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 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.
ASTM E96 Desiccant Method
The desiccant method: the test dish contains a desiccant. Leave enough space so that the shaking of the dish to mix the desiccant, which have to be done at each weighing. The test specimen is sealed to the open mouth of the dish. The rate of water vapor movement is determined by periodic weighing of the test dish.
ASTM E96 Water Method
The water method: the dish contains distilled water. Water vapor permeates through specimen into the controlled atmosphere. Through the periodic weighing of the test dish, the values can be obtained.
ASTM E96 Test Method Attention
Under different test conditions, the valued obtained may not be equivalent. As this reason, select the test conditions which are the closest with the conditions of use.
Saicheng' WPT-301B Water Vapor Permeability Tester which adopts gravimetric method complies with ASTM E96 standard.
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