Reactive dyeing leaves a sizable dye load unbonded—often 10–50%—and removing it is a high-stakes, high-cost wash game. The winning moves: staged rinses, specialty soaping agents and dispersants, and tight control of heat and pH, all backed by data and standards.
Unfixed dye load and staged rinsing
Textile dyeing invariably leaves a large fraction of dye unbonded. For reactive dyes on cotton, only 50–90% of the dyestuff actually fixes; the balance is hydrolyzed or loosely adsorbed and must be washed off (iwaponline.com). Failure to remove these unfixed dyes causes color bleeding, staining, and poor fastness (kotani-chemical.co.jp). Industry surveys note that up to 50% of dyeing costs goes into post-dye wash-off and effluent treatment (www.mdpi.com).
Consequently, comprehensive rinsing (“soaping”) steps are mandatory. In practice this means multiple rinses in sequence: typically an initial cold rinse (~20–30 °C) to dilute out salts and soluble dyes, followed by one or more hot rinses and finally an alkaline boiling wash with detergents (the soaping stage) (www.mdpi.com) (iwaponline.com). For example, a conventional reactive dye wash-off might proceed as follows at a liquor ratio (~bath-to-goods volume) ≈20:1 (www.mdpi.com):
- Cold rinse at ≈20–30 °C (10 min) to flush out stray solubles.
- Neutralization (if needed) – e.g. add ~5–10 g/L acetic acid at 20–30 °C (10 min) to neutralize residual alkali (iwaponline.com).
- Warm rinse at 50–70 °C (10 min) to begin dye diffusion.
- Alkaline soaping wash at ~100 °C, pH ~10–11 (15–20 min) with 1–2 g/L specialized soaping agent (surfactant) and additions like Na₂CO₃ (www.mdpi.com).
- Hot rinse at 80–90 °C (10 min) to remove solubilized dye and chemicals.
- Final cold rinse (20–30 °C, 10 min) with fresh water.
Such multi-stage washing (cold → hot → alkaline boil → hot → cold) requires large water volumes and energy. Kauls et al. report that reactive wash-off alone can involve several cold (~40–60 °C) and hot (~80–98 °C) rinses (iwaponline.com). In one lab simulation, “cold rinse, neutralize, warm wash, hot wash, soaping, final rinses” totaled 50+ minutes of treatment (www.mdpi.com) (iwaponline.com).
Specialty soaping and dispersant chemistry
The core of dye wash-off is a surfactant/soaping agent tailored for textiles (surfactants reduce surface tension to lift soils). These are typically non-ionic/anionic polymers with super wetting and dispersing power. A good soaping agent must remain stable in hard water and alkaline conditions, work even at lower temperatures, and have a high affinity for dye but low affinity for fiber (kotani-chemical.co.jp). In practice, products like Kotani’s “Emill” series (e.g. SK-D) are used at ~0.5–2 g/L to achieve “quick, powerful soaping” (kotani-chemical.co.jp) (kotani-chemical.co.jp).
At 75–90 °C, Kotani reports >50% of hydrolyzed reactive dye can be washed off; using an effective soaping surfactant plus additives yields nearly complete removal (kotani-chemical.co.jp) (kotani-chemical.co.jp). Dispersing agents such as sodium tripolyphosphate (STPP) and sodium lignosulfonate, plus sequesterants (binders for metal ions), keep fine dye particles in suspension; adding even 1–2 g/L STPP to the soaping bath markedly improves unfixed-dye removal (kotani-chemical.co.jp).
Large fleets also employ polymeric dye transfer inhibitors (DTIs)—for example polyvinylpyrrolidone or vinylimidazole copolymers—to “trap” any dye that comes off, preventing redeposition on other fabric (www.mdpi.com) (www.mdpi.com). Innovative wash cycles using DTIs have demonstrated dramatic resource savings—one study achieved ~90% energy and 40% water reduction over a conventional wash-off while still capturing ≥95% of unfixed dye (www.mdpi.com).
Printed fabrics often carry residual thickeners or binders (e.g., CMC, starch, PVA, acrylates). Specialized cleaners address these. In many cases, enzymatic detergents are employed: amylases or cellulases added to the wash will break down natural thickeners, greatly facilitating their removal. A Novo Nordisk process patent showed that enzymatic washing of cotton printed with reactive dyes (and polymer thickeners) drastically improved removal of both paste and dye, slashing required rinse time and water by breaking down the thickener polymer (www.freepatentsonline.com). Oxidizing agents (e.g., dilute H₂O₂ or NaClO) are sometimes used post-soaping to eliminate tannins or vat dye residues, with careful control to avoid fiber damage.
Temperature control in wash-off
Wash temperature critically impacts cleaning. Higher temperatures swell the fiber and increase dye diffusion, dramatically enhancing dye removal (www.fibre2fashion.com) (kotani-chemical.co.jp). Empirically, raising the wash from 50 °C to 70 °C “significantly increases” the rate and amount of unfixed dye washed out (www.fibre2fashion.com).
Industry practice therefore uses boiling or near-boiling soaping baths for reactive dyes (www.mdpi.com). Kotani notes that hot rinses at 70–95 °C can remove >50% of hydrolyzed reactive dye on cotton (kotani-chemical.co.jp). By contrast, if wash temperatures are kept too low, large fractions of unfixed dye will remain on the fiber.
Extremes must be managed: excessively hot or cold baths can chemically degrade dyes. High temperature and very high/low pH can hydrolyze dye chromophores (the color-bearing groups), altering color (kotani-chemical.co.jp) (www.fibre2fashion.com). In practice, a graded profile is used: initial rinses are moderate (30–60 °C) to gently flush off salts and loose dye (iwaponline.com), then temperatures ramp to 80–100 °C for soaping and final rinsing to maximize dye solubility.
pH management from neutralization to soaping
pH is equally crucial. In reactive dyeing, fixation to cotton requires an alkaline bath (typically pH 10–11 with soda ash or NaOH) (www.mdpi.com). Similar alkalinity is used in the soaping wash to keep the hydrolyzed dyes soluble. Standard practice is to adjust the soaping bath to ~pH 10–11 (e.g., with ~20–25 g/L Na₂CO₃) (www.mdpi.com).
An intermediate neutralization step is often applied after dyeing to stabilize the fabric: for example, a dilute acetic acid rinse (pH ~3–5) is used to neutralize residual alkali before the alkaline soaping (iwaponline.com). Maintaining pH prevents re-adsorption: waste dyestuff is best kept in solution. In reactive soaping, the bath is intentionally alkaline to favor fiber-dye hydrolysis and dye release. Conversely, after washing, the final rinse is often mildly acidic or neutral to ensure the fabric is safe and all dye is soluble. For precise acid/alkali additions, plants typically meter chemicals with equipment such as a dosing pump.
The Indonesian standard mandates discharged effluent remain within roughly neutral limits (pH 6.0–9.0) (www.scribd.com), so manufacturers typically trim pH to ~7 before release. Notably, extreme pH swings are avoided—too high a pH drives further hydrolysis of dyes (making more non-fixing byproducts), whereas too low a pH (acidic) can precipitate dyes or attack fiber. Kotani emphasizes that imbalanced pH can cause “discoloration due to hydrolyzing of dyestuff” (kotani-chemical.co.jp).
Outcomes, effluent, and reuse targets
Quantitatively, the effectiveness of wash-off can be measured in dye retention and compliance. A well-executed wash removes most unfixed dyes: in practice, >90% of remaining soluble chromophores can be eliminated with a proper soaping cycle (kotani-chemical.co.jp). This yields high wash fastness on the fabric (bleeding levels below industry limits) and a final bath COD amenable to treatment or reuse. Insufficient wash-off leaves residual dyes that appear as high COD/color in wastewater.
Industrial data underscore the scale. An average reactive dye batch (to dye 1 kg cotton) might use 100–150 L of water and tens of kilograms of salt and alkali (iwaponline.com) (iwaponline.com). Each wash cycle can contribute grams of dye and chemicals to the effluent. Innovations can shift these figures: polymer-assisted wash systems have demonstrated 90% reductions in energy use and 40% less water despite meeting the same fix/fastness requirements (www.mdpi.com).
For businesses, the impact is tangible. Effective wash-off delivers cleaner cloth with high colorfastness (avoiding rejects), and it eases wastewater treatment. Conversely, poor rinsing raises effluent loads—meaning higher costs and potential regulatory fines. Data from Indonesia’s textile industry shows stringent targets: even in the transition period, discharged effluent must achieve <150 mg/L COD and <50 mg/L TSS while meeting a color (true color/PtCo) ≤200 (www.scribd.com). Plants often pair rinse optimization with end-of-pipe unit operations—such as a clarifier for suspended solids, or activated carbon for organics and color—before aiming at reuse through ultrafiltration or integrated membrane systems as needed.
Practical wash-off formula
In practice, a soaping recipe for reactive-printed cotton is: heat rinses from ambient up to ~100 °C, alternate acid/alkali steps to set pH, and include ~1–2 g/L of a high-efficiency textile detergent plus dispersants (e.g., STPP, polymeric DTIs) and even enzymes for thickener removal. This multi-step routine is backed by data: e.g., 50% of reactive dyes may be washed out at 90 °C in water alone (kotani-chemical.co.jp), and specialized soapers and dispersants raise that toward 90–100% removal. Likewise, studies show controlling bath pH (neutralizing and re-alkalizing as needed) and using elevated temperatures maximize dye dissolution while preventing re-deposition (kotani-chemical.co.jp) (www.fibre2fashion.com). In pilot trials, such protocols have achieved required wash-fastness with far less energy/water (e.g., halving cycle time or slashing COD in effluent) compared to haphazard rinsing (www.mdpi.com).
Sources and regulatory anchors
Established industry and academic sources were used. Key references include Islam et al. (IWA Water Reuse Desalination, 2019) (iwaponline.com) (iwaponline.com) on reactive-dye wash processes; Martin et al. (Sustainability, 2024) (www.mdpi.com) (www.mdpi.com) on wash-off cycles and costs; Kotani Chemical (corporate tech note, 2020) (kotani-chemical.co.jp) (kotani-chemical.co.jp) on soaping chemistry; Parkes (Fibre2Fashion, 2008) (www.fibre2fashion.com) on temperature effects; Abdullah et al. (J. Natural Fibers, 2008) and US Patent 5,405,414 (www.freepatentsonline.com) for enzymatic thickener removal; and Indonesian regulations (Permen LHK No. P.16/2019) (www.scribd.com) (www.scribd.com) for effluent standards. These sources provide the quantitative and technical data underpinning the above guidelines.
