Interpretation of ASTM E96 (Test Method for Water Vapor Transmission Rate (WVTR) of Materials)
ASTM E96 is a standard developed by the American Society for Testing and Materials (ASTM) that specifies the test method for the water vapor transmission rate (WVTR) of materials. This standard is mainly used to determine the moisture permeability of materials under different temperature and humidity conditions, and is often used to evaluate the moisture and water resistance of various packaging materials (such as plastic films, paper, etc.).
The following is a specific interpretation of ASTM E96:
1. Scope of application of the standard
ASTM E96 is applicable to the evaluation of the water vapor transmission rate of materials, especially those used in packaging, construction, textiles, coatings and other industries. These materials usually need to have moisture resistance, so it is important to understand their water vapor transmission characteristics under different humidity and temperature conditions.
2. Overview of test methods
ASTM E96 provides two main test methods for measuring the rate at which water vapor passes through materials:
Method A (Desiccant Method): Keep one side of the sample dry and expose the other side to a higher humidity environment. Measure the rate at which water vapor passes through the material from the high humidity side to the dry side.
Method B (Wet Cup Method): High humidity (usually achieved with water or saturated salt solution) is maintained on one side of the sample, while the other side is exposed to a drier environment. The rate at which water vapor passes through the material from the high humidity side to the low humidity side is measured.
The two methods differ in how they control humidity conditions, but both are intended to test how well a material performs in terms of moisture resistance.
3. Test Procedure
Sample Preparation: Cut a sample of the material to a certain size and seal it in a standard test fixture to ensure that water vapor only passes through the sample.
Environmental Control: The temperature and humidity are strictly controlled during the test. The temperature range is usually 23°C (73°F), and the humidity varies depending on the method.
Measuring Water Vapor Transmission: The container is weighed periodically over a period of time to measure the rate at which moisture passes through the material. This rate is usually expressed in "grams per square meter per day" (g/m²/day).
4. Units and Calculations
The test results are usually expressed as WVTR, which is the Water Vapor Transmission Rate of the material. The formula is: WVTR = m/A* t
Where:
m: Water vapor transmission (grams)
A: Effective permeation area of ??the sample (square meters)
t: Time (days)
By calculating WVTR, the moisture permeability of the material can be obtained.
5. Influencing factors
The ASTM E96 standard emphasizes that the water vapor transmission rate of the material will be affected by many factors, mainly including:
Thickness: Generally speaking, the thicker the material, the lower the water vapor transmission rate.
Temperature and humidity: The moisture permeability of the material will change with the temperature and humidity of the environment. For example, under high humidity, the moisture permeability of some materials may increase significantly.
Surface treatment: The water vapor permeability of some materials will change after coating or laminating.
6. Practical application
ASTM E96 is widely used to evaluate the performance of various packaging materials. It is commonly used in the following industries:
Food packaging: It is necessary to prevent moisture from entering or escaping to maintain the texture and shelf life of the product.
Building materials: Building envelope materials, such as roofing membranes or air barriers, need to have appropriate moisture permeability to ensure humidity regulation inside buildings.
Textiles: Certain functional textiles, such as waterproof and breathable clothing, need to prevent moisture penetration while maintaining breathability.
7. Importance of the standard
ASTM E96 is a globally recognized standard for measuring the moisture barrier performance of materials. By using this standard, manufacturers and engineers can:
Determine the water vapor transmission rate of different materials to select suitable packaging or building materials;
Design materials and products with better moisture barrier performance;
Provide a basis for material certification, quality control and product development.
Summary
ASTM E96 standard provides two reliable test methods for measuring the water vapor transmission rate of materials. It is a key tool for evaluating the moisture barrier performance of packaging and building materials to ensure the stability and functionality of products under different humidity conditions.
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