Abstract
Nowadays, people do not have time to clean their daily cloths. Nature and textiles have very close relationship. The concept of self-Cleaning was inspired by the surface of Lotus leaves, which are well known for their ability to self-clean by repelling water and dirt. Nanotechnology had open a door for the scientist to develop self-cleaning surface which can be cleaned itself without using any laundering action. Nanotechnology is a new hope in the textiles field which can give fresh cloths every day. The application of self cleaning properties on textile surfaces by using the nanotechnology includes a vast[1] potential for the development new products. This study will cover the areas of different methods of self cleaning process, types of chemical used, application on to different fabric and products, innovation and development, present and future trend of nano self-cleaning, limitations. The self cleaning finishes has a great opportunities and has large areas of applications like Hospital garments, Sportswear, Military uniform, Smart textiles, Upholstery, Under garments etc.
Key Words: Self cleaning, nanotechnology, TiO2/ Ag, nanocomposite, PVC, photo-catalyst, pre-treatment, fabrics.
Arther Price, A. C. (1994). “Fabric Science “. New York: Fairchild Publication.
- Introduction
Textiles finishing is a process used in manufacturing of fibre, fabric, or clothing to impart the required functional properties of the fibre or fabric. The study is to understand more about nano finishing textiles, the aesthetics and functional finishes familiar with the textile finishing process and their effects on the fabrics, adverse effects and compromises of many textile finishes. The main purpose of the finishing is to make the fabric more suitable for its intended end used, and it is usually the final processing of the cloth before being cut into apparel parts or made into articles such as draperies, towels, etc.(Price Arthur et. al, 1994).
Nature has already developed an elegant approach that combines chemistry and physics to create super repellent surfaces as well as self-cleaning surfaces. The concept of self-cleaning textiles is based on the lotus plant whose leaves are well-known for their ability to ‘self-clean’ by repelling water and dirt. Nanotechnology provides this concept self-cleaning textiles which give self-cleaning as well as fresh cloths every day, this not only technically benefited but also techno economically benefited. The textile surface which can clean by itself without using any laundering action. The lotus leaf has two levels of structure affecting this behaviour – micro-scale bumps and nanoscale hair-like structures – coupled with the leaf’s waxy chemical composition.
Nano self-cleaning finishes has a large area of application. However the previous papers barely talks about the existing and invention of new product made of nano self-cleaning fabric. The affects of Nano finishing are in controversy. It is says that nanoparticles are very small that they can easily get inside the skin and may cause skin related disease especially when using nano silver particle but no research paper mention about the possible health hazards. Some of the researcher mentioned sunlight is the only best source of light for activating self-cleaning process. If sunlight is the only possible option then the application will be confined only for the outdoor wear.
No laundry sounds like a dream cloths that can clean themselves while they are being worn. Can’t imagine how many little’s of water we waste everyday to wash one garment. It’s not only that but the detergents that we used, energy and time spend. Where there is a will there is always a way to do something. Everything can be possible with the help of the advanced technology. Today Nanotechnology has successfully achieved self cleaning finishes and this will soon replace all the ordinary washing machine. What add interest to do this research is for wider and a better design application by using the self-cleaning fabric.
1.1. Objective of the study
• To study the self-cleaning finishes in textile.
• To understand the application of nanotechnology into self cleaning finishes.
• To design self cleaning finishes product.
1.2. The significance of the study
• Self cleaning finishes in the textile product helps in easy maintenance and environmental protection.
• Using of self cleaning product will save time, material, energy reduction and consequently cost-efficiency during production.
• People need not to suffer from heavy laundry bills and cleaning efforts.
• It will improve ageing behaviour by extended surface purity effect.
1.3. Research methodology
• Secondary research: articles, journals and books
• Primary: Informal discussion with the experts and experimental research.
2. Manufacturing Method
According to A. Singh and M. Gahlot 2015, the self-cleaning textiles can be manufactured by two ways
i. Traditional method: Application of fluorocarbons
ii. New method: Application of nanotechnology
i. Application of Fluorocarbon
Principle
This principle work in such a way that if the critical surface tension of solid is more than the surface tension of liquid, then liquid will wet the solid. So if the critical surface tension of solid is reduced than that of liquid, the water repellency can be achieved. The water repellency effect can be imparted on fabric by using fluorocarbons, which are the carbon compounds containing perfluorinated carbon chain. These carbon compounds form thin film around the fiber and possess a very low surface tension of around 10 dyne/cm. So the drop does not adhere to the surface fibers.
Limitation
The limitations of application of fluorocarbons are as follows:
• Fluorine compounds may cause skin related problems
• Effect will reduce after few washes
• Fabric goes yellow with exposure to heat, UV light and high relative humidity
ii. Nanotechnology Application
To overcome the above listed problems due to the application of fluorocarbons, new methods have been developed using nanotechnology, which are suitable for the production of self cleaning surface.
There are basically two types of self-cleaning surfaces involving nanotechnology. In the first place extremely water repellent, microscopically rough surfaces: dirt particles can hardly get a hold on them and are, therefore, removed by rain or by a simple rinse in water .The second example is given by photo-catalytic layers: due to a layer of nano crystalline titanium oxide, fouling organic material is destroyed by solar irradiation
The manufacturing of self-cleaning textiles using nanotechnology:-
2.1. Using Photocatalyst
2.2. Using microwaves
2.3. Using carbon nanotubes
2.4. Using Metal oxide colloidal
2.5. Using silver nanoparticles
2.6. Using chlorine halamine
2.7. Polyvinylidene Fluoride Film
2.1. Using Photocatalyst
In this process Nano-sized, Titanium dioxide and zinc oxide are used for imparting self cleaning and anti-bacterial properties. Nano-crystalline titanium dioxide sols were prepared by hydrolysis and condensation reaction of 97% titanium tetra-isopropoxide in an acidic aqueous solution (pH 1) of glacial acetic acid and 37% hydrochloric acid wherein the concentration of titanium dioxide (TiO2) precursor varied. The composites were heated at 60°C under vigorous stirring for 2 hours. It is found that the intrinsic low-stress mechanical properties of fabrics change after the self-cleaning coating treatment. The tensile extensibility of coated fabrics decreases and the surface roughness increases (Tung Sze and Daoud A, 2010).
The fabric is coated with a thin layer of titanium dioxide particles heaving 20 nanometers diameter. Titanium dioxide is a photo catalyst, when it is illuminated by light of energy higher than its band gap, electrons in TiO2 will jump from the valence band to the conduction band, and the electron (e-) and electric hole (h+) pairs will form on the surface of the photo catalyst. The negative electrons and oxygen will combine to form O2, radical ions, whereas the positive electric holes and water will generate hydroxyl radicals OH. Since both products are unstable chemical entities, when the organic compound (i.e. dirt, pollutants, and micro organisms) falls on the surface of the photo catalyst it will combine with O2′ and OH’ and turn into carbon dioxide (CO2) and water (H2 O). Since the titanium dioxide acts as a catalyst, so it is never used up. This is how the coating continues breaking down stains over and over. Zinc oxide is also a photo catalyst, and the photo catalysis mechanism is similar to that of titanium dioxide (E.M. El-Khatib 2012 and Singh A. et. al 2015).
Fig.1 a): Photocatalytic self cleaning property of Titanium dioxide
- b) Working of self cleaning textiles (https://www.technicaltextile.net).
According to E.M. EI- Khatib 2012, the self-cleaning technology in this work uses titanium dioxide photo catalyst that, when triggered by light, it decomposes dirt, stains, and harmful microorganisms and so on. Fabric samples were stained with red wine. After 20 hours of exposure to simulated sunlight, the coated fabric showed almost no signs of the red stain, whereas the untreated fabric remained deeply stained.
El-Khatib, E. (2012). Antimicrobial and Self-cleaning Textiles using Nanotechnology. 16, 157-174.
2.2. Using microwaves
A new technology developed, which make possible to attach nanoparticles to clothing fibres by use of microwaves. So chemicals that can repel water, oil and bacteria are directly bound to the nanoparticles. These two elements combine to create a protective coating on the fibres. This coating both kills bacteria, and forces liquids to bead and run off. The same technology, created by scientists working for the U.S. Air Force, has already been used to create t-shirts and underwear that can be worn hygienically for weeks without washing (Singh A. and Gahlot M. 2015).
2.3. Using carbon nanotubes
Artificial lotus leaf structures were fabricated on textiles via the controlled assembly of carbon nanotubes. Carbon nanotubes (CNTs) and surface modified carbon nanotubes are used as building blocks to biomimic the surface microstructures of lotus leaves at the nanoscale. Cotton fabrics, which otherwise have perfect water absorption; have been endowed with super hydrophobic properties.
Afterwards water contact angle was increased and found greater than 150 degree (Singh A. and Gahlot M. 2015).
Fig. 2 : Carbon nanotubes (https://www.researchgate.net
2.4. Using Metal oxide colloidal
The fabric is dipped and processed in metal oxide colloidal solution and then it is given heat treatment. Due to that fabrics get surface roughness on nanometer scale. After that through water repellent treatment, the fabrics has surface with water contact angle above 1500 (Singh A. and Gahlot M. 2015).
2.5. Using Silver nanoparticles
Water repellent coating of silver nanoparticles that offer superior resistance to dirt as well as water and require much less cleaning than conventional fabrics. Nano-Tex improves the water-repellent property of fabrics by creating nanowhiskers, which are made of hydrocarbons and have about 1/1000 of the size of a typical cotton fiber. They are added to the fabric to create a peach fuzz effect without lowering the strength of cotton (Singh A. and Gahlot M. 2015).
Fig3: Working of nanoparticles in textile surface (https://1.bp.blogspot.com/)
The above picture that the two textile surface, one which is treated with silver nano particles and other is not treated with silver nano particles. The untreated surface having dust particles, when water droplets rolls over it do not get washed off because dust particles are adhere by textile surface. While treated textile surface do not adheres the dust particles hence when water particles rolls over it dust get washed off (Singh A. and Gahlot M. 2015).
2.6. Using chlorine halamine
The technology works by attaching chlorine-containing molecules called halamines to textile fibers. Chlorine in the form of halamines has powerful bacteria-killing properties, used for example to disinfect swimming pools. Unlike chlorine gas, there are no adverse effects since toxic chlorinated carbon atoms are not generated. By sticking halamines to the cellulose fibers like cotton, the bacteria-killing effect can be bonded to the material and used again and again. Eventually, the chlorine is used up but can be regenerated with a wash in chlorine bleach. The halamine-treated fabrics kill microorganisms almost instantly on contact, so these materials are best suited for medical uses such as uniforms, wipes, bedding and towels (apparelscience.com).
Fig.4: Halamine treated fiber surface
(a) Untreated textile surface (b) Treated textile surface (Source : A. Singh and M. Gahlot)
2.7. Polyvinylidene fluoride (PVDF)
According to the paper of Zheng Zhenrong, et. al. 2015, polymer with low surface energy, and resistant to ultraviolet (UV) degradation, atmospheric chemical attacks, and algae and fungal attacks. They are highly flexible and hard to crack, thus easy to handle during installation. Hence, PVDF is usually used as the topcoat of architectural membrane structures, roof materials of vehicles, tent fabrics, raincoat material, and the cover of outdoor air-conditioners. A further modified PVDF film with a superhydrophobic property may be even more superior as the coating layer of a self-cleaning surface. Dust on this type of surface would be easily washed away by rain, which saves a great deal of manpower and cost in cleaning services.
2.8. Plasma Technology: Another solution for self cleaning property
Plasma treatment is another way to achieve self cleaning property in the textiles. It is a special coating process on which organic molecules are polymerized followed by deposition on textile surface. Ultra hydrophobic coating of nano particles imparts a rough surface morphology to textiles. Use of plasma in textiles is a method of generating multifunctional textile fibres means fibres with fire retardant and water resistance properties (Singh A. and Gahlot M. 2015).
3. Areas of Application
The self cleaning textiles have various areas for applications from fabric of home to technical textile of industries. The major areas are Apparels & accessories, medical textiles and hygienic textiles, sports wears, military & defence uniform, upholstery, outdoor textiles and automotives. Some other areas for application are glass windows, road signs and banners, bathrooms & sanitary appliances, flooring and roofing tiles, outdoor surfaces & shades, house walls and paints, ship hulls and plastic wares (Singh A. and Gahlot M. 2015).
Fig.4: self cleaning products
4. Commercially available self cleaning Products
The commercially available products in the global market with self cleaning property are such as Mincor® TX TT (Outdoor textiles like tents, umbrellas, sunshades, flags and
sails are major products), Nano Tex (Apparels like men’s shirts, dress materials etc. are main products) and Nanosphere (mainly produced Men’s shirts with self cleaning property) (Singh A. and Gahlot M. 2015).
5. Economic Significance
The economic significances of self cleaning textiles are as follows:
• Ease of maintenance and environmental protection due to reduced cleaning efforts
• Resource conservation (time, energy and money)
• Durable & long lasting
• People need not to suffer from heavy laundry bills
• Improved ageing behaviour by extended surface purity effect
6. Disadvatages/Limitations
• Self cleaning textiles take a long time to clean themselves. More active catalyst are therefore needed to speed up the cleaning process.
• The high oxidation power of the catalyst will not only degrade the stains but will also adversely affect the fibers themselves.
• The mechanical strength (i.e. tearing strength) & durability of fabric get reduced considerably. The catalyst is also skin irritant.
• Carbon nano tubes based self cleaning coatings have limited applicability as they turn dark in colour after the coating.
• Sunlight is the best source of light for activating the self-cleaning process.
6. Design opportunity
As research continues and knowledge matures in the area, more exciting developments are expected that will allow self cleaning to expand its frontiers into many as yet unknown and unexplored domains.
Designers have a great opportunity to come up with an innovative design concept in this area. As they can be applied in various areas like
— Medical textiles e.g. Hospital garments
— Sport tech e.g. Athletic wear
— Defense textile e.g. Military uniforms
— Smart textiles
— Upholstery
— Undergarments
However, for military persons or hikers, who are outside in the sun for long periods of time without the time or means to clean their clothes, self-cleaning fabric would be ideal as the sun is a good source for self cleaning. Further research would be required to test ways of applying nano particles to textiles.
7. Conclusion
The opening of new application fields for textiles will lead to a new growth stage. Self cleaning fabrics are not only repellent to water but are also resisting stains, dirt, odor and are antimicrobial as well. Water through these surfaces easily rolls off and completely cleans the surface in the process. Self cleaning effect on textile materials lead to an efficient use of materials and are therefore in agreement with the principles of sustainable development.
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