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
Introduction:
Clothing is one of the three basic human needs. From primitive age, textile is used for clothing which was extended to household and domestic purposewith progressive civilization. Thousands of years ago textile is used indifferent forms such as sail cloth, tent, protective garments, ropes etc.,basically these were all technical textiles and were mainly used for theirtechnical performance.
A smart textile are materials and structures that sense andreact 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 afantasy filled horizon.
Textiles that can think for themselves! The idea itself isvery progressive and in reality such textiles are a fact technicallypossible today and commercially viable tomorrow. The technology of SMARTTEXTILES is an integration of almost all disciplines of applied sciences like:
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 manyother applications like automobiles, robotics, aircrafts, medicine and surgeryetc. 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 werealso invented to meet the demands of the military. For example, clothing thatcan change color to produce camouflage effects for protection was developed bythe US army in collaboration with various industrial firms to meet militaryrequirements.
Smart textiles find applications in a plethora of fields.Some of the principle ones are:
3.4 Military applications:
A) Fiber optics and sensors:
An optical fiber consists of a core (e.g. 1-10 micrometer indiameter for single mode silica glass fiber) surrounded by cladding (125micrometer in diameter) whose refractive index is slightly smaller than that ofthe core. The optical fiber is normally coated with a protective layer of anoutside diameter of approximately 250 micrometer. Inside the fiber core, lightrays incident on the core-cladding boundary at angles greater than the criticalangle undergo total internal reflection and are guided through the core withoutrefraction.
The sensors made from optical fibers are small and flexible;they will not affect the structural integrity of the composite materials; andcan be integrated with the reinforcing fabric to form the backbones instructures. They are based on a technology that enables devices to be developedfor sensing numerous physical stimuli of mechanical, acoustic, electric,magnetic and thermal natures. A number of sensors can be arranged along asingle optical fiber by using wavelength-, frequency-, and time- andpolarization- division techniques to form 1-, 2 or 3- dimensional distributedsensing systems.
B) Optical sensors in textiles:
Fiber optic sensors are ideal components to be embedded intextiles structural composites for monitoring the manufacturing processes and internal health conditions.
The intelligent textile sector represents the 21stcentury of fibers and fabrics and articles made from them. This segment ispoised to rejuvenate the world textile sector completely in the coming fewyears. All in all, this field promises to have a very bright future and it ishoped that the products of this industry will make inroads into the householdsvery soon.
6. References
1. Desai A.A., Manmade Textiles in India, 47(4), 144(2004).
2. www.iitd.ac.in
3. Jayaram R.V., Bombay Technologist,50,57,(2000-2001).
4. Singh M.K., Asian Textile Journal,13(5),33,(2004).
5. Zhang X.X., Tao X.M., Textile Asia,32(8),35,(2001).
7. Menezes E., Proceedings of National Textile Conferenceon Made in India: A Brand
8.. Buschmann H.J., Schollmeyer E., Cosmetics andToiletries,119(5),105,(2004).
9.. Anon.., International Dyer, (10),6,(2004).
10. Eckman A.L., AATCC Review,4 (4),11,(2004).
11. Tao X., Smart fibers, fabrics and clothing, CRCPress, Cambridge, 34, (2000).
12. Tao X.M., Journal of Textile Institute, 91 (1),448,(2000).
13. Sastry U.R.B., Technical Textiles International,(6),31,(2004).
14. http://www.peratech.co.uk/textech.htm
15. www.media.mit.edu/~rehmi
16. Zhang X.X., Tao X.M., Textile Asia,32(8),35,(2001).
17.http://techreports.larc.nasa.gov/ltrs/PDF/2002/cr/NASA-2002-cr211773.pdf
18. www.tx.ncsu.edu/jtatm/volume3issue4/vo3_issue4_abstracts.htm
19. Hoffmann I., Textile Asia, 35 (1),62(2004).
20. Kolkmann A., Gries Th., Asian Textile Journal, 12(11-12),101, (2003).
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There are still some difficulties with shape memorymaterials that must be overcome before they can live up to their fullpotential. They are still relatively expensive to manufacture and machine comparedto 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 SMMelement2.
3.3 Medical applications:
Textilesutures:
Some types of surgical sutures may also be regarded asintelligent fibers. A suture is a length of fiber used to tie blood vessels orto sew tissues together. Many types of sutures are described as absorbablematerials: these are intelligent materials in that they hold the edges of thewound together until the wound has healed sufficiently. Only then is the suturesignificantly absorbed into the bodys system. As the wound progressively heals, the tensile properties of the suture gradually diminish over a period ofweeks. However the mass of the suture remains invariant over this period.Afterwards extensive hydrolysis occurs, with subsequent absorption into thebodys system. The complete breakdown of the suture often occurs as long as 3-6months after it was originally applied. For this purpose, we would requirebiodegradable and biocompatible polymers exhibiting shape memory. A few typesof sutures are made from the collagen of sheep or cattle intestine and aregradually degraded by enzymes in the body. Many types of absorbable sutures,however, are made from synthetic polymers and are absorbed eventually into thebody through hydrolysis of ester bonds in the polymer chains. A variety ofpolymers and copolymers have been used. Examples are:
1.Polylactic acid
2.(-CO-CH2O-CO-CH2O-)nPolyglycolic acid
3.(-O-CH2-CH2-O-CH2-CO-)nTheir copolymers with polydiaxanone
4.(-O-(CH2)5-CO-)n polycapralactone
Datawear:
The Datawear incorporates sensors ateach of the body joints plotting their position on a graph, which can becalculated 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 determinetheir absolute position (i.e. of each of the limbs). The sensors can be placedto specifications for individual applications. The datawear body unit consistsof jackets, trousers and gloves that are circuited or wired electronically forinteraction with computer. The application of datawear is to track position oflimbs in computer data, medical imaging, measurement, ergonomics, biomechanics,robotics and animation. The whole body can be monitored by datawear, which hasa particular relevance in the field of sports injuries and biomechanics.
Sensors forrecording human physiological parameters:
This clothing, also called lifeshirts, was popularised by the American Sensatex company, and is used as anundershirt. Optical fibres are spirally plaited into its structure. The wholeundershirt has been made with a special weaving technique, in one piece,without any cuttings or seams. The main task of this intelligent shirt is tomonitor human physiological parameters such as temperature and heartbeat.
It can be used with differenttextile sensors, not only optical sensors. It is also possible to includesensors into the textile structure to measure the presence of poisonous gasesin the air. The sensors collect data into a central unit, and send it to theinformation centre. Data transmission is wireless.
When incorporated in textiles, such sensors can be used tosense various battlefield hazards like chemical, biological and other toxicsubstances warfare threats in real time. The polyurethane-diacetylene copolymercan be used as the photochemical polymer for chemical sensor application. The passivecladding of the optic fiber is replaced with these sensitive materials, and thesensory system is integrated into textile structures. The pH sensitive sensorsare developed and woven into the fabric of soldiers clothing12.
Smart shirt is anintelligent clothing (not restricted to military applications only) developedby a team at Georgia Tech. led by Prof. Sundaresan Jayaraman, and now sold bythe company Sensatex for detecting bullet wounds. It functions like a computer,with optical and conductive fibers integrated into the garment. Plastic opticalfibers woven in the seamless shirt are responsible for the detection of bulletwounds. These optical wires are connected to a photo diode at one end and alaser at the other. Pulses of light are detected constantly by the diode, withthe aid of other circuitry, any interruption of the light pulse to the diodehelps to indicate the exact location of the bullets entry. The shirt alsocarries sensors for measuring temperatures, heart beat and respiration functions,along with a microphone and a hazardous gas detector.
The shirt monitorsthe wearers heart rate, EKG, respiration, temperature, and a host of vitalfunctions, alerting the wearer or physician if there is a problem. The Smart Shirt also can be used to monitor the vital signs of law enforcementofficers, fire men, astronauts, military personnel, chronically ill patients,elderly persons living alone, athletes, infants (prevention of Sudden InfantDeath Syndrome) etc. This is the worlds first wearable motherboard (or anintelligent garment for the 21st century)4. In short, thenew paradigm spawned by the Wearable Motherboard provides an excitingopportunity that can not only lead to a rich body of new knowledge but in doingso, enhance the quality of human life. The potential impact of this research onmedicine was further reinforced in a Special Issue of LIFE Magazine "MedicalMiracles for the Next Millennium" in which the Smart Shirt or WearableMotherboard was featured as one of the "21 Breakthroughs that Could ChangeYour Life in the 21st Century"2.
Auxeticmaterials:
These materials have the unusual property of becoming widerwhen 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 couldbe on the markets.
Fig 7-smart military uniform.
3.5 Computing textiles:
The integration of functional electronics into textiles canbe realized in two extreme ways. One is to produce an apparel or technicaltextile and then integrate the electronic components. The other way is to produce conductive yarns (which are feasible I practice) when producing textiles and createtextile structures with electronic functions1. Either of the wayscould be used depending on application and end use, type of fabric, cost etc.
Conductive fibers/fabrics:
Fig 8 - Sensorised leotard andsensorised glove.
The chemical properties of conducting polymers make themvery useful for use in sensors. This utilizes the ability of such materials tochange their electrical properties during reaction with various redox agents orvia 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 steelwire-wrapped polymer filament, metal clad aramid fiber, conductive polymerfiber, conductive polymer coating and special carbon fiber/fabric, have beenapplied to the manufacture of fabric sensors.
E.R. Post and coworkers engineered a few fabric structuresthat can sense pressure. The row and column fabric keyboard is a fabric switchmatrix sewn from conducting and non conducting fabric. The keyboard essentiallyconsists of two layers of highly conductive metallic organza with a resistanceof about 10 W/m and non conductive row separated by an insulating layer ofnylon netting. When pressed at the right point, the two conducting layers makecontact through spaces in nylon netting, and current flows from a row electrodeto a column electrode. The keyboard can be repeatedly rolled up, crushed orwashed, 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 QuantumTunneling effect. The electronic devices can be easily integrated into thetextiles. The QTC textile solutions enable the fabrics to function aselectronic interfaces. The technology consists of sensors and switch arrayswhich are fully fabric based, washable and maintain the comfort and feel oftextiles. These are usually integrated with innovative textile systems forsignal transmission. User feedback is provided by the integration of LEDs orthe addition of tactile devices such as domes.
QTC textile technologies are simple to integrate, low cost,offer flexibility and high reliability, proportional control and interfacesdirectly 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 wouldallow 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 textileswitch and sensor technologies.
Wearable computing:
Electronic circuits built entirely out of textiles todistribute data and power have been devised by researchers at the MIT, USA. They can perform touch sensing, and use passive components sewn from conductive yarnsas well as conventional electronic components. This creates interactive electronicdevices such as musical keyboards and graphic input surfaces. One day entirecomputers may be made from textile articles that people prefer to wear. Andthese electronic circuits are a modest beginning in that direction. Thefirst conductive fabric tried was silk organza which contains two types offibers. On the warp is a plain silk thread while running in the other directionon 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. Thesilk fiber core has a high tensile strength and can withstand hightemperatures. This allows the yarn to be sewn or embroidered with industrialmachinery. The spacing between these fibers also permits them to be taken care ofindividually, so a strip of this fabric can function like a ribbon cable. Circuitsfabricated on organza only need to be protected from folding contact withthemselves, which can be accomplished by coating, supporting or backing thefabric with an insulating layer which can also be cloth. There are alsoconductive yarns manufactured specifically for producing filters for the processing of fine powders.
These yarns have conductive and cloth fibers interspersedthroughout. Varying the ratio of the two constituent fibers leads todifferences in resistivity. These fibers can be sewn to create conductivetraces and resistive elements. While some components such as resistors,capacitors, and coils can be sewn out of fabric, there is still a need toattach other components to the fabric. This can be done by soldering directlyonto the metallic yarn. Surface mount LEDs, crystals, piezo transducers, andother surface mount components with pads spaced more than 0.100 inch apart areeasy to solder into the fabric. Once components are attached, their connectionsto the metallic yarn may need to be mechanically strengthened. This can beachieved with an acrylic or other flexible coating. Components with ordinaryleads can be sewn directly into circuits on fabric, and specially shaped feetcould be developed to facilitate this process. Gripper snaps make excellentconnectors between the fabric and electronics. Since the snap pierces the yarnit creates a surprisingly robust electrical contact. It also provides a good surface to solder to. In this way subsystems can be easily snapped into clothingor removed for washing.
Fig 9 -wearableelectronic circuit.
Several circuitshave been built on and with fabric to date, including busses to connect variousdigital devices, microcontroller systems that sense proximity and touch, andall-fabric keyboards and touchpads. Building systems in this way is easybecause components can be soldered directly onto the conductive yarn. Theaddressability 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 bemade in a single layer of fabric using capacitive sensing [Baxter97],where an array of embroidered or silk-screened electrodes make up the points ofcontact. This is shown in the figure. A finger's contact with an electrode canbe sensed by measuring the increase in the electrode's total capacitance. It isworth noting that this can be done with a single bidirectional digital I/O pin perelectrode, and a leakage resistor sewn in highly resistive yarn. Capacitivesensing arrays can also be used to tell how well a piece of clothing fits thewearer, because the signal varies with pressure.
The keypad isflexible, durable, and responsive to touch. A printed circuit boardsupports the components necessary to do capacitive sensing and output key press events as a serial data stream. The circuit board makes contact with the electrodesat the circular pads only at the bottom of the electrode pattern. In atest application, 50 denim jackets were embroidered in this pattern. Some ofthese jackets are equipped with miniature MIDI synthesizers controlled by thekeypad. The responsiveness of the keyboard to touch and timing were foundby several users to be excellent. These researchers have tried to combineconventional sewing and electronics techniques with a novel class of materialsto create interactive digital devices. All of the input devices can be made byseamstresses or clothing factories, entirely from fabric. These textile-basedsensors, buttons, and switches are easy to scale in size. They also can conformto any desired shape, which is a great advantage over most existing, delicatetouch sensors that must remain flat to work at all. Subsystems can be connectedtogether using ordinary textile snaps and fasteners. Finally, they can bewashed by like regular clothes when subjected to dirt.
3.6 Fashion:
Chameleonic textiles:
Fig10-chameleonic textiles.
These are intelligent textiles which change color (becausethe dye applied on the surface change color) with change in temperature.Chromic materials are the general term referring to materials which radiate thecolour, erase the colour or just change it because of its induction caused bythe external stimuli, such as light, heat, electricity, solvent, pressure.
The color change is especially due to application of thermochromic dyes whose color changes at particular temperature. 2 types of thermochromic systems that have been successfully applied to textiles may berecognized, the liquid crystal type and the molecular rearrangement type. Inboth the cases, the dye is entrapped in microcapsules, applied to garmentfabric like a pigment in a resin binder. The most important types of liquidcrystals for the thermo chromic systems are the so called cholesteric types,where adjacent molecules are so arranged that they form helices. Themochromismresults from selective reflection of light by the liquid crystal. Thewavelength of the light reflected is governed by the refractive index of theliquid crystal and by the pitch of the helical arrangement of its molecules.Since the length of the pitch varies with temperature, the wavelength of thereflected light is also altered, and a color change results.
An alternative way of inducing thermo chromism is by meansof a rearrangement of the molecular structure of a dye as a result of a changein temperature. The most common types of dye which exhibit thermo chromismthrough molecular rearrangement are the Spiro lactones, although other typeshave also been identified. A colorless dye precursor is microencapsulated andis solid at lower temperatures. On heating, the system becomes colored or losescolor at the melting point of the mixture. The reverse change occurs at thistemperature if the mixture is then cooled. However, although thermo chromismand molecular rearrangement in dyes has aroused a degree of commercialinterest, the overall mechanism underlying the changes in color is far fromclear cut and is still very much open to speculation7.
A temperature sensitive fabric with trade name SWAY wasmanufactured by introducing microcapsules, diameter 3-4mm to enclose heatsensitive dyes, which are resin coated hom*ogeneous over fabric surface. The microcapsuleswere made of glass and contained the dyestuff, the chromophore agent (electronacceptor) and color neutralizers (alcohol etc.) which reacted and exhibitedcolor/no color according to environmental temperature. SWAY had 4 basic colorsand 64 combined colors. It could reversibly change color at temperature greaterthan 5◦C and could be operated from -40◦C to80◦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 withnitrogen oxide, sulfur dioxide and ozone monitors. When there is pollution, thefabric changes its color from blue to orange16.
Musicaljackets4:
Fig 11 -smart mp3player.
Musical jacket turns an ordinary jacket into a wearablemusical instrument. Musical jacket allows the wearer to play notes, chords,rhythms, and accompaniment using any instrument available in the general musicscheme. It integrates fabric keypad, a sequencer, synthesizer, amplifyingspeakers, conductive organza, and batteries to power these subsystems. Thesmart suit consists of global mobile system for communication, functionalarchitecture for navigation, and electrically heated fabric panels for heating.The sensor system consists of a heart rate sensor, three position and movementsensors, ten temperature sensors, an electrical conductivity sensor and twoimpair detecting sensors. The implementations and synchronization requires auser interface (UI), a central processing unit (CPU) and a power source. Eachmain module, excluding the sensors and the user interface is set into thesupporting vests. This smart suit allows easy, fast, and cost efficient groupcommunication. A cellular telephone, loudspeaker and microphone areincorporated in the belt. By pulling a tag on this belt, communication can beachieved by groups of people.
3.7 Aviation:
Aircraft maneuverability depends heavily on the movement offlaps found at the rear or trailing edge of the wings. The efficiency andreliability of operating these flaps is of critical importance. Most aircraftin the air today operate these flaps using extensive hydraulic systems. Thesehydraulic systems utilize large centralized pumps to maintain pressure, and hydraulic lines to distribute the pressure to the flap actuators. In order tomaintain reliability of operation, multiple hydraulic lines must be run to eachset of flaps. This complex system of pumps and lines is often relativelydifficult and costly to maintain. Many alternatives to the hydraulic systemsare being explored by the aerospace industry. Among the most promising alternatives are piezoelectric fibers, electrostrictive ceramics, and shape memoryalloys.
The flaps on a wing generally have the same layout shown onthe left, with a large hydraulic system attached to it at the point of theactuator connection. "Smart" wings system is much more compact andefficient, in that the shape memory wires only require an electric current formovement. 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 memoryeffect, while the top wire is stretched bending the edge downwards, theopposite occurs when the wing must be bent upwards. The shape memory effect isinduced in the wires simply by heating them with an electric current, which iseasily supplied through electrical wiring, eliminating the need for largehydraulic lines. By removing the hydraulic system, aircraft weight, maintenancecosts, and repair time are all reduced. The smart wing system is currentlybeing developed cooperatively through the Defense Advanced Researched ProjectAgency (DARPA, a branch of the United States Department of Defense), andBoeing.
Figure 12- smart jet.
3.8 Space research:
Spacesuits:
The earliest developed Apollo spacesuits contained an innerlayer of nylon fabric with network of thin walled plastic tubing whichcirculated cooling water around the astronaut to prevent overheating. Thisinner layer was comfort layer of lightweight nylon with fabric ventilationducts, and then a three layer system formed the pressure garment. Thenaluminized Mylar was used for heat protection, mixed with four spacing layersof 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 andradio communications.
Thus we have considered the major interesting applicationsof smart textiles in various sectors. We have also considered the mechanism bywhich these smart systems operate and also reviewed the process ofmanufacturing.
Fig 13-space suite
1.1Market overview
Smart or Interactive Textiles is a new market segmentresulting from the miniaturisation of electronics and the fall in price of components and manufacturing costs for both electronics and textiles. A simultaneoustrend in the clothing industry toward manufacture of specific products for dedicated uses i.e. for running, skiing, golf and extreme sports has created aniche where smart and interactive textiles enable new functions and featuresthat can enhance a garments performance and its wearers experience.
1.2Market 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 designphase of a production. Such new technologies are immature and often promoted by start-up companies that are spin-offs from professional research. With limitedfunding to commercialise their products, the result is that some of the mostexciting technologies have not yet been exploited to the full.
1.3Market Structure
Fig-14
1.1Market Structure and stakeholders
While smart textile applications have made a limitedcommercial impact so far, with relatively small volumes of commercial products launched primarily in the high performance apparel sector predictions for growth of thesmart textile market as a whole are huge. According to the Venture DevelopmentCorporation the market for electrically enabled smart fabrics and interactivetextile technologies was worth US$340.0 million in 2005. By 2008 it is expectedto be worth US$642.1 million, representing a compound annual growth rate of28.3%. 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 mostdynamic and fast growing sectors and offers huge potential for companieswilling to take the plunge. Not surprisingly, most of the smart textileconsumer products launched so far have been introduced onto the luxury end ofthe performance clothing market where development costs can be more readilyabsorbed by higher prices.
Companies dominating this segment are those who already havea significant market share such as Nike, Adidas and ONeill. Products launchedin this sector show a clear trend toward strong design features coupled withsimple to operate functions that are highly relevant to the garments wearer inthe particular use situation. A good example of this is the Nike plus runningshoe. Cooperation with IT giant Apple has resulted in a simple user friendlyweb interface that enables runners to motivate themselves and each other byuploading data recorded by the sensor in the shoe and transferring it to astandard iPod nano. The system is stylish, simple to operate and enablesrunners to track their performance and set new targets to be reached.
Major actors in theperformance clothing segment
Adidas, Nike
ONeill, Burton, North Face,Rosner
Monitoring health andvital signs, commercial products in 2007
VivoMetrics (Lifeshirt)
Adidas, Numetrex
TextileComponents
Eleksen, Peratech Ltd,
Fibretronic
Textronics
Electronics ComponentsManufacturers
Philips
Infineon
Motorola
CSR
Electronics OEMs
Philips
Nokia
Motorola
System Integrators
Interactive Wear, Ohmatex,Fibretronix
Clothing
Polar
vMilitary (e.g.uniforms which can detect chemical threats in a battlefield)
vAirplanes (e.g.in manufacture of flaps found in aircraft wings)
vBiomedical field(e.g. manufacture of smart sutures, tissues)
vSpace research(e.g. special spacesuits designed for astronauts)
vComfort wears(e.g. fabrics which can maintain body temperature)
vSports (e.g.fabrics which can make athletes feel comfortable even in stretched bodyconditions)
vFashion clothing(e.g. fabrics which can change color according to ambient temperatures)
Smart textiles have a lot many applications besides theabovementioned ones, but before we discuss them let us concentrate on thefundamental mechanisms that make a fabric smart. In this new era the smarttextiles are considered also as textronics.
The term textronics refers to interdisciplinary approaches in the processes of producing and designing textile materials, which began about theyear 2000. It is a synergic connection (Figure 1) of textile industry,electronics and computer science with elements of automatics and metrologyknowledge.
A new quality is achieved as result of using componentelements, which thanks to mutual feedback increase their affect. This can beobtained by the physical integration of microelectronics with textile andclothing constructions. The main task of textronics is to produce multifunctional, intelligent products with complex inner structures, but which haveuniform functional proprieties. Textronic products are characterised by thefollowing features:
v Flexibility meaning facility inmodifying 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 byexternal factors (parameters) and even taking decisions, which means learningor communication with the environment.
v Multifunctionality, or the easeof realising different functions by one product.
It can bestated that textronics means the design and production of intelligent andinteractive textile materials which are characterised by variable structures orelectrical resistance, which include microchip elements and is characterisedby self-adaptive features.
Fig1-textronic
New markets for textiles
Chemical engineering developments in recent years have ledto development of textile fibres with properties such as extreme strength,lightness in weight and where fibres can change their shape dependant upontemperature or other external stimuli. These features are just beginning to beexploited in entirely new sectors, where textiles have not traditionally beenstandard materials. Applications are widely predicted to be highly diverse,covering segments from EMI shielding in automotive, planes and the like to useas moulding forms for architectural components and to reinforce and strengthenconcrete building elements.
5. Conclusion:
The smart textile industry is still at a nascent stage ofdevelopment with many new innovations in the pipeline. But it is bound tochange the way we look at textiles. These 21st century textiles willsignify the true merger of textile and information industries.
Smart textiles are a field which seems to be intellectuallyrewarding to a keen researcher. It is a challenge of sorts since we are notonly talking about smart materials but also about the use of such materials astextiles. Thus smart materials have to be intelligently engineered to be usedas textiles. Particularly if these materials are to be used as apparels, then alot of factors like feel, density, aesthetic value, processing (duringmanufacturing and after use) need to be considered. We are not just interestedin making fancy electronic components, but in making textiles which can be usedlike ordinary apparels though having the characteristics of electronic systems.Present research in smart textiles all over the world focuses on the followingbroad areas18:
1. for sensors/ actuators-
vPhoto sensitivematerials
vFiber optics
vConductivepolymers
vThermallysensitive materials
vShape memorymaterials
vIntelligentcoating/ membrane
vChemicalresponsive polymers
vMechanicalresponse materials
vMicro capsules
vMicro andnanomaterials
2. for signal transmission, processing and controls-
vNeural networkand control systems
vCognition theoryand systems
v for integrated processes and products-
vAdaptive andresponsive structures
vWearablecomputing
vBioprocessing
vTissueengineering
vChemical/ drugrelease
A particularlyinteresting objective is clothing which represents the ideal interface mediumbetween humans and their environment. Everyone wears clothes in several layersone above the other in all day-to-day situations, which means that it ispossible to accommodate micro system components comparatively simply andcomfortably. The objective should now be to focus on integrating microchip andcomputer systems as invisibly as possible into clothing, thus connecting man asunobtrusively as possible with his environment and equipping him as acommunication medium. This is a field of innovation and a future potential offascinating proportions which also opens up interesting possibilities incommercial terms. Clothing as a carrier medium is thus developing into ahigh-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 thatwill change its characteristics according to outside conditions or stimuli. Thefollowing table shows the fundamental characteristics of and difference intraditional, high performance and smart materials.
| Category | 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 electricfield. The output can be change in length, viscosity, color or conductivity.
Input(stimulus) Active materialOutput (response)
2.2. Definition:
SMART TEXTILES are defined as textiles that can sense andreact to environmental conditions or stimuli, from mechanical, thermal,magnetic, chemical, electrical, or other sources. They are able to sense andrespond 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 toperform a special function certainly count as smart textiles.
2.3. Components in smart textiles:
Three components may be present in smart textiles(materials)
vSensors
vActuators
vControlling units
The sensors provide a nerve system to detect signals. Someof the materials act only as sensors and some as both sensors and actuators.Actuators act upon the signals and work in coordination with the controllingunit to produce an appropriate output.
2.4. Classification of smart textiles:
Smart textiles are classified into three categoriesdepending on functional activity, as follows:
vPassive smarttextiles
vActive smarttextiles
vVery or ultrasmart textiles
Passive smart textiles:- The first generation of smart textiles, which can provide additional features in passive mode that is not concerning with alteration inenvironment are called passive smart textiles. Optical fiber embedded fabricsand conductive fabrics are good examples of passive smart textiles.
UV protective clothing, multilayer composite yarn andtextiles, 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 bothactuators and sensors and tune functionality to specific agents orenvironments, are called active smart textiles. These are shape memory,chameleonic, water resistant and vapor permeable (hydrophilic/ non porous), heatstorage, thermo regulated, vapor absorbing, heat evolving fabric andelectrically heated suits.
Phase change materials and shape memory materials, heatsensitive dyes etc. in textiles form active smart textiles.
Ultra smart textiles:- Very smart textiles are the third generation of smarttextiles, which can sense, react, and adapt themselves to environmentalconditions or stimuli. They are the highest levels of smart textiles. These maydeal actively with life threatening situations (battlefield or duringaccidents) or to keep high levels of comfort even during extreme environmentalchanges. These very smart textiles essentially comprise of a unit, which workslike the brain; with cognition, reasoning and activating capacities.Ultra smarttextiles are an attempt to make electronic devices a genuine part of our dailylife by embedding entire systems into clothing and accessories. Though theentire potential has not been completely realized, the developments so far canbe 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 notthink for themselves. Nevertheless they perform special functions in thepassive mode and hence the term passive smart textiles.
2.5. General methods of incorporating smartnessinto 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 forman integrated part of the textile structure and can be incorporated into thesubstrate at any of the following levels4:
vFiber spinninglevel
vYarn/fabricformation level
vFinishing level
The active (smart) material can be incorporated into thespinning dope or polymer chips prior to spinning e.g. lyocell fiber can bemodified by admixtures of electrically conductive components during production to make an electrically conductive cellulosic fiber. Sensors and activators can alsobe embedded into the textile structure during fabric formation e.g. duringweaving. Many active finishes have been developed which are imparted to thefabric during finishing. The electronic control units can be synchronized witheach other during finishing. Techniques such as microencapsulation aregenerally preferred for incorporation of smartness imparting material in thetextile substrate. However the correct material and the correct method must beselected; based on a variety of considerations.
A challenge that lies ahead is the manufacture of inherentlysmart fibers which do not need any further incorporation of smartness intothem; and which can directly woven into textiles.
3. Applications of smart textiles:
Smart textiles find a wide spectrum of applications rangingfrom daily usage to high-tech usage. Now we can review various importantapplications of such textiles. We would consider textiles used for thefollowing broad categories:
vComfort wear
vHeat protection
vMedicalapplications
vMilitaryapplications
vComputingtextiles
vFashion
vAviation
vSpace research
It should be noted that a textile mentioned in one categorycan 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 camouflagingto protect the soldier.
3.1 Comfort wear:
Multilayercomposite yarns and textiles:
Multilayer composite yarns and textiles demonstrate apossibility for achieving wear comfort in terms of absorbing sweat release fromthe human skin surface by an internal sweat absorbent layer. A cool and drythree layer composite yarn, which consists of a polyester filament yarn on thesurface, a staple polyester yarn in the middle and a polyester filament yarn inthe core, has been developed by Toyobo Co., Japan. The presence of fine fiberslying 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 toincrease moisture absorption capacity. Thus moisture gets efficientlytransferred from the surface of the fabric in contact with the skin to theouter surface of the fabric exposed to the atmosphere. The sweat thusaccumulated in the outer layer gets carried of by atmospheric air currents46.
Another way of achieving body comfort against sweat releaseis application of functional finishes to the fabric. The sweat released by thehuman body in ordinary course is evaporated by absorbing heat from the body.This maintains the body temperature constant. Fabrics treated with Snocool (coolfinish) can enhance the natural phenomenon of sweat evaporation. The finish*tself absorbs and dissipates sweat evenly throughout thus giving a coolfeeling to the wearer. The finish can also reflect light and transfer themoisture 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 tocuring at 180◦ C, for 30-45 seconds.
Cosmetictextiles:
These kinds of textiles have chemicals like cyclodextrinencapsulated into them, which leads to an inbuilt fragrance plus othermassaging and relieving effects.
Cyclodextrins are formed during the enzymatic degradation ofstarch. They are macro cyclic polysaccharides built from glucose unitscovalently 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 aretorus shaped. These molecules have been primarily used in pharmaceutics,cosmetics, and food. But now the permanent fixation of these molecules ontextiles have been studied and made possible (A cyclodextrin derivativesuitable for fixation on cotton fibers is already available commercially). Evenafter fixation the cyclodextrin molecules are able to form inclusion complexeswith organic molecules. For the use in textile finishing, β- cyclodextrinmodified with a reactive group (monochlorotriazinyl group) is used. This anchorgroup reacts with the hydroxyl groups of cellulose or with the amino groups ofwool and silk.
The organic components of sweat are complexed by thecyclodextrins in the case of textiles in contact with skin. Due to thisreaction the microbiological degradation of these substances is prevented or slowed down. Thus the formation of body odor is prevented or reduced. Thesetextiles are able to help people who are not able to use any deodorant becauseof a very sensitive skin.
However other people also can take advantages of these kindsof textiles. The complexed sweat components can be decomplexed during a normalwashing process. The complexation of sweat components by the fixedcyclodextrins can easily be shown after the extraction of these textiles withorganic solvents and an analysis of the resulting solutions using gaschromatography.
During usage these textiles release perfumes. On thecommercial side, such products are already on offer in the German market andmany more new markets are being explored8.
Another related innovation is aromatherapy7. Thisis the practice of applying and inhaling essential oils from plants as aphysical and emotional boost to the body. People inhale more deeply due to somefragrances and take extra oxygen into the body, making them healthier. Selectedfragrances have been found to specifically alter the bodys physiology,including respiration, heart rate, blood pressure, and brain activity.
Micro capsules containing specific aroma therapeuticessential oils have been impregnated on to sweaters, ties, T-shirts, and on anumber of other products. The microcapsules produced are very small, with adiameter of 5 to 10 micrometer, and a pair of stockings would contain approximately 200 million fragrant capsules. Normal physical forces during wear of the materialsrupture the microcapsule wall, releasing the desired aroma. The fragrancewithin the microcapsules, which are tightly lodged in the tiny cavities of aporous acrylic material on the textile, persists even after hard washing of thetextiles up to ten minutes.
Microencapsulated formulations of various fragrances likemusk, pineapple, rose, lavender, jasmine, lemon, peppermint etc. have beensuccessfully applied to fabrics with the help of binders. The recipe is asfollows:
vFragma1.0-5.0gpl
vPad, dry, cureat 170 ◦C-180 ◦C for 30-45 seconds.
vDeodorizing fragrances are used to prevent the build up ofmalodor during wear or use of the fabric and also when they are not in use.They operate via a number of mechanisms:
vInhibiting the enzymes responsible for producing malodor
vLowering the vapor pressure of the malodor
vReducing the perception of malodor
Intelligentbra:
A smart bra that can change its properties in response tobreast movement is being developed at University of Wollon, Australia. This bra will provide better support to active women when they will be in action. Smartbra can tighten and loosen its straps, or stiffen and relax its cups torestrict breast motion, preventing breast pain and sag. The conductive polymercoated fabrics is used in the manufacture of smart bra. The strain acting onthe fabric can be sensed by the conductive polymer that is coated on the mainfabric. The fabrics can alter their elasticity in response to information abouthow much strain they are under. The smart bra is capable of instantlytightening and loosening its straps or stiffens cups when it detects excessmovements.
Protectionagainst bacteria
AgION all natural antimicrobial technology derived from asilver based compound was used for clothing, towels etc. for NASA crew memberson an undersea mission. This provided protection against the growth ofdestructive and odor causing bacteria. Ag is one of the oldest knownantimicrobial agent and has proven effective against more than 650 strains ofdestructive and odor causing bacteria, yeast, fungi and mould. AgIONantimicrobial can be applied during the fiber extrusion process, or to fabricby a finishing process- it is a compound of Ag ions. The active ingredientbonded to ceramic material in this is completely inert. The ambient moisture inair causes low level release that maintains the antimicrobial surface. More Agis released when more humidity is encountered (which could be a cause for morebacterial growth). Thus protection against bacteria and mildew is provided.
3.2 Heat protection:
Ultraviolet protective clothing7:
Ultraviolet light is usually defined as electromagneticradiation of wavelength between 4 and 400 nm. A fraction of UV radiations fromthe sun manages to reach the Earths surface and are dangerous. There existsmart clothings which have the ability to absorb or reflect the harmful UV raysin terms of passive heat retention. This is due to the numerous pores intextile product which are by means of bulked and micro fiber constructions. Theheat retention is also possible by use of UV absorbing chemicals. A specialtyfinish can be applied to the fabric, which is composed of UV absorbers. This isapplied 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 aspadding method.
Ceramiccoated textiles:
NASA (National Aeronautics and Space Administration) hasreported the use of high performance coating system to protect material fromhigh level of solar radiations and extreme cold conditions. The fluid ceramiccan be applied as ceramic coating for thermo ceramic construction and heat protection simultaneously. The base for fluid ceramics is formed by dispersion of a specialacrylic resin in the tile form vacuumised ceramic silicon micro bodies (ceramicbubbles) of which energy is significantly throttled. The material compositionof the dispersion coating (formulation of adhesives filling agents, pigmentsand the exclusive ceramic bubble state) can be tuned to each other inconjunction with bubble partial vacuum in such a way that new and moreadvantages, characteristics and features are produced. The resulting textilesystem would demonstrate excellent sunlight reflection and thus help in heatregulation.
Thermo regulatedtextiles:
Fig 2 - Fabric with embeddedcopper wires as temperature sensors
The main objective of heat storage or thermally regulatedtextiles is to maintain the wearer in a state of thermo physiological comfortunder the widest possible range of workloads and ambient conditions. Heatstorage 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 PhaseChange Materials (PCMs) into their structures. Phase change materials aredefined as materials that can absorb, store and release large amount of energyin the form of latent heat over a narrowly defined temperature range (phasechange range) as the material changes phase or state. These are basicallylatent heat storage materials. Ice is a common example of phase changematerial. Phase change materials undergo reversible solid-liquid phase changesunder a certain set of temperature conditions10.
Phase change materials thus can act as heat buffers whenincorporated into textiles. They keep the body temperature constant byabsorbing or releasing heat in the latent form. Since the ideal body temperatureis 33.4◦C, the phase change material should be such that itundergoes phase transition at or reasonably near this temperature. The PCMsused for textile purpose are hydrated inorganic salts, polyhydric alcohol-watersolution, PEG, polytetramethylene glycol, aliphatic polyester, linear chainhydrocarbons, hydrocarbon alcohol, and hydrocarbon acid10.
The PCM can either be coated on the fabric or can beintegrated into the fiber in a microcapsule form. In a typical production process, the Phase Change Material (PCM) is introduced into the textile fiber matrixin a microencapsulate form (Micro encapsulation is a process by which very tinydroplets or particles of liquid or solid material are surrounded or coated witha continuous film of a polymeric material21). The microcapsules havewalls less than 1 micrometer thick and are typically 20-40 micrometer indiameter, 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 PCMreacts to an external temperature change is very rapid11.
NASA put the Phase Change Materials into gloves to keep thepilots hands warm. It developed textiles that aimed to improve the protection of instruments and astronauts against extreme fluctuations in temperaturein space on the basis of heat absorbing and temperature regulating technology.Vigo et al finished a polyester/cotton fabric with polyethylene glycol (PEG) asPhase Change Material and dimethylodihydroxyethyleneurea (DMDHEU) to produce a thermally active fabric having 30-50% add-on.
The main challenge in developing textile -PCM structures isthe method of their application. Encapsulation of PCMs in a polymeric shell isan obvious choice but it adds dead weight to the active material. Efficientencapsulation, core-to-wall ratio, yield of encapsulation, stability during useand integration of capsules onto fabric structure are some of the parametersthat need to be considered here2.
Shape memorymaterials:
Shape memorymaterials (SMMs) are materials that are stable at two or more temperaturestates. SMMs are able to memorize a second, permanent shape besides theiractual, temporary shape. After application of an external stimulus, e.g. anincrease in temperature, such a material can be transferred into its memorized,permanent shape. Shape memory effect is based on martensitic phasetransformation (solid-solid phase transformation). Shape memory polymers arematerials that have hard segments and soft segments e.g. polyurethane,polyester ether, styrene-butadiene copolymer etc. This is because the shapememory materials exhibit some novel performances such as sensitivity,actuation, damping and adaptive responses to external stimuli such astemperature, lighting, stress and field, which can be utilized in various waysin smart systems. A shape memory material possesses different properties below and above the temperature at which it is activated. Below this temperature, thematerial is easily deformed. At the activation temperature, the material exertsa 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 madepossible through a solid state phase change, that is a molecular rearrangement,which occurs in the shape memory material. A solid state phase change issimilar in that a molecular rearrangement is occurring, but the moleculesremain closely packed so that the substance remains a solid. In most shapememory materials, a temperature change of only about 10C is necessary toinitiate this phase change. The two phases, which occur in shape memorymaterials, are Martensite, and Austenite. The martensitephase is relatively soft while the austenite phase is rigid.
Fig 3-shape memorymaterials
When these shapememory materials are activated in garments, the air gaps between adjacentlayers of clothing are increased, in order to give better insulation. Theincorporation of shape memory materials into garments thus confers greaterversatility in the protection the garment provides against extremes of heat orcold2.
Shape memorymaterials 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 bylaminating a layer of insulation material. Variable insulation would havegreater versatility and this could be achieved by using a composite film ofshape memory polymers as inter liners. The use of shape memory alloys inmultilayer fabric systems that change shape within a certain temperature rangecan be utilized to change the density between the individual layers. Whentemperature rises an additional layer of insulating air is formed to enhance protection against heat4.
Some of the main advantages of shape memory materialsinclude:
v Bio-compatibility
v Diverse Fields of Application
v Good Mechanical Properties (strong,corrosion resistant)
