Abstract
The Reseda luteola (weld), Prangos ferulacea, and pomegranate natural dyes especially have been used as a yellow colorant from ancient times. In this study the dyeing substances in the Reseda luteola, Prangos ferulacea, and pomegranate natural dyes were extracted by the solvent extraction method. The extraction was done by water as the conventional method, and by ethanol, methanol, water-ethanol, and water-methanol mixture as novel extraction methods. The extracted colorants were used to dye wool by the pre-mordanting method. Spectrophotometric evaluations together with colorimetric studies were carried out in order to compare the absorption behaviour of the extracted dyes on wool. The obtained results indicate that the colour strength of dye extracted by solvent is better than aqueous extraction. The extracted natural dyes can be used in the textile industry for wool dyeing in the same way as synthetic dyes.
Keywords: Natural dye, Extraction, Dyeing, Wool, Solvent, Yellow.
Introduction
Since prehistoric times, natural dyes have been used to colour wool fibre as a natural protein fibre. The natural dyes can give a wide range of colours with acceptable colourfastness.1-4 The cost of dyeing with natural dyes is higher than with synthetic dyes, because of their low colour value and long dyeing time. Today, natural dyeing is practised only as a handicraft. An appropriate dyeing technique and reproducible colour yield are needed for successful commercial use of natural dyes. Natural dyes application is increased by extracting colorant from raw natural dyes. The efficiency of natural-dye extraction depends on temperature, time and media type, such as aqueous or organic solvent. The washing fastness of natural dyes can be improved by treating with metal salts as a mordant. Also, pre-mordanting increases dye uptake. A variety of colours and shades can be obtained by using different types of mordants and their combinations.1-13
The pomegranate plant originates from Persia and adjacent countries, but today it can be found in all warm countries. The dried peel of the pomegranate has been used as a dyestuff from ancient times.14-16 Granatonine is the main colouring agent in the peel of pomegranate. The granatonine is present in the alkaloid form N-methyl-garanatonine.16-17 The yellow colour in weld pomegranate plant consists of the flavonoids luteolin, isorhamnetin, kaempferol, apigenin and luteolinglucoside, which was used as a source of brilliant yellow colorant18-19.
In this work, the solvent extraction method was used to extract yellow colorant from Reseda luteola, Prangos ferulacea, and pomegranate natural dyes. The colour absorption behaviour of solvent extracted dye on woollen yarn was compared with aqueous extracted natural dye as the normal extraction method.
Materials and Methods
Iranian woollen yarn of 5/2 metric, nonionic detergent, acetic acid, ethanol, methanol, the Reseda luteola, Prangos ferulacea, and pomegranate plants, were purchased from Iranian traditional natural dyers. Texflash spectrophotometer (Datacolor) was used to measure the reflectance spectra and colorimetric parameters.
Extraction and purification of colorant from natural dye: Ethanol, methanol, water-ethanol and water- methanol mixtures were used to extract yellow colorants from Reseda luteola, Prangos ferulacea, and pomegranate by using soxhlet apparatus. A rotary evaporator was used to evaporate the solvent from the extracted solution of natural dyes. For extraction by the traditional method, water extraction, powdered Reseda luteola, Prangos ferulacea, and pomegranate were mixed with 40 times as much water, boiled for 60 min and filtered while hot to obtain the extracted dyestuffs.
Dyeing procedure: The woollen yarn was scoured in 2 g/L nonionic detergent, at liquor ratio 20:1, for 15 min at 70°C. The washed yarn was mordanted prior to dyeing by treating with Potash-alum (potassium aluminium sulfate) 5% on weight of the yarns at boil for 45 min with L: R = 40:1. At the end, yarn was scoured by water and dried in the environment.
The extracted yellow colorants were used for dyeing mordanted wool yarns. The liquor-goods ratio was 40:1. Mordanted yarns were introduced into the dyeing solutions at room temperature. The temperature was raised to the boil at 15 min and dyeing continued at the boil for 45 min.
Measurement of colour strength: The spectral reflectance of the dyed yarn was measured using a spectrophotometer at 16 wavelengths with 20nm intervals from 400 to 700nm. The colour strength as reflectance function (K/S) value was calculated by using the Kubelka-Munk equation (Equation l).
Where Rλ is the reflectance of dyed yarn at λmax, K is the absorption coefficient, and S is the scattering coefficient.Results and Discussion
The extraction efficiency of the yellow natural dyes was evaluated as a ratio of extracted dye over raw natural dyes (Equation 2). The performance of extraction methods is shown in Table 1. As shown in this table, the best extraction of Reseda luteola is obtained by water-ethanol mixture, with 32.7% efficiency. The best extraction of Prangos ferulacea is obtained by water-ethanol mixture, with 36.3% efficiency. The best extraction of pomegranate is obtained by water-ethanol mixture, with 52.3% efficiency.
The reflectance spectra of the woollen yarns, dyed with equivalent prepared dye solutions of raw and extracted natural dye, are also shown in Figure 1, Figure 2 and Figure 3, respectively, for Reseda luteola, Prangos ferulacea, and pomegranate. As shown in these figures, the reflectance of the wool dyed with raw natural dye is more than that of the extracted natural dye. Consequently, the colour strength of solvent extracted natural dye is more than water extracted dye. 
The colour strength as reflectance function (K/S) values of dyed samples is shown in Figure 4. As shown in this figure, the highest colour strength of Reseda luteola, Prangos ferulacea, and pomegranate respectively were obtained by ethanol (22.13%), ethanol (17.41%), and water-ethanol mixture (16.33%).
The CIELAB colour parameters under D65 standard illuminant and objective 1964 colorimetric standards of dyed samples are shown in Table 2, Table 3, and Table 4 respectively for Reseda luteola, Prangos ferulacea, and pomegranate. As shown in these tables, the lightness (L*) of wool dyed with aqueous extracted natural dye (extraction with water) is more than for samples dyed with solvent extracted natural dye.
The colour fullness and chroma (C*) of samples dyed with water extracted Reseda luteola and Prangos ferulacea are less than for solvent extracted natural dyes. The colour fullness (C*) of samples dyed with water extracted pomegranate is as good as for solvent extracted natural dyes. The hue angle (h) of samples dyed with raw natural dye (extraction with water) is more than for samples dyed with extracted natural dye.
Conclusion
In this study, the colorant substance present in Reseda luteola, Prangos ferulacea, and pomegranate were extracted by using the solvent extraction method. The yellow natural dyes were extracted by using water, ethanol, methanol, water-ethanol, and water-methanol.
In the best conditions, the extraction efficiency of Reseda luteola, Prangos ferulacea and pomegranate respectively are 32.7%, 36.3%, and 52.3%, which were obtained by water-ethanol mixture. The study of reflectance spectra shows that the reflectance of samples dyed with raw natural dye is more than the extracted natural dye.
Also the colour strength of solvent extracted natural dye is higher than for water extracted natural dye. The lightness of samples dyed with water extracted natural dye is more than for samples dyed with solvent extracted natural dye. In addition, the colour fullness of samples dyed with water extracted Reseda luteola and Prangos ferulacea is less than for solvent extracted natural dye. The colour fullness of samples dyed with water extracted pomegranate is as good as for solvent extracted natural dye.
The hue angle of samples dyed with water extracted natural dye is more than for samples dyed with solvent extracted colorant. The proposed method of extraction can be discussed as a new approach to increasing purity of natural dyeing for increasing their colour strength and application. On the other hand, the extracted natural dye can be used in modern dyeing machine as well as synthetic dye.
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