The Wet Processing Sequence
Fabric directly off the loom (greige goods) contains sizing starches, natural waxes, and impurities that prevent dye absorption. Preparatory wet processing is mandatory.
Desizing & Scouring
Enzymatic or oxidative removal of the sizing agents applied to warp yarns prior to weaving. Scouring uses alkali baths to remove hydrophobic natural waxes from cellulosic fibers.
Bleaching
Destruction of natural coloring matter, typically using hydrogen peroxide (H2O2), ensuring a uniform white base for consistent shade reproduction during dyeing.
Dye Classes and Affinities
Not all dyes work on all fibers. The chemical structure of the polymer dictates the necessary dye class.
| Dye Class | Target Fiber | Bonding Mechanism |
|---|---|---|
| Reactive Dyes | Cotton, Viscose | Covalent bonding with hydroxyl groups; excellent wash fastness. |
| Disperse Dyes | Polyester, Acetate | Sublimation/solid solution; dye migrates into hydrophobic fibers at high heat. |
| Acid Dyes | Wool, Silk, Nylon | Ionic bonds formed with amino groups in acidic conditions. |
| Vat Dyes | Cellulosics (Denim) | Water-insoluble dyes reduced to soluble form (leuco state), then oxidized back to insoluble state inside the fiber (e.g., Indigo). |
Mechanical and Chemical Finishing
Post-dyeing, fabrics undergo finishing to alter their drape, hand-feel, or utility. Mechanical finishes include calendering (pressing between heavy heated rollers for luster) and napping (raising fibers for softness). Chemical finishes utilize resins to impart anti-wrinkle properties, flame retardancy, or durable water repellency (DWR).