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Chapter - II

LITERATURE REVIEW & AIM AND SCOPE OF PRESENT INVEST IGATION

2.1. Fibers

Fibers are a class of material that exists like hair or continuous filament similar to

a piece of thread. They are classified as natural fiber and synthetic fibers. Natural fibers

are made from plants, animals and mineral sources. It has been used to meet basic

requirements of clothing, storage, building material, and for items of daily use such as

ropes and fishing nets. Cotton, sisal, banana, jute, hemp, ramie, pine apple, bamboo, and

silkworm are some of the sources for natural fibers. Synthetic fibers are formed by

polymerization of single unit of monomer (Example: Nylon). Some synthetic fibers are

manufactured from natural cellulose, such as rayon, modal and lyocell. Synthetic fibers

possess unique characteristics which make them popular materials, because they dry up

quickly, durable, less expensive, readily available and easy to maintain [1, 2].

2.1.1. Cotton

Cotton is native to many tropical and subtropical regions around the world, and

cultivated about 7000 years ago in Indus valley region. It has certain significant

environmental and performance advantages over the other fibers. It uses sunlight and

converts it directly to a fiber without intermediate processing steps, but other natural

fibers like silk, wool and bamboo fibers need intermediate processing steps and require a

large amount of energy to produce fibers. As a natural renewable fiber, cotton has

obvious environmental and sustainability advantages over petroleum-based synthetic

fibers and does not contribute to net green house gas emission.

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2.1.2. Chemical composition of cotton

Cotton is a soft, fluffy staple fiber that grows in a protective capsule around the

seeds of cotton plants of the genus Gossypium. It is composed almost entirely of

cellulose (88 - 96%) and impurities include protein (1.0-1.9%), wax (0.4-1.2%), ash

(inorganic salts 0.7-1.6%), pectin (0.4-1.2%) and others (0.5-0.8%). The overall

composition of raw cotton fibers depends on the type, origin, fiber maturity, weathering

and agricultural conditions [3 - 10].

2.1.3. Chemical structure of cotton

Cotton is described chemically as poly (1, 4) β-D-anhydroglucopyranose [7]. It

contains carbon, hydrogen, and oxygen with reactive hydroxyl groups. The three

hydroxyl groups that protrude from the ring are not having evenly distributed electrons

around the atoms hence polar in nature. The hydrogen bonding within the ordered regions

of the fibrils causes the molecules to draw closer to each other which increases the

strength of the fiber and also aids in moisture absorption. The structure of cotton is given

in figure 2.1.3.

.

Figure 2.1.3: Structure of cotton

2.1.4. Need for organic agriculture

Cotton production needs heavy use of insecticides, the most hazardous pesticide

which is injurious to human and animal. It covers 2.5% of the world's cultivated land but

uses 25 % of the world's insecticides, and more than 10% of the pesticides, including

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herbicides, insecticides, and defoliants [11]. Nitrogeneous synthetic fertilizers are a major

contributor to the increased N2O emissions, which are 300 times more potent than CO2 as

greenhouse gas [8] and threatening for global warming. The cotton seed hull, where many

pesticide residues have been detected, is a secondary crop sold as a food commodity. It is

estimated that as much as 65% of cotton production ends up in our food chain, whether

directly through food and oil or indirectly through the milk and meat of animals [12].

Rural farmers are lack of necessary safety equipment, protective clothing, and training for

handling hazardous pesticides. Therefore a demand arises for organic agriculture, which

protects the health of people and planet by reducing the overall exposure to toxic

chemicals.

2.1.5. Advantages of organic agriculture

Organically grown crops also yield soil with higher organic matter content,

thicker topsoil depth, higher polysaccharide content and lower modulus of rupture;

therefore reducing considerable soil erosion. Some of the contributions to the different

ecosystems include

� Protecting the surface and ground water quality

� Reduced risk in insect control by replacing insecticide with the manipulation

of ecosystems

� Long-term prevention of pests through beneficial habitat planting

� Elimination of the use of toxic chemicals used in cotton

� Conservation of biodiversity

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Hence, organic cotton production offers a healthier and cleaner product and also benefits

our planet earth [13].

2.1.6. Organic cotton

Organic cotton production is a system of growing cotton without synthetic

chemicals, fertilizers, herbicides, conventional synthetic insecticides, growth regulators,

stimulators and defoliants [14]. The organic system promotes enhanced biological

activity, encourages sustainability and commands proactive management of production.

This production system replenishes and maintains soil fertility, reduce the use of toxic

and persistent pesticides and fertilizers and build biologically diverse agriculture.

Organically grown cotton is certified by some state agencies to ensure that no

synthetic substances were used in the cultivation and harvesting of the fiber. Cotton

grown on land free of chemicals for three years is certified as “organic”. It is the most

widely used natural fiber in clothing for the production of baby wear, T-shirts, shirts,

vests, towels etc. The cotton seed oil and left out residue are fed to livestock, which

creeps into the food chain. Hence organic cotton production can replenish the

environment protection.

Cotton and organic cotton shows more or less same dyeing behavior and other

fastness properties. When compare to ordinary cotton, organic cotton has less wax

content, better absorbency and smoothness. Therefore organic cotton processing does not

require any new kind of modification in the already existing process sequence for

conventional cotton [15].

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2.2. Modification of Fibers

Natural fiber cotton have a set of properties, such as water binding capability,

flexibility, rigidity, hydrophilic and hydrophobic regions, and the ability to adhere to

themselves and other materials, which is dependent on the structure and assembly of the

major components of the fiber (hemicellulose, cellulose and lignin). A variety of

chemical techniques have been developed to change these properties by altering the fiber

or its surface, to suit the end product. Cellulosic fibers for textile uses can be modified by

addition of hydrophobic groups for water repellency, crosslinking agents for improved

performance, softeners for enhanced hand feel and also by eco-friendly chemicals and

enzymes.

2.3. Enzymes in textiles

Enzymes may be defined as biocatalysts synthesized by living cells. They are

protein in nature, colloidal and thermo-labile in character and specific in their action. It is

of utmost importance to maintain mild conditions for modification of cellulosic surfaces

to maintain fiber integrity [16]. As consequences of these limitations of chemical systems

and the nature of the fiber, enzymes are replenished to perform some of the reactions.

2.3.1. History of Enzymes

Enzymes are not living organism but which are present in living organism. The

term “enzyme” is derived from a Greek word “enzymos” which means “in the cell or

ferments”. Berzelius in 1836 coined the term catalysis (Greek: to dissolve). In 1878,

Kuhne used the word enzyme (Greek: in yeast) to indicate the catalysis taking place in

the biological systems. In 1883, Buchner achieved the isolation of enzyme system from

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cell free extract of yeast and named as zymase. James Summer in 1926 first achieved the

isolation and crystallization of the enzyme urease from jack bean and identified it as a

protein [17].

2.3.2. Types of enzymes

The International Union of Biochemistry (IUB) appointed an Enzyme

commission in 1961. Since 1964, the IUB system of enzyme classification (Table 2.3.2)

has been in force and divided enzymes into six classes based on the type of reaction

catalyzed by them [17].

Table 2.3.2: Classification of enzymes

Enzyme Class Reaction catalyzed

Oxidoreductases Oxidation – reduction reactions

Transferases Transfer of functional groups

Hydrolases Hydrolysis of various compounds

Lyases Addition or removal of H2O,CO2 & NH3 etc.

Isomerases Summarization reactions

Ligases To bind two molecules and ATP is used.

2.3.3. Properties of Enzymes

Some of the important characteristics of enzymes are as follows [18]

� Colloidal in nature.

� Have high molecular weight.

� Become inactive at high temperature.

� Active only in the limited pH range.

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� The range of specificity varies from enzyme to enzyme.

� Bio- degradable.

� Inhibited by cyanides, sulphides, etc.

2.3.4. Mechanism of enzyme action

Lock and Key analogy for enzyme action was first postulated in 1894 by Emil

Fischer. Enzymes have a specific three dimensional area within their folded region as

active sites. The substrate molecule just fits as a particular key into a lock (active site) to

form enzyme substrate complex. The active site is the specific region of the enzyme

which combines with the substrate. The binding of the substrate to the enzyme causes

changes in the distribution of electrons in the chemical bonds of the substrate and

ultimately causes the reactions that lead to the formation of products. The products are

released from the enzyme surface to regenerate the enzyme for another reaction cycle

[19] which is represented in figure 2.3.4.

Figure 2.3.4: Mechanism of enzyme action

2.3.5. Application of enzymes in textile industry

. Today enzymes have become an integral part of the textile processing, because

they are biodegradable, work under mild conditions and save precious energy. Most of

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the enzymes used in the textile industry belong to the class hydrolases. Some of the

present industrial applications of hydrolases category of enzymes are listed in the Table

2.3.5 [20, 21].

Table 2.3.5: Textile applications of hydrolases

Enzyme Substrate attacked Applications

Amylase Starch Desizing of cotton

Catalase Peroxides Peroxide removal in dyeing

Cellulase Cellulose Biopolishing & Bio finishing

Laccase Indigo dye Improvement of the look of denim

Pectinase Pectin Bioscouring - replaces caustic alkali

2.3.6. Cellulase

Cellulase enzymes are usually classified by the pH range in which they are most

effective. Acid-stable (pH 4.5 - 5.5), neutral-stable (6.0 - 7.0) and alkaline-stable (not

widely used) are the three categories that are effective for textile application [22].

Cellulases are well established in textile wet processing as agents for fiber surface

modification [23-25]. Acid cellulase enzymes are complex mixture of three major types

namely, endo-1,4-β-D-glucanases (EG) (EC 3.2.1.4), cellobiohydrolases (CBH) (EC

3.2.1.91) or exoglucanase and β-glucosidases (BG) or cellobiases (EC 3.2.1.21). The

structure of endoglucanse, exoglucanase and β-glucosidases are represented in

figure 2.3.6.

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Figure 2.3.6: Structure of (a) Endoglucanase (b) Exoglucanase and (c) β-glucosidases.

2.3.7. Sources of cellulase

Cellulase production on a commercial scale is induced by growing the fungus on

solid cellulose or by culturing the organism in the presence of a disaccharide inducer such

as lactose. Cellulolytic microbes notably the bacteria Cellulomonas and Cytophaga and

most fungi can utilize a variety of other carbohydrates in addition to cellulose. Most

commonly studied cellulolytic organisms include: Fungal species- Trichoderma,

Humicola, Pencillium, Aspergillus; Bacteria - Bacilli, Pseudomonas, Cellulomonas:

Actinomycetes - Streptomyces. While several fungi can metabolize cellulose as an energy

source, only few strains are capable of secreting a complex of cellulase enzymes, which

could have practical application in the enzymatic hydrolysis of cellulose. However, the

microbes commercially exploited for cellulase preparations are mostly limited to

Trichoderma reesei, Humicola insolens, Aspergillus niger, Thermomonospora fusca,

Bacillus and few other organisms [26].

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2.3.8. Mechanism of cellulase action

Endoglucanases randomly cleave internal glucosidic bonds within an unbroken

glucan chain in the most accessible parts of cellulose polymers and newly created non

reducing chain ends. The cellobiohydrolases cleave these non reducing chain ends into

cellobioses. Hydrolysis of cellobioses into the glucose end product is completed by

β-glucosidases [27]. However, in total crude cellulases, these three components are

present in non uniform compositions. Currently cellulase is widely used to alter cellulose

properties for potential applications in textile, pulp and paper industries [28].

2.3.9. Cellulase in biopolishing

Cotton and cotton blend fabrics contain small cellulosic microfibrils. These

fuzzy microfibrils make the surface of the garment rough and reduce the luster of the

garment. Biopolishing is a biological process in which cellulase acts on the yarn surface

and eliminates superficial microfibrils on surface to get a soft handle and an attractive

clean appearance of the fabric. Enzymatic removal of the fuzz is absolutely safe and

efficient method under mild chemical and physical conditions with accurate control.

Cavaco et. a.l studied the interaction between cellulase action and mechanical agitation

and the observed fact is that mechanical action will preferentially remove the

microfibrillar material with a high content of reducing ends [29]. The high interaction

between EG activity and mechanical agitation could completely break a piece of fabric

into microfibrillar mass whereas the CBH-rich crude will leave the main fabric structure

intact under similar treatment conditions. The role of higher level mechanical agitation on

the activity of EG and CBH was studied [29-32]. It is suggested that higher levels of

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mechanical agitation increases EG activity relative to CBH activity in a total crude

mixture [32].

2.3.10. Effect of biopolishing on fabric

Biopolishing treatment often influences certain physical properties of the fabrics

after treatment, besides improving appearance and handle values. Reduction in fabric

strength, increase in elongation at break are also realized in biopolishing, in addition to

improved handle values. It influences the dyeability and the reaction of cellulases is also

retarded by the dyestuff present in the fabric. In addition to that surface morphology,

water absorbency, tensile strength, pilling effect, crystallinity and handle of fabric.

a) Surface morphology

Cellulase hydrolysis results in systematic removal of primary and secondary walls

progressively. In the initial step of enzyme hydrolysis, the elimination of primary wall

results in the reduction in the finess of fibers and subsequently hydrolysis continues in a

sub layer [33-35]. Zadhoush et. al. suggested the combination of biopolishing shearing

and singeing, considerably reduces the surface defects [33]. After initial hydrolysis,

microfibrillar structure becomes so weakened that the enzyme penetration within the

microfibrils, causes scissioning and rupture of fibrils [36]. Obturk et. al. investigation

revealed that fibrillation increases with increase in crystalline orientation factor [37].

Cellulase monocomponents (EG I & II, CBH I & II) neither destroy nor create large or

small pores that are found in the native fibers though the process results in loss of

cellulose microfibrils [38 39]. Lee et. al. inferred that inactivated CBH enzymes cause

hole like defects along the fiber axis to an extent of 23-75 nm, after washing that

represents the images of CBH I and movement along the cellulose chain length [40].

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CBH causes a number of longitudinal and transverse cracks and many types of erosion

but among the two CBHs, the CBH II causes more surface cracks [41, 42]. Researchers in

the field of biopolishing suggested that EG and EG rich preparations are the best for

ageing and defibrillation of fiber surface while complete cellulase systems are

recommended for cleaning and depilling effects [43].

b) Water absorbency

Cellulase treated fabrics show higher energy dissipation under wet condition,

implying that they might offer slightly superior thermal comfort performance under hot

and humid conditions [44]. The improvement in water absorbency and water retention

properties are influenced by the fabric construction parameters and also extent of

hydrolysis in biopolishing process [44-48]. The other studies on biopolishing revealed

that improved wet-ability to an extent of 35-85 % depending on the construction of fabric

and also further improved in softener treatment [43, 49]. The enzyme treatment increases

transverse swelling of fiber by 14%. In cotton and cotton/linen blends, water retention

increases by 24-28%. A marginal moisture regain occurs under high level of agitation in

enzyme treatment due to defibrillation effect [44, 50-52].

c) Weight loss and tensile strength

Changes in tensile strength of fabrics depend significantly on the degree of

polymerization, crystallinity and weight loss upon enzyme treatment. Paulo et. al. and

Gulrajani et. al. studies proposed that increase in time, temperature and concentration of

cellulases decrease bending length and bending modulus significantly and reduction in

bending hysteresis greater with higher weight loss [29, 45]. Raje et. al. revealed that the

initial increase in bending stiffness is due to consolidation of fabric structure, reduction in

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interstices, while the reaction proceeds, enzymes become predominant enough to reduce

stiffness and the stiffness is further reduced with softener treatment due to decrease in

inter fiber, inter yarn frictions. Bending hysteresis decreases after treating the fabrics with

CBH rich cellulase due to cleaner surface without fibrillations [49]. Paulo et. al. studies

revealed that in EG predominant higher agitation treatment, EG activity synergistically

tear away fiber surfaces, exposing fresh surfaces for further attack and leading to loss on

breaking strength up to 35% [29, 32]. Fabrics made of ramie and linen retains higher

strength than cotton and viscose rayon fabric [50, 53, and 54]. The tear strength losses are

high in rotor spun yarn compared to ring spun yarn due to more availability of adsorption

sites [55]. The cellulase treatment influenced the tensile properties in terms of tensile

elongation, tensile and compressive resilience, shear rigidity, hysteresis, and surface

friction for about 50 % and better drape ability, reduced air permeability are also

observed [56,57]. Lenting et. al. suggested three different routes to minimize the tensile

strength loss based on the hypothesis concerning the mechanism of interaction between

cellulase action and applied shear force [58].

d) Pilling and handle

Pilling is the formation of small, fuzzy balls on the surface of a fabric.

Endoglucanase (EG) and EG rich cellulases exhibit better pilling rating at lower weight

losses compared to other components of cellulases. A remarkable reduction in pilling is

realized for about 1-2% weight loss in knitted fabrics, while in woven fabrics no

significant reduction appears till 8-9 % weight loss. But improvements are also evident

under high mechanical action and for various combinations of process parameters. Hence

a linear relationship exists between depilling and weight loss [49, 59-62].

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The enzymatic degradation of crystalline cotton cellulose is a slow process, which

could improve handling of the fabrics without excessively damaging the fabric [63, 64].

The primary hand qualities such as stiffness, smoothness and thermal performance have

been widely studied and the total hand value increases from 3.3 to 3.5 % after cellulase

treatment, which further increases up to 3.75 % with softener treatments [65, 66].

e) Crystallinity

Cellulose polymer has crystalline and amorphous regions [67]. Yu Cao et. al.

studied the crystal structures of enzyme hydrolyzed cellulosic material and changes in

structure and properties of the cellulose caused by enzymatic treatment depend on the

composition, the type of enzyme and the type of cellulosic materials. Both endoglucanase

and crude cellulase have pronounced effects on the crystallinity and structure of

cellulose. The softwood pulp is most effectively treated by enzymes, but linter is highly

resistant to enzymatic treatment in the view of the changes in the crystallinity. The

increase in crystallinity index and that in the apparent crystal size (ACS) of cellulose are

good evidence that the amorphous portion of the cellulose was more readily and quickly

hydrolyzed than the crystalline portion [68]. Sunkyu Park et. al. studied the surface and

pore structure modification of cellulose fibers upon cellulase treatment. The measurement

of polymer adsorption and crystallinity index after enzyme treatment revealed that

decrease in polymer adsorption and increase in the crystallinity index [69] are strong

evidences to support that the amorphous portion of cellulose is more readily hydrolyzed

than the crystalline region and it was also reported in other studies [ 58, 70].

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f) Dyeability

Enzyme treatment of cotton provides considerable advantages in terms of soft

touch, improved wet ability and dyeability without appreciable fiber deterioration [71].

Biopolishing of cotton fabric carried out, either before or after the dyeing process, has an

influential role on dyeability of the fabrics. The cellulase attack on dyed fabrics depends

on molecular size of dyes, dye/fiber interaction reactive groups present in the dyes and

aggregation of dye molecules, besides the process conditions [27].

Cellulase pretreatment enhances penetration of alkali during scouring and

increases the alkaline degradation of seed fragments in the subsequent processes [72, 73]

Development of newer regions for dye accessibility due to disaggregation of cellulose

leads to improvement in dyeability. Affinity of the dyes in biopolished fabric increases

initially and then decreases later due to extended hydrolysis, which reduces the

additionally developed accessible regions [74, 75]. There are two kinds of regions

accessible to dye molecule: areas that are readily digested by the enzyme and regions

that are additionally developed by the attack of cellulase. Therefore dyeing affinity was

found to increase and then decreases with increasing weight loss indicating that

additionally developed accessible regions eventually decreases with extended hydrolysis.

Hence pretreatment of cotton fabrics with cellulase improves dye uptake even in

immature fiber neps like that of matured cotton fibers [76, 77]. In reactive dyed fabrics

the K/S values are improved up to 16-19% due to removal of protruding fibers that

otherwise would decrease the scattering coefficient. Ibrahim et. al. studies on

pre-enzymatic treatment using acid/ neutral cellulase results in enhancing the extent of

post dyeing irrespective of the cellulosic substrate along with the dye class [78].

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Pretreatment of cellulosic fabric with intra and inter crystalline swelling agent and

followed by enzyme treatment and vat dye treatment showed decreased dye uptake. This

is because the swelling caused by the pretreatment accelerated higher weight loss during

enzyme treatment, led to therefore decreased dye uptake [79].

g) Denim washing

Denim washing is the aesthetic finish given to the denim fabric to enhance the

appeal and to provide strength. In denim washing, acid cellulases are used to impart

various effects to the fabrics in terms of contrast, shade and smoothness. The indigo dye

on the surface of fabric is emulsified and float out of the fabric by the interaction of

cellulose binding domain, certain hydrophobic sites and other non polar surface

available on the cellulase [80-84]. Rendle et. al. revealed that the EG I and CBH II from

Trichoderma reesei provides moderate abrasive activity on denim fabrics, while the

performance of CBH I appears to be very poor [85].

2.3.11. Recent applications of cellulase in textile

Ali Hebeish studied the effect of biopolishing on four different cotton substrates

and compared the technical properties such as, nitrogen content, tensile strength, tear

strength, whiteness index, surface roughness and wrinkle recovery angle before and after

biopolishing. These studies indicated that post-crosslinking and pre-crosslinking revealed

marginal differences in nitrogen (%), wrinkle recovery angle and whiteness index, a point

which validates the argument that cellulase enzyme could not break down the DMDHEU

crosslinks within the molecular structure of cotton containing fabrics. Meanwhile the

surface roughness obtained with pre-crosslinking is a bit higher than those with

post-crosslinking. Moreover, post-crosslinking caused higher strength loss properties than

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pre-crosslinking [86]. An-I Yeh studied the effect of particle size on enzymatic

hydrolysis of cellulose. As the particle size being reduced to submicron scale, the

production rate of cellobiose was increased at least 5-folds due to the size reduction. The

yield of glucose was also significantly increased depending upon the ratio of enzyme to

substrate. A high glucose yield (60 %) was obtained in 10 h hydrolysis when the average

particle size was in submicron scale [87].

Nithya et. al. studied the synergetic effect of DC air plasma and cellulase enzyme

treatment on cotton. The DC air plasma and cellulase enzyme treatments were found to

be effective in improving the hydrophilicity of cotton fabrics. The combination of

treatments has resulted in enhanced hydrophilicity when compared to plasma and enzyme

treatment separately. Especially enzyme and plasma treatment on fabric shows a drastic

increase in hydrophilicity of nearly 70 % and also enhancing the water retention property

due to surface modification and highest value of mean pore radius by physical etching of

fabric surface. Therefore enzyme and plasma treatment can be exploited for further

finishing process due to the improved hydrophilicity [88]. Shaikh studied the enzymatic

treatment on cellulose, cellulose 2, 3-dialdehydes, their carboxylate, dicarboxy and schiff

base derivatives. The dialdehyde cellulose was hydrolyzed to a lower extent than the

starting cellulose except at high levels of aldehyde content (above 50%) and this was

attributed to H-bonding of aldehyde with other hydroxyl groups in cellulose as well as

formation of hemiacetal and hemialdol like structures. This strategy of partial chemical

modification can open a new promising area for further research [89].

Ibrahim et. al. developed a new approach for biofinishing of cellulose containing

fabrics using cellulase under pad wet batch conditions followed by washing cycle with a

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high level of mechanical agitation to terminate the enzyme and to remove the weakened

fuzz fibers, surface pills and also to upgrade the surface and dyeing properties of

cellulose containing fabrics [90]. Sung Ho et. al. adapted a new strategy for increasing

cellulose accessibility to the enzymatic attack by ionic liquids and microwave irradiation.

Microwave irradiation not only enhanced the solubility of cellulose in ionic liquids, but

also significantly decreased the degree of polymerization of regenerated cellulose. The

rate of enzymatic hydrolysis of cotton cellulose was increased by at least 12-fold after

ionic liquid dissolution [91]. Longyun et. al. studied cationization and biopolishing of

cotton by cellulase to explore the influence of cationization on the adsorptive and

hydrolytic performance of cellulase. It is found that the hydrolytic activity toward cotton

is partially damaged by the cationization. It is attributed to the movement restriction and

inactivity of cellulase protein by the cationization [92].

Nithya et. al. investigated the synergetic effect of low temperature plasma and

enzyme treatments on the physico-chemical properties of cotton fabrics. The fabrics were

treated with DC air plasma (P), cellulase enzyme (E), enzyme preceded by plasma (PE)

and plasma proceeded by enzyme (EP). The antimicrobial activity of the treated cotton

fabrics was assessed after processing with neem leaf extract. Air permeability of the

samples has nominal variation after antimicrobial finishing [93]. Jain et. al. studies on

Fentons’s reagent and cellulase treatment on cellulose revealed that surface of cellulose

remains unaltered due to Fenton’s reagent and treatment with 0.5 mM concentration of

Fentons ‘s reagent, 2 % H2O2 for 48 h gave the highest enzyme response [94].

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2.4. Crosslinking

Cellulose crosslinking is a very important textile chemical process, and is the basis

for a vast array of durable press- and crease-resistant finished textile products. The

reactive group on the cotton molecule permits permanent attachment of new functional

compounds. In untreated cotton fabric, wrinkling can be an inconvenience, but with a

durable press finish, the same fabric can be wrinkle free when laundered and wear.

Formaldehyde is the earlier compound used for crosslinking, later it was replaced by

dimethyloldihyrdroxyethylene urea (DMDHEU) to give high performance wrinkle

resistant finishing, but the release of carcinogenic formaldehyde restricts the use in the

textile industry. Since the late 1980s, extensive efforts have been made to use

multifunctional carboxylic acids to replace the traditional DMDHEU. Several

formaldehyde-free crosslinking systems have been developed including the commercially

available addition product of 1,3–dimethyl urea and glyoxal systems based on glyoxal

with co-reactive additives and several polycarboxylic acids [95-104]. Among the new

agents being developed, polycarboxylic acids are the most promising non-formaldehyde

durable press finishes. Polycarboxylic acids with three or more carboxyl groups

(Example Citric acid (CA), Butanetetracarboxylic acid (BTCA) bonded to the adjacent

carbons of their molecular backbone are effective crosslinking agents for cellulose and

the reaction proceeds via the formation of a cyclic anhydride [104]. Yang et. al. reported

the esterification of cotton cellulose by a polycarboxylic acid requires not only the

formation of a five-membered cyclic anhydride intermediate, but also the mobility of the

anhydride intermediate to access the cellulosic hydroxyl, so that the esterification can

take place, because both the acid and cotton cellulose are in solid states. The reactivity of

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a polycarboxylic acid for esterifying cellulose is affected by the size of its molecule

[105].

2.4.1. Applications of crosslinking agents

Crosslinking agents are widely used with other chemical agents to give functional

finishing like crease resistant, antimicrobial, flame retardant and water repellency etc. to

textiles. Nowadays, use of the mentioned finishing agents in combination with bonding

agents has been extensively investigated. In recent years, many researchers have studied

the antimicrobial property of treated fabrics with chitosan [106]. Wu et. al. revealed that

treatment using the combination of maleic acid and sodium hypophosphite leads the

crosslinking of cotton cellulose and is effective in reducing the flammability of cotton

fleece [107,108]. The use of cyclodextrins and their derivatives in the textile domain is a

challenge that arose in the early 1980s, and the possibility of fixing β-CD permanently to

cotton and wool fibers with polycarboxylic acid as binding and crosslinking agents was

proposed. Montazer et. al. synthesized spacer polyester fabric by stabilizing

β-cyclodextrin on fabric using CA, BTCA and DMDHEU as crosslinking agent

[109,110] and the best yield was found with BTCA. Fluorocarbon resin is the most

effective treating agent for making fabrics water repellant [111,112]. To improve the

washing durability of water repellency, some crosslinking agents are usually used along

with the water repellent agents. Montazer et. al. studied the stability of nanosilver (Ag)

particles on the surface of cotton using BTCA and sodium hypophosphite and evaluating

its efficiency against two pathogenic bacteria, Staphylococcus aureus and Escherichia

coli, and impacts on durability and other physical features of cotton [113].

Harifi et. al. reviewed the past, present and future prospectus of crosslinking agents, their

25

role in functional finishing of textile, association with stabilization of cyclodextrin on

textile and also binding of nanoparticles on textiles [114].

2.5. Cyclodextrin

Cyclodextrins are cyclic oligosaccharides composed of glucose units linked by

α-1,4-glycosidic bonds. The alpha, beta and gamma cyclodextrins are composed of

6, 7 and 8 glucopyranose units. Each cyclodextrin unit has a hydrophobic cavity which

acts as a host for hydrophobic guest molecules. Apart from these naturally occurring

cyclodextrins, many cyclodextrin derivatives have been synthesized. These derivatives

usually produced by amination, esterification or etherification of primary and secondary

hydroxyl groups of the cyclodextrins. The solubility of the cyclodextrin derivatives is

usually different from that of their parent cyclodextrins. Virtually all derivatives have a

changed hydrophobic cavity volume and also these modifications can lead to

advantageous changes in the chemical and physical properties of guest molecules and

useful in wide range of applications.

2.5.1. History of cyclodextrin

The first written record on cyclodextrins was published in 1891 by a French

scientist Villiers. He determined its composition to be (C6 H10O5)2.3H2O and named it

“cellulosine”. In 1903, Schardinger published an article where he describes two

crystalline compounds A and B which he had isolated from bacterial digest of potato

starch. He was only able to isolate very small amounts of compound A but significantly

more of compound B which he identified as Villiers “cellulosine” [115]. Till 1911

although many of the physico-chemical properties of cyclodextrins were unknown, when

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Schardinger published his last article [116] he did lay the foundation of cyclodextrin

chemistry. Later cyclodextrins were named as Schardinger dextrin in his honour.

In 1935, γ-cyclodextrin was discovered by Freudenberg and Jacobi [117].

Freudenberg and Cramer suggested that larger cyclodextrin could exist [118] and this was

later verified by French et. al. [119,120]. However until the mid 1980s the large ring

cyclodextrins were ignored because of difficulties in their purification and preparation of

reasonable yields [121]. In 1961, evidence for the natural existence of δ-, ζ-, ξ-, and even

η-cyclodextrin (9-12 glucopyranose units) was provided [122].

Many microorganisms produce glucosyltransferases but only a few strains of

genus Bacilli, Micrococcus and Klebsiella produce cyclodextrin glucosyltransferase

(CGTase) [123]. Biotechnological advances in the 1970s lead to dramatic improvements

in the production of cyclodextrins. Genetic engineering made different types of CGTase

available and they both were more active and more specific towards production of

α-, β- or γ-cyclodextrin in highly purified state. In 1970, β-cyclodextrin (β-CD) was only

available as a rare fine chemical at a price of about US$2000 per kg. Today the annual

β-CD productions are close to 10,000 tonnes and the bulk price has lowered to about

US$ 5 per kg. The α-, β- and γ- cyclodextrins as well as several derivatives hydroxyl

propyl, methyl, maltosyl, acetyl and sulfobutyl β-cyclodextrin are produced industrially

in 1-100 tonnes. More than 100 other derivatives are available as fine chemicals and used

in various chromatographic methods and also used as potential drug carriers, stabilizers,

catalysts, etc.

27

2.5.2. Structure and properties of cyclodextrin

Cyclodextrins (α-, β- and γ-) comprises six, seven and eight glucopyranose units

in which D-glucose units are covalently linked at the carbon atoms C1 and C4. They have

a toroidal, hollow and truncated cone structure. The secondary hydroxyl groups on the

C-2 and C-3 atoms are located on the wider side of the torus, while the primary hydroxyl

groups on the C-6 are positioned on the opposite side of the torus (narrower) and are

directed away from the cavity, except if H-bonded to include guest molecules forming

inclusion complexes. The -CH groups comprising H-1, H-2 and H-4 are located on the

exterior of the molecule, while the polar sugar hydroxyl groups are oriented to the cone

exterior, and consequently the external faces are hydrophilic and provides for the aqueous

solubility of cyclodextrin. The interior of the torus offers an environment of much lower

polarity than is present in water, so it can be considered as a ‘hydrophobic cavity’, which

is lined by two rings of -CH groups (H-3 and H-5) and by a ring of glucosidic oxygen

bridge atoms, (‘ether oxygens’ (O-4 and O-5) and H-6 forms the narrower rim of

truncated cone. The amphipathic property of cyclodextrins can form soluble, reversible

inclusion complexes with water-insoluble compounds, resulting in compound

solubilization [124]. The structure of β-cyclodextrin is given figure 2.5.2 and the

properties of α-, β-, and γ-cyclodextrins are compared [124,125] in Table 2.5.2.

28

Figure 2.5.2: Structure of β-cyclodextrin.

Table 2.5.2: Properties of α-, β-, and γ- cyclodextrins

Property α-CD β-CD γ-CD

Number of glucopyranose units 6 7 8

Molecular weight (g/mol) 972 1135 1297

Solubility in water at 25○C (%, w/v) 14.5 1.85 23.2

Outer diameter (nm) 1.4-1.5 1.5-1.6 1.7-18

Cavity diameter (nm) 0.5-0.6 0.6-0.8 0.8-1.0

Height of torus (nm) 0.8 0.8 0.8

Melting onset (○C) ≈ 275 ≈ 280 ≈ 275

2.5.3. Synthesis of cyclodextrins

Cyclodextrins are produced by the treatment of CGTase and α-amylase on starch.

Initially starch is liquified by heat treatment or using α-amylase, then CGTase is added

for the enzymatic conversion. CGTases can synthesize all forms of cyclodextrins, thus

the product of the conversion results in a mixture of the three main types of cyclic

29

molecules, in ratios that are strictly dependent on the used enzyme. The poorly water

soluble β-CD (18.5 g/l) can be easily retrieved through crystallization while the more

soluble α- and γ-CDs (145 and 232 g/l respectively) are usually purified by means of

chromatographic technique [126].

2.5.4. Derivatives of β-cyclodextrin

The structure of β-CD has been modified by alkylation and hydroxyl alkylation to

improve their aqueous solubility [127,128]. The OH groups on C-2, C-3 and C-6 are

available as points of structural modification without danger of eliminating the ‘central

void’ [129]. The OH groups on C-6 are the most reactive whereas the hydroxyls at C-3

are much less reactive than those at C-2. Consequently by various molecular

manipulations, cyclodextrins can be transformed into derivatives having different

physicochemical properties [130]. Croft and Bartsch [131] and Khan et. al. [132]

reviewed the chemical methods for modifying cyclodextrin.

. The most important methylated β-cyclodextrin and 2-hydroxypropylated

β-cyclodextrin are suitable derivative due to their heterogeneous, highly water soluble

and amorphous property. Methylated β-CD is more hydrophobic than β-CD itself,

therefore, it forms a more stable (but soluble) complex with chloestrol. Its affinity to

chloestrol is so strong that it extracts cholesterol from the blood cell membranes

[133,134]. Valsartan, used in the lowering the blood pressure was prepared as inclusion

complex with β-CD and hydroxyl propyl β-CD to improve their bioavailability by

improvement in solubility [135]. Monochlorotriazinyl-β-cyclodextrin (CAVASOL W7

MCT) is the first reactive cyclodextrin derivative manufactured on an industrial scale

[136] and fixed on to cotton cellulose following a reactive dye reaction mechanism [137].

30

2.5.5. Industrial applications of cyclodextrin

Complex formation is a dimensional fit between host cavity and guest molecules

[138]. The lipophilic cavity of cyclodextrin molecules provides a microenvironment into

which appropriately sized non polar moieties can enter to form inclusion complexes

[139]. No covalent bonds are broken or formed during formation of the inclusion

complex [140]. The main driving force of complex formation is the release of enthalpy-

rich water molecules from the cavity. Water molecules are displaced by more

hydrophobic guest molecules present in the solution to attain an apolar-polar association

and decrease of cyclodextrin ring strain resulting in a more stable lower energy state

[141]. The binding of guest molecules within the host cyclodextrin is not permanent but,

rather is a dynamic equilibrium. Binding strength depends on how well the host-guest

complex fits together and on specific local interactions between surface atoms.

Inclusion in cyclodextrin exerts a profound effect on the physicochemical

properties of guest molecules as they are temporarily locked or caged within the host

cavity giving rise to beneficial modifications of guest molecules, which are not

achievable otherwise [142].

Some of the properties of guest molecules were improved like solubility

enhancement of highly insoluble guests, stabilization of labile guest against degradative

effects of oxidation, visible or UV light and heat, control of volatility and sublimation,

physical isolation of incompatible compounds, chromatographic separations, taste

modification by masking off flavours, unpleasant odours and controlled release of drugs

and flavours.

31

Cyclodextrin encapsulates each guest molecule which can lead to advantageous

changes in the chemical and physical properties of guest molecules. These characteristics

of cyclodextin or their derivatives make them suitable for application in analytical

chemistry, agriculture, food, cosmetics, pharmaceutical and textile field [124].

a) Cosmetics and toiletry

Cyclodextrin complexation of fragrance materials increase their solubility and

reduce or prevent their evaporation. Numanoglu et. al. proved that it was possible to

increase the stability and water solubility of fragrance materials linalool and benzyl

acetate [143]. The major benefits of cyclodextrin in this sector are stabilization, odour

control, and process improvement upon conversion of a liquid ingredient to a solid form,

flavour protection and flavour delivery in lipsticks, water solubility and enhanced thermal

stability of oils [144]. Cyclodextrins used in silica-based tooth pastes increase the

availability of the antimicrobial agent triclosan by complexation and resulting in an

almost threefold enhancement of triclosan availability [145]. Sunscreen agent in

cyclodextrin’s cavity limits the interaction between the UV filter and the skin, reducing

the side effects of the formulation. Similarly by incorporating cyclodextrin in

self-tanning emulsions or creams, the performance and shelf life are improved. An added

bonus is that the tan looks more natural than the yellow and reddish tinge produced by

traditional dihydroxyacetone products [146].

b) Pharmaceutical Industry

Cyclodextrins are used to suppress volatility, mask unpleasant smell and taste of

some drugs, avoid undesirable incompatibilities and also to increase stability of a drug in

the presence of light, heat and oxidizing conditions. Loftsson et. al. studies have shown

32

that the presence of water soluble drug/cyclodextrin complexes at the hydrated epithelial

surface will frequently increase the availability of dissolved drug molecules especially of

lipophilic drugs with poor aqueous solubility [147]. A novel polymeric cyclodextrin

hydrogel is used as a potential matrix release of anti-inflammatory and antifungal drug

has been investigated [148]. Hydrophilic nanogels containing CD are promising tools for

the delivery of drugs and other applications in the biomedical field [149]. The nanoscale

size of nanogels gives them a high specific surface area that is available for further

bioconjugation of active targeting agents. Bio distribution and drug release can be

modulated through size adjustments. Nagasamy et. al. studies revealed the solubility

profile of roxythromycin was significantly increased in the presence of β-cyclodextrin

[150]. Acelofenac/β-cyclodextrin dispersions were prepared to study the influence of

cyclodextrin on the solubility and dissolution rate of this poorly soluble drug. The solid

dispersion complex of drug gave a better dissolution profile as compared to pure drug and

in turn improved bioavailability [151]. Inclusion complex of ketoprofen and

β-cyclodextrin was prepared to improve dissolution profile and bioavailability of the

ketoprofen [152].

c) Food and flavour

Cyclodextrins act as molecular encapsulants, protecting the flavour throughout

many rigorous food processing methods of freezing, thawing and microwaving and

allows the flavour quality and quantity to be preserved to a greater extent and longer

period compared to other encapsulants and provides longevity to the food item.

β-cyclodextrin was used to remove cholesterol from milk and also to produce dairy

products low in cholesterol [141]. Flavour substances are stabilized with cyclodextrin to

33

avoid the loss of flavours during storage of the product or as a result of exposure to light

or oxygen; upon contact with water, the complex bound flavour substances were released

immediately. Lopez-Nicolas et. al. proved the colour preservation of fruit juice during

processing and storage [153]. Allyl isothiocyanate, a major flavour component of

mustard essential has been used as a slow release additive in

polylactide-co-polycaprolactone biopolymer film packaging. Long shelf life storage

packaging of cheese can be possible with that of the naturally derived preservative [154].

The study of oxidative stability of eugenol by inclusion with β-cyclodextrin and

2-hydroxypropyl-β-cyclodextrin and by an emulsion diffusion method with

polycaprolactone (PCL) revealed that emulsion diffusion method was more efficient than

molecular inclusion method resulting from high stability depending on storage time

[155]. Thymol, geraniol encapsulation in β-cyclodextrin and modified starch were

prepared by spray and freeze drying method. Encapsulation increased the water

solubility and protected the active compounds from oxidation [156].

d) Textile applications

Permanent fixation of cyclodextrin on different polymeric materials is another

possible use of cyclodextrin in various textile applications. Treatment of cotton fabrics

with a finishing formulation based on limonene using polymer coating methods and

Monochlorotriazinyl-β-cyclodextrin (MCT-β-CD) finished fabric, imparts toxic activity

against mosquitoes [157]. Inclusion complexes of citronella oil, citronellal and citronellol

with β-cyclodextrin are evaluated for mosquito repellent action and the highest repellent

activity was observed in the formulation which contained citronella oil & β-cyclodextrin

inclusion complex [158]. Investigation of MCT-β-CD finished cotton fabrics treated with

34

cypermethrin and prallethrin, show fast repellent action slower knockdown action and

killing action against mosquitoes [159]. The life time of the fragrance compound

(rosemary lavender, lemon and sandal wood oil) in β-cyclodextrin anchored by

heterobifunctional reactive dyes on cotton showed that fragrance was retained for longer

than 30 days [160]. Sunscreen agent octylmethoxycinnamate incorporated

monochlorotriazinyl-β-cyclodextrin grafted tencel fabric with enhanced UV screening

properties improves the resistance of the agent to washing cycles [161]. MCT-β-CD

modified cotton with aroma finishing with sandal wood oil was investigated for long

lasting fragrance. The fabric has improved tensile strength after grafting cyclodextrin

derivative [162].

Shafei et. al. produced air permeable comfortable antibacterial cotton by

application of synthesized monochlorotriazinyl-β-cyclodextrin grafted butylacrylate on

cotton fabric with epichlorohydrin and/or ZnO and which withstands the 20 washing

cycles [163]. Polyamide fibers modified with β-cyclodextrin and monochlorotriazinyl

β-cyclodextrin was imparted with antibacterial property by inclusion of quaternary

ammonium salt (3-chloro-2-hydroxypropyltrimethylammonium chloride and the treated

fabrics exhibited more heat resistance and antibacterial property [164].

Acrylamidomethylated β-cyclodextrin and monochlorotriazinyl β-cyclodextrin are

grafted separately on tencel fabric and included with hydrophobic molecules such as

fragrances, antimicrobial agents and other chemicals to produce new grafted textiles with

peculiar performance [165]. Cationic β-cyclodextrin polymer and their inclusion

complexes with butylparaben and triclosan were formed and fixed on cellulosic fabric to

impart antibacterial property. Due to strong electrostatic interaction both the polymer and

35

their inclusion complexes exhibited strong antibacterial activity [166]. The antibacterial

characteristic was imparted to cellulosic fabric by grafting of β-cyclodextrin using citric

acid as crosslinker and inclusion of silver (I) ions for the purpose of obtaining a slow

release device [167]. Miconazole nitrate incorporated antibacterial cellulosic fabric was

obtained by grafting monochlorotriazinyl-β-Cyclodextrin and the finished fabric retains

70% of antibacterial abilities even after 10 cycles of washing [168]. A novel water

soluble quarternized ammonium-β-cyclodextrin grafted chitosan was prepared for

antibacterial activity and introduction of cyclodextrin moiety with chitosan showed

higher antimicrobial activity [169]. A reactive β-cyclodextrin derivative was synthesized

by reacting β- cyclodextrin and itaconic acid and impact of the grafting of this vinyl

monomer on the performance of cotton fabric was investigated and it can be utilized for

the formation desired inclusion complex [170]. β-cyclodextrin grafted chitosan

synthesized from β-cyclodextrin citrate was investigated for their antimicrobial property

[171].

Glycidyl methacrylate/monochlorotriazinyl-β-cyclodextrin grafted cotton fabric

loaded with chlorohexidin diacetate showed good durability to antimicrobial activity after

five washings [172]. Selvam et. al. studies revealed crosslinking of synthesized sulfated

β-cyclodextrin using ethylenediaminetetraacetic acid and impregnation of silver,

titanium dioxide and zinc oxide nanoparticles for enhanced antibacterial properties

against gram negative and gram positive bacteria [173].

Surface chemical analysis of tencel and cotton treated with a

monochlorotriazinyl-β-cyclodextrin was investigated using X-ray photoelectron

spectroscopy. The bleached cotton exhibited a relatively greater fixation of the

36

cyclodextrin derivative due to greater availability of nucleophilic hydroxyl functionalities

at the fiber surface interface [174]. The permanent anchorages of MCT-β-CD on

polyester have been used to produce polyester fabric with small air permeability, a higher

hygroscopicity and a smaller breaking strength [175]. The inclusion complex of ferrocene

as a guest molecule in MCT-β-CD and their presence in cotton fabric has been studied by

infrared spectroscopy and Raman spectroscopy. Stability of the inclusion complex can be

guaranteed for long term storage at room temperature [176].

A durable antistatic property was imparted on polyester and polyester/cotton

blend fabric by chemical fixation of MCT-β-CD and chitosan by pad-dry-cure method.

The advantage of this method is that its electrical conductivity and their antistatic

property have been improved by the introduction of more number of hydroxyl groups

through cyclodextrin moiety [177]. Inclusion complex of urea phosphate with

β-cyclodextrin and MCT-β-CD and their grafting with cotton using epichlorohydrin

revealed the enhancement in thermal stability of fabric [178].

β-cyclodextrin can absorb dyes [179] and can therefore be used to reduce loss of

dye in wastewater, in addition to improved dye uniformity and preventing the running of

dyes during washing [180-182]. Dyeing of cotton polyester blends with disperses dyes

and β-CDs led to an improved dye strength and deeper dye shades [183]. Disperse dyeing

of cellulose acetate treated with β-CD showed similarly improved colour intensity as well

as the possibility of dyeing at lower temperature than conventionally used method [184].

β-CD can also act as retardant with dyes with which it can form complexes [185]. It can

replace the role of surfactants used in dyeing without the loss of dyeing quality and also

improve washing fastness in the case of nylon and cotton with reactive-disperse dyes

37

[186]. Dyeing and easy care finish can be achieved by using a formulation containing a

reactive dye, MCT-β-CD and a resin. Significant improvement of colour uniformity and

some improvements in colour depth were observed when polyacrylonitrile fibers were

dyed in the presence of β-cyclodextrin as compared to dyeing in the presence of a

commercial retardant [187].

2.6. Microorganisms

Microbes are the tiniest creatures like bacteria, fungi, algae and viruses. Bacteria

are unicellular organisms which grow very rapidly under warmth and moisture. Fungi,

molds or mildew are complex organisms with slow growth rate that stain and deteriorate

the performance properties of the fabrics. Algae belongs to either fungal or bacterial

group require continuous source of water and sun light to grow and develop darker stains

on the fabrics.

2.6.1. Classification of bacteria

Bacteria can be differentiated into two groups: 1. Gram positive bacteria 2.Gram

negative bacteria. The gram stain test was discovered in 1884 by H.C Gram to classify

bacteria based on their morphology and differential staining. In this test slides are

sequentially stained with crystal violet, iodine, then destained with alcohol and

counter-stained with safranin. Some bacteria take up gram stain, resist decolourisation

and appear violet with this stain. They are called as gram positive bacteria (Streptococcus

pyogene & Staphylococcus aureus). In some bacteria gram stain is not taken up since it is

decolorized by organic solvents. They take the counter stain and appear red. They are

called as gram negative bacteria (Escherichia coli and Pseudomonas aeruginosa). The

difference between the two groups is believed to be due to a much larger peptidoglycan

38

(cell wall) in gram positives precipitates the iodine and crystal violet in the thickened cell

wall and are not eluted by alcohol in contrast with the gram negatives where the crystal

violet is readily eluted from the cell wall of bacteria [188].

2.6.2. Structure of cell wall of gram negative and gram positive bacteria

Gram positive and negative bacteria are chiefly differentiated by their cell wall

structure. A Gram positive bacterium has a thick, multilayered cell wall consisting mainly

of peptidoglycan (150 to 500 A) surrounding the cytoplasmic membrane. The

peptidoglycan is a mesh like exoskeleton similar in function to the exoskeleton of an

insect. Unlike the exoskeleton of the insect, however, the peptidoglycan of the cell is

sufficiently porous to allow diffusion of metabolites to the plasma membrane. The

peptidoglycan is essential for the structure, for replication, and for survival in the hostile

conditions in which bacteria grow.

Gram negative cell walls are more complex than gram positive cell walls, both

structurally and chemically. Structurally, a gram negative cell wall contains two layers

external to the cytoplasmic membrane. Immediately external to the cytoplasmic

membrane is a thin peptidoglycan layer, which accounts for only 5% to 10% of the gram

negative cell wall by weight. External to the peptidoglycan layer is the outer membrane,

which is unique to gram negative bacteria. The area between the external surface of the

cytoplasmic membrane and the internal surface of the outer membrane is referred to as

the periplasmic space. This space is actually a compartment containing a variety of

hydrolytic enzymes, which are important to the cell for the breakdown of large

macromolecules for metabolism [189].

39

2.7. Antimicrobial textiles

Most textile materials are conductive to cross infection or transmission of disease

caused by microorganisms. The most trouble causing organisms are fungi and bacteria.

The growth of microorganisms on textiles can lead to functional hygienic and aesthetic

difficulties. Microbes may severely disrupt textile dyeing, printing and finishing

operations through reduction of viscosity, fermentation and mould formation. As

microbes often attack the additives applied to textiles, discoloration and loss of the

textiles functional properties such as elasticity or tensile strength can also occur. Many

times the problem can be solved by proper sterilization, but treatment of the fabric with

an antimicrobial agent is an approach that has proven successful. Antimicrobial treatment

should protect not only wearer of the textile material but also the textile itself from the

bio deterioration caused by mold, mildew and rot producing fungi [190].

40

Antimicrobial textiles have been in use for many years. During World War II,

cotton tents, tarpaulins and vehicle covers are needed to be protected from rotting caused

by microbial attack. They were treated with mixtures of chlorinated waxes, copper and

antimony salts that stiffened the fabrics and gave them a peculiar odour. After World War

II and mid to late 1950’s cotton fabrics are protected by using 8-hydroxyquinoline salts,

copper naphthenate, copper ammonium fluoride and chlorinated phenols and they are

replaced later based on the environmental and work hazards. Later chemical

modification of cotton by acetylation and cyanoethylation had limited industry

acceptance because of relatively high cost and loss of fabric strength in processing. The

inherent growth in the field of man-made fibers such as nylon, acrylics and polyester,

which has natural resistance to microbial decomposition replaced cotton in many

industrial fabrics [190].

2.7.1. Conditions for antimicrobial finishing of textile

� Durable to washing, dry cleaning and hot pressing

� Selective destroy of undesirable microorganism

� Should preferably be compatible with textile chemical processes such as dyeing

be cost effective and not produce harmful effects to the manufacturer, user and

the environment

� Easy method of application

� No deterioration effect on fabric quality

� Should meet standards in compatibility tests such as cytotoxicity, and irritation

� Should not negatively affect the quality or appearance of the textile

41

Antibacterial finished textile should satisfy certain requirements to obtain maximum

benefits [191,192].

2.7.2. Methods of application of antimicrobial agents

Antimicrobial agents can be added into the polymer prior to extrusion or blended

into the fibers during the formation synthetic fibers. In natural fibers exhaust, pad-dry

cure, coating, spray foam technique and some more methods which improve durability of

finish such as insolubilization of the active substances, treating the fiber with resin,

condensates or crosslinking agent, microencapsulation of antimicrobial agent, coating the

fiber surface, chemical modification of fiber by covalent bond formation, and use of graft

polymers, homopolymers on to the fiber.

Triclosan has been used for antibacterial finishing of natural and synthetic fibers

by conventional pad dry and exhaust method [193]. Silicone based quarternary agents are

preferably applied using padding, spraying and foam finishing methods [194]. Many

more methods such as use of nanosized colloidal solutions [195], nanoscale shell core

particles [196,197], crosslinking of active agents onto fiber using a crosslinker [198,199]

covalent bond formation [200] and polymer grafting [201] are recently adapted in

antibacterial finishing of textiles.

2.7.3. Antimicrobial agents

Many antimicrobial agents used in the textile industry are from the known food

stuff and cosmetic sector. These substances are incorporated with textile substrate

comparatively at lower concentrations. It must be ensured that these substances are not

42

only permanently effective but also that they are compatible with skin and the

environment.

Many heavy metals are toxic to microbes at very low concentrations either in the

free state or in compounds. Cotton has been pretreated with succinic acid anhydride,

which acted as ligand for metal ions to enhance the subsequent adsorption of metallic

salts and to provide antibacterial activity [202]. Quarternary ammonium compounds carry

a positive charge at the nitrogen atom in solution and inflict a variety of detrimental

effects on microbes. The attachment of quarternary ammonium to a textile substrate is

believed to be predominantly by ionic interaction between the cationic quaternary

ammonium salt and anionic fiber surface [203, 204]. Polyhexamethylene biguanides is

cationic in nature; therefore the attachment to cotton is believed to be through ionic as

well as hydrogen bonding [205]. Triclosan (2, 4, 4’-trichloro-2’-hydroxydiphenyl ether) is

a broad spectrum antimicrobial agent with minimum inhibitory concentration (MIC) of

less than 10ppm against many common bacterial species [206]. Triclosan breaks down

into 2, 8-dichlorodibenzo-p-dioxin [207,208] a toxic chemical when exposed to sunlight.

Therefore owing to such health and environmental issues, a number of leading retailers as

well as governments in Europe are concerned about or have banned the “unnecessary

use” of triclosan in textiles and some other products [209,210]. Chitosan is the

deacetylated derivative of chitin which is the main component of the shells of crustaceans

and it has a MIC of 0.05%-0.1 % (w/v) against many common bacterial species. This

antimicrobial ability, coupled with non-toxicity, biodegradability and biocompatibility is

facilitating chitosan emerging applications in textiles [211]. N-halamine compounds are

broad spectrum disinfectant and in deactivating a microorganism, the N-halamine bond is

43

reversibly reacted to N-H and the inactive substance can be recharged with chlorine in a

bleaching solution. This regenerable approach was first proposed and demonstrated for

the treatment of cotton by Sun and Xu [212]. Peroxyacids are also alternative regenerable

antimicrobial agents used in hospitals [213]. Butanetetracarboxylic acid or citric acid

onto cotton fabrics in a pad-dry-cure process exhibit antibacterial property [214]. Some

synthetic dyes are capable of exhibiting antibacterial property. Sulphanilamidodiazonium

chloride derivatives with indan-1,3-dione, gave excellent dyeing and antimicrobial results

on wool and nylon [215]. Some natural dyes have also been examined for antimicrobial

ability. Curcumin a common dye used for fabric and food coloration [216] a dye isolated

from Quercus infectoria [217] and the colorant Berberine, which contain the quarternary

ammonium group all exhibit durable antimicrobial efficacy when attached to textile

[218]. Recently naturally occurring essential oils and their chief constituents are used as

antimicrobial agents. Thymol (5-methyl-2-(1-methylethyl) phenol) is a monoterpene

present in certain Lamiaceae families, specially oreganos and thymes. It is frequently

used as flavour, but they are also becoming increasingly important naturally occurring

antimicrobial, antioxidant and antiseptic agents [219]. Eugenol (4-allyl-2-

methoxyphenol), a major component from clove oil (Eugenia caryophyllata, Myrtaceae)

has been widely used as a fragrant and flavouring agent in a variety of food, cosmetic

products and also as antibacterial agents [220]. Lemon grass oil, citronella essential oil

microcapsules impregnated cotton fabric were made for antimicrobial and mosquito

repellent cotton textiles [221,222]. With the advent of nanotechnology, metal and metal

oxide nanoparticle have tremendous application in antimicrobial finishing of textiles

[223-226].

44

2.7.4. Types of antimicrobial agents

Antimicrobial agents are classified into two types such as leaching type and

non-leaching type. In leaching type, products migrate from the garments forming a sphere

of activity (zone of inhibition) and microbes that come in the sphere are destroyed.

However in due course of time the potency decreases and thus it just hurts the microbes

giving them a chance to mutate and become resistant, increasing the risk of developing

super bugs. In non leaching type, products do not migrate from the garments and destroy

the microbes coming in contact with the surface of the garment. The microbes are not

consuming the antimicrobials as they act on the cell membrane by mechanically

interrupting them. The antimicrobial agent acts as sword and therefore do not lose its

effectiveness, when the finish is permanent and remains functional throughout the life of

the substrate and also withstand more number of laundry washing process [227].

2.7.5. Mode of antimicrobial action

A living microbe like bacterium, fungus typically has an outermost cell wall

which is mainly composed of polysaccharides. This cell wall maintains the integrity of

cellular components and shields the cell from the extracellular environment. Immediately

beneath the cell wall is a semipermeable membrane which encloses intracellular

organelles and a myriad of enzymes and nucleic acids store all the genetic information of

the organism. The survival or growth of microorganism depends on the integrity of the

cell and the concerted action and proper state of all of these components. Antimicrobial

agents either inhibit the growth (bacteriostatic) or kill (bactericidal) the microorganism.

Almost all the antimicrobial agents used in commercial textiles are biocides. They

45

damage the cell wall or alter the cell membrane permeability, denature proteins, inhibit

enzyme activity or inhibit lipid synthesis, all of which are essential for cell survival [228].

2.7.6. Methods of evaluation of antibacterial activity

The antibacterial activity can be evaluated by different test methods to know the

effectiveness of antibacterial activity. Some of the tests are ;

� Agar diffusion test

� Challenge test

� Soil burial test

� Humidity chamber test

� Fouling test

Agar diffusion test is a preliminary test to detect the diffusive antimicrobial finish.

It is not suitable for non-diffusive finishes and textile materials other than fabrics. In this

test one species of bacteria is uniformly swabbed onto a nutrient agar. During incubation,

the chemical diffuses from the disk containing the agent into the surrounding agar. An

effective agent will inhibit bacterial growth, and measurements can be made to quantify

the size of the zones of inhibition around the disks. The relative effectiveness of a

compound is determined by comparing the diameter of the zone of inhibition with the

values in a standard table [229].

In challenge test, specimens of the test material were shaken in a known

concentration of bacterial suspension and the reduction in the bacterial activity in

standard time is measured. The efficiency of the antimicrobial treatment is determined by

46

comparing the reduction in bacterial concentration of the treated sample with that of

control sample expressed as a percentage reduction in standard time [230]. In soil burial

test, the samples are buried upto 28 days. It is the most severe long term expensive test.

The loss of tensile strength or weight is compared with control sample for evaluation.

Most of the control samples must rot in about 7 days [231].

2.7.7. Benefits of antimicrobial textiles

Initially, antibacterial finishing was done with an objective to protect defense

textiles, technical textiles, uniforms and tents from being affected by microbes

particularly fungi. Novel technologies in antimicrobial finishing are successfully

employed in non-woven sector especially in medical textiles. Bioactive fiber is a

modified form of finish, which includes chemotherapeutics in their structure (synthetic

drugs of bactericidal and fungicidal qualities) which are not only used in medicine and

health prophylaxis applications, but also for manufacturing textile products of daily use

and technical textiles.

47

2.8. Aim and scope of present investigation

The present work is aimed at improvement of durability and activity of the

imparted antibacterial agent on organic cotton by eco-friendly strategies such as

biopolishing and grafting of β-cyclodextrin (β-CD) and monochlorotriazinyl-β-

cyclodextrin (MCT-β-CD).

The scope of this work is to impart durable antibacterial activity on organic cotton

using β-CD and MCT-β-CD with various antibacterial agents. The biopolishing is done

for organic cotton, with an aim to enhance the fixation yield of cyclodextrin on fabric. An

eco-friendly biopolishing process together with β-CD grafting using non-toxic citric acid

as crosslinker and covalent bonding of reactive monochlorotriazinyl-β-cyclodextrin is

aimed at an environmentally benign way in functional finishing of organic cotton.

Durable antibacterial organic cotton fabric is fabricated by incorporation of

thymol, eugenol, limonene, silver, copper and zinc ions into biopolished cyclodextrin and

MCT-β-CD finished textile. The antibacterial agent loaded organic cotton fabric and the

active core materials are characterized by UV-Vis and FTIR spectrophotometric analysis.

The changes in the surface morphology and the introduction of new functionalities are

evaluated by SEM and EDAX analysis. HPLC and AAS techniques are utilized to

estimate the quantity of active core agents on fabric. The XRD and TGA analysis brings

about changes in crystallinity and thermal stability of fabric upon functionalization with

β-CD, MCT-β-CD and antibacterial agents. The antibacterial efficacy of the active core

agent as well as their durability upon repeated washing cycles is qualitatively assessed by

agar disc diffusion test against gram positive (E.coli) and gram negative (S.aureus)

bacteria.

48

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