For this direct dye apply at high temperature and acidic medium. In this purpose direct dye is used to complete unions dyeing same color. Finally we get different color union dyed materials.ĭyeing the cotton and wool/silk fibers by using same color: In this process, firstly cotton fibers are dyeing by direct dye at low temperature and then wool/silk fibers dyeing by acid dye. There are different process to dyeing the wool/silk and cotton fibers by using different dyes. In this process soda must be used, because it works as a protector for wool/silk fibers dyeing.ĭyeing the cotton and wool/silk fibers by different color: So it is best to dyeing cotton fibers, to leaving wool/silk white. Because at low temperature direct dyes will exhaust on the cellulose and at low temperature direct dye have no affinity of wool/silk. Fig: Union Dyeingĭyeing the cotton fibers, leaving the wool/silk fibers white:ĭirect dye is used for this dyeing process. After dyeing the materials need to be washing well to remove the acid. For this process acetic or formic acid is use to instead of sulphuric acid to protect the cellulose. So it is very easy to dyeing the wool/silk in union without staining the cellulose.
Because, acid dye have no affinity of cotton fibers. In this purpose generally acid dye is used to complete union dyeing process. Union Dyeing Techniques of Protein and Cellulosic Fibers:ĭyeing the wool/silk fibers, leaving the cotton fibers white: Dyeing the protein or cellulosic fiber and leaving the other white.There are three possible ways of union dyeing of protein and cellulosic fibers. Tone-in-tone dyeing: The different fibers have the same hue but with different depths.Cross-dyeing: The different fibers are dyed different hues.Reserve dyeing: At least one fiber is undyed and remains white.Solid shade dyeing: All the fibers are identically colored.In union dyeing, there are several possibilities for coloring the different fibers: In most of these dyeing, therefore, minimizing the degree of cross-staining is essential. Staining of a fiber implies that the dye is not well fixed and the color will have poor fastness properties. Such cross-staining must be distinguished from cross-dyeing. Some of the dyes selected for coloring one component of the blend often stain the other type of fiber. Ideally, the dyeing of each type of fiber is so selective that the dyes for coloring one fiber completely reserve the other. This will be the longest type of union dyeing process. Union dyeing often involves coloring each fiber component separately using appropriate dyes in two different dyebaths. Union dyeing is a method of dyeing a fabric containing two or more types of fibers or yarns to the same shade. For this reason dyeing of mixtures of these two fibers is often referred to as union dyeing. The oldest mixture of all is wool and cotton, which is used to make cloths known as unions. The advent of regenerated and synthetic man made fibers has greatly increased the scope for making blends of two or more components. Lecturer, Institute of Textile Engineering & Information Technology Last Updated on Union Dyeing Techniques, Factors and Limitations
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