASTM E96-22 specifies many guidelines for all of the different materials and processes needed for these two methods. It also provides the calculations needed to comprehend the data generated from the Desiccant Method and the Water Method. The values generated from the procedures have applications in design, manufacture, and marketing.
ASTM E96-22: Standard Test Methods For Gravimetric Determination Of Water Vapor Transmission Rate Of Materials is available on the ANSI Webstore.
Changes to ASTM E96-22
ASTM E96-22 revises the previous edition of the same standard for test methods for water vapor transmission rate, which was published in 2021. The new version has undergone the following changes to keep its information current:
- The section covering the balance of the assembled dish mass of the apparatus was significantly expanded and restructured.
- The procedure for weighing the dish assembly in the desiccant method was updated.
- Details on plotting the weighings of the specimen at the steady state portion of the test were clarified and restructured.
- Millimeters of mercury (mm Hg) was removed as a unit of measurement for vapor pressure difference and saturation vapor pressure at test temperature values, which now exclusively use pascals (Pa).
Any past user of this standard who is interested in all the changes made to the 2022 edition can get the ASTM E96/E96M-22 Redline Standard, which comes with both ASTM E96-22 and a version of the document that clearly marks where changes have been made.
Changes to ASTM E96-21
The previous edition of this standard, ASTM E96-21, is recent enough for its users to have an interest in knowing its changes, which were numerous. The most obvious of these changes is the update to the title. ASTM E96/E96M-16 was titled, “Standard Test Methods for Water Vapor Transmission of Materials,” while ASTM E96/E96M-21 expanded its title to “Standard Test Methods For Gravimetric Determination Of Water Vapor Transmission Rate Of Materials.”
The standard document contains numerous clarifications and updates throughout its text. This includes new sections on:
- vapor pressure difference in a common controlled atmosphere
- requirements for when the specimen area is larger than the mouth area
- testing of materials of homogenous composition and physical structure
- requirements for testing an additional blank specimen
- specimen thickness measurement
- warpage and breakage of the seal of the specimen to the dish during testing
- determination and utilization of steady state
ASTM E96-21 also features a new Appendix X5, “Examples of Calculations.”