Desizing - Size Removal

Desizing removes sizing agents (starch, PVA, CMC, acrylics applied during warping 3-15% by weight) from woven fabrics improving wettability and dye penetration. Desizing methods: (1) Enzymatic desizing (most common for starch)—α-amylase enzymes (bacterial or fungal origin, optimal pH 5.5-7.0, temperature 60-70°C) hydrolyzing starch α-1,4-glycosidic bonds into water-soluble dextrins, maltose, glucose removable by washing, achieving 95-98% size removal in 30-60 min with minimal fiber damage. (2) Oxidative desizing—hydrogen peroxide or sodium hypochlorite oxidizing starch at high pH, faster (15-30 min) but risk of cellulose degradation (5-10% strength loss), used when combining with scouring/bleaching. (3) Acid desizing—dilute sulfuric or hydrochloric acid (0.5-2%) hydrolyzing starch at 70-80°C, rarely used (fiber damage risk, corrosion). (4) Rot steeping—bacterial fermentation decomposing starch, traditional method (12-24 hours), unpleasant odor, environmental issues, largely obsolete. Size-specific: PVA removed by hot water washing (80-95°C), synthetic sizes requiring alkaline hydrolysis or enzymes (pectinase, cellulase cocktails). Testing: iodine test (starch reacts forming blue complex, visual assessment), water drop test (wettability—instant spreading indicates complete desizing), and weight loss measurement. Consequences of incomplete desizing: uneven dyeing (sized areas repelling water/dye 20-40% shade variation), poor fastness (dye not penetrating properly), and finishing defects (size interfering with resin application).