Collection of material
The dyeing material of Quercus robur L. (fruit cups) was collected from Dachigam wild life sanctuary, Srinagar, and mordant materials Salix alba L. (wood) and Populus deltoides Bartram ex Marsh. (wood) were collected from university outskirts at Srinagar city (Plate 1). Wool and cotton were purchased from Government Silk Weaving Factory and Poshish (JKHDC) outlet at Srinagar (J&K). Silk was procured from J&K Govt. Silk Weaving Factory at Rajbagh, Srinagar, and pashmina fabric was purchased from FS Shawls, Srinagar.
Preparation of dyeing material
The shade dried fruit cups of Quercus robur L. were washed with distilled water and dried in a tray drier at 80 °C for 2 h. The material was finely powdered with the help of a grinding machine and passed through a standard test sieve (BSS-14). The resultant material was then used as dye material.
Preparation of mordant
The wood of Salix alba and Populus deltoides was burn completely into ash and soaked in distilled water for 15 days. The resultant solution was filtered and kept under refrigeration for future usage.
Extraction of dye
For complete extraction of the dye in aqueous solution, soxhlet apparatus was used. One litre of distilled water was used for 100 g of the plant material. The material was kept for reflux for about 8 h at 80–85 °C. The extracted material was evaporated at 65 °C using rotary vacuum evaporator, and the material was reduced to one fourth of its original volume to obtain the final dyeing extract.
Scouring of fabrics
All the test fabrics (wool, cotton, silk and pashmina) were cut into 5 × 6 cm and were washed for 20 min with 2 % non-ionic soap (Labolene) at 50 °C by keeping the material-to-liquor ratio at 1:50 for silk and pashmina and 1:80 for cotton and wool fabrics. The material was then washed thoroughly with plenty of tap water and was soaked in distilled water for 30 min prior to dyeing (Plate 2).
Dyeing of fabrics
The process of the dyeing was carried out in a water bath by maintaining the material-to-liquor ratio of 1:60 for wool and pashmina fabrics, 1:40 for cotton fabric and 1:60 for silk fabric, respectively. The dyeing of wool, silk and pashmina fabrics was performed at acidic pH by adding required amount of acetic acid (CH3COOH), whereas cotton fabric was dyed at basic pH by adding sodium carbonate (Na2CO3), which acts as an electrolyte for cellulosic fibres, containing higher bonds than protein fibres. All the test fabrics were dipped in 100 ml of dyeing solution of 4 % dye (OWM) at room temperature. The material was then removed and washed with 1 % of detergent and water 2–3 times followed by squeezing and drying operations at room temperature.
Mordanting
The process of mordanting was carried out by adopting pre-, simultaneous and post-mordanting methods using 4 % of mordant solution and maintaining 1:50 material-to-liquor ratio. The process of mordanting was carried at 60–75 °C with gentle stirring and continued for 1 h.
Percent absorption determination
Amount of the dye absorption by the selected textile fabrics was evaluated by recording the optical density (ƛ max) of the dyeing solution both before and after dyeing process using a ultraviolet-visible adsorption spectra (UV-VIS) PC-based double beam spectrophotometer (Systronics 2202). The OD at ƛ max was recorded over the range of 200–800 nm. The final value of the percent absorption was calculated by using the following equation.
$$ \mathrm{Percent}\kern0.5em \mathrm{absorption}=\frac{\mathrm{O}.\;\mathrm{D}\kern0.5em \mathrm{before}\kern0.5em \mathrm{dyeing}-\mathrm{O}.\;\mathrm{D}\kern0.5em \mathrm{after}\kern0.5em \mathrm{dyeing}}{\mathrm{O}.\;\mathrm{D}\kern0.5em \mathrm{before}\kern0.5em \mathrm{dyeing}}\times 100 $$
Evaluation of CIE colour coordinates (L*a*b*C*h° and ∆E)
The colour coordinates of the dyed and undyed fabrics were determined by chromometer (Model CR-2000, Minolta, Osaka, Japan) equipped with 8-mm measuring head and AC illumination (6774 K) based on CIE system (International Commission on Illumination). Manufacturer’s standard white plate was used for calibration of the instrument. L*, a* and b* coordinates were recorded by the measuring instrument directly, whereas values of Chroma (C*), hue angle (h°) and total colour change (∆E) were calculated by below mentioned equations.
$$ \begin{array}{l}\mathrm{Chroma} = {\left({a}^{*2} + {b}^{*2}\right)}^{1/2}\hfill \\ {}\mathrm{Hue}\ (h) = \mathrm{t}\mathrm{a}{\mathrm{n}}^{-1}\;b*\kern0.1em /\kern0.1em a*\Big)\hfill \end{array} $$
The value of the total colour change was calculated from L*, a* and b* values using the following equation.
Total colour change (∆E):
$$ \left(\Delta E\right) = {\left[{\left(\Delta L*\right)}^2 + {\left(\Delta a*\right)}^2 + {\left(\Delta b*\right)}^2\right]}^{1/2} $$
where
∆L* = L* sample − L* standard
∆a* = a* sample − a* standard
∆b* = b*sample − b* standard
Determination of colour strength (K/S)
The value of the colour strength (K/S) of the fabrics was recorded using a JAYPAK-4802 colour matching system (Jay Instruments Ltd., Mumbai, India) at D65 illuminate/10 Deg observer. The reflectance of the samples was measured at 360–760 nm. The K/S value in the visible region of the spectrum (400–700 nm) was calculated based on the Kubelka-Munk equation mentioned below
$$ \frac{K}{S}=\frac{\left(1-R\lambda \right)2}{2\times R\uplambda} $$
where K is the coefficient of absorption, S is the scattering coefficient and R is the surface reflectance value of the sample at a particular wavelength, where maximum absorption occurs for a particular dye/colour component.
Relative colour strength
The relative colour strength (K/S value at maximum wavelength) was calculated by adopting the following equation.
$$ \mathrm{Relative}\kern0.5em \mathrm{colour}\kern0.5em \mathrm{strength}=\frac{\left(K\kern0.1em /\kern0.1em S\right)\kern0.5em \mathrm{extracted}}{\left(K\kern0.1em /\kern0.1em S\right)\kern0.5em \mathrm{raw}} $$
Determination of colour fastness properties
The retention of the dye by the fabrics were evaluated by different colour fastness tests as per ISO 105-B02 for light, ISO 105 X-12 for rubbing and ISO 105-C01 for washing, respectively. Grades for the colour change and colour staining were assigned as per ISO 105-AO2 and ISO 105-A03 in conformity with the evaluators.