What are the factors that affect the waterproofness of fabrics?1

1. The wettability of the fiber surface when the contact angle of the fiber is less than 90°When the fiber aggregate material is a water-conducting material, the tight structure will only lead to more capillary pores, and wicking water-conducting occurs. When the wetting angle of the fibers is greater than 90 degrees, the fiber aggregate has water resistance. At this time, the tighter the fabric structure and the smaller the gap between the fibers, the better the water repellency. It can be seen that the structural organization and the number of voids in the fabric can only be discussed on the premise of the known fiber contact angle to discuss its water repellency or water conductivity. The water droplets reach equilibrium on a flat fabric surface (excluding pseudo-wetting). At this time, the contact angle refers to the gas—liquid section and solid—The angle of the liquid between the liquid interfaces. Thereby, it can be judged whether the water droplets infiltrate the fabric. Figure 1. Schematic diagram of contact angle Figure 2. Actual measurement of contact angle Contact angle (°) Can wetting state 0 Complete wetting and spreading 0-90 Wettable positive wetting 90 No wetting Zero wetting 90-180 No wetting Negative wetting 180 No wetting at all The coating of the fabric can reduce the water permeability of the fabric by coating the surface of the fabric with a continuous film layer that is impermeable and insoluble in water, which often makes the fabric airtight and hard to the touch. It is generally not suitable for clothing, but can be used for tarpaulin or umbrella etc. If a microporous coating film is used, a coated fabric with excellent waterproof performance and breathable and moisture-permeable 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 coating materials, changes in relative humidity will not affect their waterproof performance. The increase in temperature will increase the expansion of fibers. Fibers are anisotropic materials, and the radial expansion is greater than the longitudinal expansion, resulting in reduced voids between fibers. For water repellent fabrics, this is beneficial for 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 increases. Conversely, as the temperature decreases, the pores between fibers or in the coating film tend to increase. Therefore, the water repellency will decrease accordingly. But in general, this change is relatively small, so the impact is not obvious. More about Rain Tester: http://www.standard-groups.com/TextileGarment/