If most dye leaves the bath but much of it washes out afterwards, which result fits?
A Low exhaustion, high fixation
B No uptake, high fixation
C High exhaustion, low fixation
D No exhaustion, full fixation
Answer: C. High exhaustion, low fixation. Dye left the bath and reached the fabric, but a substantial fraction did not remain fixed after wash-off.
Why does higher temperature often improve disperse dye penetration into polyester?
A Fibre pores close completely
B Polyester becomes cellulose
C Dye gains covalent groups
D Polymer mobility increases
Answer: D. Polymer mobility increases. Greater segmental motion in the polymer can help dye molecules diffuse within the fibre.
At 6 L of liquor per kilogram of dry goods, what bath volume is needed for 90 kg?
A 15 L
B 150 L
C 900 L
D 540 L
Answer: D. 540 L. Every kilogram of goods requires 6 L, so multiply by 90.
Readings exceed the linear absorbance calibration range. What is the best response before estimating residual dye concentration?
A Ignore the calibration
B Increase nominal dye uptake
C Dilute by a known factor
D Change fibre identity
Answer: C. Dilute by a known factor. Dilution brings the sample into the valid range. The known factor converts the reading to the original concentration.
Why can adding electrolyte help anionic dye approach cotton in a conventional bath?
A It forms fresh cellulose
B It screens charge repulsion
C It neutralizes all dye
D It oxidizes dye completely
Answer: B. It screens charge repulsion. Electrolyte can screen the repulsion between the anionic dye and the negatively charged textile surface.
From 2.0 g of initial dye, 0.5 g remains in the bath after dyeing. What is exhaustion, assuming uptake accounts for the difference?
A 25%
B 50%
C 150%
D 75%
Answer: D. 75%. Uptake is 1.5 g out of the original 2.0 g.
Only the polyester component of a blend becomes blue in a chosen process. Which term describes this result?
A Full blend saturation
B Selective dyeing
C Optical brightening
D Uniform cross staining
Answer: B. Selective dyeing. The route preferentially colours one fibre type while leaving the other substantially less coloured.
Exposing a reduced vat dye bath to air too early can cause what fault?
A Complete dye hydration
B Permanent dye solubility
C Premature insoluble dye formation
D Loss of cotton hydroxyls
Answer: C. Premature insoluble dye formation. Oxidation regenerates the insoluble dye. If it occurs early, penetration can suffer.
From a 10 g/L dye stock, what volume supplies 0.25 g of dye to a lab dip?
A 25 mL
B 2.5 mL
C 250 mL
D 4 mL
Answer: A. 25 mL. Dye mass divided by concentration gives 0.025 L.
Before dye enters a fibre, what transport step moves it across the liquid boundary layer?
A Internal fibre diffusion
B External mass transfer
C Fibre finishing
D Dye polymerization
Answer: B. External mass transfer. Dye must move through the liquor near the fibre surface before it can diffuse through the fibre interior.
Imagine two fabrics with similar surface shade but different depth of dye penetration. What property is different?
A Internal dye distribution
B The bath’s initial pH
C Dye charge necessarily
D Original fabric yardage
Answer: A. Internal dye distribution. Surface appearance does not uniquely describe how dye is distributed through the fibre cross section.
Prepare an exhaust recipe at 1.5% owf for 80 kg of dry goods. How much dye is required?
A 5.33 kg
B 1.20 kg
C 2.00 kg
D 0.12 kg
Answer: B. 1.20 kg. Multiply dry goods mass by 0.015.
Two systems reach the same equilibrium uptake at different times. Which aspect differs?
A Unit of concentration
B Dyeing kinetics
C Fibre weight necessarily
D Final equilibrium uptake
Answer: B. Dyeing kinetics. The difference is the rate at which each process approaches its final equilibrium.
Before fixing colour continuously, the fabric carries much more dye liquor near one selvage. Which equipment condition should be checked?
A Uneven pad nip pressure
B Excess yarn twist everywhere
C Different lightfastness grades
D Unequal fibre melting point
Answer: A. Uneven pad nip pressure. Uneven pressure across the padding nip can cause different retained liquor amounts across the fabric.
After padding, the wet mass is 90 g and the dry mass was 50 g. What is the wet pickup?
A 40%
B 44.4%
C 125%
D 80%
Answer: D. 80%. The 40 g liquor pickup is 80% of the 50 g dry mass.
Comparing the same dye’s uptake on two fabrics, which value should be recorded alongside bath temperature?
A Fibre identity
B Machine paint colour
C Room door width
D Operator seat height
Answer: A. Fibre identity. Dye affinity and transport depend on the textile substrate, so fibre type is part of a useful comparison.
Migration can help level a dyeing before fixation by doing what?
A Releasing all fibre groups
B Repeating the wash test
C Redistributing absorbed dye
D Increasing yarn linear density
Answer: C. Redistributing absorbed dye. Mobile dye can redistribute between regions, helping reduce early shade differences.
Holding a mixed alkaline reactive dye solution too long before application may reduce bonding for what reason?
A Dye can hydrolyse first
B The dye enters polyester
C Salt becomes a binder
D Cotton turns into nylon
Answer: A. Dye can hydrolyse first. Some reactive groups can react with water before they have a chance to bond to cellulose.
Suppose dye concentration is 2 g/L and liquor ratio is 10 L/kg. What is the applied dye percentage on dry fabric?
A 0.02% owf
B 2.0% owf
C 20.0% owf
D 0.2% owf
Answer: B. 2.0% owf. Each kilogram receives 20 g of dye, or 2% of its dry mass.
The core of a dyed yarn package is pale while the outside is dark. What should be checked first?
A Fibre identification stain
B Yarn dye lightfastness
C Loom shed settings
D Liquor flow through yarn
Answer: D. Liquor flow through yarn. Restricted circulation through the package can produce uneven radial dye uptake.
When a dyeing reaches equilibrium, what is true about transfer between liquor and fibre?
A Molecular motion stops entirely
B All dye leaves the liquor
C No net dye transfer
D All fibre sites are filled
Answer: C. No net dye transfer. At equilibrium, opposing molecular transfers balance on average. Dye may still remain in both phases.
Of 4 g initially added, the textile retains 2.4 g after wash-off. What fraction of the initial dye remains fixed?
A 24%
B 2.4%
C 60%
D 40%
Answer: C. 60%. Initial-basis fixation is 2.4 divided by 4.
A fabric dyelot appears darker at fold lines even though there is enough dye in the bath. What should be assessed before increasing dye dosage?
A Only yarn fibre diameter
B Only the dye container mass
C UV detector wavelength
D Fabric movement and folding
Answer: D. Fabric movement and folding. Persistent folds can expose fabric regions to different flow and contact conditions. More dye does not correct uneven exposure.
Dye X and dye Y are mixed in a 3:2 mass ratio. How much X is in 100 g of the blend?
A 30 g
B 60 g
C 66.7 g
D 40 g
Answer: B. 60 g. Three out of five parts of the blend are dye X.
Uneven scouring shows up as patchy shade after dyeing. What is the likely connection?
A Local wettability differs
B Bath colour changes class
C Yarn twist becomes identical
D Every region exhausts equally
Answer: A. Local wettability differs. Areas that wet or absorb differently can take up unequal amounts of dye.