13

CHAPTER 2

LITERATURE REVIEW

2.1 NANO TECHNOLOGY – AN INTRODUCTION

Nano technology deals with small structures (or) small sized materials

of nano meter scale. This chapter of research thesis is dedicated to deal with

the published literature on multifunctional finishing of fabrics, various

processes of functionalization and the concept and application of using TiO2

and ZnO nano-particles for functional finishing and the concept and

mechanism of photo catalytic oxidation. The methods of synthesis of TiO2

and ZnO nano-particles and the required functional properties which can be

added to the textiles by way of treatment with nano-particles are discussed.

Textile finishing encompasses all the operation involved in (or) applied

in treatment of fabrics from grey fabric stage to final finished fabric stage

with the ultimate aim of improving the appearance and handle value of the

fabrics. In this research thesis the term is employed to include all the

processes that usually applied after coloration and improvise certain qualities

of the fabrics. Such improved fabric characteristics may include appearance,

fashion aspects and high performance properties for both personal needs and

industrial applications.

The fundamental difference between finishing and functional finishing

lies in the area of improvement in functional requirement of fabrics. While

finishing applies to general nature of added properties the functional finishing

has a focused specific enhancement of the fabric properties and performance.

14

The nature of textile fabric substrate, whether woven, knitted (or) non –

woven (or) the type of yarn used in fabric like staple yarn (or) continuous

filament yarns plays a major role in deciding the means and methods of

applying functional finish to fabrics. Kathirvelu et al (2006). gave a detailed

account on functional finish of textiles by using traditional and conventional

type of chemicals.

Several research attempts were made to combine various finishes in

one bath. The economical advantages are that the main objectives are met in

one application and drying process. However the technological problem

encountered during such one bath finishing are many like similar nature of

effects help each other processes for example silicone elastomers impart water

repellency and softness enhance antistatic properties and finally the antistatic

finishes are made with softening. The finishes that are contradictory in nature

are counteracting each others, for example, hydrophobic finishes and

hydrophilic antistatic finishes (or) stiffening and elastomeric finishes (or)

stiffening and softening finishes.

The properties of final finished products are decided by the chemical

nature and the structure of natural, artificial and synthetic fibre. There are

several characteristics of fibres, both positive and negative properties, which

deserves due consideration in deciding the final applications for example,

some fibres easily burn (cellulose), some burn slowly and self – extinguish

(wool, silk) (or) some burn and melt (Synthetic fibres).

Cotton is known to possess the advantages of being imparted with a

wide variety of functional properties. Cellulosic fibres are chemically reactive

and similarly the natural protein fibres such as wool. Synthetic fibres are not

very reactive and many are inert. The cotton molecule has reactive groups

which permit permanent attachment of these functional compounds.

15

2.2 FUNCTIONAL FINISHES FOR TEXTILES

The recent advances in functional textiles have been in the direction of

adding features to the basic product and also to address the new emerging

problem that are associated with functions of textiles. The process of

imparting the desired functional properties to textile and clothing materials is

better known as functionalization (Burniston et al 2004). Three different

approaches are thought of in the area of developing functional textiles.

� New fibres / yarns

� New type of textile construction / production technology

� New types of textile finishing

In all cases the objective is to develop specific properties which enable

them to perform a particular function in the final product in a better way.

They are expected to be high – tech products with additional novel functions.

Many of them are used with the aim of improving wear, contour, safety and

health protection.

The use of specialized fibres that have required characteristics for

performing special functions, either by the characteristics of the polymer (or)

by additives before fibre spinning, can be a possible method for achieving

functional properties in textiles. The functional textiles are explained with

help of a schematic diagram given below:

16

Figure 2.1 Schematic diagrams on functional textiles

In alternate method, yarn (or) fabric engineering with different fibres (or)

different layers can also be employed.

2.3 OBJECTIVES OF FUNCTIONAL TEXTILE FINISHES

The versatility of textile fibres offers many avenues for functional

finishes that can add their own form of functionality, modify existing

properties of fibres (or) create new benefits that are unique. Textile industry

and researchers have developed increasingly many types of functional

finishes. The objective is to enhance comfort feeling to the consumers. There

are two broad divisions of functional finishes namely, physical based finishes

and chemical based finishes. At the present scenario of stricter regulations

being imposed on chemical substances, the phases of developments in

physical based finishes have gained momentum. A bird’s eye view of the

applications of nano technology in textile fabrics is give below:

17

Figure 2.2 Nano-technology in Fiber and Textile Manufacturing

In chemical based finishes, conventional methods of finishing can be

employed such as exhaustion, padding, low add-on processes, foam

application, printing, coating etc. Recently newer and alternatives methods of

finish applications like micro encapsulation etc have been developed. Certain

newer functional capabilities like slow and long term release of chemicals

during usage of fabric can be achieved from new methods. Nano technology

has emerged out to open new possibilities in functional finishes. Surface

modification by means of chemical modification, by the application of a

surface layer (or) by more environmental friendly treatment like enzymes (or)

physical modification with plasma technology are few techniques to mention

here.

Nanotechnology

in textiles

Nano fibers

and yarns

Nano finished

textiles

• Development of Single and

Multi - walled nano fibers,

such as Carbon Nano – Tube

(CNT) composite fibers.

• Production of nano fibers,

using electro-spinning

process.

• Nanotechnology can also

improve surface properties

and functionality of cotton

fabrics.

• A variety of chemical

finishes and coatings can be

developed.

18

Consumers demand newer and improved functional properties in

textiles. Globally the demands for technical textiles have increased as their

high performance properties are enhanced.

2.4 APPLICATION OF FUNCTIONAL FINISHES AND NANO

TECHNOLOGY

Nano textile finishing deals with application of ultra fine particles

produced using nano technology. In recent times, nanotechnology is

increasingly attracting global attention. It has a huge potential in a wide range

of end uses (Beringer et al 2004). The new and unique properties of nano

materials have attracted scientists, researches and business persons because of

their economical advantages. It is interdisciplinary and emerging field which

fundamentally manipulates structural materials to the nano level (or)

molecular level. Nanotechnology encompasses a wide range of technologies

concerned with structures on the nano meter scale. It has revolutionized

material science and led to the development and evolution of a range of new

improved materials.

By way of controlling atoms and molecule, one can generate functional

materials, devices and systems of nano meter scale by precisely placing the

individual atoms thereby creating excellent properties hither to unknown and

unexplored (Kathirvelu et al 2008e).

A glimpse through literature offers facts about many nanotechnology

based innovations that has great promise to the future. Nanotechnology has

already taken an important part of our daily life in one form (or) the other.

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2.4.1 Effect of Particle Size

Nanotechnology is based on the fact that the properties of materials

can change drastically when the particle size falls below 100nm. The size of

nano-particles matters a lot with respect to the deciding of its importance nano

technology encompasses the structures whose thickness is smaller than 100

nm in one dimension. It exploits the characteristics of material that are in the

transitional zone between the atomic and microscopic level. The manufacture

and amputation of such nano level structures are also covered under this

umbrella. When the particle size is below 100nm there happens a drastic

change in the properties of materials. Surprisingly it may result in novel and

significantly improved physical, chemical and biological properties. They

exhibit fundamentally new behavior, when the size falls below a critical level.

The performance characteristics and functionalities that are previously

thought to be not possible are now made available for exploitation. It is a

convergent technology where the interdisciplinary interaction of sciences

mostly likes chemistry and physics play a vital role.

Nano-particles may either be natural (or) incidental (or) engineered and

may be amorphous (or) crystalline (or) polymeric (or) composites. They may

be of non metal metallic, semiconductor (or) a combination. The shape of

nano-particles may be spheres, tubes, rods, horns and placeless.

Kathirvelu et al (2008d) reported the size and chemical composition

decides their physical properties. Their reactivity depends on the surface

chemistries including surface defect and impurities. The decreasing size of

nano-particles results in fundamental changes in properties of material. When

the particle size is reduced there is an enormous increase in the specific

surface area. The two different approaches generally thought of in nano-

particles production are top down and bottom up types. Schematic

representations of particle size and surface area at nano scale given below:

20

Particle size

10 cm 1 mm 1µm 1nm

Surface area

1 100 1, 00,000 10,000,000

Figure 2.3 Schematic representations of particle size and surface area

at nano scale

The top down approach is like precision engineering which starts from

the micro level structure and the components are gradually miniaturized. They

are primarily featured in physics. It involves enlarging the surface and

separation of the particles. It results in increase in free energy making the

system less stable. The second type of bottom – up approach is basically

assembling from atomic (or) molecular components which results in complex

structures. It is exploited well in chemistry and biology. In sol gel technique

colloidal particles are produced which ensures the particle size to be of nano

and no energy is required to enlarge the specific surface area.

21

2.4.2 Advantages of Two Different Approaches

In the “top down” approach of breaking down the bigger particles into

smaller nano-particles, the disadvantages are less precision, production of

waste and pollution and more energy consumption. In the “bottom up”

approach where the sub nano level particles are assembled to nano-particles,

they pose certain advantages like absolute precision, no wastage, positive

control on process, less energy required and more eco friendly nature.

2.4.3 Nanotechnology in Textiles

Nanotechnology has been playing are important role in recent

textile application (Kathirvelu 2003). The very first commercial application of

nanotechnology in textiles was in lifestyle applications. Surprisingly textiles

and cosmetics were among the first disciplines to use nano materials. It is

believed that textile fabrics gives one of the safest platform for the application

of nano-particles. There has been an underlying synergy between textiles

industry and nanotechnology which make it possible for large potential of

commercial exploitation. It is understood that the large amount of interfacial

area of both nano size particles and fibres in fabrics could be employed in a

more purposeful way that augers well for commercial textile potential

(sparkle news 2006). Due to their large surface area to volume ratio and high

surface energy, nano-particles can provide high durability of finish on fabrics.

This presents better affinity on fabrics and leading to better durability of the

function (Wong et al 2006). It is obvious that this coating of nano-particles

results in negligible and insignificant danger in physical and mechanical

properties like handle value, strength, air permeability and wetting properties

(Xin 2006). Very low consumption levels of chemicals and energy are the

advantages of using nano-particles in textile finishing.

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Surface coating of textiles with nano sized particles of metal oxides

has gained more importance presently due to their specific advantages. Multi

functional properties like UV blocking, antibacterial, soil release and self

cleaning are achieved through nano coating. Both TiO2 and ZnO in nano-

particles form are capable of imparting self cleaning property to textiles. Nano

silver particles are very effective in imparting antibacterial property to

textiles. However its high cost is the major disadvantage. Nano-particles

coating influences the other fabric properties like Tensile strength, bursting

strength, Bending rigidity and air permeability. TiO2 is a wide band gap and

non toxic semiconductor. It has got a high degree of photo catalytic and self

cleaning properties. The catalytic activity of TiO2 is based on the electron /

hole pair formation due to photo excitation. Due to large surface area per unit

mass and volume, nano TiO2 particles show high degree of photo – catalytic

activities. The photo catalytic activity of TiO2 nano particle coatings depends

on the phase, the crystallite size and porosity of the coatings and the particle

size. Preparation of single phase aqueous solution of nano crystalline anatase

TiO2 at a low temperature of 38°C by using sol gel method was reported by

(Daoud et al 2004). By using chemical co precipitation – peptisation method

preparation of TiO2 solution at 72°C was reported by (Xing et al 2004).

Preparation of TiO2 sol with surface protective agent was reported. They also

reported characteristics of sol particles and evaluated the photo catalytic

activity. Both TiO2 and ZnO are bio – safe, bio compatible and can be used

for biomedical application without coating. Vigneshwaran et al (2006)

reported their work on ZnO soluble starch nano composites and synthesis of

nano ZnO using water as a solvent and soluble starch as a stabilizer. Yadav

et al (2006) studied and reported the performance of nano ZnO by wet

chemical method using Zinc nitrate and Sodium hydroxide as precursors and

soluble starch as stabilizing agent. Alessio Becheri et al (2007) reported their

work on synthesis and characterization of nano ZnO particles and their

application on cotton and wool fabric resulting in UV shielding. Kathirvelu et

23

al (2008a,b) reported their findings on nano ZnO using Zinc nitrate and

Sodium Hydroxide. Nanotechnology in textile applications general overview

are given below:

Figure 2.4 General overview of nanotechnology in textile applications

The present day applications of nano technology in textile industry are

in fibres, yarns, fabrics, nonwovens, finishing like dyeing and coating,

electronic textile and fibre modification.

2.4.4 Nanotechnology in Fibres, Fabrics And Dyeing

Production of nano-sealed synthetic fibres like Polyester, Polyamide

and Polypropylene is a promising application in fibres. The thermal,

electrical, mechanical and chemical properties of fibres can be improved by

24

using nanotechnology. New products like breathable textile laminates and

super absorbency fibres with open pore structure are possible in a variety of

polymers. High specific surface area of nano-particles makes it attractive for

usage in medical textiles. Polymeric nano fibres with nano-sealed diameters

are more suitable to such applications.

Huang (2005) reported that the decreasing fibre diameter reduces the

contact angle between fibres resulting in excellent wetting behavior of final

product. Nanotechnology is applied in production of light weight fibres which

exhibit greater strength. (Nyati 2005) reported that nano fibre exhibit high

surface area, small fibre diameter, good filtration properties, thin layers and

high permeability.

The “die swell” effect is known as swelling of polymer when passing

through the capillary tube in electro spinning process. This could be

eliminated by addition of carbon nano tube to commercial polymer. In result,

the improvement strength of fibre against the high voltage between capillary

tube and collector. This helps in increasing the spinning speed in fibre

production. In an another interesting area of development, the hygroscopic

nature of polyester fibre can be increased by 30 times by coating it with a 50

nanometer film made up of 20 layers on the outside of fibre.

Wang et al (2004) reported a nylon filament yarn with the double

moisture uptake of conventional yarn in medical textile cardio vascular graft

made of woven and knitted structure are used to replace arteries in by-pass

surgery. Machine embroidered implants are used for connecting nerves during

reconstruction shoulder surgery. Wound healing dressings are another area of

developments in medical fields opening up new unexplored characteristics of

nano fibres.

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Dyeing is another important area where nanotechnology finds

applications. Polypropylene is known to be a fibre most difficult to dye

because of absence of dye fixation sites. In polypropylene fibre dye site can

be created with nano die particles with modified quaternary ammonium salt.

The dyeing cost is also reduced .Since nano-particles have large surface area

they can be used as solvent for non-ionic, anionic, cationic dyes by using

nano clay and modified nano-clays. Such sorbent can be added to the polymer

matrix in polypropylene to improve the dyeability. Sparkle news (2006)

reported that nano clay textile composition have good dyeability, colour

fastness and less cost in dyeing and less waste water treatment problems. Also

report that they result in additional functional property improvement like

strength, UV absorbance and fire resistance. Mechanical blending of nano

clays can be added to the polypropylene matrix by using heat, in melting or

dissolving process

2.4.5 Nano Finishing Process

Perhaps the finishing of textiles is the most interesting area of

application for Russel (2002) reported the first work on nanotechnology in

textile called nano-tex. The exploitation of nanotechnology in textile finishing

was later taken up by an increased number of companies. Among the

techniques used to apply nano-particles onto textiles, coating is employed

majoritly. Cramer et al (2003) reported that the composition of coating

usually composed of nano-particles, a surfactant, ingredients and a carrier

medium for applying coating onto fabrics. Several methods like spraying,

transfer printing brushing, washing, rinsing and padding may be employed

Yen et al (2003) report that padding is the most widely used one.

A Padder is employed to apply nano-particles onto the fabric followed

by drying and curing. The functional properties that can be imparted to textile

by this method may include water repellences, soil resistance, wrinkle

26

resistance, anti-bacterial, anti-static, UV protection, flame retardation and

improvement of dyeability. It may also be used to impart new functional

properties like energy storage and communication.

Nano tex R was another commercial textile finish developed. Schulte

(2005) reported on the application of TiO2 nano-particles for textile finishing.

Nano-care R is reported to impart a new carefree wrinkle resistance finish

with minimum stains offering excellent liquid repellency and wrinkle

resistance. Another commercial finish nano-dry R was able to transport

perpiration away from the body and drying it quickly. Nano-fresh R is Known

to capture body odour giving the wearer an odurs free feeling. Schulenburg

et al (2008) reported about nano-pel R which makes the fabric breathable at

the same time being liquid and stain repellent.

2.4.6 Principles of Certain Commercial Types of Nano Textile Finishes

Nano-pel, a water and oil repellent treatment, can be applied to cotton,

wool, polyester, nylon, rayon and blended textiles. Nano-care, a wrinkle

resistant and oil repellency finish, is for pure cotton fabrics. Lennox Kerr

et al (2003) reported that both the above finishes have set a benchmark in

water and stain repellent performance of textiles.

Monomers containing methacrylate and per- fluoroalkyl group

producing a copolymer which exhibits water and oil repellency, where as a

fluorine- free monomer gives improved adhesivenes to fibre. Similarly Sahin

(1996) reported a monomer capable of improving durability through self-

crosslinking or reaction with reactive groups. According to Sello et al (1984)

these copolymer when treated with textiles liberate formaldehyde which is

detrimental to environmental safety.

27

The basic principles of nano-whiskers, according to Jain (2004),

consists of oligomeric or polymeric side branches attached to a flexible spine.

The branches stand outward from the surface to give a protection against

water or oil particles. Another variant of such a finish which does not produce

formaldehyde is called Nano-Tex Banks et al (1994) reports that the

formulation is capable of providing formaldehyde- free wrinkle resistance and

water and oil repellence when combined with a formaldehyde free resin such

as dimethyl urea glyoxal (DMUG) or butane tetra carboxylic acid (BTCA).

Kathirvelu et al (2006) reported the commercial application called

Nano-Dry a three – dimensional molecular network is created surrounding a

fibre , that is nano-net architecture made with nano fibres. Synthetic fibres

like Nylon and Polyester exhibit hydrophobic nature.

In Nano- dry treatment, a hydrophilic network of nano net of durable

absorbent nano fibre is created on the hydrophobic substrate fibre of synthetic

fibre. This leads to a durable hydrophilic treatment. However the other

properties of synthetic material such as strength, colour fastness and hand

value are not affected. Jain (2004) reported that the Nano-Dry treatment

imparts durability by the combination of covalent attachment to the fibre

surface and the use of nano molecules. Approximately the percentage of

solids loading onto the fabric surface is 0.1-0.15% by weight of the fabrics.

The problem of build-up of static charges occurs in synthetic fibres

even at high RH levels. Nano-Tex is a treatment developed to impart the

positive qualities of cotton and synthetic.

28

Figure 2.5 The schematic representation of the 3-D molecular nano-net

of Nano-Dry

This finish is aiming to create a permanently attached carbohydrate

sheath around each synthetic fibre of the web. This gives the dual advantages

of utilizing the most desirable characteristics of both synthetic core and of the

natural sheath.

Figure 2.6 Schematic representation of a Nano-Touch treated fibre

Absorbent net of

Nano- material Manmade material

Manmade fibre

Nano-Touch sheath

29

In another development a permanent attachment of the carbohydrate

sheath is created around synthetic fibre, commercially known as Nano-

Touch. It consists of Nano- Wrap artchitecture which is hydrophilic in nature

with increased moisture regain. It also exhibits a durable antistatic nature,

according to (Jain 2004).

2.5 THE BASIC OF PHOTO-CATALYSIS

Fujishima et al (1972) describe photo-catalysis as a reaction which uses

light to activate a substance which modifies the rate of a chemical reaction

without being involved itself.

Figure 2.7 Schematic diagram of operation of a photo-chemically

excited TiO2 particle

Substances which promote reactions in the presence of light are

generally photo catalists. Deshpande et al (2006) reported that Zinc oxide,

Titanium di oxide, Zincsulphide, Tungsten oxide, Strontium titanate and

Hematite are photo catalysis materials. In a heterogenous photo-catalytic

system, semiconductor particles which are in close contact with a liquid or

gaseous reaction medium, when exposed to light gets to excited state and

initate subsequent reaction like redox and molecular transformations. TiO2 is

one such a material which exists in three crystalline forms; rutile, anatase and

30

brookite. Fujishma et al (1972) reported the photocatalystic splitting of water

on TiO2 electrodes.

Figure 2.8 Schematic diagrams showing the actions of a photo-catalyst

(NanoTiO2 -top) and the resultant benefits (bottom)

Teichner (2008) reported that TiO2 is a semi conductive material that

can be chemically activated by light, even though it absorbs only 5% of the

solar light reaching the earth. TiO2 produces pairs of electrons and holes when

UV radiation is absorbed by it. The electrons of valence band become excited

Photocatalyst

TiO2

CO

H2O

UV Lamp

Ultraviolet Ray

Organic Compound

+ H2O + O2

TiO2

Photocatalytic Reaction

VOC

and

Odour Bacteria Germs Fungus L

igh

t

Lig

ht

Odour

removal

Self-Cleaning

action

Air

Purification

Sterilization

31

when light falls on it with the excess energy the electron is moved to the

conduction band. Therefore thus the negative electron (e-) and the positive

holes (h+) pair is created. The energy difference between the valance and

conduction bands is called the Band Gap. The wave length of the light

necessary for photo excitation is given by the formula;

1240 (planeks constant, h) / 3.2 eV (band gap energy) = 388Am

The positive hole reacts with water molecule to form hydrogen gas and

hydroxyl radical. The negative electron reacts with oxygen molecule to form

oxide union. This reaction is fast at room temperature and atmospheric

pressure.

2.5.1 Nano TiO2 in Textiles

Ever since the introduction of nano-particles in textiles, efforts were on to

produce finished fabrics with multiple functional performances. Lee et al

(2003) reported the use of nano silver particles for imparting antibacterial

properties. Yadav et al (2006) published the research work on the use of ZnO

nano-particles for anti-bacterial and uv blocking properties. ZnO& TiO2 have

the advantages of being non-toxic and chemically stable. Colemana et al

(2005) reported that TiO2 has strong Oxidising power of its holes, high photo

stability and redox selectivity. Its commercial availability and ease of lab

preparation makes it more advantageous. It has three types of crystal structure

Viz, anatase, rutile and brookite. Anatase structure of TiO2 nano-particles are

the most active in photo catalysis. TiO2 nano-particles are generally produced

by using three methods Viz. wet synthesis, dry synthesis and milling. The

Bottom-Up approach is employed in both wet and dry synthesis where as the

Top-Down approach is used in the milling method (Kathirvelu et al 2008c).

Sol-gel and precipitation methods are known as wet approaches. Dry

32

synthesis includes combustion, furnace and plasma synthesis according to

(Daoud et al 2004).

However the matter of great difficulty is achieving the uniformity of

size distribution of the nano-particles in all these methods. To less extent the

degree of agglomeration is another factor of concern. Certain degree of spread

in nano particle size is inevitable. The process parameter employed in

synthesis has influence over the size distribution. The particle size distribution

uniformity can be improved by adopting additional separation steps. However

the drawback in this case is that the process yield parcentage is affected.

Burniston et al (2004) revealed that nano-particles agglomerate together even

at lower temperature than their bulk size counter parts. High energy inputs or

temperature during synthesis may lead to more agglomeration by coaleseing

together of particles.

The band gap value is 3.0 eV for the rutile type TiO2 and 3.2 eV for

anatase type. Both of this structure absorbs only UV rays. Daoud et al (2004)

reported that the rutile type can absorb rays that are closer to the visible light

rays. According to Bozzi et al (2005), the anatase type of TiO2 exhibits higher

photo catalytic activity than the rutile type.

2.6 SYNTHESIS OF TiO2 NANOPARTICLES

Synthesis of Nano-particles in general involves the manipulation of

inorganic, organic and biological systems. Many new methods and devices

are being constantly brought into the field by various researchers. Over the

past decade, nano-particles have evolved as a separate class of materials.

Surprisingly various science disciplines have come together in the making and

synthesis of nano-particles. Nano-particles of ZnO in one end, find

application in hygiene products like diapers and on the other end used to alter

the characteristics of solid rocket propellents by addition.

33

The techniques of synthesis of nano-particles are divided into three

types Viz, UV Vapour-Phase, Solution Precipitation and the Solid-state

process. Sometimes two or more of these types are combined for synthesis.

During the early stages of development the Vapour-phase method was in use.

Presently the solid state processer is most widely used for micron sized

particles. According to the published literature, Ferro corporation, one of the

leading nano powder manufacturer, uses the solid state synthesis method.

Hundreds of form of lithium cobalt oxide nano powder is being produced by

using solid- state synthesis.

Lee et al (2006) reported that TiO2 nano-particles should fulfil a wide

range of requirements such as particle size, size distribution, morphology,

crystallinity and phase etc. so as to become useful and suitable for application.

Manufacture or synthesis of TiO2 nano-particles with well defined physical

and chemical properties has been a challenging task. Many researches have

published this works related to a variety of methods used for synthesis of

TiO2 nano-particles. Trunga et al (2004) reported the sol-gel process, Wu

et al (2006) about hydrothermal method and Kim etal (2003) reported on

solvothermal and emulsion precpitation methods.

According to Lee et al (2003) photo assisted sol-gel method was yet

another variant of the sol-gel technique. The other newer techniques reported

in the literature include oxidation of titanium tetrachloride in a modified

diffusion flame reactor, crystallization in reverse micelles or in the

supercritical CO2 and polymer templating method. Nano-particle synthesized

through different methods exhibit distinct physiochemical properties. Certain

wet chemical methods have been developed to synthesis powder with

spherical shape and uniform size. Arami et al (2007) reported that sol-gel

process, emulsion and pyrolysis have been used to prepare mono dispersed

34

spherical TiO2 nano-particle. It is important that the nano-particle exhibits

crystallinity and narrower size distribution. Sol-gel synthesized TiO2 nano-

particle are amorphous and require further calcinations steps to improve

crystallization such heat treatment lead to particle agglomentation and change

in size, sol-gel method for TiO2 nano-particle has another disadvantage of the

use of costly organic solvents. Similarly methods like forced hydrolysis and

homogeneous precipitation have the disadvantages of very low reaction time

due to very long concentration of the reacting formulations. Anatase TiO2

nano-particle can be synthesized hydrothermal methods using amorphous

TiO2. Chang et al (1995) reported a technique by using TiCl4. Deshpande

et al (2006) reported a method by using TiOCl2 aqueous solution Riv et al

(2006) reported sol-gel method using titanium alkoxides. Fang et al (2003)

reported hydrothermal methods amorphous TiO2, TiCl4 or TiOCl2 or TiO2

aqueous solution and sol-gel method using titanium alkoxides.

In order to regulate the physiochemical properties of TiO2 nano-

particle, organic modifiers are used in synthesis. Such modifiers include

hydroxyl group containing, carboxylate group and amine group containing

organics. As discussed earlier a variety of methodologies for synthesizing

TiO2 nano-particle have been invertigated by researchers. The commonly

used starting materials (Precusors) in the above methods are Titanium Iso-

propoxide, titanium tetra chloride, titanium (IV) sulphate and amorphous

titanium di oxide.

Another important technical aspect in TiO2 nano-particle is the

arrangements of nano-particle into well define structures or assemblies or

porous aggregates. Such nano structure exhibits unique properties like pore

size, thermal stability and their reproducibility. Yang et al (2006) reported

35

that the interaction between the primary building block is controlled in such a

way that at ambient conditions the nanostructure with useful properties is

formed. Sumio (2005) reported a large no .of such nano structure, their

synthesis and their unique properties.

2.6.1 Sol-Gel Method for Synthesis Of Tio2 Nano-Particles

One of the most widely used and successful technique for preparing

TiO2 nano-particle is sol-gel technique. By careful control of the process

parameter and the chemical structure of the starting precursor, the nano-

particle properties can be altered. Bessekhouad et al (2003) reported the sol-

gel based method by hydrolysis and polycondensation of titanium alkoxide ,

Ti(OR) n to form Oxopolymers, which are then transformed into an oxide

network. Ristic et al (2005) reported that the microstructure of TiO2 nano-

particle (anatase & rutile) decide its photo catalytic activity.

Dhage et al (2004) reported a method consisting of using titanium (iv)

n-butoxide (Tico-bu) 4) in isoprophl alcohol (i-PrOH) Acetylaceton (acac)

was used as a chemical addition to moderate the reaction speed. Deionised

water was used for hydrolysis in solution with i-PrOH under mechanical

stirring. White precipitate of titanium oxy hydroxide was obtained and

washed with water for several times. The molar ratio of these reactants

Ti(O-BU)4: H2O: I- Prop. OH: acac=1:100: 2: 0.01. Then HNO3 was added to

the final solution and refluxing at 850C for 8 hrs was found to influence the

size of TiO2 nano-particle. Then the sol was gelled by drying at 1000C for

3hours and then calcined in vaccum (400-7000C) to give TiO2 nano-particle.

36

2.6.2 Flame Spray Pyrolysis

Processes that are yielding high production rate, continuous production

and relatively low cost like flame spray pyrolysis are of more commercial

importance. This method yields fine, pure and single-phase particles. Chang

et al (2007) reported the properties like phase composition and particle sizes

of nano-particle obtained by flame spray pyrolysis. The process is basically

evaporating through pyrolysis the liquid droplet of precursor to obtain TiO2

nano-particle. The precursor solution was obtained by dissolving titanium

tetra isopropoxide (TTIP) in solvent. These prepared nano-particle exhibit

high purity and clear crystallinity.

The experimental set up consists of an ultrasonic atomizer, a diffusion

flame burner and a thermo phoretic sampler. A liquid droplet of precursor was

generated by ultrasonic atomizer, at 1.7MHz Frequency. The argon gas burner

evaporates solvent and precipitates the nano-particle. Hydrogen gas was used

as a fuel while oxygen and air were used as oxidants. Droplets of precursor

were supplied to the flame zone through the central tube. The argon gas flow

rate was 2lit/min. in the central tube. Through the second tube the gas was

passed at 1lit/min to keep the straight path way of the liquid droplets in the

flame region. Through the outer tube, hydrogen, oxygen and air were passed

at certain flow rate. A cold glass tube cooled at 12oC by cooling water flow is

used to collect nano-particle finally. The concentration of precursor liquid and

flame temperature influence particle size.

A new method called one-pot synthesis used trichloroethylene as

reaction medium. Trunga et al (2004) discussed that the method has

advantage over multicomponent solution system when TiO2 is used as a

reinforcement for polymer dissolved in trichloroethylene.

37

Trichloroethylene 60ml was mixed with 2ml of Titanium Isopropoxide

with water and stirred rigorously at room temperature. Hydrolysis and

condensation reaction occured. The prepared powder was washed by ethanol

and acetone for several times, dried at 1000C in vaccum for 3days and heated

at 4000C for 10 hrs in air.

Kim et al (2003) reported a method by hydrolysis of TEOT (tetra

ethylor thotitanate) in two stage mixing process. They attempted further to

make a continuous process by small reactor which controlled the rate of

nucleation. An ageing tube was employed for controlling the growth of nano-

particle. The hydrolysis rate is controlled by water vapourization and feed rate

of TEOT solution. The apparatus has a small reactor for two feed reagents

water and TEOT, a syringe pump a heating tape for vapouring H2O and a long

silicon tube for ageing the particles. The small reactor is continuously fed

with the two feeds.

TiO2 Primary nuclear is generated by the polymerization of the

hydrolysis product. According to Hong et al (2003), a part of them is grown to

fine nano-particle while passing through the ageing tube. In this part of

literature survey a review has been made over the various methods developed

for synthesis of nano-particles. Each method has it own merits and demerits.

The choice of method and precursor depend on the end use

requirement of nano-particle. According to Bessekhouad et al (2003) in

future, these methods could be suitably changed to meet the specific

functional needs of nano-particle.

38

2.7 SYNTHESIS OF ZnO NANO-PARTICLES

Zinc oxide is a semiconductor of n type and with direct band gap. Chen

et al (2003) reported various techniques used to synthesize ZnO nano-particle

both chemical and physical methods. The chemical method include thermal

hydrolysis technique, hydrothermal processing and sol-gel method. Physical

methods are spray pyrolysis, vapour condensation and thermo chemical

decomposition of precursor. Presently the vapour phase and sol-gel methods

are widely used. In case of vapour phase method the drawback is that the

powder is in the agglomerate form due to difficulty in control of reaction

condition. Also it is slow process and more energy consuming.

The sol-gel method though producing uniform ZnO nano-particles,

requires stricter control on reaction condition. Due to high costs it is not

commercialized but suitable for research only. Discussed the problem

associated with the poor yield efficiency of ZnO nano-particles and the

difficulity associated with particle size control. New and other methods were

tried in recent years like thermal decomposition, supercritical precipitation

and colloidal synthesis. Ma et al (2008) discussed a method by thermolysis of

Zinc oxide propionate as a precursor and trioctyl phosphine oxide at a high

temp of 160oc. Guo et al (2000) reported various methods of ZnO nano-

particle synthesis under the broad section namely physical , thermal and

chemical methods. Um et al (2007) reported a method called the levitational

gas condensation (LGC) method. Um et al (2007) reported a modified method

of LGC and phase evolution.

The main parts of such an apparatus are high frequency induction

generator, levitation and evaporation chamber and oxygen concentration

39

control unit. Wang et al (2004) reported a new combustion method, in which

the mixture of Zinc nitrate and fuel powder is ignited to form ceramic oxides.

Rapid heat conduction takes place resulting in quick reduction of temperature.

Fine ZnO nano-particles can be produced without agglomeration. Glycine was

used as fuel for this purpose due its inexpensiveness and its heat of

combustion being more on the negative side when compared with urea or

citric acid.

In another study reported, Zinc nitrate was used as the precursor. It has

the dual function of being a precursor and an oxidant. Zinc Nitrate of

analytical grade and glycine were mixed at a desired molar ratio. The mixture

became like transparent slurry matter. Vigourous stirring was carried out to

make a homogenous mixture. Then it was heated to 100oC using a hotplate to

dry it. The dired up precursor is now having combustibility. A mini gas

burner was employed for combustion of precursor. A large volume of gases

evolved during combustion. This method has the advantages of simplicity,

less cost and speed.

Another method was reported by Ko et al (2006) for synthesis of ZnO

nano powder. This rapid method is based on DC thermal plasma synthesis

yielding a high production rate.

By changing the plasma gas combination and flow rate it was possible

to control the shape of ZnO nano-particle .The new type of DC plasma reactor

operated at 70 Kw and atmospheric pressure. Zinc powder with impurities

less than 50 ppm was used in this process. The Zinc powders were passed

through nitrogen gas and made to fall on plasma flame. Then it was

vapourised, oxidized and finally quenched.

40

2.8 STRUCTURAL CHARACTERIZATION OF NANO -PARTICLES

According to Wang (2000), there are several methods used for

characterization of the nano-particle.

X-ray powder Diffraction method (XRD) for studying the crystal

structure of nano particles, Fourier Transform Infrared Spectroscopy (FTIR)

for identifying the name of chemical groups and bonds, Transmission

Electron Microscope (TEM) for identifying the nano-particle diameter,

Particle Size Analyser (PSA) for measuring the range of size of nano-particles

and Scanning Electron Microscopy (SEM) for capturing the images capturing

the images containing topological information of fabrics.

2.8.1 X-Ray Powder Diffraction Method (XRD)

It is a very useful experimental technique to study the crystal structure

of solids. Structural parameters like lattice constant and geometry, orientation

of single crystals, preferred orientation of polycrystals, defects and stresses

can be studied using this technique (Jenkins et al 1996). Identification of

unknown materials are also a possibility by using this technique. In this

method a collimated x-ray beam is made incident on a specimen and

diffracted by the crystalline phases is the specimen. The wave length ranges

from 0.7 to 2Å. According to Bragg’s law.

2 sinA d θ= (2.1)

where;

d = the spacing between atomic planes in the crystalline phase and

A = the X-ray wavelength.

41

The intensity of the diffracted x ray is measured. This is a function of

the diffraction angle 2θ and the specimen’s orientation.

According to Jenkins and Snydes the specimen’s crystalline phases and

its structural properties are identified by using the diffraction pattern.

According to scherer’s equation the crystalline domain diameter D, is given

by the following equation;

0.89

cosD

W

λ

θ

×=∆ ×

(2.2)

where;

λ = the wavelength of the incident X-ray beam, (1.54 A˚ for the Cu Kα)

θ = the Bragg’s diffraction angle

∆W = the full width of the X-ray pattern line at half peak-height in radians

and

K = 0.89 (constant)

2.8.2 Fourier Transform Infrared Spectroscopy (FTIR)

This technique is based on the assumption that molecules and crystals

can be considered as system of balls (atoms or ions) connected by springs

(chemical bonds). In such system the frequency of vibration depends on the

mass of the balls (atomic weight) and the stiffness of the springs (bond

strength). They can be set into vibration. The mechanical molecular and

crystal vibrations are at very high frequencies in the order of 1012 to 1014 Hz

(3-300 µm wave length) which is in the Infrared Region. It is a useful

technique for identifying the nature of chemicals (organic or inorganic

nature). Also the components of an unknown mixture can be quantified. The

42

chemical bonds can be determined by the analysis and interpretation of the

infrared absorption spectrum. The FTIR spectra are unique for a compound

and generally accepted as the finger print of the chemical nature of

compound. The FTIR spectra of organic compounds are generally very rich

and detailed where as that of inorganic compounds are much simpler.

In this instrument the infrared beam radiation intensity is measured

before and after it interacts with the sample as a function of light frequency.

Infrared spectrum is a plot of relative intensity time output of the

interferometer is subjected to a Fourier Transform to convert it to the familiar

infrared spectrum (Intensity frequency). This helps to identify the atomic

arrangements and the concentrations of the chemical bonds present in the

sample.

2.8.3 Transmission Electron Microscope (TEM)

TEM is a technique in which the electrons are accelerated to 100kev or

higher (up to 1MeV). A thin specimen (less than 200nm) is used to capture

the projection by mean of the condenser lens system. The electron beam

penetrates the sample thickness either un deflected or deflected. TEM offers

very high magnification ranging from 50 to 106 and has the advantage of

image production with diffraction information from a single sump. The shape

and size of nano-particles can be characterized using TEM apparatus

operating at 80Kv. TEM samples were placed on carbon coated copper grids.

They are prepared from diluted dispersion of nano-particles in 2 – propanol.

43

2.8.4 PARTICLE SIZE ANALYZER (PSA)

The PSA testing instruments working under dynamic light scattering

principle. The scattering angle is 90º. The PSA is an innovative photon cross

correlation sensor allowing for simultaneous measurement of particle size and

stability of opaque emulsions and suspensions in the nanometer reign. The

observation of the diffraction pattern at finite distance is done through a lens

(L) placed between the laser source and the detector. The diffraction patterns

of particles having the same size converge at the same point whatever them

location with respect to the lens. This theory is applicable for large particles

compared to the wavelength. The first zero on the detector is 1.22 lf/d, laser

as a source of coherent intense light of fixed wavelength. He-Ne gas lasers

(λ=0.63µm) are the most common as they offer the best stability (especially

with respect to temperature) and better signal to noise than the higher

wavelength laser diodes. It is to be expected when smaller laser diodes can

reach 600nm and below and become more reliable that these will begin to

replace the bulkier gas lasers. Usually this is a slice of photosensitive silicon

with a number of discrete detectors. It can be shown that there are an

optimum number of detectors (16-32) increased numbers do not mean

increased resolution. For the photon correlation spectroscopy technique (PCS)

used in the range 1nm 1µm approximately, the intensity of light scattered is so

low that a photomultiplier tube, together with a signal correlate is needed to

make sense of the information. Some means of passing the sample through

the laser beam. The Agilent E4440A PSA high-performance spectrum

analyzer measures and monitors complex RF and microwave signals up to

26.5 GHz. With optional external mixing, the frequency coverage expands to

110 GHz by Agilent external mixer and to 325 GHz by other vendors' mixer.

The shape and size of the nanoparticles were obtained through PSA, using a

NANOPHOX (0143 P) Particle Size Analysis.

44

2.8.5 Scanning Electron Microscopy (SEM)

SEM produces images containing topographical information. It can

also provide details of the chemical composition near the surface of the

material. It is the most widely used technique for characterization of nano

materials (Howard et al 1980). The SEM image provides details in the

morphology and microstructures of nano meters. The instrument has

magnification in the range of 10 to 3, 00,000. The samples were kept on

specimen structure with double sided adhesive tape. Gold was coated on

sample by sputtering technique and examined with SEM make Jeol Model

JSM – 6360.

2.9 ANTIBACTERIAL ACTIVITY

The functional performance in textiles required by consumer include:

Antibacterial activity, UV protection, self cleaning and stain releasing.

Microbes like bacteria, virus, and fungi etc are posing a lot of hazards to

human beings (Sawai, 2003). The system of immunity bestowed to human

beings by the nature saves us to protect from micro organisms. Textile fabrics

are known to be potential infusions and odours. They can adhere to textile

substrates and grow very rapidly. Humidity, dirt and sweat offer best

environment for them to grow. Sometimes they can cause stains under warm

and damp condition. Such offensive odours and discoloration on textiles

renders them unusable. The tensile strength and water permeability are also

affected. Fabrics like leisure wear, sportswear, mattresses, carpets etc are

more prone to bacterial growth. Ramachandran et al (2004) reported that

during fabric finishing and wet storage attack by bacterial organism are more

severe. Antibacterial finish is a requirement on the textile substrate for the

protection of the wearer.

45

Silver is a well known anti-bacterial material. Silver ions exhibit a

broad spectrum of antibacterial activity. Micro encapsulation of sliver

compound and coating on to textile is one among the methods for imparting

antibacterial finish to textiles. In another possible method nano-particles of

silver can be added to fibre polymers like polystyrene co-malefic anhydride

(Ki et al 2007).

Textiles generally do not exhibit resistance to bacterial growth.

Therefore such a functional finish is developed with nano silver, titanium

dioxide and zinc oxide solutions (Kamal Gupta et al 2007). Studies reveal that

both nano-particles of TiO2 & ZnO are very effective in imparting bacterial

resistance to textiles besides nano silver particles. Duran et al (2007) reported

that nano sized particles render a better antibacterial effect due to more

number of particles. The photo catalysis reaction of the metal oxide ions is

responsible for creating a sterilizing effect on textiles due to liberation of

active oxygen molecules.

2.9.1 UV Protection

Recent research studies reveal that it is essential that human skin is

protected by textiles from the harmful UV rays from the sun. UV rays have

wavelength ranging from 150 to 400nm. Long term exposure of human skin

to UV rays results in damages like skin ageing, photo dermatitis, erythema,

(skin reddening), sun burn, skin cancer, eye damage and DNA damage /

alteration. The National Institutes of Health, USA reported that the main

cause of skin cancer is UV radiation from the sun. Hatchb reported that 90%

of skin cancer cases can be prevented by way of sun protection.

Textile is an excellent medium to protect the skin from the incident UV

rays. Textiles can absorb, reflect and scatter UV rays. When dyed, the UV

protection ability is improved further. The fibre type or composition, moisture

46

content, type and concentration of dye particles, presence of optical whiteners

etc have influence over the degree of UV protection ability of textiles. UV

protection finish is the single major influencing factor that decides the ability

of textiles to block UV rays. When UV rays are incident over a fabric surface,

absorption, transmittance and reflection occurs. These three aspects depend

up on surface smoothness, fabric cover factor and the presence of delustrants,

dyes and UV absorbers. It is essential to mention here that UV absorbers

deflect UV rays thus protecting the skin. The intensity and distribution of UV

radiation depends on geographical location, time of day and season. The

wavelength of UV radiation decides the degree of damage to the human skin

for example; wavelength less than 300nm do the most of skin damage.

According to Hilfiker et al (1996) the wavelengths of UVR of maximum

danger to skin are 305 – 310 nm. The erythemal effect is multiplied by the

intensity of sunlight. Now it becomes clear that textiles must possess the

ability to protect the wearer from UVR of wavelength in the range of 300 –

320nm. Sun Protection Factor (SPF) is an index quantifying the effectiveness

of such protection. It is the ratio of the potential erythemal effect to the actual

erythemal effect transmitted through the fabric by the radiation (Gambichler

et al 2001).

Incase of textiles it is more appropriate to call SPF as Ultraviolet

Protection Factor (UPF). The term SPF is more often used in cosmetics

example sun protection lotions, creams etc. It gives a relative measure of how

much longer a person can be exposed to sunlight continuously before a skin

irritation occurs. It is generally accepted that a textile fabric with UPF >40 is

excellent in protection of human skin against UV rays. According to Mentera

et al (2003) the maximum theoretical value for UPF is 200 and in practice

80% of this value for UPF can be realized.

47

Incident radiation

Reflected radiation

Absorbed radiation

� Transmitted rSuper fine

Fibres

In general, summer wear textiles like shirts, blouse, T-shirt, swimwear,

beach wear, sportswear etc deserve UV protective finishes. Industrial textiles

like awnings, tents and blinds may also be treated for such a finish (Hatchb

et al 2006).

Figure 2.9 Schematic representation of the mechanism of UV protection

A textile fabric of sufficient weight per square meter provides a

good degree UV protection even with no finishing. The type of fibre

influences the UPF of fabrics. Wool and Polyester exhibit significantly higher

value of UPF while Cotton and Silk showing lower values. Nylon is placed in

between. Nylon & Polyester are coated with delustrants which is TiO2 and

hence strongly protects from UV Radiation.

48

If it is assumed that the only possibility of transmission of UV rays

through fabric is the spacing between the yarns then the maximum value of

UPF theoretically is,

1 UPFmax = -------------------------- (2.3)

1 – Cover factor

According to Raleigh’s scattering theory the scattering of light is

inversely proportional to the fourth power of wave length. The optimum

particle size for scattering the radiation is 20 to 40nm according to (Burniston

et al 2004). Obviously, nano-particles of above size does scatter UV rays

more effectively. Xing et al (2004) reported that TiO2 & ZnO nano-particles

often increased surface area and exhibits more absorption properties in the

UV region.

2.9.2 Self-Cleaning Action

Nano-sized silver, titanium dioxide and zinc oxide are used for

imparting self-cleaning and antibacterial Properties. Metallic ions and

metallic compounds display a certain degree of sterilizing effect. It is

considered that part of the oxygen in the air or water is turned into active

oxygen by a catalyst containing the metallic ion, thereby destroying the

organic substance to create a sterilizing effect. Nano-materials possess

enhanced catalytic abilities due to their highly stressed surface atoms which

are very reactive. With the use of nano-sized particles, the number of particles

per unit area is enormously increased.

Thus, the photocatalyst is the substance which can modify the rate of

chemical reaction using light irradiation without being altered or consumed in

the end. The process of photo catalysis can be better explained with the help

49

of a schematic diagram comparing the actions of a man-made photocatalyst

(nano-TiO2) with a natural one (chlorophyll).Chlorophyll of plants is a typical

natural photocatalyst (Fujishima et al 1999). The difference between

chlorophyll photocatalyst to man-made nano TiO2 photo catalyst is, usually

chlorophyll captures sunlight to turn water and carbon dioxide into oxygen

and glucose, but on the contrary photocatalyst creates strong oxidation agent

and electronic holes to breakdown the organic matter to carbon dioxide and

water in the presence of photocatalyst, light and water (Fujishima et al 2000).

When it is illuminated by light of energy higher than its band gap, electrons in

TiO2 will jump from the valence band to the conduction band, and the

electron (e–) and electric whole (h+) pairs will form on the surface of the

photocatalyst. The negative electrons and oxygen will combine to form O2–

radical ions where as the positive electric holes and water will generate

hydroxyl radicals OH (Kathirvelu et al 2008).

Since both products are unstable chemical entities, when the organic

compound falls on the surface of the photocatalyst it will combine with O2 -

and OH- and turn into carbon dioxide (CO2) and water. This cascade reaction

belongs to the oxidation reduction class and its action is schematically

illustrated. During the reaction, photocatalyst is able to decompose common

organic matter in the air, such as molecules causing odour, bacteria and

viruses or organic stain and dirt.

Furthermore, when photocatalytic titanium dioxide is exposed to

sunlight, it exhibits super-hydrophilic behavior, which allows partially

decomposed stain/dirt residues on the surface to be washed away easily.

50

Figure 2.10 Titanium dioxide in a photocatalyst action

Different types of chemical are also used to convert nano particles

like Zinc oxide, titanium dioxide, titanium iso-propoxide, Zinc nitrate, silver

nitrate etc., to convert into nano particles.

2.9.3 Soil Release Finishing

The ability of fabrics that facilitate the removal of soil during

laundering and other common household condition is a desirable requirement.

Kissa et al (1984) reported several methods of removal of soil from fabrics.

In first method, adsorption of detergent and absorption of water

remove soil by penetration of soil by wash liquid, emulsification of soil and

roll up of oily soil. The second method involves mechanical work by means

of hydrodynamic flow to remove soil, flexing of fibres to free out soil trapped

in between fibres, surface abrasion and swelling of fibres to enhance (Cooke

51

1987). Through textile chemical finishing the actions like roll up of oily soil,

penetration of soil-fibre interface and finish swelling can be controlled.

According to Kissa et al (1984), there are the two steps involved in the

soil release process in textiles. In the first step the wash liquid is penetrated

between the soil particles and the textile surface and then the soil is removed

away by the mechanical action. In the second step soil removal is determined

by the detergent nature type and mechanical action.

Self cleaning textiles are the new developments in this direction. They

are based on the fact that the textiles are capable of cleaning themselves to

some extent under certain conditions. They are able to free themselves from

dirt and stains. No detergents or chemicals are needed in such cleaning

process. In the modern day living, consumers prefer such self cleaning

textiles.

2.10 METHODS OF APPLYING NANO-PARTICLES ON TEXTILES

According to Miles (2003) three methods are available to apply nano

particle finish to textiles such as Simple dip and dry method, Pad-dry-cure

method and Spraying method

In simple dip and dry method the nano-particles are used in the

colloidal state with dispersing agent. The fabric is dipped for 10 minutes and

taken out and dried by means of sun drying or hot air or microwave oven

drying. In pad-dry-cure method, a padding mangle is used to apply nano-

particles in the form of a suspension. The nano-particles are pressed inside the

textiles by pressure of padding rollers. The fabric is then dried and cured to

ensure fixation. A binder is employed to bind the nano-particles to fabric

surface. A dispersing agent is used to make a suspension solution of nano-

particles. In the spraying method, a spray gun is employed to spray the

52

colloidal suspension of nano-particles on fabrics. A hand held spray gun with

compressed air supply and feed tank is used for this purpose. A binder may or

may not be used to bind the nano-particles on the fabric surface.

2.11 TESTING OF FUNCTIONAL PROPERTIES

The fabric samples treated with nano-particles are tested for four

special functional properties namely Antimcrobial activity, UV protection

factor, Soil release characteristics and the self- cleaning action.

2.11.1 Evaluation of Antibacterial Activity

The antibacterial activity was tested by adopting the quantitative

assessment method as per AATCC test method 100 – 2004 (AATCC 2007).

Staphylococcus Aureus American type Culture Collection No.6538 was used

for Gram positive bacteria and Klebsiella Pneumoniae, American type culture

collection no.4352 for Gram negative bacteria. The reduction of bacteria was

calculated in percentage by using the formula,

R = 100 (B – A) / B (2.4)

where;

R = Percentage reduction in bacteria

A = the number of bacteria recovered from the inoculated treated test

specimen swatches in the jar incubator over 24 hours.

B = the number of bacteria recovered from the incubated treated test

specimen swatches on the jar immediately after inoculation (at

Zero contact time)

53

2.11.2 Evaluation of Ultra-Violet Protection Factor

The instrumental or in-vitro method is used for evaluating the

ultraviolet protection factor of the fabric. It is done as per the AATCC test

method 183 (AATCC 2005). UV-Vis spectrophotometer is used to measure

the blocking of erythemal weighted UVR through fabrics. After collecting

transmittance data’ the UPF is calculated by using a formula. The UV-Vis

spectrophotometer has an integrating sphere on which the fabric sample is

placed. A direct beam of UV radiation of one wavelength and of known

quantity is made to fall perpendicular to the fabric sample. The amount of UV

radiation transmitted through the fabric is measured. The beams of UV

radiation are chosen at all wave length in the UV range at 2 (or) 5nm

intervals.

The transmittance data is collected at all wave lengths. The data is used

to calculate the UV protection factor and the percent transmittance values.

The relative power data of different UV wavelengths to cause skin redness are

collected using human subjects and are given in the erythemal action spectra.

UPF can be calculated by using the formula;

λλλλ

λλλ

∆×Τ××Ε

∆××Ε

=

∑

∑

S

S

UPFnm

nm

nm

nm

400

280

400

280 (2.5)

where:

λΕ = Relative Erythemal spectral effectiveness

λS = Solar spectral irrradiance in wm-2 nm-1

λΤ = Average Spectral transmittance of fabrics

54

λ∆ = The band width in nm

λ = The wave length in nm

2.11.3 Evaluation of Soil Release Characteristics

The soil release property was assessed by adopting a modified stain

release test. The stain profiles of the untreated samples were compared to that

of treated samples. The effectiveness of stain release was compared with the

AATCC ratings as per Test method 175: 2003 (AATCC 2007).

2.11.4 Evaluation of Self Cleaning Action

The self-cleaning activity was assessed with respect to following

parameters:

• Effect of method of preparation and hence the characteristics of

nano-particles

• Time of exposure

• Durability of finish

• Damage to textile

The self-cleaning action / photoactivity of the TiO2 coated cotton

fabric was investigated by exposing the samples containing adsorbed coffee

stain to visible irradiation. The measured quantity of 6% coffee solution was

introduced on the cotton fabric and was allowed to spread. One half of each

stain on the fabric was exposed to the sunlight for 12 – 48h, while the other

half was covered with a black paper to prevent its irradiation from sunlight.

The exposed part of the stain was compared with that of the covered part for

self – cleaning action. Gretag Macbeth, Color eye 7000Å spectrophotometer

was used to follow the photodegration of coffee stain. The self – cleaning

action was quantified by comparing K/S values (absorption to scattering

coefficient) of the exposed and unexposed portions of the same stain. The K/S

55

value of unexposed part of the stain was taken as 100 and relative decrease in

K/S value of exposed part was calculated using the following relationship

(Kamal Gupta et al 2008)

(K/S) unexposed – (K/S) exposed

% decrease in K/S of exposed = ----------------------------------x 100 (2.6)

(K/S) unexposed

where;

K is the absorption co-efficient and

S is the scattering co-efficient.

The durability of finish was assessed by subjecting the nano-particles

coated textile to five wash cycles, and the self-cleaning activity of the coating

was assessed after every wash cycle.

The following aspects are yet to be addressed and very hard to find

research work by in these aspects. The present research work include the

following aspects:

i) Multifunctional finishing of textiles by using different precursors using

sol-gel and wet chemical methods on cotton fabric.

ii) A comparative performance of TiO2 & ZnO nano particle coating on

fabrics made of cotton.

iii) A comparative performance of functional testing of TiO2 & ZnO nano-

particles with special reference to physical characteristics. The plan of

research work has been thoughtfully designed to include these aspects

in this research work.