Quantifying Radial Fixation Gradients in Ultra High Twist Viscose Ply Yarns under Dynamic Alkali Steaming
Dense viscose ply yarns require controlled swelling alkali blends to eliminate core fixation gradients during dynamic steam fixation.
Sodium Carbonate Fixation
Alkaline Activation
Water-soluble salts that raise the pH of a dye bath are necessary to initiate chemical reactions between reactive dyes and cellulosic fibers. In the application of reactive dyes to cotton, sodium carbonate fixation creates the necessary alkaline environment to deprotonate the hydroxyl groups on the cellulose polymer. This activation allows the dye molecule to react directly with the fiber.
Covalent Bonding
Chemical bonding between the dye and the substrate ensures that the color becomes a permanent part of the fabric. Once the pH is raised during sodium carbonate fixation, the dye molecules form a covalent bond with the cellulose, which resists subsequent laundering. This process locks the colorant into the molecular structure of the cotton.
Colorfastness Quality
Incomplete dye reaction leads to bleeding and poor wash fastness during consumer use. Achieving proper sodium carbonate fixation prevents unfixed dye molecules from remaining loosely trapped within the fiber matrix, ensuring high wet-fastness ratings. This processing step is essential for garments that undergo frequent high-temperature washing.
In addition, it reduces the amount of after-soaping required to clear the fabric, saving both energy and water during the rinsing cycles.
Process Optimization
Temperature control during the alkali addition prevents premature dye hydrolysis in the bath. If sodium carbonate fixation is started too early or at too high a temperature, the dye reacts with water instead of the cellulose. This reaction wastes chemical inputs and yields lighter shades than specified.