Self Cleaning Textiles: New Concept of Textile Finishing

Self Cleaning Textiles:
Self cleaning textile means the textile surface which can be cleaned itself without using any laundering action. Now a days peoples are very busy in their work that they do not have time for clean their daily wear cloths also people who are working in kitchens having headache to wash their garments. Also military peoples have to survive in such drastic condition that they cannot wash their cloths.

Nano technology provides a new concept self cleaning textiles which gives self cleaning as well as fresh cloths every day, this not only technically benefited but techno economically also benefited.

Mechanism of self cleaning
  1. The Lotus effect
  2. Photocatalytic coatings
  3. Easy to clean finishing
Self-cleaning textiles using the Lotus Effect
In many applications, the use of textiles is limited due to their soiling and wetting behaviour. To overcome this limitation, textiles are improved with a variety of finishes of different product classes. Recently, products have been invented that make use of the Lotus Effect and implement self-cleaning properties to a textile surface. The successful realization of this effect leads to a significant reduction in the cleaning requirement of such surfaces.

To achieve self-cleaning properties nature uses an efficient method, which has been perfectly realized on the leaves of the lotus plant. Besides this species, selfcleaning properties can be found on a variety of other biological surfaces, such as cabbage, reed and nasturtium. The main function of nanostructured superhydrophobic surfaces in nature is probably the protection against pathogenic organic contamination like bacteria or spores. These are regularly removed from the leaves by rainfall.

Although discovered already in the 1970s, Barthlott and his team in the 1990s identified the reason for the self-cleaning properties and named it the ‘Lotus Effect’. It is based on the specific properties of micro- and nanostructured superhydrophobic surfaces, which are always completely cleaned by rainfall: the contact area of water and dirt particles is largely minimized by the double structured surface. This in combination with hydrophobic chemistry results in extremely high contact angles that let water drops roll off at the slightest inclination, in so doing, taking up all adherent particles and removing them, leaving behind a clean and dry surface.

On many of these surfaces even high-viscous liquids (e.g. honey) drip off. The Lotus Effect is based on a minimization of the contact area of hydrophobic surfaces by an overlapping double structure approximately 100 nm to approximately 100 μm in size.

Because of this active principle, the Lotus Effect differs from the ‘soil-repelling’ and ‘soil-release’ function. As the Lotus Effect depends only on physicochemical characteristics it is independent of the living system and can be transferred into technical systems. The first commercial products with the Lotus Effect were wall painting and roof tiles. The term ‘Lotus Effect’ is a registered trademark for many applications.

Lotus Effect: The self-cleaning property of the lotus plant, named the ‘Lotus Effect’, is based on the specific properties of micro- and nanostructured ultrahydrophobic surfaces, which are always completely cleaned by rainfall: the contact area of water and dirt particles is largely minimized by the double structured surface.

Self-cleaning Function in Textile:
In the technological implementation, various methods have been used to avoid the adhesion of dirt and to improve the release of dirt. 
 
Water drop on superhydrophobic textile surface
Rebounding droplet from a superhydrophobic surface
Smooth surfaces without specific hydrophilicity or hydrophobicity Extremely smooth surfaces show a reduced soiling behaviour because particles have only low mechanical hold and can be removed by air or liquids. However, the adhesion of residues from drying of liquids or filming cannot be prevented. To remove them, detergents (surfactants) and mechanical support are necessary.

Therefore, the self-cleaning effect of smooth hydrophilic surfaces is low. With extremely smooth surfaces low soiling is sufficient to impair the aesthetic impression crucially, long before the function is limited (e.g. paints and panes).

Smooth hydrophilic surfaces
Hydrophilic coatings force aqueous drops to spread out to very thin surface films. Therefore, residues from drying up are deposited relatively evenly with little interference on the surface. Moreover, the extremely good wettability facilitates the cleaning effect of aqueous solutions. An improvement of the self-cleaning ability can be achieved by the introduction of photo-catalytic effects, as for example with the use of titanium dioxide. Organic dirt components can thereby be decomposed to low-molecular-weight products such as CO2 and H2O.

Smooth hydrophobic surfaces
If hydrophobic coatings are applied to smooth surfaces, the soiling behaviour can be reduced and the self-cleaning effect increased. Aqueous solutions drip off, so that the formation of residues by drying is decreased. In the textile sector, the water and oil repellency treatment of fibres with fluorine-based chemistry for the decrease of soiling of clothing and technical textiles is well examined and has reached technical maturity.

Rough hydrophobic surfaces (Lotus Effect surfaces)
If overlapping structures in dimensions of some micrometres and superposed structures of 50 to some hundred nanometres are applied to surfaces, and the chemistry of the surface is hydrophobic, soiling behaviour can be dramatically reduced and a real self-cleaning effect can be achieved. The effective surface contact area for dirt particles is extremely minimized by the surface structure and thus the adhesion is very low. Simply with drops of water rolling over the surface dirt particles are removed. Also, oily soiling can be washed off such surfaces by agitated water. When a drop of water rolls over such a surface, dirt particles lying on it are removed by adhesion to the surface of the drop.

Because of the roughness of the surface and the consequential low contact area, the adhesion energy of the particle to the solid surface is very low. Consequently, dirt particles from a superhydrophobic surface are completely removed, in contrast to a smooth hydrophobic surface where the energy is higher allowing only for the relocation of particles. For a smooth surface, the adhesion energy between particle and solid surface is relatively higher than between particle and water drop.

On rough surfaces, like textiles, the kinetic energy of a drop that falls onto it results in another positive effect for the dirt removal: particles lying in cavities of the rough solid surface are not reached by a drop that simply rolls over it. As a result of the impact when falling on the surface the drop deforms, so that it penetrates into the cavities and reaches the particles lying there.

Application of self cleaning textile
 

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