Lesson 1Pretreatment steps for 100% cotton: desizing, scouring, bleaching and typical process rangesOutline pretreatment of 100% cotton, including desizing, scouring, and bleaching. Discuss process ranges, key parameters, and how uniform pretreatment underpin level dyeing and reproducible shade on cotton.
Desizing methods and enzyme versus oxidative routesScouring chemistry, alkali dosage and temperatureBleaching systems, stabilizers and whiteness targetsRinsing and neutralization after pretreatmentImpact of pretreatment quality on dyeing behaviorLesson 2Batch sequencing, dye lot scheduling and best practices to minimize re-dyeing and contaminationCover planning of dye lots, batch sequencing, and scheduling to reduce re-dyeing, contamination, and shade variation. Emphasise machine loading, colour grouping, and communication between planning and dye house.
Lot size, fabric grouping and machine loadingDark-to-light and sensitive shade sequencingHandling re-dye lots and partial batch correctionsCommunication between planning and dye houseDocumentation and traceability of each dye lotLesson 3Dyeing methods: batch dyeing (jet, jigger), continuous dyeing, and pad-steam; process choices for knit and woven fabricsCompare batch and continuous dyeing methods for knits and wovens, including jet, jigger, pad-dry, and pad-steam. Discuss process selection, productivity, shade control, and fabric quality considerations.
Jet dyeing principles and settings for knitsJigger dyeing control for woven fabricsPad-dry and pad-steam continuous dyeing linesProcess selection for fabric type and shade depthEnergy, water use and productivity comparisonLesson 4Reactive dye chemistry fundamentals and common recipes for cotton dyeingIntroduce reactive dye chemistry on cotton, including dye-fibre bonding, hydrolysis, and fixation. Present common dye classes, reaction mechanisms, and standard recipes for light, medium, and dark shades on 100% cotton.
Reactive dye classes and functional groupsCellulose structure and reactive dye bondingHydrolysis, fixation and unfixed dye behaviorStandard light, medium and dark shade recipesAlkali selection for cold and hot brand dyesLesson 5Key process parameters to control: liquour ratio, pH, temperature profiles, time, salt and alkali dosingExplore critical wet processing parameters and how liquor ratio, pH, temperature profile, time, and salt or alkali dosing interact to control dye uptake, levelness, and reproducibility in cotton dyeing operations.
Effect of liquor ratio on dye uptake and levelnesspH control for reactive dye fixation and stabilityTemperature profiles and heating rate optimizationTime control, holding periods and migration balanceSalt and alkali dosing curves and addition methodsLesson 6Dye bath management and recipe control to prevent lot-to-lot shade variationExplain how to design, charge, and monitor dye baths to avoid shade variation. Focus on recipe verification, addition sequences, bath reuse, and in-bath corrections to maintain consistent shades between production lots.
Recipe sheet verification and raw material checksSalt and alkali addition sequence and timingBath reuse, topping up and correction limitsIn-bath shade checks and on-line adjustmentsCleaning protocols to avoid cross contaminationLesson 7Auxiliaries affecting shade and pilling (sequesterants, levelling agents, dispersing agents, softeners)Cover roles of sequestering, levelling, dispersing agents, and softeners in controlling shade and pilling. Discuss selection criteria, dosage, and compatibility with reactive dyes and pretreatment residues in cotton processing.
Sequestering agents and water hardness controlLeveling agents for uniform dye distributionDispersing agents to prevent particle aggregationCationic and silicone softeners and handle effectsAuxiliary compatibility and foaming considerationsLesson 8Washing cycles and aftertreatments that influence color fastness and pillingDetail washing-off stages and aftertreatments wey remove unfixed dye, improve colour fastness, and reduce pilling. Emphasise sequence design, water quality, and chemical selection for durable, low-pilling dyed cotton fabrics.
Soaping stages for reactive dye washing-offRinsing efficiency, water quality and temperatureSoaping agents and chelants for unfixed dye removalAftertreatments to improve wet and rubbing fastnessMechanical and chemical approaches to reduce pillingLesson 9Sampling and spectrophotometric shade evaluation: delta E, standard illuminants, illuminant/observer settings, and tolerance limitsDescribe sampling procedures and spectrophotometric shade evaluation. Cover delta E calculations, standard illuminants, observer settings, and tolerance limits used to approve or reject production dye lots.
Bulk and lab sampling procedures for dye lotsInstrument calibration and standardization stepsCIELAB coordinates and delta E calculationsChoice of illuminant and observer combinationsSetting and managing commercial shade tolerancesLesson 10Common causes of shade variation (uneven dye exhaustion, bad liquor distribution, temperature gradients, mismatched recipe or water quality)Analyse frequent causes of shade variation, including uneven exhaustion, liquor distribution issues, temperature gradients, recipe errors, and water quality. Provide diagnostic approaches and corrective actions for mills.
Uneven dye exhaustion and migration problemsPoor liquor circulation and fabric loading issuesTemperature gradients and sensor inaccuraciesRecipe, weighing and dispensing mistakesWater quality, hardness and contaminant effects
