**2.3 Photochromic dyes**

Photochromic dyes change its chemical structure due to UV rays. Photochromic effect was first time seen on the tetracene and after that it was observed in potassium salt of dinitomethane [43]. In 1960 first photochromic spiropyrans was developed using printing technique by Ksnebo ltd, Japan. In 1998, photochromic dyes were first time used in textiles to produce camouflage effect. Photochromic dyes also decolorise. This decolourisation is called negative photochromism [44]. Various metal oxides, alkaline earth metal sulphides come under the category of Photochromic dyes. Photochromic dyes are water insoluble hence cannot be applied on wool and cotton [45]. Presently Researches are also going on Water-soluble photochromic dyes. These dyes are relatively cheaper option for textiles and leather. Spirooxazine-based Water-soluble photochromic dyes having sulphonate group have been developed. Sulphonate gp impart water solubility. These water-soluble photochromic dyes are mainly for proteins fibres [46]. The wash fastness and photostability of these dyes are moderate [47].

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packaging [63].

*Application of Smart and Functional Dyes in Textiles DOI: http://dx.doi.org/10.5772/intechopen.96045*

temperature raised to 60 o

kept to 1:50. The fabric is dyed at 120 o

this method the fabric is dried at 80 o

**2.4 Chemo chromic dyes**

**2.5 Solvatochromic dyes**

tion of photochromic colourants [55–57].

was done to reduce the temperature to 70 <sup>o</sup>

tell the intensity of UV rays to get protection accordingly [53].

(250 g) and aqueous acetic acid. The dyeing was started at 40o

C and then to 90 <sup>o</sup>

Application of photochromic dyes can be done on the window curtains and facades. This would be helpful to control sunlight [48]. Heat sensitive photochromic dyes also used as temperature indicator [49, 50]. Dupont company are also working on the camouflaging property of these photochromic dyes to develop camouflaging clothing for armies [51, 52]. Flexible UV sensors based on Photochromic dyes also change its colour due to UV rays which makes a UV detective fabric which help to

Different application methods have been reported to apply Photochromic dyes and pigments. In a study exhaust method (direct Coloration), photochromic colourants were used with auxiliaries such as dispersing agent and ceramic balls

Photochromic colourants as disperse dyes has also been used to dye polyester using exhaust dyeing technique. Photochromic colourants are insoluble in water therefore organic solvents such as Acetone is used to dissolve the photochromic colourant. After dissolution of colourant, dispersing agent is added. Acetic acid is also used to maintain the weak acidity (4.5) of solution. This weak acidity helps to minimise the degradation of colourant. The material to liquor ratio of solution was

tained for 20 minutes with in the solution of sodium hydroxide, sodium dithionite

Photochromic colourants can also be applied through pad dry cure method. In

of curing temperature for 3 minutes. Microencapsulation was also used for applica-

Chemo chromic dyes change its colour due to differences in pH. Phthalides, fluoranes, triarymethines, and simple azo dyes are the examples of pH sensitive dyes [58]. Conventional exhaust dyeing, solgel method as well as prior addition to electrospinning solution has been reported as methods of application for chemo chromic dyes. Chemo chromic dyes can be used in identify the proteins (of certain microbes) with change of colour. This identification with changing colour indicates the presence of microbes in textiles [59]. Therefore, Application area of Chemo

Solvatochromic dyes work on the principle of Solvatochromism which corresponds to reversible changes of colour due to solvent polarity. The change in colour is occurred due to shifting in maximum absorption of different solvents [61]. There are two types of solvato chromism i.e. positive solvatochromism and negative solvatochromism. Positive solvatochromism corresponds to a hypsochromic shift induced by a decrease of solvent polarity" and "negative solvatochromism corresponds to a hypsochromic shift induced by an increase of solvent polarity" [62]. Common example Solvatochromic dyes are pyridinium, merocyanine, and stilbazolium dyes. Solvatochormic dyes can be applied in the textiles using microencapsulation technique. Assembly of microsphere on fabric causes colour change on drying and wetting of the fabric. Application of Solvatochromic dyes in textiles is very limited. These dyes can be used to identify the stale or toxic food due to colour change of

and a non-ionic surfactant. Material to liquor ratio was maintained to 1:30.

chromic dyes can be widened to medical textiles bandages [60].

C [54].

C. This 70 o

C for 45 min. Further, rinsing in cold water

C for 2 minutes in hot air, followed by 140°C

C temperature was main-

C temperature and

*Application of Smart and Functional Dyes in Textiles DOI: http://dx.doi.org/10.5772/intechopen.96045*

*Dyes and Pigments - Novel Applications and Waste Treatment*

systems perhaps occur due to equilibrium between molecular species like acid–base, keto-enol, lactim-lactam, stereoisomers or between different crystal structures [33]. Among inorganic thermochromic substances, few examples of metal oxides are known such as indium oxide, zinc oxide, chromium hemitrioxide-alum earth [34]. Application of thermochromic dye on textile can be done using 3 methods which can be used exhaust, continuous method, microencapsulation and printing. In exhaust method thermochromic pigment are applied on to textile with a cationic agent, non-ionic dispersing agent and binder using Material to liquor ratio 1:30

 C temperature for half hour [35]. In continuous method thermochromic dye, cationic and non-ionic dispersing levelling agent are applied with acrylic soft binder solution. This solution is applied on textiles through pad dry cure machine. Drying of samples is generally done at 80°C for 3 min while curing is done at 140°C for 2 to 3 minutes [36]. In microencapsulation method, microcapsules were created using colourless dye, precursor and colour developer [37]. These materials melt and solidifies with respective to the application of heat and cold. On melting these material changes its colour, while on solidification come back to its original colour. Various novel colour effects as well as camouflage designs can be produced using combination of thermochromic, non-thermochromic and mixture of both on the conductive cotton [38]. These thermochromic dyes can take heat from there nearby environment such as sun rays and cause a reversible change in the colour of textiles. These dyes are also establishing their presence in the field of Protective clothing for military [39]. Protective clothing using thermochromic colourant can mimic the colour of its surrounding environment with the change in temperature. Even sometimes colour can change with body temperature. Thermochromic dyes on textiles also used to protect a brand from fake imitation [40]. Microparticles (made of thermochromic and photophoresent dyes) and binder are used to make the brand logo. These logos can be temporary and permanent based on the binder used. The logo made up of thermochromic dye change colour with body temperature [41]. Thermoregulation is also a very imp application of thermochromic dye which is based on heat absorbance (in case of dark colours) and reflectance (in case of light colours). A suitable example of this phenomenon is coating of thermochromic dyes on firemen's uniform on high temperature. The Colour of uniform will be converted to white colour which reflect the heat. Thermochromic dyes can also do thermoregulation via expanding or shrinking the textiles fibre. This Shrinking and expanding of fibres in a fabric causes opening or closing of pores which help regulate the

passage of air to the body according to external environment [42].

photostability of these dyes are moderate [47].

Photochromic dyes change its chemical structure due to UV rays. Photochromic effect was first time seen on the tetracene and after that it was observed in potassium salt of dinitomethane [43]. In 1960 first photochromic spiropyrans was developed using printing technique by Ksnebo ltd, Japan. In 1998, photochromic dyes were first time used in textiles to produce camouflage effect. Photochromic dyes also decolorise. This decolourisation is called negative photochromism [44]. Various metal oxides, alkaline earth metal sulphides come under the category of Photochromic dyes. Photochromic dyes are water insoluble hence cannot be applied on wool and cotton [45]. Presently Researches are also going on Water-soluble photochromic dyes. These dyes are relatively cheaper option for textiles and leather. Spirooxazine-based Water-soluble photochromic dyes having sulphonate group have been developed. Sulphonate gp impart water solubility. These water-soluble photochromic dyes are mainly for proteins fibres [46]. The wash fastness and

**102**

**2.3 Photochromic dyes**

at 70 o

Application of photochromic dyes can be done on the window curtains and facades. This would be helpful to control sunlight [48]. Heat sensitive photochromic dyes also used as temperature indicator [49, 50]. Dupont company are also working on the camouflaging property of these photochromic dyes to develop camouflaging clothing for armies [51, 52]. Flexible UV sensors based on Photochromic dyes also change its colour due to UV rays which makes a UV detective fabric which help to tell the intensity of UV rays to get protection accordingly [53].

Different application methods have been reported to apply Photochromic dyes and pigments. In a study exhaust method (direct Coloration), photochromic colourants were used with auxiliaries such as dispersing agent and ceramic balls (250 g) and aqueous acetic acid. The dyeing was started at 40o C temperature and temperature raised to 60 o C and then to 90 <sup>o</sup> C [54].

Photochromic colourants as disperse dyes has also been used to dye polyester using exhaust dyeing technique. Photochromic colourants are insoluble in water therefore organic solvents such as Acetone is used to dissolve the photochromic colourant. After dissolution of colourant, dispersing agent is added. Acetic acid is also used to maintain the weak acidity (4.5) of solution. This weak acidity helps to minimise the degradation of colourant. The material to liquor ratio of solution was kept to 1:50. The fabric is dyed at 120 o C for 45 min. Further, rinsing in cold water was done to reduce the temperature to 70 <sup>o</sup> C. This 70 o C temperature was maintained for 20 minutes with in the solution of sodium hydroxide, sodium dithionite and a non-ionic surfactant. Material to liquor ratio was maintained to 1:30.

Photochromic colourants can also be applied through pad dry cure method. In this method the fabric is dried at 80 o C for 2 minutes in hot air, followed by 140°C of curing temperature for 3 minutes. Microencapsulation was also used for application of photochromic colourants [55–57].

#### **2.4 Chemo chromic dyes**

Chemo chromic dyes change its colour due to differences in pH. Phthalides, fluoranes, triarymethines, and simple azo dyes are the examples of pH sensitive dyes [58].

Conventional exhaust dyeing, solgel method as well as prior addition to electrospinning solution has been reported as methods of application for chemo chromic dyes. Chemo chromic dyes can be used in identify the proteins (of certain microbes) with change of colour. This identification with changing colour indicates the presence of microbes in textiles [59]. Therefore, Application area of Chemo chromic dyes can be widened to medical textiles bandages [60].

#### **2.5 Solvatochromic dyes**

Solvatochromic dyes work on the principle of Solvatochromism which corresponds to reversible changes of colour due to solvent polarity. The change in colour is occurred due to shifting in maximum absorption of different solvents [61]. There are two types of solvato chromism i.e. positive solvatochromism and negative solvatochromism. Positive solvatochromism corresponds to a hypsochromic shift induced by a decrease of solvent polarity" and "negative solvatochromism corresponds to a hypsochromic shift induced by an increase of solvent polarity" [62]. Common example Solvatochromic dyes are pyridinium, merocyanine, and stilbazolium dyes. Solvatochormic dyes can be applied in the textiles using microencapsulation technique. Assembly of microsphere on fabric causes colour change on drying and wetting of the fabric. Application of Solvatochromic dyes in textiles is very limited. These dyes can be used to identify the stale or toxic food due to colour change of packaging [63].


#### *Dyes and Pigments - Novel Applications and Waste Treatment*

#### **Table 1.**

*Types of smart dyes used in textile industry.*

### **2.6 Mechanochromic dyes**

Mechanachromism is a phenomenon in which a polymer changes it colour due to deformation such as elongation and compression. Elongation and compression occur due to the change in pH, temperature. Mechanachromic dyes are the organic dyes which is applied on polymer and causes changes in colour due to certain mechanical pressure. Mechanochormic dye cannot act alone it require a polymer (material) because only polymer can deform (elongate or compress). In a study 1,4-bis (R-cyano-4- methoxystyryl)-2,5-dimethoxybenzene9 (C1-RG, F) has been incorporated in polyethylene using melt processing technique [64]. In another research mechanochromic polymers have been developed by incorporating a dye filled microcapsules [65]. In a study Polydiacetylenes (PDA) was synthesised by thermal polymerisation of diphenyl sulphide containing bisdiacetylene. It is reported in that study that PDA changes its colour from blue to red due to elongation and compression. In the cool (non-extended state) form, the material has a

**105**

of phenolic compounds [74–78].

*Application of Smart and Functional Dyes in Textiles DOI: http://dx.doi.org/10.5772/intechopen.96045*

can change colour due to deformation (**Table 1**).

nature. Types functional dyes are as follows:

**3.1 Antimicrobial/antibacterial dye**

**3. Types of functional dyes**

particular colour, this particular colour changes due to mechanical abrasion which causes heating of surface. Mechanochromic colourants can be physically dispersed in form of supramolecular aggregates in a matrix in a polymer. Covalent insertion of chromophoric units into the macromolecule backbone or side chains has also been used to apply mechanochromic colourants [66]. Application area of mechanochromic dyes can be done in footwear and shaped garment industry in which product

Functional groups like -OH, -NH2, − COOH of dyes offer various functional properties when applied onto the textile [67]. Both natural and synthetic dyes can perform various functions after application on textiles. Now days more emphasise is being given to the green and sustainable functional dyes which directly comes from

Microbes and bacteria cause several kinds of dermal infection, body odour and several other severe health issue [68]. Antimicrobial dyes provide the protection from variety of micro-organisms like gram-positive bacteria such as *Staphylococcus aureus, Streptococcus epidermidis and Bacillus cereus* and gram-negative bacteria such as *Escherichia coli, Klebsiella pneumonia, Shigella flexneri and Proteus vulgaris* and other microbes [69]. A large no. of antimicrobial dyes possesses antimicrobial activity against human pathogen but very few have been reported for textiles. Number of researches have been conducting to find out the antimicrobial properties in various synthetic and natural dyes. Various studies reported that synthetic dyes such as direct, cationic, reactive and disperse dyes provides antimicrobial property to the fabric after dyeing. In a study it was found that Direct Blue 168 dye and copper sulphate as mordanting agent incorporate antimicrobial properties in the acrylic fabric [70]. Similarly, antimicrobial dyes based on azo heterocyclic and/or homocyclic Systems also have biocidal behaviour [71]. Multifunctional antimicrobial dyes have also been developed by adding a functional gp (quaternary ammonium salt group) to a traditional aminoanthraquinoid dye [72]. Most research has been focused on polycationic systems that are more supple for modification. Reactive dyes form homopolar bonds with textile substrates. The synthesised thiazolidinone derivatives exhibiting antimicrobial properties. Synthesised monoazo disperse dyes showed better results against gram positive as well as gram negative bacteria [73]. Application of natural dyes on textiles also offer antimicrobial textiles. Phenolic compounds such as anthraquinones, flavonoids, tannins, naphthoquinones and others in natural dyes are responsible for the antimicrobial activity. When these phenolic compounds reacted with textiles, formation of complex form. This complex hinders (bacteriostatic) or kill (bactericidal) the enzyme production in microbes. At present more emphasis is being given to antimicrobial activity of natural dye due to various environmental concern. From various studies it was found that natural dyes extracted from Pomegranate (*Punica granatum)* peels, Henna (*Lawsonia inermis*) leaves, *M. composita* leaves, Madder (*Rubia tinctorium*) root, safflower, *Rumex maritimus (*Golden dock*)*, *Indigo (Quercus infectoria) leaves,* Berberine provides antimicrobial properties to the fabric. Application of Natural dyes such as peony, clove, *Coptis chinensis* (Chinese goldthread) and gallnut on fabric also provides protection against *Staphylococcus aureus* due to presence

chromophoric units

*Application of Smart and Functional Dyes in Textiles DOI: http://dx.doi.org/10.5772/intechopen.96045*

particular colour, this particular colour changes due to mechanical abrasion which causes heating of surface. Mechanochromic colourants can be physically dispersed in form of supramolecular aggregates in a matrix in a polymer. Covalent insertion of chromophoric units into the macromolecule backbone or side chains has also been used to apply mechanochromic colourants [66]. Application area of mechanochromic dyes can be done in footwear and shaped garment industry in which product can change colour due to deformation (**Table 1**).
