Gravimetric method is one of the classic methods for measuring the water vapor transmission rate of materials. The following is a detailed introduction to the gravimetric water vapor transmission rate meter:
Gravimetric method principle
The gravimetric water vapor transmission rate meter determines the water vapor transmission rate by measuring the mass change of the sample over a certain period of time. The basic steps are as follows:
1. Sample preparation:
Select and cut the sample to be tested to ensure that the sample size and thickness meet the test requirements.
2. Sample loading:
Install the sample in the test chamber of the transmission rate meter, usually a sealed container.
One side of the container is filled with water or saturated salt solution (to provide constant humidity), and the other side is kept dry.
3. Test process:
A stable humidity environment is formed on one side, and the other side is kept at low humidity by desiccant or dry air.
Water vapor diffuses from the high humidity side to the low humidity side through the sample.
4. Mass measurement:
The mass change of the desiccant is measured regularly by a precision balance (because the desiccant absorbs water vapor).
Record the mass change at different time points.
5. Data Analysis:
Calculate the water vapor transmission rate based on the mass change and test time. The formula is usually:
WVTR=▲M/AT
Where ▲M is the mass change, A is the sample area, and T is the test time.
Gravimetric Water Vapor Transmission Rate
Advantages and Limitations
Advantages:
High accuracy: The weighing method has high accuracy, especially suitable for low permeability materials.
Direct measurement: The water vapor transmission rate is directly measured by mass change, and the data is intuitive and reliable.
Limitations:
Long time: The test time is long, usually taking hours or even days.
Complex operation: Precise sample preparation and measurement operations are required, and high requirements for experimental condition control are required.
Applications
Food packaging: Evaluate the moisture resistance of food packaging materials to extend the shelf life of food.
Pharmaceutical packaging: Ensure that pharmaceutical packaging materials can effectively prevent moisture and maintain the stability and effectiveness of drugs.
High barrier materials: Detect the water vapor transmission performance of high barrier films and coatings.
Maintenance and Calibration
Regular calibration: Use standard samples to calibrate the instrument regularly to ensure the accuracy of the measurement results.
Equipment maintenance: Keep the instrument clean, check and replace the desiccant regularly.
The gravimetric water vapor transmission rate meter is an important tool for evaluating the moisture resistance of materials and is suitable for a variety of fields. If more detailed instructions or recommendations for specific models are required, further requirements and application background can be provided.
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