Abstract: When textile assumes an additional function over and above the conventional purpose, it may be regarded as Smart Textile. And if this additional functionality changes with change in use conditions, then textile may be regarded as Active smart or intelligent textile
Clothing is one of the three basic human needs. From primitive age, textile is used for clothing which was extended to household and domestic purpose with progressive civilization. Thousands of years ago textile is used in different forms such as sail cloth, tent, protective garments, ropes etc., basically these were all technical textiles and were mainly used for their technical performance.
A smart textile are materials and structures that sense and react to environmental conditions or stimuli, such as those from mechanical, thermal, chemical, electrical, magnetic or other sources.
Textile science today stands on a novel, unexplored and a fantasy filled horizon.
Textiles that can think for themselves! The idea itself is very progressive and in reality such textiles are a fact technically possible today and commercially viable tomorrow. The technology of SMART TEXTILES is an integration of almost all disciplines of applied sciences like:
v Textile chemistry
v Fiber technology
v Cloth manufacturing technology
v Material science
v Structural mechanics and aviation hydraulics
v Electronics and instrumentation
v Artificial intelligence
v Molecular biology and organic chemistry
v Molecular engineering and nanotechnology
v Information technology
v Theory of chaos and randomizations.
These myriad sciences are blended with one another to produce fashionable textiles which make our lives comfortable and luxurious. SMART TEXTILES, however, are not just restricted to clothing and apparels but extend to many other applications like automobiles, robotics, aircrafts, medicine and surgery etc. The importance of these materials is so profound at some places (e.g. military battlefields) that they virtually act as life saving materials.
Like many post World War-I innovations, smart textiles were also invented to meet the demands of the military. For example, clothing that can change color to produce camouflage effects for protection was developed by the US army in collaboration with various industrial firms to meet military requirements.
Smart textiles find applications in a plethora of fields. Some of the principle ones are:
Figure4. Recording of human breathing; (a) textile sensor in the form of a belt fastened around the patients chest, (b) a record of the breathing rhythm.
3.4 Military applications:
Optical fiber sensors integrated into textiles:
A) Fiber optics and sensors:
An optical fiber consists of a core (e.g. 1-10 micrometer in diameter for single mode silica glass fiber) surrounded by cladding (125 micrometer in diameter) whose refractive index is slightly smaller than that of the core. The optical fiber is normally coated with a protective layer of an outside diameter of approximately 250 micrometer. Inside the fiber core, light rays incident on the core-cladding boundary at angles greater than the critical angle undergo total internal reflection and are guided through the core without refraction.
The sensors made from optical fibers are small and flexible; they will not affect the structural integrity of the composite materials; and can be integrated with the reinforcing fabric to form the backbones in structures. They are based on a technology that enables devices to be developed for sensing numerous physical stimuli of mechanical, acoustic, electric, magnetic and thermal natures. A number of sensors can be arranged along a single optical fiber by using wavelength-, frequency-, and time- and polarization- division techniques to form 1-, 2 or 3- dimensional distributed sensing systems.
B) Optical sensors in textiles:
Fig 6-optical sensors
Fiber optic sensors are ideal components to be embedded in textiles structural composites for monitoring the manufacturing processes and internal health conditions.
One expects smart textiles to be the next biggest revolution in the textile industry after the manufacturing of synthetic fibers.
On the manufacturing front, the textile industry in the past decade or so, has changed dramatically due to more attention on smart textiles. The western world today focuses extensively on research and applications of smart textiles compared to the classical ordinary clothing sectors. In the next twenty years; the smart fiber sector is expected to scale astronomical heights so much so that they would become indispensable to human beings.
On the commercial front, however, these textiles are still to realize aspirations of potential buyers who would like to have the product at reasonable prices. But that is quite natural since any new technology takes its own time to get fully commercialized. And the smart textile industry is hardly a decade old. It can be anticipated that this industry will have a huge market of its own, and the market will not be made entirely of the affluent class; in fact majority of consumers would be from the middle class world over. Instead of cutting prices all the time, the textile industry should focus on delivering customized products with enhanced functionality features like say, smartness. The future does not lie in cutting costs all the time, but in being innovative at every process of product design.
Considering the current trends, the worldwide textile industry is over 50 million metric tons per year, and if smart textiles can capture only a measly 1% (which is quite possible), it still means an industry worth more than 1 billion11.
The intelligent textile sector represents the 21st century of fibers and fabrics and articles made from them. This segment is poised to rejuvenate the world textile sector completely in the coming few years. All in all, this field promises to have a very bright future and it is hoped that the products of this industry will make inroads into the households very soon.
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There are still some difficulties with shape memory materials that must be overcome before they can live up to their full potential. They are still relatively expensive to manufacture and machine compared to other materials such as steel and aluminum. Most of them have poor fatigue properties; this means that while under the same loading conditions (i.e. twisting, bending, compressing) a steel component may survive for more than one hundred times more cycles than an SMM element2.
3.3 Medical applications:
Some types of surgical sutures may also be regarded as intelligent fibers. A suture is a length of fiber used to tie blood vessels or to sew tissues together. Many types of sutures are described as absorbable materials: these are intelligent materials in that they hold the edges of the wound together until the wound has healed sufficiently. Only then is the suture significantly absorbed into the bodys system. As the wound progressively heals, the tensile properties of the suture gradually diminish over a period of weeks. However the mass of the suture remains invariant over this period. Afterwards extensive hydrolysis occurs, with subsequent absorption into the bodys system. The complete breakdown of the suture often occurs as long as 3-6 months after it was originally applied. For this purpose, we would require biodegradable and biocompatible polymers exhibiting shape memory. A few types of sutures are made from the collagen of sheep or cattle intestine and are gradually degraded by enzymes in the body. Many types of absorbable sutures, however, are made from synthetic polymers and are absorbed eventually into the body through hydrolysis of ester bonds in the polymer chains. A variety of polymers and copolymers have been used. Examples are:
1. Polylactic acid
2. (-CO-CH2O-CO-CH2O-)n Polyglycolic acid
3. (-O-CH2-CH2-O-CH2-CO-)n Their copolymers with polydiaxanone
4. (-O-(CH2)5-CO-)n polycapralactone
The Datawear incorporates sensors at each of the body joints plotting their position on a graph, which can be calculated on a computer. The sensors are made from conductive elastane. Datawear clothes consists a bunch of magnetic position sensors, the TCAS (manufacturer) system measures the angle of each of these joints to determine their absolute position (i.e. of each of the limbs). The sensors can be placed to specifications for individual applications. The datawear body unit consists of jackets, trousers and gloves that are circuited or wired electronically for interaction with computer. The application of datawear is to track position of limbs in computer data, medical imaging, measurement, ergonomics, biomechanics, robotics and animation. The whole body can be monitored by datawear, which has a particular relevance in the field of sports injuries and biomechanics.
Sensors for recording human physiological parameters:
This clothing, also called life shirts, was popularised by the American Sensatex company, and is used as an undershirt. Optical fibres are spirally plaited into its structure. The whole undershirt has been made with a special weaving technique, in one piece, without any cuttings or seams. The main task of this intelligent shirt is to monitor human physiological parameters such as temperature and heartbeat.
It can be used with different textile sensors, not only optical sensors. It is also possible to include sensors into the textile structure to measure the presence of poisonous gases in the air. The sensors collect data into a central unit, and send it to the information centre. Data transmission is wireless.
When incorporated in textiles, such sensors can be used to sense various battlefield hazards like chemical, biological and other toxic substances warfare threats in real time. The polyurethane-diacetylene copolymer can be used as the photochemical polymer for chemical sensor application. The passive cladding of the optic fiber is replaced with these sensitive materials, and the sensory system is integrated into textile structures. The pH sensitive sensors are developed and woven into the fabric of soldiers clothing12.
Smart shirt is an intelligent clothing (not restricted to military applications only) developed by a team at Georgia Tech. led by Prof. Sundaresan Jayaraman, and now sold by the company Sensatex for detecting bullet wounds. It functions like a computer, with optical and conductive fibers integrated into the garment. Plastic optical fibers woven in the seamless shirt are responsible for the detection of bullet wounds. These optical wires are connected to a photo diode at one end and a laser at the other. Pulses of light are detected constantly by the diode, with the aid of other circuitry, any interruption of the light pulse to the diode helps to indicate the exact location of the bullets entry. The shirt also carries sensors for measuring temperatures, heart beat and respiration functions, along with a microphone and a hazardous gas detector.
The shirt monitors the wearers heart rate, EKG, respiration, temperature, and a host of vital functions, alerting the wearer or physician if there is a problem. The Smart Shirt also can be used to monitor the vital signs of law enforcement officers, fire men, astronauts, military personnel, chronically ill patients, elderly persons living alone, athletes, infants (prevention of Sudden Infant Death Syndrome) etc. This is the worlds first wearable motherboard (or an intelligent garment for the 21st century)4. In short, the new paradigm spawned by the Wearable Motherboard provides an exciting opportunity that can not only lead to a rich body of new knowledge but in doing so, enhance the quality of human life. The potential impact of this research on medicine was further reinforced in a Special Issue of LIFE Magazine "Medical Miracles for the Next Millennium" in which the Smart Shirt or Wearable Motherboard was featured as one of the "21 Breakthroughs that Could Change Your Life in the 21st Century"2.
These materials have the unusual property of becoming wider when they are stretched and narrower when they are compressed- in other words, they have a negative Poissons ratio. These materials have other useful properties including high fracture toughness, indentation, resistance and energy absorption. Therefore they have potential applications in many fields such as bulletproof vests or helmets and impact resistance products, as well as showing promise for garments. Some well known synthetic materials are auxetic and soon auxetic fibers could be on the markets.
Fig 7-smart military uniform.
3.5 Computing textiles:
The integration of functional electronics into textiles can be realized in two extreme ways. One is to produce an apparel or technical textile and then integrate the electronic components. The other way is to produce conductive yarns (which are feasible I practice) when producing textiles and create textile structures with electronic functions1. Either of the ways could be used depending on application and end use, type of fabric, cost etc.
Fig 8 - Sensorised leotard and sensorised glove.
The chemical properties of conducting polymers make them very useful for use in sensors. This utilizes the ability of such materials to change their electrical properties during reaction with various redox agents or via their instability to moisture and heat.
Many conductive fibers and yarns e.g. metallic silk organza, stainless steel filament, copper, silver and gold or stainless steel wire-wrapped polymer filament, metal clad aramid fiber, conductive polymer fiber, conductive polymer coating and special carbon fiber/fabric, have been applied to the manufacture of fabric sensors.
E.R. Post and coworkers engineered a few fabric structures that can sense pressure. The row and column fabric keyboard is a fabric switch matrix sewn from conducting and non conducting fabric. The keyboard essentially consists of two layers of highly conductive metallic organza with a resistance of about 10 W/m and non conductive row separated by an insulating layer of nylon netting. When pressed at the right point, the two conducting layers make contact through spaces in nylon netting, and current flows from a row electrode to a column electrode. The keyboard can be repeatedly rolled up, crushed or washed, without affecting its electrical properties4.
Peratech Ltd., UK and Canesis, UK have collaborated to produce cloth keyboards by the SOFTswitch technology. This technology is based on Quantum Tunneling effect. The electronic devices can be easily integrated into the textiles. The QTC textile solutions enable the fabrics to function as electronic interfaces. The technology consists of sensors and switch arrays which are fully fabric based, washable and maintain the comfort and feel of textiles. These are usually integrated with innovative textile systems for signal transmission. User feedback is provided by the integration of LEDs or the addition of tactile devices such as domes.
QTC textile technologies are simple to integrate, low cost, offer flexibility and high reliability, proportional control and interfaces directly with existing electronic circuits14.
SOFTswitch technology can also be used to make spacesuits, musical jackets, smart clothing, I-wear, data wear, wearable computers, intelligent interior surfaces, flexible computing interfaces, advanced learning products, clinical pressure monitoring etc. Thus, SOFTswitch technology would allow us to connect any of our favorite clothing with electronic equipments, say an MP3 player or a radio etc. at a reasonably low cost with the textile switch and sensor technologies.
Electronic circuits built entirely out of textiles to distribute data and power have been devised by researchers at the MIT, USA. They can perform touch sensing, and use passive components sewn from conductive yarns as well as conventional electronic components. This creates interactive electronic devices such as musical keyboards and graphic input surfaces. One day entire computers may be made from textile articles that people prefer to wear. And these electronic circuits are a modest beginning in that direction. The first conductive fabric tried was silk organza which contains two types of fibers. On the warp is a plain silk thread while running in the other direction on the weft is a silk thread wrapped in thin copper foil. This metallic yarn is prepared just like cloth-core telephone wire, and is highly conductive. The silk fiber core has a high tensile strength and can withstand high temperatures. This allows the yarn to be sewn or embroidered with industrial machinery. The spacing between these fibers also permits them to be taken care of individually, so a strip of this fabric can function like a ribbon cable. Circuits fabricated on organza only need to be protected from folding contact with themselves, which can be accomplished by coating, supporting or backing the fabric with an insulating layer which can also be cloth. There are also conductive yarns manufactured specifically for producing filters for the processing of fine powders.
These yarns have conductive and cloth fibers interspersed throughout. Varying the ratio of the two constituent fibers leads to differences in resistivity. These fibers can be sewn to create conductive traces and resistive elements. While some components such as resistors, capacitors, and coils can be sewn out of fabric, there is still a need to attach other components to the fabric. This can be done by soldering directly onto the metallic yarn. Surface mount LEDs, crystals, piezo transducers, and other surface mount components with pads spaced more than 0.100 inch apart are easy to solder into the fabric. Once components are attached, their connections to the metallic yarn may need to be mechanically strengthened. This can be achieved with an acrylic or other flexible coating. Components with ordinary leads can be sewn directly into circuits on fabric, and specially shaped feet could be developed to facilitate this process. Gripper snaps make excellent connectors between the fabric and electronics. Since the snap pierces the yarn it creates a surprisingly robust electrical contact. It also provides a good surface to solder to. In this way subsystems can be easily snapped into clothing or removed for washing.
Fig 9 -wearable electronic circuit.
Several circuits have been built on and with fabric to date, including busses to connect various digital devices, microcontroller systems that sense proximity and touch, and all-fabric keyboards and touchpads. Building systems in this way is easy because components can be soldered directly onto the conductive yarn. The addressability of conductors in the fabric make it a good material for prototyping and it can simply be cut where signals lines are to terminate. Keyboards can also be made in a single layer of fabric using capacitive sensing [Baxter97], where an array of embroidered or silk-screened electrodes make up the points of contact. This is shown in the figure. A finger's contact with an electrode can be sensed by measuring the increase in the electrode's total capacitance. It is worth noting that this can be done with a single bidirectional digital I/O pin per electrode, and a leakage resistor sewn in highly resistive yarn. Capacitive sensing arrays can also be used to tell how well a piece of clothing fits the wearer, because the signal varies with pressure.
The keypad is flexible, durable, and responsive to touch. A printed circuit board supports the components necessary to do capacitive sensing and output key press events as a serial data stream. The circuit board makes contact with the electrodes at the circular pads only at the bottom of the electrode pattern. In a test application, 50 denim jackets were embroidered in this pattern. Some of these jackets are equipped with miniature MIDI synthesizers controlled by the keypad. The responsiveness of the keyboard to touch and timing were found by several users to be excellent. These researchers have tried to combine conventional sewing and electronics techniques with a novel class of materials to create interactive digital devices. All of the input devices can be made by seamstresses or clothing factories, entirely from fabric. These textile-based sensors, buttons, and switches are easy to scale in size. They also can conform to any desired shape, which is a great advantage over most existing, delicate touch sensors that must remain flat to work at all. Subsystems can be connected together using ordinary textile snaps and fasteners. Finally, they can be washed by like regular clothes when subjected to dirt.
These are intelligent textiles which change color (because the dye applied on the surface change color) with change in temperature. Chromic materials are the general term referring to materials which radiate the colour, erase the colour or just change it because of its induction caused by the external stimuli, such as light, heat, electricity, solvent, pressure.
The color change is especially due to application of thermo chromic dyes whose color changes at particular temperature. 2 types of thermo chromic systems that have been successfully applied to textiles may be recognized, the liquid crystal type and the molecular rearrangement type. In both the cases, the dye is entrapped in microcapsules, applied to garment fabric like a pigment in a resin binder. The most important types of liquid crystals for the thermo chromic systems are the so called cholesteric types, where adjacent molecules are so arranged that they form helices. Themochromism results from selective reflection of light by the liquid crystal. The wavelength of the light reflected is governed by the refractive index of the liquid crystal and by the pitch of the helical arrangement of its molecules. Since the length of the pitch varies with temperature, the wavelength of the reflected light is also altered, and a color change results.
An alternative way of inducing thermo chromism is by means of a rearrangement of the molecular structure of a dye as a result of a change in temperature. The most common types of dye which exhibit thermo chromism through molecular rearrangement are the Spiro lactones, although other types have also been identified. A colorless dye precursor is microencapsulated and is solid at lower temperatures. On heating, the system becomes colored or loses color at the melting point of the mixture. The reverse change occurs at this temperature if the mixture is then cooled. However, although thermo chromism and molecular rearrangement in dyes has aroused a degree of commercial interest, the overall mechanism underlying the changes in color is far from clear cut and is still very much open to speculation7.
A temperature sensitive fabric with trade name SWAY was manufactured by introducing microcapsules, diameter 3-4mm to enclose heat sensitive dyes, which are resin coated homogeneous over fabric surface. The microcapsules were made of glass and contained the dyestuff, the chromophore agent (electron acceptor) and color neutralizers (alcohol etc.) which reacted and exhibited color/no color according to environmental temperature. SWAY had 4 basic colors and 64 combined colors. It could reversibly change color at temperature greater than 5◦C and could be operated from -40◦C to 80◦C.
Danial Cooper has designed a jacket that is useful for protecting the wearer from pollution. The front panels are made of nylon fabric embedded with nitrogen oxide, sulfur dioxide and ozone monitors. When there is pollution, the fabric changes its color from blue to orange16.
Fig 11 -smart mp3 player.
Musical jacket turns an ordinary jacket into a wearable musical instrument. Musical jacket allows the wearer to play notes, chords, rhythms, and accompaniment using any instrument available in the general music scheme. It integrates fabric keypad, a sequencer, synthesizer, amplifying speakers, conductive organza, and batteries to power these subsystems. The smart suit consists of global mobile system for communication, functional architecture for navigation, and electrically heated fabric panels for heating. The sensor system consists of a heart rate sensor, three position and movement sensors, ten temperature sensors, an electrical conductivity sensor and two impair detecting sensors. The implementations and synchronization requires a user interface (UI), a central processing unit (CPU) and a power source. Each main module, excluding the sensors and the user interface is set into the supporting vests. This smart suit allows easy, fast, and cost efficient group communication. A cellular telephone, loudspeaker and microphone are incorporated in the belt. By pulling a tag on this belt, communication can be achieved by groups of people.
Aircraft maneuverability depends heavily on the movement of flaps found at the rear or trailing edge of the wings. The efficiency and reliability of operating these flaps is of critical importance. Most aircraft in the air today operate these flaps using extensive hydraulic systems. These hydraulic systems utilize large centralized pumps to maintain pressure, and hydraulic lines to distribute the pressure to the flap actuators. In order to maintain reliability of operation, multiple hydraulic lines must be run to each set of flaps. This complex system of pumps and lines is often relatively difficult and costly to maintain. Many alternatives to the hydraulic systems are being explored by the aerospace industry. Among the most promising alternatives are piezoelectric fibers, electrostrictive ceramics, and shape memory alloys.
The flaps on a wing generally have the same layout shown on the left, with a large hydraulic system attached to it at the point of the actuator connection. "Smart" wings system is much more compact and efficient, in that the shape memory wires only require an electric current for movement. The shape memory wire is used to manipulate a flexible wing surface. The wire on the bottom of the wing is shortened through the shape memory effect, while the top wire is stretched bending the edge downwards, the opposite occurs when the wing must be bent upwards. The shape memory effect is induced in the wires simply by heating them with an electric current, which is easily supplied through electrical wiring, eliminating the need for large hydraulic lines. By removing the hydraulic system, aircraft weight, maintenance costs, and repair time are all reduced. The smart wing system is currently being developed cooperatively through the Defense Advanced Researched Project Agency (DARPA, a branch of the United States Department of Defense), and Boeing.
Figure 12- smart jet.
3.8 Space research:
The earliest developed Apollo spacesuits contained an inner layer of nylon fabric with network of thin walled plastic tubing which circulated cooling water around the astronaut to prevent overheating. This inner layer was comfort layer of lightweight nylon with fabric ventilation ducts, and then a three layer system formed the pressure garment. Then aluminized Mylar was used for heat protection, mixed with four spacing layers of Dacron. These were covered with a non flammable and abrasion protective layer of Teflon-coated beta cloth. The outer layer was Teflon communication cloth. The backpack unit contained a life support system providing oxygen, water and radio communications.
Thus we have considered the major interesting applications of smart textiles in various sectors. We have also considered the mechanism by which these smart systems operate and also reviewed the process of manufacturing.
Fig 13-space suite
1.1 Market overview
Smart or Interactive Textiles is a new market segment resulting from the miniaturisation of electronics and the fall in price of components and manufacturing costs for both electronics and textiles. A simultaneous trend in the clothing industry toward manufacture of specific products for dedicated uses i.e. for running, skiing, golf and extreme sports has created a niche where smart and interactive textiles enable new functions and features that can enhance a garments performance and its wearers experience.
1.2 Market drivers
Low cost fibre and textile manufacturing in Asia and India has caused significant cut backs in production in Western Europe and has pressed traditional textile companies to look to new technologies to add value in the design phase of a production. Such new technologies are immature and often promoted by start-up companies that are spin-offs from professional research. With limited funding to commercialise their products, the result is that some of the most exciting technologies have not yet been exploited to the full.
1.3 Market Structure
1.1 Market Structure and stakeholders
While smart textile applications have made a limited commercial impact so far, with relatively small volumes of commercial products launched primarily in the high performance apparel sector predictions for growth of the smart textile market as a whole are huge. According to the Venture Development Corporation the market for electrically enabled smart fabrics and interactive textile technologies was worth US$340.0 million in 2005. By 2008 it is expected to be worth US$642.1 million, representing a compound annual growth rate of 28.3%. While some predictions do not agree on the total value of the market, they are all agreed that the market for smart textiles is one of the most dynamic and fast growing sectors and offers huge potential for companies willing to take the plunge. Not surprisingly, most of the smart textile consumer products launched so far have been introduced onto the luxury end of the performance clothing market where development costs can be more readily absorbed by higher prices.
Companies dominating this segment are those who already have a significant market share such as Nike, Adidas and ONeill. Products launched in this sector show a clear trend toward strong design features coupled with simple to operate functions that are highly relevant to the garments wearer in the particular use situation. A good example of this is the Nike plus running shoe. Cooperation with IT giant Apple has resulted in a simple user friendly web interface that enables runners to motivate themselves and each other by uploading data recorded by the sensor in the shoe and transferring it to a standard iPod nano. The system is stylish, simple to operate and enables runners to track their performance and set new targets to be reached.
Major actors in the performance clothing segment
ONeill, Burton, North Face, Rosner
Monitoring health and vital signs, commercial products in 2007
Eleksen, Peratech Ltd,
Electronics Components Manufacturers
Interactive Wear, Ohmatex, Fibretronix
v Military (e.g. uniforms which can detect chemical threats in a battlefield)
v Airplanes (e.g. in manufacture of flaps found in aircraft wings)
v Biomedical field (e.g. manufacture of smart sutures, tissues)
v Space research (e.g. special spacesuits designed for astronauts)
v Comfort wears (e.g. fabrics which can maintain body temperature)
v Sports (e.g. fabrics which can make athletes feel comfortable even in stretched body conditions)
v Fashion clothing (e.g. fabrics which can change color according to ambient temperatures)
Smart textiles have a lot many applications besides the abovementioned ones, but before we discuss them let us concentrate on the fundamental mechanisms that make a fabric smart. In this new era the smart textiles are considered also as textronics.
The term textronics refers to interdisciplinary approaches in the processes of producing and designing textile materials, which began about the year 2000. It is a synergic connection (Figure 1) of textile industry, electronics and computer science with elements of automatics and metrology knowledge.
A new quality is achieved as result of using component elements, which thanks to mutual feedback increase their affect. This can be obtained by the physical integration of microelectronics with textile and clothing constructions. The main task of textronics is to produce multifunctional, intelligent products with complex inner structures, but which have uniform functional proprieties. Textronic products are characterised by the following features:
v Flexibility meaning facility in modifying the construction at the stage of design, production and exploitation; for example, modular construction;
v Intelligence of the textiles referring to the possibility of an automatic change in properties influenced by external factors (parameters) and even taking decisions, which means learning or communication with the environment.
v Multifunctionality, or the ease of realising different functions by one product.
It can be stated that textronics means the design and production of intelligent and interactive textile materials which are characterised by variable structures or electrical resistance, which include microchip elements and is characterised by self-adaptive features.
New markets for textiles
Chemical engineering developments in recent years have led to development of textile fibres with properties such as extreme strength, lightness in weight and where fibres can change their shape dependant upon temperature or other external stimuli. These features are just beginning to be exploited in entirely new sectors, where textiles have not traditionally been standard materials. Applications are widely predicted to be highly diverse, covering segments from EMI shielding in automotive, planes and the like to use as moulding forms for architectural components and to reinforce and strengthen concrete building elements.
The smart textile industry is still at a nascent stage of development with many new innovations in the pipeline. But it is bound to change the way we look at textiles. These 21st century textiles will signify the true merger of textile and information industries.
Smart textiles are a field which seems to be intellectually rewarding to a keen researcher. It is a challenge of sorts since we are not only talking about smart materials but also about the use of such materials as textiles. Thus smart materials have to be intelligently engineered to be used as textiles. Particularly if these materials are to be used as apparels, then a lot of factors like feel, density, aesthetic value, processing (during manufacturing and after use) need to be considered. We are not just interested in making fancy electronic components, but in making textiles which can be used like ordinary apparels though having the characteristics of electronic systems. Present research in smart textiles all over the world focuses on the following broad areas18:
1. for sensors/ actuators-
v Photo sensitive materials
v Fiber optics
v Conductive polymers
v Thermally sensitive materials
v Shape memory materials
v Intelligent coating/ membrane
v Chemical responsive polymers
v Mechanical response materials
v Micro capsules
v Micro and nanomaterials
2. for signal transmission, processing and controls-
v Neural network and control systems
v Cognition theory and systems
v for integrated processes and products-
v Adaptive and responsive structures
v Wearable computing
v Tissue engineering
v Chemical/ drug release
A particularly interesting objective is clothing which represents the ideal interface medium between humans and their environment. Everyone wears clothes in several layers one above the other in all day-to-day situations, which means that it is possible to accommodate micro system components comparatively simply and comfortably. The objective should now be to focus on integrating microchip and computer systems as invisibly as possible into clothing, thus connecting man as unobtrusively as possible with his environment and equipping him as a communication medium. This is a field of innovation and a future potential of fascinating proportions which also opens up interesting possibilities in commercial terms. Clothing as a carrier medium is thus developing into a high-tech product, which will substantially enhance its status.
2. Fundamental considerations:
2.1 Smart materials
A smart polymer or material can be described as a material that will change its characteristics according to outside conditions or stimuli. The following table shows the fundamental characteristics of and difference in traditional, high performance and smart materials.
Fundamental material characteristics
Fundamental system behaviors
Traditional materials: Natural materials (stone, wood) fabricated materials (steel, aluminum, concrete
Materials have given properties and are acted upon
Materials have no or limited intrinsic active response capability but can have good performance properties
High performance materials: polymers, composites
Material properties are designed for specific purposes
Very good performance properties
Smart materials: Property-changing and energy exchanging materials
Properties are designed to respond intelligently to varying external conditions or stimuli
Smart materials have active responses to external stimuli and can serve as sensors and actuators
The input can be temperature, pH, or magnetic or electric field. The output can be change in length, viscosity, color or conductivity.
Input (stimulus) Active material Output (response)
SMART TEXTILES are defined as textiles that can sense and react to environmental conditions or stimuli, from mechanical, thermal, magnetic, chemical, electrical, or other sources. They are able to sense and respond to external conditions (stimuli) in a predetermined way. Textile products which can act in a different manner than an average fabric and are mostly able to perform a special function certainly count as smart textiles.
2.3. Components in smart textiles:
Three components may be present in smart textiles (materials)
v Controlling units
The sensors provide a nerve system to detect signals. Some of the materials act only as sensors and some as both sensors and actuators. Actuators act upon the signals and work in coordination with the controlling unit to produce an appropriate output.
2.4. Classification of smart textiles:
Smart textiles are classified into three categories depending on functional activity, as follows:
v Passive smart textiles
v Active smart textiles
v Very or ultra smart textiles
Passive smart textiles:- The first generation of smart textiles, which can provide additional features in passive mode that is not concerning with alteration in environment are called passive smart textiles. Optical fiber embedded fabrics and conductive fabrics are good examples of passive smart textiles.
UV protective clothing, multilayer composite yarn and textiles, plasma treated clothing, ceramic coated textiles, conductive fibers, fabrics with optical sensors, are some examples of passive smart textiles.
Active smart textiles:- The second generation of smart textiles have both actuators and sensors and tune functionality to specific agents or environments, are called active smart textiles. These are shape memory, chameleonic, water resistant and vapor permeable (hydrophilic/ non porous), heat storage, thermo regulated, vapor absorbing, heat evolving fabric and electrically heated suits.
Phase change materials and shape memory materials, heat sensitive dyes etc. in textiles form active smart textiles.
Ultra smart textiles:- Very smart textiles are the third generation of smart textiles, which can sense, react, and adapt themselves to environmental conditions or stimuli. They are the highest levels of smart textiles. These may deal actively with life threatening situations (battlefield or during accidents) or to keep high levels of comfort even during extreme environmental changes. These very smart textiles essentially comprise of a unit, which works like the brain; with cognition, reasoning and activating capacities.Ultra smart textiles are an attempt to make electronic devices a genuine part of our daily life by embedding entire systems into clothing and accessories. Though the entire potential has not been completely realized, the developments so far can be termed as only rudiments of very smart textiles.
For example, spacesuits, musical jackets, I-wear, data wear, sports jacket, intelligent bra, smart clothes, wearable computer etc.
Passive smart textiles are lifeless but very smart textiles, are the most dynamic levels of artificial intelligence in textiles5. In fact, passive textiles may not be termed as really smart since they do not think for themselves. Nevertheless they perform special functions in the passive mode and hence the term passive smart textiles.
2.5. General methods of incorporating smartness into textiles:
Textile to behave smartly it must have a sensor, an actuator (for active smart textiles) and a controlling unit (for very smart textiles). These components may be fiber optics, phase change materials, shape memory materials, thermo chromic dyes, miniaturized electronic items etc. These components form an integrated part of the textile structure and can be incorporated into the substrate at any of the following levels4:
v Fiber spinning level
v Yarn/fabric formation level
v Finishing level
The active (smart) material can be incorporated into the spinning dope or polymer chips prior to spinning e.g. lyocell fiber can be modified by admixtures of electrically conductive components during production to make an electrically conductive cellulosic fiber. Sensors and activators can also be embedded into the textile structure during fabric formation e.g. during weaving. Many active finishes have been developed which are imparted to the fabric during finishing. The electronic control units can be synchronized with each other during finishing. Techniques such as microencapsulation are generally preferred for incorporation of smartness imparting material in the textile substrate. However the correct material and the correct method must be selected; based on a variety of considerations.
A challenge that lies ahead is the manufacture of inherently smart fibers which do not need any further incorporation of smartness into them; and which can directly woven into textiles.
3. Applications of smart textiles:
Smart textiles find a wide spectrum of applications ranging from daily usage to high-tech usage. Now we can review various important applications of such textiles. We would consider textiles used for the following broad categories:
v Comfort wear
v Heat protection
v Medical applications
v Military applications
v Computing textiles
v Space research
It should be noted that a textile mentioned in one category can find use in other categories as well. For example, chameleonic textiles (textiles that change color) are discussed as fashion wear. But they are of profound significance in the military since uniforms made out of them can help in camouflaging to protect the soldier.
3.1 Comfort wear:
Multilayer composite yarns and textiles:
Multilayer composite yarns and textiles demonstrate a possibility for achieving wear comfort in terms of absorbing sweat release from the human skin surface by an internal sweat absorbent layer. A cool and dry three layer composite yarn, which consists of a polyester filament yarn on the surface, a staple polyester yarn in the middle and a polyester filament yarn in the core, has been developed by Toyobo Co., Japan. The presence of fine fibers lying in the middle leads to greater porosity, which enhances capillary action, conveying the absorbed sweat to the yarn surface. The coarser polyester yarn (filament) in the yarn interior has a Y-shaped crossed section in order to increase moisture absorption capacity. Thus moisture gets efficiently transferred from the surface of the fabric in contact with the skin to the outer surface of the fabric exposed to the atmosphere. The sweat thus accumulated in the outer layer gets carried of by atmospheric air currents46.
Another way of achieving body comfort against sweat release is application of functional finishes to the fabric. The sweat released by the human body in ordinary course is evaporated by absorbing heat from the body. This maintains the body temperature constant. Fabrics treated with Snocool (cool finish) can enhance the natural phenomenon of sweat evaporation. The finish itself absorbs and dissipates sweat evenly throughout thus giving a cool feeling to the wearer. The finish can also reflect light and transfer the moisture faster than normal from body to fabric and finally to atmosphere. Fragrances can also be imparted to the finish.
The recipe is as follows7:
Snocool SRB liquid: 3-10 gpl is used.
The material is padded at 70% expression, subjected to curing at 180◦ C, for 30-45 seconds.
These kinds of textiles have chemicals like cyclodextrin encapsulated into them, which leads to an inbuilt fragrance plus other massaging and relieving effects.
Cyclodextrins are formed during the enzymatic degradation of starch. They are macro cyclic polysaccharides built from glucose units covalently linked at the C1 and C4 carbon atoms. Depending on the number of glucose units one can distinguish between a-(six), b-(seven) and g-(eight units of monomer) cyclodextrins. These molecules are torus shaped. These molecules have been primarily used in pharmaceutics, cosmetics, and food. But now the permanent fixation of these molecules on textiles have been studied and made possible (A cyclodextrin derivative suitable for fixation on cotton fibers is already available commercially). Even after fixation the cyclodextrin molecules are able to form inclusion complexes with organic molecules. For the use in textile finishing, β- cyclodextrin modified with a reactive group (monochlorotriazinyl group) is used. This anchor group reacts with the hydroxyl groups of cellulose or with the amino groups of wool and silk.
The organic components of sweat are complexed by the cyclodextrins in the case of textiles in contact with skin. Due to this reaction the microbiological degradation of these substances is prevented or slowed down. Thus the formation of body odor is prevented or reduced. These textiles are able to help people who are not able to use any deodorant because of a very sensitive skin.
However other people also can take advantages of these kinds of textiles. The complexed sweat components can be decomplexed during a normal washing process. The complexation of sweat components by the fixed cyclodextrins can easily be shown after the extraction of these textiles with organic solvents and an analysis of the resulting solutions using gas chromatography.
During usage these textiles release perfumes. On the commercial side, such products are already on offer in the German market and many more new markets are being explored8.
Another related innovation is aromatherapy7. This is the practice of applying and inhaling essential oils from plants as a physical and emotional boost to the body. People inhale more deeply due to some fragrances and take extra oxygen into the body, making them healthier. Selected fragrances have been found to specifically alter the bodys physiology, including respiration, heart rate, blood pressure, and brain activity.
Micro capsules containing specific aroma therapeutic essential oils have been impregnated on to sweaters, ties, T-shirts, and on a number of other products. The microcapsules produced are very small, with a diameter of 5 to 10 micrometer, and a pair of stockings would contain approximately 200 million fragrant capsules. Normal physical forces during wear of the materials rupture the microcapsule wall, releasing the desired aroma. The fragrance within the microcapsules, which are tightly lodged in the tiny cavities of a porous acrylic material on the textile, persists even after hard washing of the textiles up to ten minutes.
Microencapsulated formulations of various fragrances like musk, pineapple, rose, lavender, jasmine, lemon, peppermint etc. have been successfully applied to fabrics with the help of binders. The recipe is as follows:
v Fragma 1.0-5.0gpl
v Pad, dry, cure at 170 ◦C-180 ◦C for 30-45 seconds.
v Deodorizing fragrances are used to prevent the build up of malodor during wear or use of the fabric and also when they are not in use. They operate via a number of mechanisms:
v Inhibiting the enzymes responsible for producing malodor
v Lowering the vapor pressure of the malodor
v Reducing the perception of malodor
A smart bra that can change its properties in response to breast movement is being developed at University of Wollon, Australia. This bra will provide better support to active women when they will be in action. Smart bra can tighten and loosen its straps, or stiffen and relax its cups to restrict breast motion, preventing breast pain and sag. The conductive polymer coated fabrics is used in the manufacture of smart bra. The strain acting on the fabric can be sensed by the conductive polymer that is coated on the main fabric. The fabrics can alter their elasticity in response to information about how much strain they are under. The smart bra is capable of instantly tightening and loosening its straps or stiffens cups when it detects excess movements.
Protection against bacteria
AgION all natural antimicrobial technology derived from a silver based compound was used for clothing, towels etc. for NASA crew members on an undersea mission. This provided protection against the growth of destructive and odor causing bacteria. Ag is one of the oldest known antimicrobial agent and has proven effective against more than 650 strains of destructive and odor causing bacteria, yeast, fungi and mould. AgION antimicrobial can be applied during the fiber extrusion process, or to fabric by a finishing process- it is a compound of Ag ions. The active ingredient bonded to ceramic material in this is completely inert. The ambient moisture in air causes low level release that maintains the antimicrobial surface. More Ag is released when more humidity is encountered (which could be a cause for more bacterial growth). Thus protection against bacteria and mildew is provided.
3.2 Heat protection:
Ultraviolet protective clothing7:
Ultraviolet light is usually defined as electromagnetic radiation of wavelength between 4 and 400 nm. A fraction of UV radiations from the sun manages to reach the Earths surface and are dangerous. There exist smart clothings which have the ability to absorb or reflect the harmful UV rays in terms of passive heat retention. This is due to the numerous pores in textile product which are by means of bulked and micro fiber constructions. The heat retention is also possible by use of UV absorbing chemicals. A specialty finish can be applied to the fabric, which is composed of UV absorbers. This is applied during dyeing under a reductive process. Fabshield 50 Plus (the finish) is in 3.5-5% proportion in the dye bath and is applicable by exhaust as well as padding method.
Ceramic coated textiles:
NASA (National Aeronautics and Space Administration) has reported the use of high performance coating system to protect material from high level of solar radiations and extreme cold conditions. The fluid ceramic can be applied as ceramic coating for thermo ceramic construction and heat protection simultaneously. The base for fluid ceramics is formed by dispersion of a special acrylic resin in the tile form vacuumised ceramic silicon micro bodies (ceramic bubbles) of which energy is significantly throttled. The material composition of the dispersion coating (formulation of adhesives filling agents, pigments and the exclusive ceramic bubble state) can be tuned to each other in conjunction with bubble partial vacuum in such a way that new and more advantages, characteristics and features are produced. The resulting textile system would demonstrate excellent sunlight reflection and thus help in heat regulation.
Thermo regulated textiles:
Fig 2 - Fabric with embedded copper wires as temperature sensors
The main objective of heat storage or thermally regulated textiles is to maintain the wearer in a state of thermo physiological comfort under the widest possible range of workloads and ambient conditions. Heat storage and thermo regulated textiles are novel textiles that can absorb, redistribute and release heat by phase change in low melting materials, according to changes in surrounding temperature or by some other mechanism4.
These textiles basically incorporate the so-called Phase Change Materials (PCMs) into their structures. Phase change materials are defined as materials that can absorb, store and release large amount of energy in the form of latent heat over a narrowly defined temperature range (phase change range) as the material changes phase or state. These are basically latent heat storage materials. Ice is a common example of phase change material. Phase change materials undergo reversible solid-liquid phase changes under a certain set of temperature conditions10.
Phase change materials thus can act as heat buffers when incorporated into textiles. They keep the body temperature constant by absorbing or releasing heat in the latent form. Since the ideal body temperature is 33.4◦C, the phase change material should be such that it undergoes phase transition at or reasonably near this temperature. The PCMs used for textile purpose are hydrated inorganic salts, polyhydric alcohol-water solution, PEG, polytetramethylene glycol, aliphatic polyester, linear chain hydrocarbons, hydrocarbon alcohol, and hydrocarbon acid10.
The PCM can either be coated on the fabric or can be integrated into the fiber in a microcapsule form. In a typical production process, the Phase Change Material (PCM) is introduced into the textile fiber matrix in a microencapsulate form (Micro encapsulation is a process by which very tiny droplets or particles of liquid or solid material are surrounded or coated with a continuous film of a polymeric material21). The microcapsules have walls less than 1 micrometer thick and are typically 20-40 micrometer in diameter, with a PCM loading of 80-85%. The small capsule size provides a relatively large surface area for heat transfer. Thus, the rate at which the PCM reacts to an external temperature change is very rapid11.
NASA put the Phase Change Materials into gloves to keep the pilots hands warm. It developed textiles that aimed to improve the protection of instruments and astronauts against extreme fluctuations in temperature in space on the basis of heat absorbing and temperature regulating technology. Vigo et al finished a polyester/cotton fabric with polyethylene glycol (PEG) as Phase Change Material and dimethylodihydroxyethyleneurea (DMDHEU) to produce a thermally active fabric having 30-50% add-on.
The main challenge in developing textile -PCM structures is the method of their application. Encapsulation of PCMs in a polymeric shell is an obvious choice but it adds dead weight to the active material. Efficient encapsulation, core-to-wall ratio, yield of encapsulation, stability during use and integration of capsules onto fabric structure are some of the parameters that need to be considered here2.
Shape memory materials:
Shape memory materials (SMMs) are materials that are stable at two or more temperature states. SMMs are able to memorize a second, permanent shape besides their actual, temporary shape. After application of an external stimulus, e.g. an increase in temperature, such a material can be transferred into its memorized, permanent shape. Shape memory effect is based on martensitic phase transformation (solid-solid phase transformation). Shape memory polymers are materials that have hard segments and soft segments e.g. polyurethane, polyester ether, styrene-butadiene copolymer etc. This is because the shape memory materials exhibit some novel performances such as sensitivity, actuation, damping and adaptive responses to external stimuli such as temperature, lighting, stress and field, which can be utilized in various ways in smart systems. A shape memory material possesses different properties below and above the temperature at which it is activated. Below this temperature, the material is easily deformed. At the activation temperature, the material exerts a force to return to a previously adopted shape and becomes much stiffer.
The two unique properties of pseudo elasticity and shape memory effect possessed by these materials are made possible through a solid state phase change, that is a molecular rearrangement, which occurs in the shape memory material. A solid state phase change is similar in that a molecular rearrangement is occurring, but the molecules remain closely packed so that the substance remains a solid. In most shape memory materials, a temperature change of only about 10C is necessary to initiate this phase change. The two phases, which occur in shape memory materials, are Martensite, and Austenite. The martensite phase is relatively soft while the austenite phase is rigid.
Fig 3-shape memory materials
When these shape memory materials are activated in garments, the air gaps between adjacent layers of clothing are increased, in order to give better insulation. The incorporation of shape memory materials into garments thus confers greater versatility in the protection the garment provides against extremes of heat or cold2.
Shape memory materials are already finding application in clothing. UKs defense clothing and textiles agency is designing garments with these materials to protect wearers against heat or cold. Cold protection in leisure wear is usually achieved by laminating a layer of insulation material. Variable insulation would have greater versatility and this could be achieved by using a composite film of shape memory polymers as inter liners. The use of shape memory alloys in multilayer fabric systems that change shape within a certain temperature range can be utilized to change the density between the individual layers. When temperature rises an additional layer of insulating air is formed to enhance protection against heat4.
Some of the main advantages of shape memory materials include:
v Diverse Fields of Application
v Good Mechanical Properties (strong, corrosion resistant)