In continuous open-width preparation of woven cotton sheeting intended for alkaline scouring and hydrogen peroxide bleaching, starch-based size films on warp yarns constitute the primary water-insoluble barrier removed before mercerizing. Mesophilic α-amylase applied by pad-batch hydrolyzes the α-1,4-glycosidic linkages in amylose and amylopectin into lower-molecular-weight dextrins that are readily dispersed in the subsequent hot wash. The preferred production route runs at 25–40 °C and pH 5.5–6.5, which avoids the fabric strength loss and oxalate formation associated with high-temperature oxidative desizing on cotton. A horizontal two-bowl or three-bowl padder is set to deliver 70–80% wet pickup on dry fabric weight, and the enzyme concentration is typically 0.3–1.5 g/L in the pad trough along with 0.5–2.0 g/L of a nonionic wetting agent. The padded web is wound on a low-tension A-frame or large-roll batching station and wrapped in polyethylene film; dwell time is held between 6 h and 24 h depending on fabric construction, woven density, and plant temperature. Process control requires that the batch does not form dried edges or condensate drips, because evaporative moisture loss concentrates auxiliary salts and stops enzymatic hydrolysis at the selvedge. Residual starch after washing is checked qualitatively by iodine staining according to AATCC 94-2017; a negative blue-violet response confirms that the size film has been degraded. Chemical inputs for this route are expected to conform to ZDHC MRSL 3.1, hold an OEKO-TEX ECO PASSPORT certification, and appear on approved input lists under GOTS 7.0 when organic cotton is processed. Within the European Union, the formulation is placed on the market under REACH Regulation (EC) No 1907/2006, and the finished textile must satisfy the chemical safety requirements of GB 18401-2010 for Class B products if imported into China. The desizing enzyme is not effective on polyvinyl alcohol, carboxymethyl cellulose, or acrylic copolymer sizes; if mixed synthetic sizes are present, a combined oxidative-enzymatic pad-steam route or a separate oxidative step is required. Baths contaminated with residual hypochlorite from bleach cleaning cycles depress enzyme activity, so separate dosing lines and complete rinsing between oxidative and enzymatic stages are mandatory. Finished terminal articles from this pad-batch desizing route include 100% cotton woven bed sheeting, shirting, table linen, and sateen bed covering.

Does Jigger Processing Leave Residual Starch on Yarn-Dyed Poplin?

The jigger treats woven fabric in open width under low liquor ratio, but its discontinuous immersion and squeezing cycle can leave starch residues at the fabric surface if the enzyme contact time is too short or the bath temperature falls below the mesophilic activity window. For yarn-dyed poplin, the operational target is to remove starch without mobilizing unfixed dye or triggering cross-colour staining during the long dwell between ends. The enzyme dosage is set at 0.1–0.5% owf, bath pH is maintained at 6.0–6.8, and the temperature is controlled between 45 °C and 60 °C at a liquor ratio of 1:5–1:8. Treatment time of 30–60 min over multiple jigger passes is sufficient for starch hydrolysis; a nonionic penetrating agent at 0.2–0.5 g/L assists size wet-out on densely sett poplin. After enzyme treatment, the bath is drained and the fabric is washed in a counterflow sequence at 80 °C with a nonionic detergent, followed by cold rinsing. Chemical inputs applied to yarn-dyed goods are screened against ZDHC MRSL 3.1 and OEKO-TEX ECO PASSPORT; finished fabric is evaluated for colour fastness to washing according to ISO 105-C06:2010 and for dimensional change according to ISO 6330:2021 where applicable. The terminal products include yarn-dyed poplin shirting, dobby shirtings, and cotton lining fabrics. If colour bleed is observed, the desizing bath should be buffered below pH 7.0 and the temperature reduced toward the lower end of the recommended interval, because vat and reactive dye desorption from sized yarns increases as pH and temperature rise. The use of open-width jigger machines with variable tension control is preferred; excessive fabric tension during the low-liquor contact stage can set crease marks that remain visible after finishing.

When denim garments arrive at the laundry from cut-and-sew operations, warp yarns carry starch-based sizing that stiffens seams and prevents uniform mechanical abrasion in subsequent stone washing or cellulase treatment. An exhaust-style desizing step in a front-loading washer-extractor removes the starch size before pumice stones or neutral cellulase systems are introduced, and the mesophilic α-amylase operates at 40–60 °C and pH 5.5–7.0. The enzyme dose is 0.2–0.8% owg on garment weight, with a liquor ratio of 1:8–1:12 and a residence time of 15–40 min depending on denim weight and starch add-on. Programmable washer-extractors with reversing intervals of 25–35 rpm are used to achieve mechanical flexing without excessive garment tangling. Denim laundries operating under ZDHC Wastewater Guidelines v2.2 and Bluesign system black limits require desizing formulations free of alkylphenol ethoxylates and phosphates; the enzyme preparation should hold OEKO-TEX ECO PASSPORT certification. The desizing bath should remain below pH 7.5, because higher alkalinity promotes indigo redeposition onto pocket linings and weft yarns; a nonionic anti-redeposition agent at 0.3–0.5 g/L is dosed when washed-down indigo concentration rises. The amylase preparation must be free of cellulase side activity, since even low cellulase contamination can reduce tensile strength before the intended abrasion step. Garment tensile strength retention is monitored by ASTM D5035-11(2019) on construction seams and high-abrasion panels. Terminal garment types include five-pocket jeans, denim jackets, skirts, and shorts; the desizing step is considered complete when the fabric shows no blue-violet colour in an iodine spot test aligned with AATCC 94-2017. Batch-to-batch variation arises mainly from differences in starch add-on from weaving mills, and laundries adjust enzyme dose upward within the stated range for stiff, heavily sized denim while maintaining pH below 7.0 to avoid back staining.

Terry Towel Preparation and the Starch–Cellulose Interface

Terry constructions present a high pile density and low ground-warp tension tolerance; starch size is applied to ground and pile warps to survive weaving, but must be removed before bleaching to allow uniform hydrogen peroxide penetration and loop openness. Mesophilic desizing enzyme for terry towel preparation is dosed at 0.3–1.2 g/L in pad-batch or 0.2–0.6% owf in jigger processing, with bath pH held between 5.5 and 6.5 and temperature at 30–45 °C. Pad-batch dwell time ranges from 8 h to 16 h, and the fabric is wrapped in polyethylene film to avoid edge drying. Open-width processing is mandatory because rope-form treatment crushes wet pile loops and creates permanent pile distortion, so low-tension padder and A-frame batching are used before hot wash at 85–95 °C with nonionic detergent. The finished towels for direct skin contact fall under OEKO-TEX Standard 100 Class I criteria; process chemicals must appear on GOTS 7.0 approved input lists when organic cotton is used. Absorbency is assessed by AATCC 79-2018, and residual starch is detected by AATCC 94-2017 before peroxide bleaching. Terminal products include bath towels, bathrobes, beach towels, and kitchen towels. If the batch is allowed to dry or if low-moisture conditions persist in the plant, starch degradation stops before adequate hydrolysis and the subsequent scouring step shows uneven capillary rise; published production-scale data for overdry batch failures in terry mills are limited, but the iodine spot test and AATCC 79-2018 results provide the required release judgement.

When Heat-Set Polyester–Cotton Blends Require Starch Hydrolysis Without Fiber Swelling

Polyester–cotton blends that have passed through a tenter heat-setting stage develop a less swellable polyester phase; residual starch on the cotton component is physically less accessible to water and enzymatic cleavage, yet strong oxidative desizing introduces alkali-induced ester hydrolysis risk to the polyester component. Mesophilic α-amylase removes starch size without the fiber swelling and alkali damage associated with hydrogen peroxide or sodium hydroxide intensive systems. For pad-batch application on heat-set poly/cotton workwear twill, the enzyme is dosed at 0.4–1.0 g/L, pH is maintained at 5.5–6.5, temperature is held at 40–50 °C, and dwell time is 8–16 h with wet pickup of 65–75%. A nonionic wetting agent is added at 0.5–1.0 g/L to improve size wet-out on the hydrophobic polyester fraction; low-tension padder deflection rolls prevent crease formation on heat-set fabric. After enzyme batching, the fabric is washed at 80 °C with sequestrant-free detergent, since calcium-binding agents can destabilize residual enzyme and create uneven desizing at the interface between cotton and polyester. Workwear and uniform fabrics imported into the European Union require conformity with REACH Regulation (EC) No 1907/2006 Annex XVII; chemical inputs should meet ZDHC MRSL 3.1 and OEKO-TEX ECO PASSPORT. The enzyme will not remove polyvinyl alcohol, polyester size, or waxes carried over from spinning; if the size mix contains PVA or CMC, a separate oxidative desizing or size-respecific blend is required. Terminal articles include poly/cotton workwear, uniforms, bed sheeting, and pillow ticking. Published mill data on enzyme diffusion into heat-set blend interfaces are limited; therefore a plant validation using AATCC 94-2017 and AATCC 79-2018 is recommended before bulk production.

Reactive Printing Pretreatment Requires Complete Size Removal Before Alkaline Scouring

Residual starch on cotton print cloth before rotary screen printing reacts with reactive dyes during steaming, lowering colour yield and producing uneven ground colour after washing. A mesophilic α-amylase pad-batch step before alkaline scouring hydrolyzes starch into water-extractable dextrins that are removed prior to alkali treatment, preventing starch–reactive dye adduct formation in the print paste. The enzyme is applied at 0.5–1.5 g/L, pH 5.5–6.0, temperature 30–40 °C, and wet pickup 70–80%, with batching time of 12–24 h. After batching, the fabric is washed at 85 °C with nonionic detergent and then checked for residual starch by iodine spot test according to AATCC 94-2017; if a blue-violet colour persists, the batch is extended or the fabric is reprocessed before scouring. Chemical inputs and pretreated fabric should conform to GOTS 7.0 where organic cotton is used; finished printed textiles must meet OEKO-TEX Standard 100 Class I or Class II depending on end use, and colour fastness to washing is assessed by ISO 105-C06:2010. The critical pH limit is 5.0; below this value enzyme activity falls and the acid can hydrolyze cellulose over long batch times, while above 6.5 the mesophilic amylase stability drops and residual starch may survive. Terminal printed articles include rotary screen printed cotton apparel fabric, printed bed linen, table linen, and decorative textile. Because reactive print cloth is often mercerized after desizing, complete starch removal also prevents caramelized starch deposits on mercerizing rolls and subsequent colour specks in the print ground.