Dirt repellence

Water- and dirt-repelling coatings have nanoparticles pointing outwards. Water is in touch with the surface at only a few points due to the surface tension it contracts to droplets which roll off ( lotus effect ). 

Of a large number of possible fluorinated acrylates, the homopolymers and copolymers of fluoroalkyl acrylates and methacrylates are the most suitable for practical applications. They are used in the manufacture of plastic lightguides (optical fibers) resists water-, oil-, and dirt-repellent coatings and other advanced applications [14]. Several rather complex methods to prepare the a-fluoroalkyl monomers (e.g., a-phenyl fluoroacrylates, a-(trifluoromethyl) acrylic and its esters, esters of perfluoromethacrylic acid) exist and are discussed in some detail in [14]. Generally, a-fluoroacrylates polymerize more readily than corresponding nonfluorinated acrylates and methacrylates, mostly by free radical mechanism [15], Copolymerization of fluoroacrylates has been carried out in bulk, solution, or emulsion initiated with peroxides, azobisisobutyronitrile, or y-irradiation [16]. Fluoroalkyl methacrylates and acrylates also polymerize by anionic mechanism, but the polymerization rates are considerably slower than those of radical polymerization [17]. 

Plasma-induced hydrophobization of cottonfabric in conjunction with increased specific surface area leads to an interesting and practically important effect. Water droplets are able to effectively remove dirt particles from the surface of the cotton fabric. This phenomenon is illustrated in Fig. 9-29 for the case of HMDSO-plasma-treated cotton fabric (Hocker, 2002) and is usually referred to as the Lotus effect. Thus, the highly hydrophobic plasma-treated surface of cotton with specific plasma-modified surface topography is extremely dust- and dirt-repellant in contact with water. As an important consequence, the plasma-treated surface also becomes repellant to bacteria and fungi. The effect is relevant not only to cotton fiber but to some other materials as well. 

Polyethylenes of lower molecular mass are added as slip and matting agents to paints and printing inks and can also produce dirt-repellent and abrasion-resistant effects. The wax dispersions are produced by hot dissolution and precipitation in aromatic hydrocarbons. This is not necessary with commercial microcrystalline grades. Aqueous dispersions of polyethylene are important as polishing agents. 

Samanta et al., 2013). Hydrophilic, hydrophobic, and dirt-repellent coatings using different plasma technologies were reported by Bhosale et al. (2013). Antibacterial activity was obtained by plasma sputtering of silver and copper on dyed cotton (Shahidi et al., 2010 Shahidi, 2015). At the same time, an improvement in the fastness properties was observed. 

Ease of cleaning, dirt-repellence, self-cleaning... 

Dirt repellence is a desirable property for a large number of textile products used in outdoor applications. It can be obtained by finishes or coatings, although the smoothing of the textile surface by calender rolls is also known to be an effective method. For the repellence of oily contamination, silicon compounds, carboxymethyl celluloses and fluorocarbon finishes are applied to the fibres or to the textile material. 

Material and textile construction Coating (+ finish) Dirt repellence Life expectancy (years) Flexing durability Applications/remarks... 

Textiles from animals are commonly made from their hair or fur. in most cases, these fibers are non-scaled and non-coated with natural oils. On the other hand, wools, which refer to the hairs of goats and sheep, are scaled structures with a wax-like coating also known as lanolin which is hydrophobic and dirt-repellent. Further, woolen yarns are bulky and formed from non-parallel, carded fibers, whereas worsted yarns are finer and are spun from long, combed (parallel) fibers. Other animals producing wools include alpaca, llamas, angora rabbits, camels, and silkworms. 

The two layer, core-sheath monofilament is an interesting development, which can combine a strong core with good dirt-repellent properties. Thus the core could be made from strong polyester, coated with a sheath of fluoropolymers. 

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