Desizing

Desizing is a preparatory processing step in textile manufacturing in which sizing agents applied to warp yarns are removed from woven fabric. Size helps protect yarns during weaving by reducing friction and breakage, but it can impede dye penetration, finishing, and fabric hand if left in place. Effective desizing improves dye uptake, uniformity, and wettability of the fabric.

Sizing agents vary by fiber and process. Natural starches (such as corn or wheat starch) and their derivatives are common, along with synthetic polymers like polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC). Some fabrics may use dextrins or other modified starches. The choice of desizing method depends on the size composition, fabric type, environmental considerations, and downstream finishing steps.

Desizing methods are typically categorized as enzymatic, chemical, or a combination. Enzymatic desizing uses alpha-amylase to break down starch-based sizes into soluble fragments that are washed away. Acid desizing employs sulfuric acid to hydrolyze starch-based sizes. Oxidative desizing uses oxidizing agents such as hydrogen peroxide to assist breakdown of the size. Alkaline desizing with caustic solutions may be used for certain synthetic sizes. The selection aims to maximize size removal while minimizing damage to the fabric and reducing environmental impact.

Process considerations include temperature, pH, and contact time. Enzymatic desizing is often performed at moderate temperatures and near-neutral pH, and is favored for being more eco-friendly due to lower chemical load and easier effluent treatment. All methods require thorough washing to remove hydrolyzed fragments and additives, followed by neutralization, drying, and preparation for scouring, bleaching, or dyeing.