COLOR CHANGE STUDY BY RETREATMENT WITH DIRECT DYES. STUDY CASE

Abstract

In this paper we presented a study on the color change by retreatment with different agents, of materials dyed with direct dyes.Direct dyes are organic or inorganic substances that contain double-bonded chromophore groups, which have a major role in the affinity of dyes for cellulosic fibers. Direct dye fixation is done by: hydrogen bonds, van der Waals bonds, dipole forces between dye and fiber.The dyeing process is influenced by the following parameters: dye concentration, electrolyte concentration, temperature and bath hydromodule.Most direct dyes do not have adequate color fastness to wet or light treatments. Therefore, these color fastness need to be improved by various retreatment processes.In order to improve the color fastness to wet and light treatments, it is possible to change the structure of the dye by complexing (metal salt treatment), redoing by diazotization and coupling, insolubilization with cationic agents (cationic salts or synthetic resins). The optimal method of treatment is dictated by the structure of the dye and the advantages and disadvantages of each method.In this study, metal salts of CuSO4, K2Cr2O7 and cationic salts (Aniofix D) were used for the retreatment. Following these retreatments, varieties of tint and color variations of the dyeing colors appeared. Tint and color changes must be considered when making dyeing recipes.

Keywords

• retreatment
• color fastness
• direct dyes
• metal salts
• cationic salts