desize

Desizing is the chemical or enzymatic removal of sizing compounds that were applied to yarn before weaving. Weavers coat warp yarns with starch, gum, wax, or synthetic polymers to stiffen them and reduce breakage during the loom run. Once weaving is complete, these materials must come out before dyeing, printing, or finishing can proceed effectively. Without desizing, dyes penetrate unevenly, prints lack definition, and the fabric feels stiff and unpleasant.

The process varies by sizing type and desired speed. Hot water and mild alkali (sodium carbonate or caustic soda at pH 10-12) work for starch-based sizes; enzyme-based desizing uses amylase to break down starch molecules at 60-70°C over 30 to 60 minutes. Synthetic sizes may require hotter water, stronger alkali, or specialized solvents. Desizing happens in jet dyeing machines, padders, or open-width washers where cloth contacts the chemical liquor repeatedly as it moves through the bath.

Common faults and trade-offs

Incomplete desizing leaves opacity and uneven dye uptake. Over-desizing, especially with caustic, weakens cellulose fibers and causes yellowing or loss of tensile strength. Desizing also consumes significant water and generates chemical effluent; plants must manage pH and organic loading before discharge. In modern mills, enzymatic desizing is preferred for cotton and linen because it is gentler, more selective, and easier to control than chemical routes.

The name comes straightforwardly from its function: to remove the size. In textile mills, it is a mandatory stage that sits between loom and dye house. Efficiency matters because desizing time and chemical cost flow directly into production schedules and margins. Some mills combine desizing with scouring (alkali washing to remove oils and waxes) in a single operation to save time and water.