Because of the complex interactions of the components in dyeing system, many variable must be controlled in order to produce high quality dyeings. Variations in dyeing nay be of several types including substrate variations, variations in chemicals (including water), variations in preparation of the substrate for dyeing and procedural variations.
Substrate variations
Several types of substrate variations may cause variations in dyeability of textiles. Cotton maturity is an excellent example of a variation in raw material that can have a major effect on dyeability. The secondary wall in the immature cotton fiber is not completely developed. Since dyes adsorb on the cellulose molecules in the fiber , immature fibers do not dye the same as mature fibers. Different dyes are absorb to the presence of immature cotton fibers range from the presence of clumps of white , undyed fibers to off shade materials resulting from different uptake of the different dyes in the dye formulation .More subtle fiber differences than gross differences in cotton maturity can also affect dyeability of the fiber . Minor differences in dyeability of cotton fiber should not be a problem where appropriate blending of fiber is done in the yarn manufacturing processes.
Variations in chemicals
Variations in water or auxiliary chemicals used in the dyeing process can cause dyeing defects. The dye itself is probably the best example of a possible chemical variation that can affect dyeing. Dyes can vary in strength , a measure of the colour depth per unit of dye used, or in hue.
Variations in preparation
Consistent preparation of the substrate for dyeing is critical to consistent dye application . Variations in preparation often cannot be corrected in dyeing and cause defects or off-quality product. Thermoplastic synthetic fibers such as nylon and polyester are subject to variation in dyeability resulting from differences in the “ heat history” or “energy history” of the fibers. Just a few degrees of difference in temperature of heat setting or small change in tension on fibers, yarns, or fabric in manufacturing can cause dyeing rate differences. Differences in dyeability due to differences in rate of dye uptake can sometime be overcome by increasing dyeing time or by adding auxiliary chemical to the dyebath.
Procedural variations
Procedural variations must be closely controlled in dyeing. Obviously, dye and chemical computations and weightings must be correct. Reproduction of dyeing cycle time, dyeing temperature, rate of temperature rise, and agitation of the substrate and dyebath must all be controlled for dyeing to be successful.
