Abstract
Smart
textiles are materials and structure that sense and react to environmental
conditions or stimuli, such as those from mechanical, thermal, chemical,
electrical, magnetic or other sources. The
Phase Change Materials are those which change their phase from solid to liquid
upon heating and back to solid from liquid when temperature is drop down.
During their phase change from Solid to liquid they absorb, distribute and
store the heat, and release it when going a phase change from liquid to solid.
Thus it keeps the wearer skin’s temperature constant by absorbing the excess
heat and releasing it when required. PCM possesses the ability to change
their phase with a certain temperature range which can be controlled by choosing the various phase change material
according to the end use of the product. This paper discuss about the principle
of Phase Change Material, Its different type available. The different technology
used for the incorporation of phase change materials into textile substrate and
their application with limitation is also been discussed.
Keywords: Phase Change Temperature, Technical textiles, Microclimate, Microencapsulation, Perspiration, Temperature, Thermocules and
Thermal Regulation.
1. Introduction
The textile industry has reached a
highly advanced stage with the different types and qualities of fabrics that
can be manufactured. The history of textiles and fibers spans
thousands of years, beginning with the style change from animal skins to the
first fabric used to clothe humanity. But during the relatively short period of
the past 50 years, the fiber and textile industries have undergone the most
revolutionary changes and seen the most remarkable innovations in their history.
Technical textiles are reported to be the fastest growing sector of the textile
industrial sector [6]. In recent years, significant progress has been achieved
in the area of technical textiles, fibers, yarns, fabrics and other structures
with added-value functionality have been successfully developed for technical
and/or high performance end-uses. Technical textiles were promoted as
alternative materials for a limitless range of applications, including civil
engineering, the automotive industry, aerospace and the medical industry. The huge advancement in the Technical textiles industry and
the accurate control on the mechanization process offer an innovative environment
for new product, namely Smart textiles. Smart textiles are materials and
structure that sense and react to environmental conditions or stimuli, such as
those from mechanical, thermal, chemical, electrical, magnetic or other sources
[15]. In the
last decade one of emerging technologies is microencapsulated Phase Change
Materials which are being developed to provide significantly enhanced thermal management for fibers, foams and textiles with
application to apparel and technical textiles. The different
types of Smart textile materials are: Phase Change Material, Chromic Colors, Shape memory materials, Auxetic material, HoIofiber, Stomatex, Stimuli-responsive hydrogels
and membranes and Electronic textile [1, 4].
Suitable technical equipment is becoming more and more important for
authorities and the military. Not only are electronics, hard and software
playing a large role, there are also increasing demands for apparel. The call
for Smart fabrics is becoming more and more insistent. A new generation of
these fabrics features Phase Change Materials (PCMs) which are being developed
to provide significantly enhanced thermal management for fibers, foams and
textiles. These Phase Change Materials are able to absorb, store and release
excess body heat when the body needs it resulting in less sweating and
freezing, while the micro climate of the skin is influenced in a positive way
and efficiency and performance are enhanced. An Outlast Jacket Containing Phase
Change Material is shown in Fig: 1, which
maintain the wearer skin temperature in a comfortable zone.
Fig: 1 Outlast Phase Change Jacket
According to this definition textiles containing PCM are considered as smart
because they react immediately to changes in environmental temperature and
adapt to the prevailing hot or cold condition [2]. Phase change technology
originates from the NASA (National Aeronautics and Space Administration’s)
research program of the 1970s.The aim of this program was to provide astronauts
and instruments with better protection against extreme fluctuation of
temperature in space and since then research work has been carried out by
scientists and now textiles
with phase change materials (PCMs) are used in numerous products and
applications from apparel, underwear, socks, accessories and shoes to bedding
and sleeping bags. PCMs can even be found in specialty items, such as
antiballistic vests, automotive, medical or special industrial applications,
where warmth and energy play a role.
2.
Principle
Working of PCM Fabric
The
principal function of clothing assembly is to provide the wearer with
protection against undesirable environments. Due to the fact that a human being
is homeo thermal, the human body regulates temperature in narrow limits around
370C [2]. But Fabrics containing PCMs appear to be effective in
contributing to apparel comfort by buffering and reducing overheating, the
cause of perspiration. The fabrics with PCM react immediately to changes in
environmental temperature and adapts to the prevailing hot or cold conditions. The Phase Change Materials changes their
phase from solid to liquid upon heating and back to solid from liquid when
temperature is drop down. During their phase change from Solid to liquid they
absorb, distribute and store the heat, and release it when going a phase change
from liquid to solid. When temperature rise occurs as a result of body
activity or a higher environmental temperature, PCM reacts by absorbing the
heat. Storing this surplus energy the PCM liquefies. This phase change produces
a temporary cooling effect in the clothing layers. The Working of Phase Change Material is also shown in Fig: 2. Once the PCM has
completely melted, the storage of heat stops. The PCM releases the stored heat
with a drop of environmental temperature or when the body is at rest, and a
temporary warming effect occurs in clothing layers. This heat exchange produces
a buffering effect in clothing layers, minimizing changes in skin temperature.
Fig:
2 Working Principle of PCM
The PCMs keep
the wearer more comfortable by absorbing excess body heat when it creates too
much heat and by releasing stored heat when the body needs it most. The
Thermocules work with the body to regulate temperature and humidity better than
fabrics or insulation alone.
3. Benefits of PCM:
The
followings are the benefits that can be obtained by incorporation of PCM into a
textile substrate:
a)
A cooling effect, caused by absorption of heat by
the PCM.
b)
A heating effect, caused by release of heat from the
PCM.
c)
A thermo-regulating effect, resulting from either
absorption of heat or release of heat by the PCM which keeps the temperature of
wearer constant in the comfort zone.
d)
An active thermal barrier effect resulting from
either heat absorption or heat emission of the PCM and creating a thermal
barrier in surrounding substrate, which, regulates through the substrate and
adapts the heat flux to thermal needs.
e)
The
cross-linked PEG treated fabric have antibacterial activity,
resiliency/antiwrinkling, wear, toughness, absorbency and exsorbency of
liquids, improved abrasion and linting resistance, decreased static propensity
and increased oily soil release[5].
4.
Types of Phase
Change Materials
There are different
types of phase change material which change their phase over a specific
temperature range. So according the end use we can have different PCMs. Few
example of phase change materials with their phase change temperature (PCT) and
their Heat storage capacity:
4.1 Hydrated Inorganic Salt:
Hydrated
inorganic salt is an inorganic salt crystal with n water molecules. The
hydrated inorganic salt that can be used in the manufacture of heat-storage and
thermo-regulated textiles and clothing usually has a heat-absorbing and -releasing
temperature interval of about 20 to 40 °C. Table: 1 shows some of the hydrated
inorganic salts.
Table: 1, Hydrated Inorganic Salts [5]
4.2 Hydrocarbons:
The Phase Change Temperature
(PCT) or Melting temperature for the hydrocarbons can be manipulated by
selecting no. of carbon atoms. The PCT can be achieved from -5ºc to 60ºc by
having no. of carbon atoms from 13-28. By selecting the no. of carbon atoms the
PCT could be control as shown in Fig: 3. The Melting temperature of
Hydrocarbons increases with increase in no. of carbon items. As shown in Fig: 3 the 20 number of carbons gives the Tm of
37.5º C
which means the hydrocarbon which is having 20 number of carbon atom will
change its phase from solid to liquid over 37.5º C temperature and back from
liquid to solid below 37.5º C temperature. Fig:
3, PCT vs No. of Carbon atoms [2]
4.3 Polyethylene glycol:
Paraffin
waxes have the heat storage capacity of 150-200kj/kg with the PCT or melting
temperature ranges from 35º C to 63º C. According to the end use of product
different phase change temperature for PEG can be chosen as per Table: 2. The
melting temperature for polyethylene glycol increases with increase in
molecular weight.
Table: 2, Molecular weight and
melting temperature of Polyethylene glycol [2]
4.4 Fatty acids and Vegetable oils:
Fatty acid and mineral oils their heat Storage capacity range
153-182 kj/kg with Phase change temperature range(PCT)/Melting temperature of 30º-60ºc.
5.
Incorporation of
PCM into Fabrics[2,5,7]:
Since the process of phase change is dynamic; therefore, the
materials are constantly changing from a state to another depending upon level
of physical activity of the body and outside temperature. The thermo-regulating
characteristic is possible in manmade fiber by adding PCM microcapsules to a
polymer solution prior to fiber extrusion. In the process, PCM microcapsules
are integrated inside the fiber itself.
These PCM is first microencapsulated by a polymer coating in a sphere shape.
The diameter of molecule is as small as 15-40µm. Then these microcapsules can
be applied to textile substrate by any of the following method.
5.1 Fiber
technology
The first step in any technology of PCM is Microencapsulation. The microencapsulated PCM fibers could store heat over long
periods .Microencapsulation is the process of
capturing small amounts of phase change materials in a shell material so that
the phase change materials are permanently enclosed and protected. The protective polymer shell is very durable and
designed to withstand textile production methods used in fiber, yarn spinning,
weaving, knitting, and coating applications.
5.2 Coatings
PCM could be
incorporated into the textiles by coating using polymer such as acrylic, polyurethane,
etc, and applied to the fabric. There are various coating processes available such
as knife-over-roll, knife-over-air, pad-dry-cure, gravure, dip coating, and
transfer coating.
To prepare the coating composition,
microspheres containing phase change material are wetted and dispersed in a
dispersion of water solution containing a surfactant, a dispersant, an antifoam
agent and a polymer mixture. The coating would be then applied to a textile substrate.
In an alternative embodiment, an extensible fabric would be coated with an
extensible binder containing microencapsulated phase change material to form an
extensible, coated fabric. Preferred phase change materials include paraffinic
hydrocarbons.
5.3 Lamination
In this technology microcapsules would be mixed into a water-blown polyurethane foam mix
and these foams are applied to a fabric in a lamination process, where the
water is taken out of the system by drying process. The excellent honeycomb structure
obtained during foam formation made considerable amount of still air trapping
possibility, thus, leading to an increased passive insulation. Although the
presence of PCM micelles in cells can easily be distinguished.
Beside chemical
protective suits the PCM can also improve the thermo-physiological wearing
comfort of other protective garments made of nonwovens such as surgical gowns,
uniforms, or garments worn in clean rooms. The cooling effect of the PCM
can delay the temperature rise and, hence, the moisture rises in the
microclimate substantially. As a result, the wearing time of the garments can
be extended significantly without the occurrence of heat stress as a serious
health risk.
6.
Microencapsulation:
Microencapsulation
is a process in which tiny particles or droplets are surrounded by a coating to
give small capsules many useful properties. In a relatively simplistic form, a microcapsule is a small sphere with a
uniform wall around it. Microencapsulation is also
known as micro packaging of solids and liquids.
The material inside the
microcapsule is referred to as the core, internal phase, or fill, whereas the
wall is sometimes called a shell, coating, or membrane. The Fig: 4 show microencapsulated
paraffin by a polymer. It is an innovative technology for packing of
solids and liquids. Fig: 4
Microcapsule containing paraffin [2]
The microcapsules are produced by depositing a thin polymer
coating on small solid particles or liquid droplets, or on dispersion of solid
in liquids. The core particles (active substance) from microcapsule can be
released under controlled conditions to suit a specific purpose. The core
substance from the microcapsule can be released by friction, by pressure, by
dissolution through the polymer wall coating or by biodegradation. Most
microcapsules have diameters between a few micrometers and a few millimeters.
7. Application of Phase Change Materials
Fabrics
containing micro PCMs have been used in a variety of technical textile
applications such as apparel, automotive textiles, domestic textiles, medical
products,
7.1 Apparel:
Major
end-use of textile containing PCM in Apparel includes:
7.1.1
Life
style apparel - Smart jackets, Vests, Men's and Women's hats, Gloves.
Some peoples
have jobs where they go to and from a cold storage facility or transport
vehicle and a warm building or outside environment on an intermittent basis.
PCM protective
garments improve the comfort of workers as they go through these environmental
step changes. It has been observed that garments made with PCMs or “dynamic
insulation” will keep a person warm longer than conventional insulation when
worn in cold environment. Fig: 5 Jacket Containing PCM
7.1.2
Outdoor
active wear apparel -jackets and jacket lining, boots, golf shoes, trekking
shoes, socks, ski and snowboard gloves.
Safety helmets have a thermal
resistance of approximately 1.0 m2 k/w and due to their structure
the heat generated by the wearer can be dissipated only by means of convection.
But with the incorporation of micro PCM in the helmet liner leads to
substantial reduction of the microclimate temperature in the head area.
7.1.3
Protective garments.
Protective garments.
In the case of chemical or biological protective
clothing a conflict between the protective function of clothing and the
physiological regulation of body temperature may occur. The conflict led to
discomfort and physical strain and in extreme cases can put the person at risk
from heat stress. The Outlast Protective garment (Body Armor) contains the
microencapsulated PCM thus providing more comfortable Protective textile. The Outlast
provide many kinds of protective clothing which contains the microencapsulated
PCM ranges from Vest to Body Armor. The Fig: 6 show an Outlast Body armor
containing Phase Change Material. Fig: 6 Outlast Body Armor
7.2 Automotive Textiles:
A Car Interiors
containing Phase Change Material is shown in Fig: 7
. During the
summer, the temperature inside the passenger compartment of an automobile can
rise substantially-for instance, when the car is parked outside. In order to
stabilize the interior temperature while driving the car, many models are
equipped with air conditioning systems; however, providing sufficient cooling
capacity requires a lot of energy. On the other side, during the winter months,
the driver and the passengers are often confronted with low temperatures,
especially as they first get in the car. Fig: 7
Car Interior containing PCM
. During the
summer, the temperature inside the passenger compartment of an automobile can
rise substantially-for instance, when the car is parked outside. In order to
stabilize the interior temperature while driving the car, many models are
equipped with air conditioning systems; however, providing sufficient cooling
capacity requires a lot of energy. On the other side, during the winter months,
the driver and the passengers are often confronted with low temperatures,
especially as they first get in the car. Fig: 7
Car Interior containing PCM
As result, some models have heating systems
installed in the driver’s seat which are supplied by the car’s battery. Due to
additional systems for monitoring and controlling various functions in cars,
the power supply needed for their operation has steadily increased over the
past years. In order to prevent further demands on the battery’s capacity,
manufacturers are searching for all kinds of energy savings.
7.3 Aerospace:
Phase change technology originates from the NASA
(National Aeronautics and Space Administration’s) research program of the
1970s.The aim of this program was to provide astronauts and instruments with
better protection against extreme fluctuation of temperature in space and since
then research work has been carried out by scientists. In
Aerospace the PCM is used in space suits and as a cover protection for
instruments against the severe temperature changes of outer space.
Fig: 8, Space Suit with PCM
7.4 
Medical
Products:
Medical
Products:
PEG-treated
fabric may be useful in medical and hygiene applications where both liquid
transport and antibacterial properties are desirable, such as surgical gauze,
nappies and incontinence products [5]. Textile containing PCM can keep the skin
temperature within the comfort range, so they can be used as a bandage. If a therapeutic blanket
made of a flexible PCM composite contains a micro PCM having a transition
temperature below normal skin temperature, it can be used for cooling febrile
patients in a careful and controlled manner. Fig: 9, Wound
Care bandage
A
careful selection of the phase change temperature makes it possible to avoid
the danger of overcooling the patient that is inherent with ice packs.
Alternatively, a blanket with PCM can be useful for gently and controllably reheating
hypothermia patients.
7.5 Others:
There
are numerous others application for textile containing Phase Change Material,
Some of the popular uses of PCM in textile are:
The
PCM is used in tarpaulin cloth so that temperature of inside the tarpaulin can
be maintained as shown in Fig: 10.
Fig: 10 Tarpaulin fabrics with PCM
The
PCM is also used in the Covering cloth for some sensitive items which require a
maintained and control temperature as shown in Fig: 11.
Fig: 11 Cover Fabric for sensitive items
The PCM can also be used in baterry warmers, agriculture,
building material and geotextile[17].
8. Limitation
Besides
the very important functions and application of Textile containing PCM, It
posses few limitation due to which the textile containing phase change material
are not so popular, the limitation of textile containing phase change materials
are:
a) The limitation
with phase change materials is that this phenomenon only occurs over a specific
temperature or temperature range for any specific PCM and When the Latent heat
of the PCM is fully absorbed or released the thermo regulating effect stops.
b)
The
clothing structure should be carefully engineered otherwise it can release the
absorbed heat to the environment rather than to the wearer’s body.
c)
If
the amount of PCM presence is more to get higher heat storage, the fabric
become very stiff because of higher amount of PCM.
9.
Conclusion
The
intelligent textiles and smart clothing is emerging field in the world of
textiles. The textile industry has already focused for several years on
enhancing the functional properties of textiles. Phase Change Material, Chromic
Colors, Shape memory materials, Auxetic material, HoIofiber, Stomatex,
Stimuli-responsive Hydrogels and membranes and Electronic textile are examples of Smart textiles that are already
commercially available in the market. The textiles containing phase
change materials (PCMs) are used in many products and applications from apparel,
underwear, socks, accessories and shoes to bedding, sleeping bags, car Seats,
Wound care bandages, space suit and protective garment. PCMs are even find
their application in some specialty items, such as antiballistic vests,
automotive, medical or special industrial applications, where warmth and energy
plays a vital role.
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