With the continuous improvement of people’s quality of life and the continuous progress of the textile industry, some basic functions of traditional textiles can no longer meet the needs of people. Various functional textiles have received extensive attention, and the performance requirements of fabrics are becoming more and higher.
Definitions of Waterproofing and Water Permeability of Fabrics
In daily life, people often contact with water, which put forward waterproof requirements for all kinds of textile. The waterproof and permeable properties are two sides in one property of the fabric, which refers to the resistance to water wetting and permeation by the water of the fabrics.
Influencing Factors of Fabric Permeability or Waterproof
The fabric permeability is the ability of liquid water to penetrate from one side to the other. There are three main factors affecting for the waterproof and water permeability of the fabric.
1 The wettability of fiber surface: The wettability of fiber is related to the compactness of fiber structure when the structure is close, the waterproof effect is better.
2 Fabric coating: Adopt waterproof, a multi-microporous coating can form a good waterproof, water permeability, and good air permeability coating fabric, mostly used in cloak or rain cloak, and so on.
3 Environment: For water conducting fabric, the relative humidity increases, the moisture absorption of the fiber increases, and the water conductivity of the fabric increases.
The Testing Categories of Fabric Waterproofing
The main indexes of the fabric waterproof are dip water grade, hydrostatic pressure resistance grade, and water permeation capacity, and there are two kinds of test methods: spray method and hydrostatic pressure method. In order to measure the water permeability or waterproofing of fabrics, different methods are used depending on the actual use of the fabric, and the corresponding indexes are used to express the water permeability of fabrics.
1 Hydrostatic Pressure Method
Hydrostatic pressure refers to the water permeability of fabrics under a certain water pressure. It is suitable for all kinds of fabrics, including those treated with waterproofing. Hydrostatic pressure method is used to measure the waterproofing of fabric, there are static pressure method and dynamic pressure method. Static pressure is used for water-conducting fabrics, and dynamic pressure is used for coated or compact fabrics.
In the AATCC 127 test method, cut at least three samples with an area of 200mm*200mm along the diagonal direction of the tested sample. The waterproofing of the two sides of the sample is different, which should be marked. Test with distilled water at (21±2)℃ and the test area is 100cm². The water pressure is increasing at a constant rate, if there are 3 water droplets in different places on the sample, the test will be finished (however, if the water droplets exudated within the 3mm of the sample clip, it is ineffective). The results are the average values of three samples under the same conditions. The larger the test value, the greater pressure required for the water seepage, and the better its waterproofing. The hydrostatic pressure tester was used in the test.
2 Spray Method
The spray method is to evaluate the waterproofing of fabric by comparing the standard sample of a various wetting degree to the water stains characteristics (through continuous spraying onto the sample after a fixed time) of the sample. The spray method is a simulation of the degree to which clothing gets wet when drizzled.
In the AATCC 22 test method, fix the sample with an iron ring with the diameter is 152.4mm, and the surface of the sample was flat and without a wrinkle. Spray the distilled water (250ml) on the sample of 150mm under the nozzle for 25~30s. Then compare the spray sample surface with the standard chart card and rated. The Spray tester was used in the test.
3 Rain Test Method
Rain test method is to simulate the waterproof of fabrics exposed to air when heavy rain. This method is applicable to any fabric with or without waterproof treatment. The principle: wrap the test sample around the weighing absorbent paper and weigh the absorbent paper again after the test. The difference between the two times of weight is the water permeability of the sample.
In the AATCC 35 test method, place a standard absorbent paper of 15.2cm*15.2cm at the back of the sample, weight the standard absorbent paper, and accurate to 0.1g. On the vertical rigid surface, clamp the sample on the sample holder, place it in the middle of the spray, 30.5cm away from the nozzle, then spray the water flow at (27±1)℃ on the sample horizontally for 5 min. After spraying, remove the absorbent paper carefully and weigh it quickly to 0.1g. Calculate the weight of the paper during spray, and take the average value of the test data. The rain tester was used in the test.
4 Wicking Method
The wicking measurement is the most commonly used and the simplest method for measuring the water absorption of fabrics. The test sample is usually cut into a long strip, one end of the test sample is suspended on the iron frame, the other end is in contact with the water surface (or immersed in water at a certain height). After a certain time, measure the height of the water climbing through the pores of the fabric fiber. Fabric with good water conductivity, strong water absorption, fast water absorption, high climbing height per unit time.
If in the testing process, because of the fabric structure and the yarn color, the water climbing process is not obvious, it is not easy to observe by the naked eye, we can add a little coloring agent in the water.
In practice, different fabrics use different testing methods to better measure the water permeability or waterproofing of fabrics.
1 Because of its structure, the water permeability of coated fabric can be tested by spray, rain and hydrostatic pressure, but not by wicking method.
2 In general, in the wicking method, it is found that the water absorbency of knitted fabrics is better than that of woven fabrics.
3 Wet fabric cannot be tested by hydrostatic pressure, but can be tested by spray method.