Redox system initiated improved low-temperature colouration of real silk with metal-complex dyes for energy conservation

Abstract

Silk has always been the symbol of royalty due to its lustrous appearance and peach like softness. It can be dyed in bright shades with the available natural and many synthetic dyestuffs. The slight cationic character of silk makes it possible to be dyed with anionic synthetic dyes such as acid, metal complex, reactive and selected direct dyes. The main objective of colouration of a textile fibre should be to maintain the permanency of the color and not allow any damage of the fibre. However, conventional dyeing of silk by exhaust dyeing method with these dyes is usually performed at near boiling temperature, which substantially damages the silk fibre, loses its magnificent luster and deteriorates its qualities. Many approaches have been adopted to decrease this potential damage of silk fibre. One such effort is redox system initiated low temperature dyeing of silk substrate to preserve its aesthetic characteristics. The redox system is formulated by the utilization of glucose and hydrogen peroxide as reducing agent and oxidizing agent respectively. The dyeing of silk substrate is performed with metal-complex dyes at low-temperatures and compared with the conventional exhaust dyeing performed at 90o C. Conventionally, an ionic bond is formed between the silk fibre and the anionic dye(s) when the dyeing is performed at or near boil. However, the redox system has aided a much strong covalent bond formation between the metal-complex dyestuff and the silk substrate at much lower temperatures than the conventional dyeing temperature. The dyeing performance has been evaluated spectrophotmetrically in terms of colour strength (K/S) values and the results are compared with the conventionally dyed samples. Fastness characteristics (wash, light and rub, both wet and dry) of various dyed samples are also evaluated and compared with each other. Keywords: Mulberry silk, metal-complex dyes, exhaust dyeing, redox system, free-radical