THE TEXTILES OF FUTURE
1.0 Introduction
Intelligent textiles
represent the next generation of fibres, fabrics and articles produced to
respond in time. It can be described as textile materials that think and act
for themselves. This means, it has keep us warm in cold environments or cool in
hot environments or provide us with considerable convenience in our normal
day-to-day affair. Intelligent textiles are not confined to the clothing sector
alone. It is used in protection, safety, added fashion and convenience. The
most important intelligent materials at present in are classified as 1) Phase change materials, 2) Shape memory materials, 3)
Chromic materials 4)Conductive materials and 5)Electronics incorporated
textiles.
2.0 Phase Change Materials
(PCM)
Every material absorbs heat
during heating process and its temperature will rise constantly. The heat
stored in the material is released into the environment through a reverse
cooling process and the material temperature decreases continuously. A normal
textile material absorbs about one kilo joule per kilogram of heat while its
temperature rises by one degree Celsius. Phase Change Material (PCM) will
absorb higher amount of heat when it melts. This thermo regulating effect of
textiles can be obtained with the application of PCM.
Fig1: PCM Incorporated
Clothing
Figure 1.describes the PCM
incorporated clothing action A paraffin-PCM, absorbs approximately 200
kilojoules per kilogram of heat if it undergoes a melting process. During the
complete melting process, the temperature of the PCM and its surrounding area remains
constant. The paraffin's are either in solid or liquid state. In order to
prevent the paraffin's dissolution in the liquid state, it is enclosed into
small plastic spheres with diameters of only a few micrometers. These
microscopic spheres containing PCM are called PCM-microcapsules. The
microencapsulated paraffin is either permanently locked in acrylic fibres and
in polyurethane foams or coated onto the surface of a textile structure.
Normal garments do not
balance the heat generated and released in to the environment from the body.
PCM incorporated textiles provide good thermal balance due to its thermo
regulating effect. PCM controls the heat flux through the garment layers and
adjusts the heat flux to the thermal circumstances, for example, if the heat
generation of the body exceeds the possible heat release through the garment
layers into the environment, the PCM will absorb and store this excess heat. On
the other hand, if the heat release through the garment layers exceeds the
body's heat generation during lighter activities, the heat flux through the
garment layers is reduced by the heat emission of the PCM. The figure2 shows
the thermoregulation effect of PCM incorporated clothing over the conventional
clothing.
ntensity and duration of the
PCM's active thermal insulation effect depend mainly on the heat storage
capacity of the PCM-microcapsules and the applied quantity. Thin high-density
materials support for cooling process. Thick and less dense textile structure
leads to more efficient heat release. To ensure a suitable and durable active
thermal insulation effect in an active-wear garment, it is necessary to apply
the correct PCM in the appropriate quantity. The selected PCM is normally
microencapsulated and incorporated in a textile substrate. Requirements of the
textile substrate in a garment application include sufficient breath ability,
high flexibility and mechanical stability. The substrate incorporated with
PCM-microcapsules needs to be integrated into a suitable location of the
garment design and certain design principles need to be taken into account.
3.0 Shape Memory
Polymers(SMP)
These types of materials can
revert from the current shape to a previously held shape, usually due to the
action of heat. This technology has been extensively pioneered by the UK
Defense Clothing and Textiles Agency. 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 against extremes of heat or cold.
Shape memory alloys, such as
nickel-titanium, used to provide increased protection against sources of heat,
even extreme heat. A shape memory alloy possesses different properties below
and above the temperature at which it is activated. Below this temperature, the
alloy is easily deformed. At the activation temperature, the alloy exerts a
force to return to a previously adopted shape and becomes much stiffer. The
temperature of activation can be chosen by altering the ratio of nickel to
titanium in the alloy.
Cuprous-zinc alloys are
capable of a two-way activation and therefore can produce the reversible
variation needed for protection from changeable weather conditions. They will
also react to temperature changes brought about by variations in physical
activity levels.
A shape memory alloy is
usually in the shape of a spring. The spring is Fig3: A Shape memory polymer in
action
flat below the activation
temperature but becomes extended above it, which is shown in the figure 3. By
incorporating these alloys between the layers of a garment, the gap between the
layers can be substantially increased above the activation temperature. In
consequence, considerably improved protection against external heat is
provided.
For clothing applications,
the desirable temperatures for the shape memory effect to be triggered will be
near body temperature. Polyurethane films, which can be incorporated between
adjacent layers of clothing. With temperature of the outer layer of clothing
has fallen sufficiently, then polyurethane film responds so that the air gap
between the layers of clothing becomes broader. Bi-Material Film laminates rely
on differing coefficients of thermal expansion to produce a reversible bending
effect. Encapsulated Bi-Gels absorb liquid at differing rates according to
temperature, which causes them to bend used to actuate variable insulation
system. Other uses of SMPs in domestic purpose are in shower mixer valves,
coffee makers, rice cookers, safety shut off valves for fuel lines in the event
of fire and in air conditioning systems.
4.0 Chromic Materials
Chromic materials are the
general term referring to materials which radiate the color, erase the color or
just change it because its induction caused by the external stimuli, as
"chromic" is a suffix that means color. It can be classified depend
on the Stimuli. Out of this the first four chromic materials are important and
has potential to cater the market
. Photochromic: external
stimuli energy is light.
. Thermochromic: external
stimuli energy is heat.
. Ionochromic: external
stimuli energy is pH value
. Electrochromic: external
stimuli energy is electricity.
. Piezorochromic: external
stimuli energy is pressure
. Solvatechromic: external
stimuli energy is liquid.
. Carsolchromic: external
stimuli energy is electron beam.
4.1 Photochromic
:
In this kind of chromism the
color change is due to the intensity of the light(UV radiation also). The
photochromic dyes interact with the electromagnetic radiation in the near UV
(300-400nm),Visible(400-700nm) and near IR(700-1500nm) to produce verity of effects,
which is reversible when the radiation is withdrawn. Photochromism is of Two
types. Positive and Negative. In Positive Photochromism the colorless substance
converted in to colored object when exposed in to the light due to
Uni-molecular reaction system. Bi molecular reaction system is called Negative
Photochromism i.e. from colored to colorless. the transformation is between two
states that have different absorption spectra. It may be induced in one or both
the direction by electromagnetic radiation. This process is a non destructive
process., but side reactions may occur. Oxidation is
the major cause for the degradation of the Photochromism. Main class of
Photochromism is Spiropyrans. It is used in Optical switching data and Imaging system rather then the textile
applications.
4.2 Thermochromic:
Thermally induced reversible
color change occur in the thermochromism. A large variety of substrates such as
Organic ,Inorganic Orgonomatallic and Macro molecular
systems exhibit this phenomena. Mercury Iodide salts like Ag2 HgI4 shows color
change from yellow to orange at
4.3 Ionochromic dye:
These chromic materials are
sensitive to pH. Widely used these classes dyes are Phthalides, Triarylmethans
and Fluorans. In analytical chemistry these dyes are used extensively. There
are no commercial application of these dyes in textiles but direct thermal
printing can be used. In this process substrate contain both the color former
and acid co reactant in a single layer. simply by heating the surface of the
paper with a thermal head causes the components to react and to produce color.
4.4 Electochromic dye:
The material that change
color upon the application of Voltage are called electrochromes. This is due to
oxidation and reduction process with in the electochromic material. This are of
three types. First type, the coloring species remain in the solution. In the
second type the reactants are in solution but the colored product is of solid.
In the third type is both reactant and the color is in form of solid e.g.
composite Film. Most available electochromic dyes are of inorganic oxides such
as cobalt oxide, nickel oxide, molybdenum trioxide. A research is going on in MIT,USA to use thin film composite electrode material with
layer by layer assembly technique, to identify whether electrochemical cell is
fully charged or discharged by using color change. The most important
commercial application of the electrochemic dye in the textile is of
US-Military IR camouflage material (Dynam IR®) .
4.5 Solvantochromic dye:
The Solvantochromism is a
reversible variation of the electronic spectroscopic properties (absorption and
emission)of a chemical species, induced by the solvents. It is one of the
oldest chromism have been described as long as ago 1878.This is used as probes
for application in polymer characterization. Where they can be used to look for
localized polar features at the molecular level.
Chromic dyes contain highly
specialized components that require extraordinary careful manufacturing
technique and has great potential for both fashion and higher end market.
5.0 Conductive materials
Exploration of human/machine
interaction and wholly new types of interface sensor
technology has resulted in the development of sensory fabric. These materials
also afford designers new opportunities in developing for product markets. The
ability to dispense with fixed casings, rigid mountings and inflexible
substrates facilitates new radical possibilities in flexible, user-friendly
interfacing textiles. By using conductive plastics, pressure sensitive inks and
piezo films the above application succeeded in textiles. The main emphasis is
currently on X-Y position sensing and pressure sensors.
5.1 X-Y position sensing
The structures of these
materials offer the capability of reading the location, within a fabric sheet
(Pad), of a point of pressure (such as a finger press). It is possible to
incorporate this function into an elastic sheet structure, allowing the sheet to
conform to many 3-D shapes, including compound curves, while still accurately
measuring an X-Y position. The Fabric structures that provides an X-Y position
function can also be used to provide accurate 'switch matrix' functionality.
Interpreting electronics are used to identify the location of switch areas in
any configuration to suit product requirements. Since this is done in software, an endless array of configurations can be
addressed at the touch of a piece of fabric.
5.2 Pressure sensors
Readings can be obtained from
smart fabrics according to force and area. This allows the user to
differentiate between separately identified inputs ranging from high-speed
impact to gentle stroking. The force/area reading is versatile, as fabrics can
be constructed to be more sensitive to either force or area.
There are other applications
for conductive materials such as heated clothes for extreme winter conditions
or heated diving suits to resist very cold water. In these cases a heat or
energy source is needed as the conductive material is not able to generate
energy, it is only capable of conduction, to distribute the heat throughout the
entire garment or suit.
The advantages and benefits
that conductive materials over the existing wire system are uniform temperature
distribution, pliability, strength (resistance to flex and stress),
non-corrosive nature, and cost effectiveness.
6.0 Other Intelligent
textiles
6.1 Stomatex®
Patterned new cold protection
apparel. Cell foam materials such as neoprene and polyethylene can be used in
the construction of garments. Stomatex® NE is ideal for close contour fitting
apparel for unhindered body movement. Stomatex® PE is a lightweight apparel and
has a significant cost advantage over neoprene. Stomatex® PE is suitable for use
in multi-layered clothing systems and footwear where weight may be an important
factor.
6.2 Hydroweave®:
Patterned product is meant
for comfortably in extreme cold and wet condition. Super water-absorbing
polymer fibre blended into fibrous matting, this matting is positioned between
a breathable exterior shell and a conductive, waterproof inner lining. The breathable
outer shell can be made from a variety of woven or knitted fabrics to deliver
the performance needed for a wide range of applications. The inner lining is a
thermally conductive micro-porous membrane. This special material allows
perspiration to escape, and keeping the wearer cool and dry. The advantages are
. Evenly distributes cooling
effect over the entire fabric.
. Flexibility.
. Wearer will feel good
comfort.
. Machine-washable.
. Re-usable.
6.3 Photonic fibres:
Dielectric mirror alternative
layers of two materials with different refractive indices produce Photonic band
gap. It reflects light in a certain range of wavelength and absorb light out
side this range this fibres can be woven in to a fabric to form shields and
filters in military operations. Bar codes made with this fibre are authentic.
6.4 Electronic systems
incorporated in Textiles
There have been some very
exciting developments recently regarding clothing with electronic systems
incorporated into the constituent fibres and fabrics. Some examples of this
are:
1.Music t-shirts- they allow
to the wearer listen his/her favorite music stored on a chip, or to tune into
the favorite radio station. They can also have moving images on the back.
2.Businessman garments-,
which has a microphone, incorporated in the collar, a display, and a personal
digital assistant in the sleeve.
3.Solar energy re-charge
jacket- it includes some tools for creative playing and communication, such as
a camera, display and microphone attachments.
4.Massage kits- It gives a
soothing massage to the wearer that can be regulated depending on the level of
relaxation desired by the user by applying vibration and pressure.
7.0 Summary
In the coming years, clothing
products will increasingly assume intelligent functions. Clothing will combine
the functions of medium, carrier and interface for an extremely wide range of
micro system applications. This new generation of "intelligent
textiles" places considerable new demands on innovative ability within the
clothing