Water Vapor Transmission, Water Vapor Permeance, Water Vapor Permeability
Water vapor transmission (WVT) is determined by dividing the rate of weight change by the area of the test specimen. Water vapor permeance is in general the degree to which a material admits water vapor. Water vapor permeability is related with the thickness of the material.
Calculation of Water Vapor Transmission, Water Vapor Permeance, Water Vapor Permeability
The permeance and permeability are calculated from the WVT. The permeance is calculated by dividing the WVT by the vapor pressure across the material under test. The permeability is calculated by multiplying the permeance by the thickness of the material.
ASTM D1653 standard and Test Method
ASTM D1653 standard determines the water vapor transmission rate of films of paint,lacquer,vanish, and other organic coatings. The films may be free films or be applied to porous substrates. Under ASTM D1653 standard, there are two test methods: dry cup method and wet cup method.
ASTM E96 standard and Test Method
ASTM E96 standard is used to test paper, plastic films, other sheet materials, fiber-boards, gypsum and plaster products, wood products, and plastics. ASTM E96 standard introduces two basic methods: the desiccant method and the water method.
The difference of ASTM E96 standard and ASTM D1653 standard
The testing scope of ASTM E96 standard is more wider, which can evaluate many materials, including coatings which is mainly tested under ASTM D1653 standard.
ASTM D1653 includes directions for preparation of a free film, whereas ASTM E96 does not.
ASTM E96 requires that permeance values exceeding 2 perm are corrected for resistance due to still air and specimen surface. ASTM D1653 does not specify the correction.
Saicheng' WPT-301B Water Vapor Permeability Tester which adopts gravimetric method complies with ASTM E96 standard and ASTM D1653 standard.
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