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What are the water permeability and waterproof tests (i)?

Views: 1000     Author: Site Editor     Publish Time: 2023-05-15      Origin: Site


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Measuring the water permeability or water resistance of a fabric is to measure its water repellency or water conductivity. Different methods are used depending on the actual use of the fabric, and various corresponding indicators are used to express the water permeability or water resistance of the fabric.

1. Hydrostatic pressure method

The hydrostatic method refers to the water permeability of fabrics under a certain water pressure, and it is applicable to all kinds of fabrics, including those with waterproof finishing.

The water repellency of a fabric is related to the water resistance of the fibers, yarns and fabric structure and is not the same as water spray and rain onto the fabric surface. The water resistance of fabrics is measured by hydrostatic pressure method, which includes static pressure method and dynamic pressure method. The static pressure method is to apply hydrostatic pressure on one side of the fabric, and measure the water output under this hydrostatic pressure, the water drop time, and the hydrostatic pressure value at a certain water output. The hydrostatic pressure value can be the height of the water column or the pressure. In the actual measurement, the water permeability per unit area and unit time (mL/cm2·h) is measured. For waterproof fabrics, measure the time required for water droplets to appear on the other side of the sample, or observe the number of water droplets that appear on the other side after a certain period of time.

The dynamic pressure method is to apply a water pressure P that increases at a constant speed on one side of the sample until the other side is penetrated by water and a certain amount of water droplets appear. The principle of the imposed water pressure P is the same as that of the static pressure method, except that P is a variable. This method is more suitable for coated fabrics or fabrics with tight structure. The waterproof performance of fabrics is reflected by hydrostatic pressure. Fabrics with high hydrostatic pressure have strong waterproof performance, while fabrics with low hydrostatic pressure have weak waterproof performance. Water-conducting fabric has strong moisture absorption capacity, and it will get wet when it meets water. It has no water resistance and will not generate hydrostatic pressure.

In the AATCC 127-2003 test method experiment, take at least three samples with a size of 200mm×200mm along the diagonal direction of the sample to be tested. The water resistance of the two sides of the sample is different, mark it well, and test it with distilled water at (21±2)°C, the test area is 100cm2, the test surface is in contact with water, and the water pressure increases at a speed of 60mbar/min (or 10mm/s). The test is terminated when water drops seep from 3 different places on the sample. However, if the water drops seep within 3mm from the sample clamp, it is invalid. The measured results are the average of three test samples under the same conditions. The larger the test value, the greater the pressure value required for water to seep out of the sample, and the better its water resistance.

2. Spray method

The spraying method is to evaluate the water resistance of the fabric by continuously spraying or dripping water on the sample, observing the water stain characteristics on the surface of the sample after a certain period of time, and comparing it with the samples of various degrees of wetting. The spray method is to simulate the degree to which the clothes are wet when it is exposed to light rain. This method is applicable to all waterproof treated fabrics and untreated fabrics, and the measured waterproof results have a great relationship with fibers, yarns, fabric treatments and fabric structures.

It is usually measured by a spray water repellency tester. In the AATCC 22-2005 test method, the test sample is fixed with an iron ring with a diameter of 152.4mm. The sample is in a tensioned state, and the surface is flat and free of wrinkles. Spray 250mL of distilled water from the standard nozzle at 45°, and spray the sample at 150mm below the nozzle for 25-30s. Tap the bottom of the iron ring with the sample on the solid object once, the test surface is opposite to the solid object, and then rotate the iron ring 180° and tap once, then compare, grade and evaluate the surface of the sprayed sample with the standard chart Water repellency of the fabric. There are 5 ratings, with 5 being the best and 1 being the worst. Level 5 - no water drops on the surface of the test sample; level 4 - slight wet spots on the surface of the test sample; level 3 - obvious rain drops on the surface of the test sample; level 2 - the surface of the test sample The surface of the sample is partially wet; Class 1—the surface of the sample tested is completely wet.

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