Recently, interest in the use of natural dyes has been growing rapidly due to the result of stringent environmental standards imposed by many countries in response to toxic and allergic reactions associated with synthetic dyes1. Until about 150 years ago all dyes were natural substances, derived mainly from plants and animals. The natural dyes present in plants and animals are pigmentary molecules 2, 3, which impart colour, to the materials. Pigmentary molecules containing aromatic ring structure coupled with a side chain are usually required for resonance and thus to impart colour. There is a correlation of chemical structure with and chromogen-chromophore with auxochrome.
Chromogen is the aromatic structure containing benzene, naphthalene or anthracene rings. The chromogen chromophore structure is often not sufficient to impart solubility and cause adherence of the dye to the fibre, but the presence of auxochrome or bonding affinity groups enhances adherence properties of the dye to the fabrics. With the world becoming more conscious towards ecology and environment, there is greater need today to revive the tradition of natural dye and dyeing techniques as an alternative of hazardous synthetic dyes. The traditional method of dyeing is extremely crude. It is well known that the rural folk dye the yarn by heating chopped leaves or flowers of the plant in water. The process lacks proper shade calculation and reproducibility of shade for subsequent dyeing processes. It is also laborious and time-consuming.
There are several plants/plant parts that provide natural dyes4–9 which are used in the textile industry. The literaturereveals10–15 the chemical composition and biological study of the different parts of Delonix regia ‘Gulmohur’, but no reports exist so far on the extraction of natural dyes from D. regia and their applications. The present investigation deals with the extraction of natural dyes from different flower parts of D. regia and their applications on textiles. D. regia grows in all warm and damp parts of India, and is considered to be one of the most beautiful trees in the world. The tree produces striking flame-like scarlet and yellow flowers during spring before the leaves emerge.
Flowers are brilliant red, the uppermost petal streaked with tallow or yellow-and-white, petals stalked, their distal part abruptly expanded, orbicular, with wavy-crinkled edges, each about 4–6 cm long. Stamens decline together, curving out and down. It has been reported16 that the Gulmohur flower contains flavonoids such as leucoanthocyanin and carotenoids such as lutein, zeaxanthin, violoxanthin, neoxanthin, auroxanthin,5,6-monoepoxylutein, antheraxanthin and flavoxanthin, which are responsible for dyeing. Work has been carried out to prepare eco-friendly natural dyes from different parts of Gulmohur flower and application of colouring materials on cotton and silk yarns. Different parts such as petal, calyx, petal with reproductive organ and whole flowers were extracted separately with methanol as solvent at room temperature. Different parts of the flower were extracted in different time intervals such as 3 h (part I) and subsequently 6 h (part II).
The plant parts (100 g) were taken in pure methanol (500 ml) as solvent for extraction. The organic solvent was then distilled-off to get a brownish-black coloured pasty mass. Total yield of the mass was 8%. The pasty mass (1 g) was used in 20 ml of 0.5% sodium hydroxide solution to make a dye solution for different fabrics such as cotton and silk. The dyeing bath temperature was maintained at 60°C and time of dyeing was 45 min for every procedure at pH range 7–8. Light fastness study of the dyed yarn was carried out by washing with water, soap, rubbing, drying at room temperature and then direct sunlight and exposing the dry yarn to Digi-light for its fastness properties. Silk fabrics showed attractive shades with the dye materials, but cotton fabrics offered dull shades which do not give light fastness properties. Some of the findings are reported in Table 1.
In case of Sl.-1 and Sl.-2, the dye concentrations are the same at the time of dyeing with different dyeing conditions. The Sl.-1 offers golden yellow shades in presence of turmeric on silk fabrics whereas Sl.-2 offers olive green in presence of alum as mordant. The result of dyeing depends upon the concentration of dye after extraction as well as the dyeing condition. However, the dye concentration in Sl.-4 and Sl.-6 is the same as the result for both the cases are similar under the same dyeing conditions. Sl.-4 and Sl. - 6 both give olive green shade using alum as mordant. Sl.-3 gave dark tan shade with turmeric powder and Sl.-5 gave saddle brown shades without mordant with different dyeing conditions. Colouring material extracted from the petal along with reproductive organ (Sl.-7) offers dark brown shades without mordant on silk fabrics, whereas Sl.-8 gave brown shades with alum as mordant. Sl.-9 gave brown shades on silk fabrics without using any mordant. The shades are compared with the nearest equivalent shades according to pantone textile colour guide.
The study revealed the production of varied natural colours from plant pigments. The present investigation emphasizes the utilization of waste flowers for value-addition. Future investigation will be directed towards developing ecofriendly dyes for textile and handloom industries. This will also have an impact on the economic growth of the rural weaver communities.
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