What are the factors that affect the waterproofness of fabrics?

1. The wettability of the fiber surface. When the contact angle of the fiber is less than 90°, the fiber assembly material is a water-conducting material, and the tight structure will only lead to more capillary pores, and wicking water will occur. When the infiltration angle of the fiber is greater than 90 degrees, the fiber assembly has water resistance. At this time, the tighter the fabric structure, the smaller the gap between the fibers, the better it is to repel water. It can be seen that the structure of the fabric and the number of voids can only be discussed for water repellency or water conduction performance under the premise of known fiber contact angle. The water droplets reach an equilibrium state on the flat fabric surface (excluding pseudo-wetting phenomenon). At this time, the contact angle refers to the liquid angle between the gas-liquid interface and the solid-liquid interface. In order to determine whether the water droplets infiltrate the fabric. Figure 1. Schematic diagram of contact angle Figure 2. Actual measurement of contact angle Contact angle (°) whether wetting state 0 completely wetting spreading 0-90 wetting positive wetting 90 non wetting zero wetting 90-180 non wetting negative wetting 180 not wetting at all In the steady state table 1. The size of the contact angle and its corresponding infiltration state 2. The coating of the fabric is coated with a layer of impermeable and insoluble continuous film layer on the surface of the fabric, which can reduce the water permeability of the fabric, which is often also It makes the fabric airtight and has a hard hand feel. It is generally not suitable for clothing, but it can be used for canopy cloth or umbrellas. If a microporous coating film is used, a coated fabric with excellent waterproof performance, breathability and moisture permeability can be formed, which is suitable for clothing. 3. Environmental conditions Since most of the water-repellent fabrics or coated fabrics are made of non-hygroscopic fibers or coated materials, changes in relative humidity will not affect their waterproof performance. The increase in temperature will increase the expansion of the fiber. The fiber is an anisotropic material, and the radial expansion is greater than the longitudinal expansion, resulting in a reduction in the space between the fibers. For water-repellent fabrics, this is conducive to the improvement of water repellency. For the porous coating film, the pores will also become smaller when heated, so the water repellency remains unchanged or slightly increased. Conversely, when the temperature decreases, the holes between the fibers or in the coating film tend to increase. Therefore, the water repellency will be reduced. But in general, this change is relatively small, so the impact is not obvious. More about rain resistance tester: http://www.standard-groups.com/TextileGarment/
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