Abstract
In the twenty first century, product and machinery developments have taken place in all the fields of engineering and technology. Similarly, textile is also not lagging behind the pace of development when compared to other engineering discipline. Many researches both in domestic and at international level has been done on the advanced textile applications like smart fibres and smart textiles in the recent years. This article disseminates the informations related to smart fibres and textiles, their application areas like medical care, protective clothing, shape memory textiles, sports textiles etc. No doubt that smart textiles have wide application and prospects in the near future similar to the smart phones.
Keywords: Smart fibres, smart textiles, shape memory textiles

1.0. Introduction
The concept of Smart textiles was proposed from University of Virginia United States to Japanese scholar in the year 1989. He integrated information science into the material and developed smart materials. The term smart textiles mean intelligent materials. Smart textiles mean the textiles that are able to sense stimuli from the environment, to react to them and adapt to them by integration of functionalities in the textile structure. The stimulus as well as the response can have an electrical, thermal, chemical, magnetic or other origin. The first applications of smart textiles can be found in clothing. Smart clothing is defined as a new garment feature which can provide interactive reactions by sensing signals, processing information, and actuating the responses. They are capable of showing significant change in their mechanical properties such as shape, colour and stiffness, or their thermal or electromagnetic properties,

Typical examples of smart textiles are fabric and dyes that will change their colour where the clothes are made out of conductive polymers which give light when they get electromagnetic signals. They also regulate fabrics the surface temperature of the garments in order to achieve physiological comfort. The first smart textile material was silk thread which has a shape memory.

2.0. Smart fibres
a. Shape memory fibre Shape memory fibres are referred to a fibre which possesses shape memory effect. It means that when a deformed fibre is given some external stimulus by means of pressure and temperature, the deformed fibre would return to its original shape. Shape memory fibres include shape memory alloys, shape memory hydrogels and shape memory polymers. However, shape memory polymers have more advantages than shape memory alloys in terms of their characteristics like high recovery from strain, easy processing, low cost and low density.

b. Photo- chromic fibre
They are photo sensitive colour changing substances which has organic compounds containing isomers. Such photo- chromic fibres undergo reversible configuration under the action of light. The discolouration is under the action of irradiating ultra violet light or visible light spectrum which causes certain compounds to undergo changes in their molecular structure or electronic energy levels to form new compounds with different absorption spectra.

c. Optical fibre
A kind of composite fibre which can enclose light energy and transmit it in a wavelength mode. It is also called as smart fibre and provide excellent transmission performance. Optical fibre consists of two parts, a code and a cladding. The core is 1 to 10 micrometre in diameter for single mode silica glass fibre surrounded by 1.25 micrometre cladding whose refractive index is slightly smaller than that of the core. The optical fibre is coated with a protective layer of an outside diameter of approximately 250 micrometre. When light rays incident on the core-cladding boundary is at angles greater than the critical angle, the light rays undergo total internal reflection and are guided through the core without any refraction.

d. Temperature sensitive fibre
Temperature sensitive fibres are the fibres whose properties will change reversibly with temperature. The “ Ventcool” fibre developed by Mitsubishi Rayon Corporation stretches instantly when the humidity is high and quickly crimp when the humidity is low according to the environment conditions. It means that the fibre has dynamic response to changes and is called as dynamic fibre.

e. Conductive fibres
Conductive fibres possess excellent specific resistance and electrical conductivity, absorb electromagnetic waves, detect and transmit electrical signals. Conductive fibres can be rougly divided into electron conductive fibres, ion conductive fibres and inductive fibres.

f. Health smart fibre
Health smart fibres are developed for the enhancement of people’s awareness against anti-bacterial, safety and impact resistant fibre. Among them selective anti-bacterial fibre (smart fibre) will inhibit or kill the surface bacteria by the addition of anti-bacterial agent. “Nylstar” a smart polyamide fibre developed by the US have long anti-bacterial effect and safer too by incorporating anti-bacterial agent into the fibre.

3.0. Applications
3.1. Shape memory textiles
Shape memory textile is a kind of material with shape memory function introduced into textile through weaving or finishing.  The Italian company Corpo Nove designed a “lazy shirt”. When the outside temperature is high, the sleeves of the shirt will automatically roll from the wrist to the elbow within a few seconds; conversely, when the temperature drops, the sleeves can automatically recover and can also be automatically ironed. Shape memory fabrics can be developed into  fashions, protective clothing and accessories with different functions. With the in-depth research on shape memory materials and the further improvement of textile processing technology, shape memory functional textiles will be further developed.

3.2. Colour-changing textiles
Color-changing textiles refer to textiles that can display different colors with changes in external environmental conditions, such as light, temperature, pressure, etc. With its unique properties, color- changing textiles are widely used in various fields. Civilian can be used to make fashionable color- changing clothing and ever- changing decorative fabrics, military camouflage can be used in military, anti-counterfeiting field can be used as anti-counterfeiting materials, widely used in bills, certificates and trademarks. Color-changing textiles can be obtained by the following three methods: adding colorchanging fibers to the fabric; dyeing with color-changing dyes; printing with color-changing paint. The fabric made out of color changing materials has good hand feel, good washing resistance and long-lasting discoloration effect.

3.3. Smart temperature control textiles
Smart temperature control textiles mainly include three types of thermal insulation textiles, cool textiles and automatic temperature control textiles. For thermal insulation textiles, the thermal insulation materials  developed are mainly solar thermal storage fibers and far- infrared fibers. The solar thermal storage thermal insulation fibers are used to achieve thermal insulation. The principle is that the fibers absorb visible light and infrared rays from sunlight, and then heat radiation to the human body, and finally achieve the effect of heat preservation. Compared with sunlight thermal storage fiber, far infrared fiber has better thermal insulation performance. The reason is that it absorbs the heat emitted by the human body and radiates a certain wavelength of far infrared rays to the human body to reduce the loss of heat by promoting blood circulation, thereby achieving the purpose of heat preservation. Cool fabrics generally add metal oxides to polyester fabrics, and use metal oxides to reduce the possibility of clothing fading due to ultraviolet rays and light, and to ensure that the interior of the clothing is cool. Cool fabrics are especially useful for people who work in extremely cold environments (such as traffic police in winter) need clothes to warm them and display safety signals at the same time, which is very meaningful to them. Based on such requirements, there is a great need to develop smart textiles that integrate thermal regulation and light-emitting functions, and use advanced coaxial electro spinning to realize light-emitting temperature- regulated smart textiles.

3.4. Self-cleaning textiles
The trend of manufacturing self-cleaning coatings is nowadays a growing need which can remove both inorganic and organic pollutants through two different mechanisms: rolling water droplets and by photo catalysis.  Rolling water droplets refer to the lotus-shaped or cauliflower-shaped surface, coupled with low surface energy, will form dirty particles on the surface of the fabric, causing the water droplets to roll off and absorb dust, soil, inorganic and organic pollutants. A contact angle of greater than 150 degree is required in this mechanism. Photo catalysis is the decomposition of organic dirt by light, which can be easily removed during washing.

3.5. Wearable Technology and Health
Wearable technology wearable devices, smart electronic devices that can be worn on the body as implants or accessories. Such devices are activity trackers that enable objects to exchange data through the internet with humans or any other connected devices without requiring human intervention. A typical example is the smart watch. Apart from the consumer electronics, it is being incorporated in to navigation systems and health care also. Wearables can be used to collect data on a
user’s health such as

• Heart rate
• Blood pressure
• Walking steps
• Time spent on exercising

A recent development made on the smart fabrics is more beneficial for the persons who do exercise in gymnasium. The smart T- shirt has hidden letters like Time to stop” which will not be visible in the normal condition. After exercising in the gym, the sweat produced on the body is absorbed by the T-shirt and the hidden letters begin to appear informing the wearer to stop. Currently, other applications in health care are measuring blood alcohol content, measuring the sickness, athlete’s performance etc. Although smart textiles are in use, they can only collect data from the user about his well-being but for not making decisions about one’s health.

 3.6. Sutures in medical applications
A suture is a length of fibre used to tie the blood vessels or to sew tissues together. A typical example is polypropylene fibre generally used as a suture material in eye surgeries for patients when corneal grafting is needed. Many types of sutures are intelligent and absorbable materials as they hold the edges of the wounds together until the wound sufficiently heals. As the wound progressively heals, the tensile properties of the suture diminish and get absorbed into the body system. A few types of sutures are made from collagen of sheep or cattle intestine and are gradually degraded by enzymes in the body. Polymers of polylactic acid, poly glycolic acid, copolymers of polydiaxanone are synthetic polymers used as absorbable sutures in medical applications.

3.7. Optical sensors in military applications
Fibre optic sensors are ideal components to be embedded in textiles structural composites. Such sensors can be used to sense various battlefield hazards like chemical, biological and other toxic substances used in warfare times thereof in real time. The polyurethane –diacetylene copolymer can be used as a photochemical polymer for chemical sensor applications. The passive cladding of the optic fibre is replaced with these polymeric sensitive materials and the sensory system is integrated into textile fabrics. Another development is the pH sensitive sensor is also developed and woven into fabric for soldiers clothing.  Smart shirt developed by the Georgia Tech University is quite useful for detecting bullet wounds during the war. It functions like a computer with optical and conductive fibres integrated into the garment. Plastic optical fibres are woven in the seamless shirt is mainly responsible for detecting the bullet wounds. These optical wires are connected to a diode at one end and a laser at the other end. Pulses of light received by the diode are analyzed by a circuitry and if there is any interruption of light to the diode helps to identify the exact location of the bullet in the body.

3.8. Smart fibres in fire fighting
High performance fibres generally lose strength after exposed to high temperatures which undetected and in the worst case, can tear more precisely when the lives depend on them. Few examples are ropes used by firefighting brigades, suspension ropes used in construction sites. Researchers in Swiss have developed a special coating which changes its colour when exposed to high temperatures by friction or fire. Coatings on the rope is made up of 3 layers that the fibre actually changes colour when subjected to heat. The first layer (base) is silver coated on polyester (PET) and high tech Vectran fibres. This serves as a reflector. The second layer is the intermediate layer, titanium-nitrogen oxide which ensures that the silver layer is stable. Thereafter follows the amorphous layer, a coating of Germanium antimony tellenium (GST) which is 20nm thick. This layer initiates the colour change when is subjected to elevated temperatures. At high temperatures, it crystallizes and change the colour from blue to white. The colour change is due to the physical phenomenon interference. Depending upon the chemical composition of the temperature sensitive layer, this colour change can be adjusted to a temperature range between 100 deg to 400 deg.

3.9. Market Overview and major players
The global market was worth more than $2.5 billion in revenue in 2012 and is expected to cross $8 billion in 2018, growing at a healthy CAGR of 17.7% from 2013 to 2018. In terms of products, wrist-wear accounted for the largest market revenue in 2012, with total revenue  of the most established wearable electronic products – wrist-watches and wrist-bands combined, crossing $850 million. Smart textiles is now limited in the developed countries. It will be the next generation’s textile. So, there will be possibility of developing countries to earn huge profit. But they need more research and funding as well as technologies to implement this innovation. Some of the major players dominating this industry are E. I. Du Pont De Nemours and Company, Intelligent Clothing Ltd., Interactive Wear AG, International Fashion Machines Inc., Kimberly-Clark Health Care, Milliken & Company, Noble Biomaterials Inc., Outlast Technologies Inc, QinetiQ North America, Royal Philips.

4.0. Conclusion
Smart fibers /smart textiles and their applications are research hotspots in today’s textile field, as well as future development trends. Smart textile materials are the backbone of high- tech functional textiles. The application of smart fibers and smart textiles is becoming more open and consumer acceptance is increasing.

At present, the main application fields of smart fibers and smart textiles are: medical health care, military protection, firefighting, entertainment and sports, and clothing consumption. Moreover, it appears that this is only possible by intense co-operation between people from various backgrounds and disciplines such as microelectronics, computer science, material science, polymer science, biotechnology, etc. More research work is also emphasized on certain areas like high performance
fibres and their utility.

References
1. Huang M and Chu J 2018 J.Tianjin Textile Technology 6 43-6
2. Yang L 2017 J.China High-tech Zone 5 60-1
3. Melliand International, May 2021.
4. X. Zhang and X. Tao, Smart textiles: Passive smart, Textile Asia, pp. 45-49, June 2001, Smart textiles: Very Smart, Textile Asia, pp. 35-37, August 2001.
5. Textile institute, Smart Fibers, Fabrics and Clothing (Tao, X. Ed.), Florida: CRC Press, 2001.

Authors

                            

Dr. G. Nagarajan                               Ms. Anusuya A

Strategy Expert                             Associate Consultant

Texcoms Textile Solutions, Singapore

Author Profile

Anusuya