Factors Affecting Reactive Dye Fastness
2016-09-09 08:24 | writer: admin
The reactive dyes to dye the cellulosic fiber in the forms of covalent bond is to be combined with fiber forming chemical bonding. Thus, in theory, covalent bonding between dyes and fibers, can give dyed good color fastness. But in fact, the textile will be faded, discoloured and stained etc during the test, wash and storage process. Especially when dyed dark color, the wet grinding fastness and soaping staining fastness, and when dyed the light color, the light fastness and chlorine fastness all all not good. There are two reasons that cause it’s poor color fastness: one is the dyes’ problem, the other one is the problem of dyeing.
1, the dye problem
Reactive dyes to dye cellulose fibers, although chemical combined with the fibers in the forms of covalent bond, when the dye is wet, heat, light, acid, alkali or oxidant, some parts of the parent structure would be changed. For example, the azo group decomposes, amidogen oxidation, complex metal ion separation, or dye fiber covalent bond hydrolytic cleavage etc, which may result in discoloration and some lower color fastness of dyed. For another example, the covalent bond of reactive dye and cellulose macromolecule will be broken in certain conditions, changed to forhydrolysis dyes and fall off, which makes the dyed do not have good wet grinding fastness and light fastness
2, the dyeing problem
The reactive dyes in use, the correct or not dyeing method directly affect the color fastness of dyed. For example, improper melting dyes, hydrolysis of dyes, stiff water quality, too many calcium and magnesiumm, makes the dyes gathered and precipitation; improper solid color conditions caused low fixation rate; washing after dyeing and poor soaping, unclean removed the unfixed dyes; the finished product with acid and alkali, hydrolysis of dyes and chain scission increased, all can makes surface dyeing increase. As for the surface dyeing, it refers to the dyes attached on the fiber but not bonded. They including: partially or fully hydrolyzed dyes, adsorbed on the fiber but not participate in reaction, ethylene vitriol ester group has been occurred elimination reaction, sulfate group already took off, the dyes not bounding with fiber. Since the floating dye fibers have different degrees of affinity, which brings washable dye difficult. Therefore, in practical use, the floating dyes on the fibers can not be completely removed by water washing and soaping.