Water-repellent textiles usually resist wetting when worn in intermittent rain but do not provide adequate protection against driving rain. Unlike waterproof fabrics, water-repellent textiles have open pores making them permeable to air, water vapor, and liquid water (at high hydrostatic pressure). In order to obtain a water-repellent fabric, a hydrophobic material is applied to the fiber surface. As a result of this procedure, the fabric remains porous allowing air and water vapor to pass through. A downside is that in extreme weather conditions the fabric leaks.
The advantage of hydrophobic textiles is the enhanced breathability, however, they offer less protection against water. Water-repellent fabrics are used mainly in the production of conventional clothing or as an exterior layer of waterproof clothing. The hydrophobicity can be either permanent (due to the application of water repellents, DWR) or temporary.
1. Inherent water-repellent textile materials.
2. Textile materials finished with water repellant.
Water repellency is specific to compact textile structures. Thus, inherent water-repellent materials are (a) high density woven fabrics, made of very fine yarns and filaments and (b) nonwoven materials.
The hydrophobization of the textile materials is achieved by using different chemicals. These substances orient their hydrophobic groups towards the textile fibers thus forming a protective brush against water. The water hydrophobization agent applied on the surface of the garment allows the water drops to maintain their shape without spreading onto the fibers. In general, the main limitations of the water-repellent treatments refer to the extended surface porosity.
Hydrophobization can be achieved through the use of several technologies and/or materials. The main types are the following:
1. Hydrophobization with additives (aluminum organic salts, aluminum soaps, paraffin emulsions with aluminum salts).
2. Hydrophobization with resin type reactive agents.
3. Hydrophobization through chemical modification of the fibers.
4. Textile finishing with nanoparticles. Oleophobization techniques give textile materials the property of repelling oils and thus creating protection against dirt and smudges while increasing the hydrophobization effect. Fluorocarbon resins are often used as oleophobization agents.
5. Plasma treatment of the textile materials, plasma polymerization or plasma depositing of organic-silicone polymers can give a hydrophobic character to materials that are typically not hydrophobic (like cotton, for example).
The traditional technology used for producing water-repellent textiles requires a huge amount of water. This is related to two problems: 1) water pollution, and 2) high energy consumption. In contrast, plasma treatment does not require these large volumes of water or wet chemicals, or a large amount of energy required to dry the fabric.
Textile materials are valuable thanks to properties like strength, flexibility, light weight, etc. Moreover, other properties adding more functionality such as hydrophobicity, oleophobicity, or antibacterial activity further increase their value. However, few textiles are inherently water repellent and none are oil repellent. Traditionally, water repellency of textiles is achieved by the application of functional chemicals, followed by careful drying. Some of these chemicals include metal salts, pyridinium-based finishes, silicone finishes, and fluorocarbon. Among them, only fluorocarbon finishes can repel both oil and water.
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