it on 100% pure cotton. It revealed that different shades from cauliflower can be prepared using different mordants [83].
Singam et al. studied natural dyes based on Lawsonia inermis, Azadirachta indica and Curcuma longa were used to produce eco-friendly and non-toxic fabric for the people. The extraction process of natural dyes is an aqueous technique and then proceeded to hot bath dyeing later. The aim was to find the optimum concentration of natural dyes and super hydrophobic coating removal from cotton fabric for the green technology dyeing process [84]. Pan and his colleague explored that extract of Deodara, Jackfruit and Eucalyptus leaves yield light brown and light mustard shades on jute fabric. Fastness properties toward washing showed good in all manners [85].
ii. Dyeing Condition for Protein Material
Wool and silk fibers both have complex chemical structure and are susceptible to alkali treatment. They respond very well in acidic conditions. Mehtab et al. have utilized neem bark (A. indica) for dyeing of wool yarn. They optimized dyeing conditions such as pH 4.5, dye concentration 0.05 g per gram of wool, dyeing time 60 min and temperature 97.5 °C indicated good light and wash fastness properties [86]. Bechtold et al. isolated colorant from ash-tree bark (Fraxinus excelsior L.) for dyeing on wool. Meta mordanting process with FeSO4.7H2O was applied, which revealed that 1-2 gm extraction of bark is sufficient to dye 1 g wool yarn [87]. A study has been conducted by Jayalakshmi and Amsamani for application of Annatto and Catechu using bio-mordants to dye wool. Mordanting and dyeing were conducted by then at room temperature for 30 min. Myrobalan and Karavelum (Babul) bark were used in 1% concentration as biomordant while liquor of Tamarind and Green tea were used for fixing treatment. The experiment concluded that use of natural mordant and fixing agents improve color fastness of wool [88]. Mohammad et al. extracted colorant from Henna leaves for dyeing woolen yarn. Dyeing was conducted by using 1, 5, 10 and 20% of dye concentrations with 1:40 Material to liquor (M:L) ratio at 30 °C. Thirty six shades were obtained by varying concentrations of dye and mordants [89].
Uddin evaluated the performance of dyes taken from Mango leaves for silk dyeing. Dye extraction conditions were optimized such as the temperature, time, and material-to-liquor ratio found to be 98 °C, 60 min, and 1:10, respectively. Dyeing was done on silk with the ferrous sulfate, alum (potassium aluminum sulfate), and tin (stannous chloride) as fixing agents individually and using four different combinations of these mordants at 60 °C for 60 min keeping M:L ratio of 1:30 [90]. Swamy observed the coloring potential of one Gymnosperm Casuarina equisetifolia leaves and applied on silk fabric where color strength of dye was improved by using different mordants [91]. Banerjee et al. studied natural dyes isolated from Camellia sinensis, A. cepa, Laccifer lacca and Iron ore. Dyes employed on Eri silk yarn with different mordants [92]. Shukla et al. collected eleven species of lichens from different regions of Himalaya to extract dye and applied it on Silk, Tussar silk and Absorbent cotton. The lichens can produce orange, yellow, blue grey, purple and brown color dyes. However, the author recommended that due to small size of lichens and slow growth they could serve for local handlooms but cannot fulfill the requirements of textile industries [93]. Khan et al. demonstrated that Myrobalan, Gallnut and Pomegranate extract can be used as a dyeing agent on wool yarn. Three different mordants like Alum, Copper sulfate and Ferrous sulfate combined with above agents improved fastness properties [94].
iii. Dyeing condition for synthetic fiber
Nylon is a synthetic polymer containing amide link known as synthetic fiber. Lokhande and Dorugade attempted dyeing of nylon fabric with two different techniques viz. open bath and HTHP (high temperature and high pressure) dyeing. Natural dyes extracted from Onion (A. cepa), Lac (L. lacca) and Turmeric (C. longa) were applied with various mordants on Nylon Fabric. HTHP Dyeing has been found to give better results as compared to the open bath dyeing [95]. A study has been conducted by Miah et al. on nylon fabric dyed with onion extract using various mordants such as Alum, Copper sulphate and Potassium dichromate by HTHP dyeing methods [96].
Exhaust dyeing method is commonly used for the application of natural dyes on polyester fabrics. The dyeing of polyester is conducted using material: liquor ratio in 1:15–1:50, temperature above 90 °C and pH ranges from 4–8 for 60–90 min [97]. Elnagar et al. reported UV/ozone pretreatment was employed to activate fiber and improve dye ability of polyester and nylon. Fabrics were pre mordanted by ferrous sulfate 6% (owf) keeping material to liquor ratio 1:15 at 60 °C for 60 min. Dye isolated from Curcumin and Saffron and applied on nylon and polyester [98]. Shahin et al. studied the process of dyeing polyester fabric with Chinese Rhubarb “Dolu” (Rheum officinale) after optimization. The dyeing process was performed with 50% dye extract at temperature 100 °C for 60 min and M:L ratio 1:100 [99]. Guizhen reported that Rhizoma coptidis colorant can be used on acrylic fiber successfully. Dyeing carried out different concentrations of dye at 60 and 95 °C for 5 h keeping material liquor ratio 1:200 and pH adjusted at 6.5 [100].
1.11 Evaluation of the Dyed Fabric
1.11.1 Color Strength or K/S Value
Color strength or K/S value is the most important parameter to test the quality check of a sample in terms of depth of the color dyed on fabric. Strength of any colorant is related to absorption property. Reflectance (%) of the dyed fabric samples can be measured by using a spectrophotometer. The Kubelka–Munk theory gives the following relation between reflectance and absorbance:
where R is the reflectance, K is absorbance and S is the scattering.
The above equation is used for detection of color strength. Color strength of the dyed fabric influenced by the increase of reflectance value. When shade percent increases, reflectance percent & color strength (K/S) decreases. If shade percent is more but color depth is less than quality of textile does matter a lot for customers and selling manufacturers as well. Color strength of a textile is a quality control assurance system. It is also important to know about the color combination by which color is produced. So, it makes the necessity of color strength testing in textile industries. Color strength or K/S value were carried out by different scientists for natural dyed fabrics [50, 51, 101].
1.11.2 Color Fastness Properties
Colorfastness can be defined as a property of any dyed textile material to retain its original color without fading, changing or running during washing, wetting, cleaning, exposure to light, heat or any influences. The color fastness standards or protocol generally used by the American Association of Textile Chemists and Colorists (AATCC) and the International Organization for Standardization (ISO). After testing, the color of the sample is compared by “Gray Scale for Color Change” and a “Gray Scale for Staining’’. Color Fastness uses a rating system from1 to 5, where 5 indicate excellent and 1 shows very poor results. The main color fastness tests are as follows:
1 Colorfastness to Washing: the ability of dye to resist during washing of fabric called washing fastness.
2 Colorfastness to Light: light fastness is resistance of dye during the exposure to light or heat.
3 Colorfastness to Rubbing: the ability to sustain original color of dyed fabrics by abrasion or rubbing.
4 Colorfastness to Perspiration: the ability to not fade when dyed fabric is perspired.
Natural sources provide a large range of color with various shades on textile materials. To use dyed material every day, the color should remain on the fabric in any situation. Therefore, researchers and scientists attempted several trials and found very good results for fastness [102, 103].
1.12 Some Special Characteristics of Naturally Dyed Fabric
1.12.1 Antimicrobial Properties
Textile materials are the carriers of microorganisms