**4. Classification of natural dyes/ colouants**

Natural dyes can be classified (Gulrajani & Gupta, 1992) in a number of ways. The earliest classification was according to alphabetical order or according to the botanical names. Later, it was classified in various ways, e.g. on the basis of hue, chemical constitution, application class etc.


Dyeing of Textiles with Natural Dyes 33

e. Natural dyes can also be classified on the basis of their chemical constitution (Dedhia,

i. Indigoid dyes: Indigo and tyrian purple are the most common examples of this class. Another blue dye, woad also possesses indigo as the main dyeing

ii. Anthraquinone dyes: Almost all the red natural dyes are based on the anthraquinoid structure having both plant and mineral origin. Madder, lacs, kermes, cochineal are some of the dyes possess this type of structure. These are

iii. Alphanaphthoquinones: Typical example of this class is lawsone (henna), cultivated mainly in India and Egypt. Another similar dye is juglone, obtained from the shells of unripe walnuts. These dyes are generally disperse dyes and give

iv. Flavonoids, which yield yellow dyes can be classified under flavones, isoflavones, aurones and chalcones. Flavones are colourless organic compounds. Most of the natural yellows are derivatives of hydroxyl and methoxy substituted flavones and isoflavones. Common example is weld (containing luteolin pigment) giving

v. Di-hydropyrans: Closely related in chemical structure to the flavones are substituted di- hydropyrans, *viz.* haematin and its leuco form, haematoxylin. These are important natural dyes for dark shades on silk, wool and cotton. Logwood,

vi. Anthocyanidins: The naturally occurring member of this class includes carajurin, a direct orange dye for wool and cotton. It is obtained from the leaves of bignonia

vii. Carotenoids: The class name carotene is derived from the orange pigment found in carrots. In these, the colour is due to the presence of long conjugated double bonds.

i. **Mordant dyes** are dyestuffs which require a mordant in their application as they have no affinity for the fiber being dyed. A mordant dye should have electron donating groups capable of forming a complex with the transition metal salt, e.g.,

ii. **Vat dyes** are water insoluble dyes which are first converted to their water soluble form (reducing with Na- hydrosulphite and then solubilising it with alkali) and then applied to the fibres. The true colour is produced only on oxidation followed

iii. **Direct dyes** are those dyes that have tremendous affinity for the cellulosic fibres. They are dyed from a boiling dye bath. Turmeric, harda, pomegranate rind etc*.* are

iv. **Acid dyes** are applied from an acidic medium. The dye molecules have either sulphonic or carboxylic group (s) which can form an electrovalent bond with amino groups of wool and silk. An after treatment with tannic acid known as back

v. **Disperse dye** has a relatively low molecular mass, low solubility and no strong solubilizing groups. Disperse dyes can be applied on to hydrophobic synthetic fibre from neutral to mildly acidic pH. They can also be applied to silk and wool. These

tanning improves the fastness of these type of dyes, *e.g.,* saffron.

f. Another method of classifying natural dye is on the basis of the method of application

1998).

component.

generally mordant dyes.

brilliant and fast colours on both wool and silk.

brazil wood and sappan-wood are the common example.

madder, fustic, persian, berries, kermes, cochineal etc.

by treatment with a hot soap solution, *e.g.*, indigo.

the few of the direct natural dyes.

shades of orange.

chica.

(Gulrajani & Gupta, 1992).


Table 1. Showing the number of natural dyes in each hue as per the colour index.

On the basis of hues, natural dyes can be classified as follows:



Table 2. Showing some common natural dyestuffs obtained from different vegetable origin.

Mineral origin colourants are derived from specific mineral natural source or so-called mineral colours are produced from purified inorganic compounds. Some of the important mineral colourants are chrome-yellow, iron-buff, narkin-yellow, Prussian-blue and manganese brown. Animal origin lac, cochineal and kermes have been the principal natural dyes yielding from the insects.

i. Red colour dyes: most red dyes are hidden in roots or barks of plants or camouflaged in the bodies of dull grey insects. They are almost invariably based on anthraquinone and its derivatives. These dyes are stable to light and washing. ii. Yellow colour dyes: Yellow is the liveliest and perhaps the most abundant of all hues in nature. About 90% of the yellow dyes are flavonoids. Generally, they produce pale shade with quicker fading except turmeric, which produce dull deep shade but considered to be susceptible to light as they emit fluorescence. Wash fastness rating of natural yellow dyes ranges from fair to excellent, e.g., tesu,

iii. Blue colour dyes are indigo and woad, give excellent fastness to light and washing. iv. Black colour dyes: Black shades, generally obtained from tannin rich plant natural dyes and appreciably substantive towards cellulosic and protein fibre, imparts good overall fastness properties. Examples – logwood, harda, custard

d. On the basis of origin, natural dyes are broadly classified into three categories: vegetable, mineral and animal origin. About 500 vegetable origin dyes, colouring matter derived from root, leaf, bark, trunk or fruit of plants, are as follows in

Bark/ Branches Purple bark, Sappan wood, Shillicorai, Khair, Red, Sandalwood Leaf Indigo, Henna, Eucalyptus, Tea, Cardamon, Coral Jasmine,

Table 2. Showing some common natural dyestuffs obtained from different vegetable origin. Mineral origin colourants are derived from specific mineral natural source or so-called mineral colours are produced from purified inorganic compounds. Some of the important mineral colourants are chrome-yellow, iron-buff, narkin-yellow, Prussian-blue and manganese brown. Animal origin lac, cochineal and kermes have been the principal natural

Fruits/Seeds Latkan, Pomegranate rind, Beetle nut, Myrobolan (Harda)

Root Turmeric, Madder (Manjistha), Onions, Beet-root

Lemon Grass Flowers (Petals) Marigold, Dahlia, Tesu, Kusum

**CI Natural No. of Dyes Percent**  Yellow 28 30.4 Orange 6 6.5 Red 32 34.8 Blue 3 3.3 Green 5 5.5 Brown 12 13 Black 6 6.5 Table 1. Showing the number of natural dyes in each hue as per the colour index.

On the basis of hues, natural dyes can be classified as follows:

turmeric, kapila.

apple etc.

**Part of the Plants Dyestuffs** 

dyes yielding from the insects.

table-2

	- i. Indigoid dyes: Indigo and tyrian purple are the most common examples of this class. Another blue dye, woad also possesses indigo as the main dyeing component.
	- ii. Anthraquinone dyes: Almost all the red natural dyes are based on the anthraquinoid structure having both plant and mineral origin. Madder, lacs, kermes, cochineal are some of the dyes possess this type of structure. These are generally mordant dyes.
	- iii. Alphanaphthoquinones: Typical example of this class is lawsone (henna), cultivated mainly in India and Egypt. Another similar dye is juglone, obtained from the shells of unripe walnuts. These dyes are generally disperse dyes and give shades of orange.
	- iv. Flavonoids, which yield yellow dyes can be classified under flavones, isoflavones, aurones and chalcones. Flavones are colourless organic compounds. Most of the natural yellows are derivatives of hydroxyl and methoxy substituted flavones and isoflavones. Common example is weld (containing luteolin pigment) giving brilliant and fast colours on both wool and silk.
	- v. Di-hydropyrans: Closely related in chemical structure to the flavones are substituted di- hydropyrans, *viz.* haematin and its leuco form, haematoxylin. These are important natural dyes for dark shades on silk, wool and cotton. Logwood, brazil wood and sappan-wood are the common example.
	- vi. Anthocyanidins: The naturally occurring member of this class includes carajurin, a direct orange dye for wool and cotton. It is obtained from the leaves of bignonia chica.
	- vii. Carotenoids: The class name carotene is derived from the orange pigment found in carrots. In these, the colour is due to the presence of long conjugated double bonds.
	- i. **Mordant dyes** are dyestuffs which require a mordant in their application as they have no affinity for the fiber being dyed. A mordant dye should have electron donating groups capable of forming a complex with the transition metal salt, e.g., madder, fustic, persian, berries, kermes, cochineal etc.
	- ii. **Vat dyes** are water insoluble dyes which are first converted to their water soluble form (reducing with Na- hydrosulphite and then solubilising it with alkali) and then applied to the fibres. The true colour is produced only on oxidation followed by treatment with a hot soap solution, *e.g.*, indigo.
	- iii. **Direct dyes** are those dyes that have tremendous affinity for the cellulosic fibres. They are dyed from a boiling dye bath. Turmeric, harda, pomegranate rind etc*.* are the few of the direct natural dyes.
	- iv. **Acid dyes** are applied from an acidic medium. The dye molecules have either sulphonic or carboxylic group (s) which can form an electrovalent bond with amino groups of wool and silk. An after treatment with tannic acid known as back tanning improves the fastness of these type of dyes, *e.g.,* saffron.
	- v. **Disperse dye** has a relatively low molecular mass, low solubility and no strong solubilizing groups. Disperse dyes can be applied on to hydrophobic synthetic fibre from neutral to mildly acidic pH. They can also be applied to silk and wool. These

2011):

coloured aqueous extract of mariegold.

jack fruit wood having pH 11.

pH 4.5 and MLR 1:20.

Dyeing of Textiles with Natural Dyes 35

Many scientists have reported the optimized process of extraction of natural dyes from source. Colour from leaves of eucalyptus hybrid, seeds of cassia tora and grewia optiva are extracted by using aqueous medium under varying conditions (Dayal & Dobhal, 2001). Natural dyes are extracted from biomass products namely cutch, ratanjot, madder (Khan et al, 2006) and from hinjal, jujube bark (Maulik & Pradhan, 2005) in aqueous medium. An attempt has been made to extract natural dye from the coffee-seed for its application in dyeing textiles like cotton and silk (Teli & Paul, 2006). Grey jute fabric is dyed with extracts from deodar leaf (Pan et al, 2003) jackfruit wood and eucalyptus leaf by soaking it soft water and boiling it for 4 hours separately. Extraction (Verma & Gupta, 1995) of natural dyes is also reported from overnight soaked wattle bark in distilled water followed by boiled it in pressure vessel and filtered it to obtain a residual dye powder of about 15 to 20 % (w/w) of the bark. Colours are extracted from marie gold and chrysanthemum flowers by boiling the dry petals with acidified or salt water and reported it to be the best (Deo & Paul, 2000; Sarkar et al 2005 & 2006; Saxena et al, 2001). Natural colour extraction process has also been optimized in aqueous media for various source natural dye materials as follows (Konar,

 Pomegranate Rind: Pre-cut and dried rind is initially crushed to powder form and then it is extracted in water using an optimized condition of extractions using MLR- 1:20, temperature -90°C and time - 45 min and then it is filtered to obtain approximately 40% (w/w) clear extract of coloured aqueous solution of pomegranate rind having pH 11. Mariegold (Genda): Dried petal of mariegold is initially crushed to powder form and then extracted in water using an optimized condition of extraction using MLR 1:20 at 80°C for 45 min at pH 11 and then it is filtered to obtain approximately 40% (w/w)

 Babool (Babla): Sun- dried chips (pre-cut) of babool bark is initially crushed to powder form and then it is extracted in water using an optimized condition of extractions, by boiling in water at 100°C for 120min. and using MLR 1:20 and then it is filtered to obtain 40% (w/w) clear extract of coloured aqueous solution of babool having pH 11. Catechu (Khayer): Pre-dried powder of catechu is initially crushed to powder form and then extracted in aqueous medium using an optimized condition of extractions by heating in water bath at 90°C having MLR 1:20 and then it is filtered to obtain 40%

 Jack fruit wood: Pre-cut and dried chips of jack fruit wood is initially crushed to powder form and then colour is extracted in water using an optimized conditions of extractions by boiling in water at 100°C for 30 minutes and using ML ratio (MLR) 1:10 and then it is filtered to obtain 40% (w/w) clear extract of coloured aqueous solution of

 Red sandal wood: Dried pre-cut chips are crushed to powder form and colour is extracted under optimized conditions by heating it in water at 80°C for 90 minutes at

Due to increasingly stringent environmental regulations, supercritical fluid extraction (SFE) has gained wide acceptance in recent years as an alternative to conventional solvent extraction for separation of organic compound in many analytical and industrial process. In recent past decade, SFE has been applied successfully to the extraction of a variety of organic compounds from herbs, other plant material as well as natural colourant from

(w/w) extract of coloured aqueous solution of catechu having pH 12.

**5.2 Extraction by non-aqueous and other solvent assisted system** 

dyes can be post-mordanted with chromium, copper and tin salts, *e.g.,* lawsone and many other flavone and anthroquinone dyes.

vi. **Basic or cationic dyes** on ionization give coloured cations and form an electrovalent bond with the –COOH group of wool and silk. These dyes are applied from neutral to mildly acidic pH. These dyes have poor light fastness, *e.g.,* berberine.

#### **5. Extraction process of colour component from natural dyes**

Extraction of colour component from source natural dye material is important step for dyeing any textile substrate to maximize the colour yield. Moreover, standardization of extraction process and optimizing the extraction variables both, for a particular source natural dye material have technical and commercial importance on colour yield and cost of extraction process as well as dyeing cost. The natural dyes can be taken from various vegetable sources like flowers, stem or wood, roots, bark, etc. as well as animal sources and mineral sources. The colour component present in these sources needs to be extracted so that it can be applied suitably on textiles. Natural dyes of different origin can be extracted using aqueous method i.e. by using water for the extraction with or without addition of salt/acid/alkali/alcohol in the extraction bath, supercritical fluid extraction, enzyme assisted extraction, alcoholic/organic solvent extraction by using relevant extracting equipment or soxhlet extraction method with use of alcohol and benzene mixture and finally to filterate, evaporate and to dry using ultra filtration equipment or centrifuge rotatory vacuum pump/or by extraction under reduced pressure. Now a days, there has been industrial methods available for extracting colour components/purified colour substances from natural dyes for their easy applications.

The collected source material is generally shadow dried in air or sun dried within a temperature range of 37-40°C for the moisture content of the source natural dye material is reduced to 10-15% with proper drying since most of the material have moisture content of 40-80% and can not be stored without drying. After drying, grinding is carried out to break down the material into very small units or preferably powder form. Extraction refers to separating the desired colour component by physical or chemical means with the aid of a solvent. Optimum conditions of extraction variables are determined through extracting the natural colour component from source material by varying extraction parameters of liquor and measuring the optical density of corresponding coloured liquor by using spectrophotometer. Also, the gravimetric yield of colour can be measured by filtering the extraction liquor through standard filtration process followed by evaporation of solvent, washing and finally drying to get the purified natural colour.

#### **5.1 Aqueous extraction system**

For optimizing the extraction method of colour component in aqueous medium, dried and finely cut source material of natural dye is grinded in powdered form and then the colour component is extracted in water employing a standard process. The aqueous extraction of dye liquor is carried out under varying condition, such as time of extraction, temperature of extraction bath, pH of extraction liquor, concentration of colour-source material (powdered form of source natural dye material) and Material-to-liquor ratio (MLR). In each case, the optical density or absorbance value at a particular (maximum) absorbance wavelength for the aqueous extract of the natural dye material can be estimated using UV-Vis absorbance spectrophotometer.

many other flavone and anthroquinone dyes.

substances from natural dyes for their easy applications.

washing and finally drying to get the purified natural colour.

**5.1 Aqueous extraction system** 

spectrophotometer.

**5. Extraction process of colour component from natural dyes** 

dyes can be post-mordanted with chromium, copper and tin salts, *e.g.,* lawsone and

vi. **Basic or cationic dyes** on ionization give coloured cations and form an electrovalent bond with the –COOH group of wool and silk. These dyes are applied from neutral

to mildly acidic pH. These dyes have poor light fastness, *e.g.,* berberine.

Extraction of colour component from source natural dye material is important step for dyeing any textile substrate to maximize the colour yield. Moreover, standardization of extraction process and optimizing the extraction variables both, for a particular source natural dye material have technical and commercial importance on colour yield and cost of extraction process as well as dyeing cost. The natural dyes can be taken from various vegetable sources like flowers, stem or wood, roots, bark, etc. as well as animal sources and mineral sources. The colour component present in these sources needs to be extracted so that it can be applied suitably on textiles. Natural dyes of different origin can be extracted using aqueous method i.e. by using water for the extraction with or without addition of salt/acid/alkali/alcohol in the extraction bath, supercritical fluid extraction, enzyme assisted extraction, alcoholic/organic solvent extraction by using relevant extracting equipment or soxhlet extraction method with use of alcohol and benzene mixture and finally to filterate, evaporate and to dry using ultra filtration equipment or centrifuge rotatory vacuum pump/or by extraction under reduced pressure. Now a days, there has been industrial methods available for extracting colour components/purified colour

The collected source material is generally shadow dried in air or sun dried within a temperature range of 37-40°C for the moisture content of the source natural dye material is reduced to 10-15% with proper drying since most of the material have moisture content of 40-80% and can not be stored without drying. After drying, grinding is carried out to break down the material into very small units or preferably powder form. Extraction refers to separating the desired colour component by physical or chemical means with the aid of a solvent. Optimum conditions of extraction variables are determined through extracting the natural colour component from source material by varying extraction parameters of liquor and measuring the optical density of corresponding coloured liquor by using spectrophotometer. Also, the gravimetric yield of colour can be measured by filtering the extraction liquor through standard filtration process followed by evaporation of solvent,

For optimizing the extraction method of colour component in aqueous medium, dried and finely cut source material of natural dye is grinded in powdered form and then the colour component is extracted in water employing a standard process. The aqueous extraction of dye liquor is carried out under varying condition, such as time of extraction, temperature of extraction bath, pH of extraction liquor, concentration of colour-source material (powdered form of source natural dye material) and Material-to-liquor ratio (MLR). In each case, the optical density or absorbance value at a particular (maximum) absorbance wavelength for the aqueous extract of the natural dye material can be estimated using UV-Vis absorbance Many scientists have reported the optimized process of extraction of natural dyes from source. Colour from leaves of eucalyptus hybrid, seeds of cassia tora and grewia optiva are extracted by using aqueous medium under varying conditions (Dayal & Dobhal, 2001). Natural dyes are extracted from biomass products namely cutch, ratanjot, madder (Khan et al, 2006) and from hinjal, jujube bark (Maulik & Pradhan, 2005) in aqueous medium. An attempt has been made to extract natural dye from the coffee-seed for its application in dyeing textiles like cotton and silk (Teli & Paul, 2006). Grey jute fabric is dyed with extracts from deodar leaf (Pan et al, 2003) jackfruit wood and eucalyptus leaf by soaking it soft water and boiling it for 4 hours separately. Extraction (Verma & Gupta, 1995) of natural dyes is also reported from overnight soaked wattle bark in distilled water followed by boiled it in pressure vessel and filtered it to obtain a residual dye powder of about 15 to 20 % (w/w) of the bark. Colours are extracted from marie gold and chrysanthemum flowers by boiling the dry petals with acidified or salt water and reported it to be the best (Deo & Paul, 2000; Sarkar et al 2005 & 2006; Saxena et al, 2001). Natural colour extraction process has also been optimized in aqueous media for various source natural dye materials as follows (Konar, 2011):


#### **5.2 Extraction by non-aqueous and other solvent assisted system**

Due to increasingly stringent environmental regulations, supercritical fluid extraction (SFE) has gained wide acceptance in recent years as an alternative to conventional solvent extraction for separation of organic compound in many analytical and industrial process. In recent past decade, SFE has been applied successfully to the extraction of a variety of organic compounds from herbs, other plant material as well as natural colourant from

Dyeing of Textiles with Natural Dyes 37

For enzyme assisted extraction process (Tiwari et al 2010) single or mixed enzyme (e.g. pectinase : cellulase, 2:1) is sprayed on source material and left for overnight for better soaking. This material is then taken into 500 ml conical flask with 250 ml water of pH 10 and shaken in orbital shaker at 150 rpm for 40-80 minutes at optimum temperature. The extraction solution is ready for dyeing textile material or can be filtered and drying as ready

The aqueous extraction of the corresponding dye solution is double filtered in fine mesh nylon cloth and sintered glass crucible and the filtrate is evaporated using a vacuum oven at lower temperature (70°C) to a semi-dried solid mass and the same is then put in a cage of the wrapped filter paper and further subjected to extraction in soxhlet apparatus using 1:1 alcohol:toluene mixture for 10 cycles for 2h at 70ºC. The alcohol- toluene extract of the colour components is finally subjected to evaporation in a water bath at 50ºC to get a semi-dry mass of the pure colour components. Finally, this dry mass of the colour components is washed with 100% acetone followed by washing with methyl alcohol and final drying in air to obtain the dry powder of the pure colour components of the

For characterization, purified dye powder is to be taken for preparation of 1% aqueous dye solution separately and is subjected to wavelength scan in a micro processor or computer attached UV-Vis absorbance spectrophotometer for 190-1100 nm range. Further, individual purified natural dye powder is washed once again in distilled water and in 100% acetone in sequence before final drying and may be subjected to FTIR Spectroscopy study in double beam FTIR spectrophotometer using KBr disc technique for characterization of its chemical nature and functional group present in the natural dyes, which are responsible for solubilisation and mordanting power of natural dyes as well as its

For study of thermal behaviour by DSC (differential scanning calorimetry) study, individual purified natural dye powder is to be washed in distilled water followed by further washing in 100% acetone before final drying and then may be subjected to DSC or TGA (thermogravimetric analyser) study by standard method, for determining the different transition temperature of the purified dyes including temperature of degradation/dissociation. Thermal characterization by DSC/TGA is necessary for understanding the nature of thermal dissociation of natural dye component at different

UV-Vis spectral scan of aqueous/non-aqueous extract/solution of purified natural dyes having both UV-zone and visible zone (190-700 nm or higher) indicating peaks and troughs in different wave length shows its main hue, absorption etc. Peaks and troughs in visible zone thus indicate main colour and absorption. UV-Zone with/without peaks shows the

UV-Visible spectroscopic studies are carried out by different scientists (Erica et al, 1995) to identify the UV-Vis spectral scan of a number of natural dyes viz, madder, cochineal, indigo, etc., using different solvents for extraction. Neem bark (Mathur et al, 2003) colourant shows two absorption maxima at 275 and 374 nm while beet sugar shows three absorption bands at

property of the dye under UV-light, this may be correlated with fastness behaviour.

purified dye material for further use.

corresponding natural dyes.

**6. Purification and characterization of natural dyes** 

hypsochromic/bathochromic shift of the main hue.

dyeing temperatures as well as application temperature.

**6.1 UV-Visible spectroscopic study** 

source natural dye material. With increasing public interest in natural products, SFE may become a standard extraction technique for source natural dye material and other herbs and food items. Supercritical fluid extraction using carbon dioxide as a solvent has provided an excellent alternative to the use of chemical solvents. Over the past three decades, supercritical CO2 has been used for the extraction and isolation of valuable compounds from natural products.

Supercritical fluids are utilized to extract and purify natural colourant from eucalyptus bark (Vankar et al, 2001). Extraction of dye from food is best achieved with ethanol/oxalic acid. The comparative behaviour of other red food dyes is also studied and a process is developed for the extraction of natural dye from the leaves of teak plant is carried out using aqueous methanol (Nanda et al, 2001). A brick red shade from dyeing for silk/wool using the isolated dye in presence of different mordants is achieved. Attempts (Bhattacharya, 2002; Patel & Agarwal, 2001) has been made to standardize colourant derived from arjun bark, babool bark and pomegranate rind. Extraction (Agarwal et al 1992; Singh & Kaur, 2006) of well grounded henna leaves, directly in a solvent assisted dyeing process, employing organic solvent:water (1:9) as the dyeing medium is studied and superior dyeing properties are obtained, when applied to polyester. Natural dye (Raja & Kala, 2005) is obtained from the grape skin waste by using soxhlet extractor, and latter on distilled it under vacuum to obtain the concentrated dye solution. Colourant/dye is extracted by using a reflux condenser; source dye material is refluxed for 1 hour and filtered it to yield natural colourant (Eom et al, 2001).

#### **5.3 Extraction by acid and alkali assisted system**

Colour from euphorbia leaves (Dixit & Jahan, 2005) under acidic pH by adding hydrochloric acid and under alkaline pH by adding sodium carbonate both, in aqueous media are extracted for dyeing silk fabric. Extraction of colour in alkali media from nuts of acacia catechu (Sudhakar, 2006) is carried out for colouration of protein fibre based fabric. Dye extracted from jatropha seed gives a range of bright, even and soft colours on textiles when extracted under acid/alkali condition (Radhika & Jacob, 1999). Extraction of colour component from jackfruit wood under various pH conditions is carried out and reported that the optimum conditions for extraction is at pH-11.0 (Samanta et al, 2007). Red colour is extracted from red sandal wood (Samanta et al, 2006)under various pH conditions and it is reported that the optimum conditions for extraction of colour component is acidic pH like 4.0. Orangish yellow colour is extracted from tesu (palash flower) and maroon red colour can be obtained from Indian madder when extracted at alkaline conditions under aqueous medium (Samanta et al, 2010 & 2011).

#### **5.4 Natural colour extraction by other methods**

For ultrasound assisted extraction process (Sumate et al, 2008; Tiwari et al 2010) of natural colour, a standard extraction protocol may be used as 250 ml of solvent and 25 gm of powdered source natural dye material are taken in 500 ml beaker being immersed into the ultrasonic bath with working frequency of 27-30 MHz at 160 V under a controlled water level at about 2-3 cm from the bottom of the bath. To estimate the extraction yield at different time, temperature, pH and MLR for optimizing the extraction variables, 1.0 ml liquid is pipette out and then diluted to make 10.0 ml volume in each case. This solution is centrifuged at about 2000 rpm to remove the suspension. Finally, the concentration (% w/w) of the diluted solution is measured spectrophotometrically at a definite wavelength (λmax).

source natural dye material. With increasing public interest in natural products, SFE may become a standard extraction technique for source natural dye material and other herbs and food items. Supercritical fluid extraction using carbon dioxide as a solvent has provided an excellent alternative to the use of chemical solvents. Over the past three decades, supercritical CO2 has been used for the extraction and isolation of valuable compounds from

Supercritical fluids are utilized to extract and purify natural colourant from eucalyptus bark (Vankar et al, 2001). Extraction of dye from food is best achieved with ethanol/oxalic acid. The comparative behaviour of other red food dyes is also studied and a process is developed for the extraction of natural dye from the leaves of teak plant is carried out using aqueous methanol (Nanda et al, 2001). A brick red shade from dyeing for silk/wool using the isolated dye in presence of different mordants is achieved. Attempts (Bhattacharya, 2002; Patel & Agarwal, 2001) has been made to standardize colourant derived from arjun bark, babool bark and pomegranate rind. Extraction (Agarwal et al 1992; Singh & Kaur, 2006) of well grounded henna leaves, directly in a solvent assisted dyeing process, employing organic solvent:water (1:9) as the dyeing medium is studied and superior dyeing properties are obtained, when applied to polyester. Natural dye (Raja & Kala, 2005) is obtained from the grape skin waste by using soxhlet extractor, and latter on distilled it under vacuum to obtain the concentrated dye solution. Colourant/dye is extracted by using a reflux condenser; source dye material is refluxed for 1 hour and filtered it to yield natural

Colour from euphorbia leaves (Dixit & Jahan, 2005) under acidic pH by adding hydrochloric acid and under alkaline pH by adding sodium carbonate both, in aqueous media are extracted for dyeing silk fabric. Extraction of colour in alkali media from nuts of acacia catechu (Sudhakar, 2006) is carried out for colouration of protein fibre based fabric. Dye extracted from jatropha seed gives a range of bright, even and soft colours on textiles when extracted under acid/alkali condition (Radhika & Jacob, 1999). Extraction of colour component from jackfruit wood under various pH conditions is carried out and reported that the optimum conditions for extraction is at pH-11.0 (Samanta et al, 2007). Red colour is extracted from red sandal wood (Samanta et al, 2006)under various pH conditions and it is reported that the optimum conditions for extraction of colour component is acidic pH like 4.0. Orangish yellow colour is extracted from tesu (palash flower) and maroon red colour can be obtained from Indian madder when extracted at alkaline conditions under aqueous

For ultrasound assisted extraction process (Sumate et al, 2008; Tiwari et al 2010) of natural colour, a standard extraction protocol may be used as 250 ml of solvent and 25 gm of powdered source natural dye material are taken in 500 ml beaker being immersed into the ultrasonic bath with working frequency of 27-30 MHz at 160 V under a controlled water level at about 2-3 cm from the bottom of the bath. To estimate the extraction yield at different time, temperature, pH and MLR for optimizing the extraction variables, 1.0 ml liquid is pipette out and then diluted to make 10.0 ml volume in each case. This solution is centrifuged at about 2000 rpm to remove the suspension. Finally, the concentration (% w/w) of the diluted solution is measured spectrophotometrically at a definite wavelength (λmax).

natural products.

colourant (Eom et al, 2001).

medium (Samanta et al, 2010 & 2011).

**5.4 Natural colour extraction by other methods** 

**5.3 Extraction by acid and alkali assisted system** 

For enzyme assisted extraction process (Tiwari et al 2010) single or mixed enzyme (e.g. pectinase : cellulase, 2:1) is sprayed on source material and left for overnight for better soaking. This material is then taken into 500 ml conical flask with 250 ml water of pH 10 and shaken in orbital shaker at 150 rpm for 40-80 minutes at optimum temperature. The extraction solution is ready for dyeing textile material or can be filtered and drying as ready purified dye material for further use.
