Raw Khair (cutch) chips were collected from the local market and then washed with tap water and sun dried. The dried chips were ground to make them powder. A detailed extraction method was followed to extract the dye from the acacia powder. Finally, the extracted dye was applied to the silk fabrics following the necessary steps of scouring, mordanting and dyeing and is discussed below.
2.1. Dye Extraction: The natural dye was extracted from raw Khair by aqueous, alkaline, acidic, and alcoholic medium using standard procedure (Samanta and Agarwal, 2009). In the aqueous technique, 10g of raw Khair powder was added to 100 ml of distilled water and boiled at 90° for 120 min. In the acidic technique, 10g of raw Khair powder was added to 100 ml 1% of HCl solution and boiled at 90° for 120 min. In the alkaline technique, 10g of raw Khair powder was added to 100 ml 20 g/L NaOH solution and boiled at 90ºC for 120 min. In the alcoholic technique, 10g of raw Khair powder was added to ethanol in water at a volume ratio 1:3(v/v) and boiled at 90 ºC for 120 min. The hot dye extract was filtered through the fine cotton fabric and allowed to cool. Finally, it was filtrated once again through Whatman 40 filter paper. The extracted dye solution was dried in an oven at 60–70ºC to get the powder formed. The absorption spectra of the dye extracts were measured using a UV-Vis spectrophotometer.
2.2. Scouring of Silk Silk fabrics were washed in a solution containing 0.5 g/L Na2CO3 and 2 g/L non-ionic detergent solution at 50 ºC for 25 min, keeping the Material to Liquor ratio (M:L) at 1: 40. The scoured material was thoroughly washed with tap water and dried at room temperature. Then it was soaked in distilled water for 15 min prior to dyeing or mordanting.
2.3. Mordanting Four different laboratory grade mordants were used, i.e., potassium aluminum sulphate (AlK(SO4)2.12H2O), copper sulphate (CuSO4.5H2O), ferrous sulphate (FeSO4.7H2O) and stannous chloride (SnCl2.2H2O). The samples were subjected to pre-mordanting (before dyeing) with 5% potash alum and 3% with other mordants on the weight of fiber (o.w.f). The temperature of the dye bath was raised to 80°C over a period of half an hour and left at that temperature for another 30 minutes (Monali et al., 2016). The mordanted fabric was immediately used for dyeing because some mordant are light sensitive (Jothi, 2008; Kulkarni et al., 2011).
2.4. Dyeing The extracted liquor was used to dye silk fabrics in a previously prepared dye bath of Acacia catechu. The initial temperature of the dye bath was 40 ºC which was slowly raised up to 90 ºC. The dyeing process was carried out for 60 minutes keeping the material to liquor (M: L) ratio of 1:50 with stirring occasionally (Deshmukh and Dongre 2015). The material was left in the dye bath overnight to complete the dyeing process. In the next day, the dyed fabrics were taken out from the dye bath and washed well under running tap water and dried under shade.
2.5. UV-Visible Spectral Analysis UV absorption spectra of the extracted dyes were recorded at wavelength of 200 to 800 nm on a UVmini-1240, Shimadzu, Spectrophotometer.
2.6. Color Fastness Test: The colorfastness of the dyed fabrics was assessed by light, wash, perspiration and rub fastness. Light fastness was analyzed by exposing the dyed material to direct sunlight for 24 hours. The color fastness to light was evaluated by comparison of color change of the exposed portion to the unexposed original material (Samanta and Agarwal 2009). The wash fastness was tested by washing the dyed fabrics with non ionic soap water (2 gm/lit). The color fastness to perspiration of dyed silk fabrics were measured using ISO-105-F 10: 1998 analyzer and the dry and wet rub fastness of the dyed silk samples were tested using a crock-meter based on ISO-105-X12-2001 by mounting the fabric on a panel and giving ten strokes for dry and wet rub fastness tests. The samples were assessed for staining on adjacent white fabrics.