Factsheet

Dyeing, Pre-Treatment and Finishing's

Group 20

Dyeing

Indigo DyeDye Type:Vat Dye

→ Synthetically produced

→ Insoluble in water and it has to be converted into a water soluble form by

reducing under alkaline conditions

Process of reduction of indigo:Bacterial reductionChemical reduction

Electrochemical reductionCatalyic hydrogenation

Electrocatalytic hydrogenation

Dyeing takes place:before weaving

at the warp yarns

(Paul, Indigo properties, 2015)

Production Methods

Rope Dyeing

- 12-36 cables fed into scouring baths containing wetting agents, detergents and sodium

hydroxide

-cables fed into rinsing baths

-cables dipped into a bath of leuco indigo

-squeezed

-exposure to air for oxidation

-washed in baths

-softener box

-drying

(Paul, Continious dyeing techniques, 2015)

Slasher Dyeing-Section beams of warp yarns are forced into a

sheet of yarns

- Scouring section to remove natural impurities

- Indigo dyeing section : sheet passes through, to achieve deep shades

- Dried on cylinders after rinsing

- Size box (containing sizing agent) : sheet passes through, yarns absorb the size

- Drying section: sheet is dried by hot steam rolls

- Beam winder: yarns are wound onto for weaving

(Paul, Continious dyeing techniques, 2015)

Loop Dyeing- One single bath, one squeezing unit

- Passing through pre-treatment boxes

- Continuous passage of yarns that occurs between yarn creel and dye box represents a

loop form

- Wash boxes

- Drying cylinders

- Sizing unit

(Paul, Continious dyeing techniques, 2015)

Chemicals used:Aniline, Sulphur, Sodium hydroxide, Hydrosulphate and Formaldehyde.

(Paul, Indigo properties, 2015)

Major issues:Reducing agents and the huge volume of effluents and quality control involves the

monitoring of dye bath parameters like PH,

Environmental impact

sodium hydrosulphite and leuco indigo concentration and the temp of the dye bath

(Paul, Indigo dye, 2015)

→ These chemicals can be harmful to both humans through inhalation and the environment

where they are discharged after dyeing.

→ Wastewater effluence is a huge threat to the environment and the textile industry as a whole;

even when water is treated, some chemical residues may remain.

→ 10-50% of the dye solution will end up in waste water

→ problems for human and environmental health

→ major source of dye loss corresponds to the incomplete fixation of the dyes during the textile

fiber dyeing step

→ materials that end up in the water bodies are effluents containing a high organic load and

biochemical oxygen demand

→ causes changes in the biological cycles of the aquatic biota, particularly affecting the

photosynthesis and oxygenation processes of the water body

→ Vat dyes in waste water behave like pigments

(Koppert, Leon, Luiken, Mulder, & Steen,Garment dyeing and printing, 2016)

Pre-Treatment

Scouring

To remove natural fats, waxes, protein and other constituents, as well as dirt, oil and other

impurities

Raw cotton may contain between 4 and 12% of these impurities by weight.

MethodImpregnation with sodium hydroxide (alkali) > incubation > rinsing with water (to neutralize

pH).

ProcessFabric width: with Jigger or Pad batch.

Rope: with J-box or Kier.

Environmental impactThe process can take from six to twelve hours

making it energy intensive.

Large amounts of highly contaminated waste water with a high pH, has to be neutralized

(Koppert, Leon, Luiken, Mulder, & Steen,Pretreatment, 2016)

(Erkens, 2017)

Bleaching

Natural color is destroyed to create a more white look

Environmental impact →chlorine bleach is known to be extremely toxic

to the environment and to consumers

→chlorine-based chemicals are still often used to bleach fabric

→large amounts of highly contaminated waste water

→high use of energy in processing at high temperatures

→An alternative bleaching method which is oxygen-based (hydrogen peroxide) can be used

(Koppert, Leon, Luiken, Mulder, & Steen,Pretreatment, 2016)

Method→chemical bleaching is performed in a wash

with enzymes of bleaching chemicals in order to remove part of the indigo dye applied

→results in a much lighter shade of the jeans, but also in a decrease of the mechanical strength

of the jeans

→bleaching chemicals can be applied by impregnating the jeans in a bath with the

chemicals (resulting in an even lighter shade) or can be applied spot-wise, resulting in bleached

spots

MachinesDiscontinuous: Kier, Jigger, Winch.

Continuous: Pad roll, J-box

(Erkens, 2017)

Optical Brightener MethodDuring Bleaching

Environmental impact→Optical brightening agent is called cyanuric

chloride and is classified as very toxic, harmful→Some optical brighteners cause allergic skin

reactions

→Toxic to fish and other animal and plant life and have been found to cause mutations in

bacteria

→Not biodegradable, remaining in wastewater for long periods of time

→Negatively affecting water quality, animal and plant life

(Koppert, Leon, Luiken, Mulder, & Steen,Pretreatment, 2016)

→ occurs in the wash and care label and the sewing thread of the pocket

→makes the fabric even whiter by absorbing invisible ultraviolet light and re-emit the energy

in the lower end of the visible spectrum

→fluorescent whitening agents

→hydrophilic water-soluble compounds used also in laundry detergents

(Erkens, 2017)

Singeing

Projecting fiber ends are burned away using one or more banks of gas flames or other heat

sources. Improve pilling abilities.Singeing is carried out on both yarns and fabrics

Environmental impact The process has a low environmental impact;

however dust andvolatile organic compounds are produced

(Koppert, Leon, Luiken, Mulder, & Steen,Pretreatment, 2016)

Method→The material is exposed to a gas flame toburn off protruding fibers that cause non-

uniform dye uptake

→No chemical agents arerequired except for a water bath that is used to quench any sparks (in integrated systems this

is often the desizing vat).

(Erkens, 2017)

Desizing

Removal of sizes and other substances applied as weaving aids

Methods: →High temp. washing (soluble size)

→Oxidative treatment: persulfate or peroxide

The complete removal of size is required for all woven fabrics prior to dyeing

Water soluble size may simply be washedOut

water insoluble size must first be subjected to chemical or enzymatic

degradation

(Erkens, 2017)

Environmental impact

Water insoluble size prevents size recovery and so a large burden is placed on waste water

streams.

The size which is washed off, ends up in the wastewater and can represent over 70% of the

total COD value of wastewater from a denim mill

Not Biodegradable

(Koppert, Leon, Luiken, Mulder, & Steen,Pretreatment, 2016)

→Enzymatic treatment: enzymes like e.g. baylase amylase)

Process:Continues (pad batch) or discontinues (jigger,

winch)

(Erkens, 2017)

Mercerization

Swelling of cotton with sodium hydroxide → improved luster and dye efficiency

(Erkens, 2017)

Environmental impact: If discharge is required then the alkali is

neutralizedleading to the discharge of large quantities of

salt

→ Large amount of water use

Methods:→Baths containing concentrated solutions of

sodium hydroxide (20- 30%)are used

→either be reused or the NaOH recovered and employed in other pre-treatment steps

If discharge is required then the alkali is neutralized

leading to the discharge of large quantities of salt.

(Erkens, 2017)

→needs neutralization before discharge

(Koppert, Leon, Luiken, Mulder, & Steen,Pretreatment, 2016)

Finishes

Softening Improve abrasion resistance, increase tear strength and diminish the risk of

stitching thread, needle breakage during garmenting and provide a smooth or soft

hand to the garment

Environmental impactOnly small quantities enter the wastewater

(Koppert, Leon, Luiken, Mulder, & Steen,Finishing, 2016)

Types of Softener The major types of softeners are anionic, cationic, non-ionic, silicones and special

softener

MethodApplied in several steps of the

production chain→ last rinse of the garment finish

SanforizationDone in order to reduce the amount of

shrinkage that can happen after the first wash

The result of sanforization leads to 1-3% shrinkage, as opposed to 10% shrinkage with

unsanforized (shrink to fit) denim.

(n.g., 2017)

Environmental impactThe process has a low environmental impact;

however, a large energy use is needed for that kind of finishing

MethodMade from cloth that has been stretched, fixed

and shrunk in length at the mill

Process:

Washing / Rinsing

Rinsing

StagesDyeing, Desizing, Washings, Finishing's and

Softening

→ Major water consumption stages are the rinsing stages of dyeing operations

(Paul, Garment washing and finishing, 2015)

Consumer washing use of a jeansAt the climate change impact the water consumption of consumer use is 23%.

Also the climate change impact of consumer use is 37%.

→Very useful to only wash your jeans every 10 times.

(levistrauss, 2015)

Washing

Purpose- Final process in denim production

- Related to aestethic, quality and value

- Final effects can be achieved -> by the influence of chemicals, washing conditions and

washing equipment used

(Paul, Garment washing and finishing, 2015)

Aims-preshrinking for good dimensional stability

during selling and use

- removing sizing agent and unfixed dyes-wash with hydrogen peroxide

- improving hand feel through various finishing processes (e.g. softening)

- improving aestethic properties through e.g. bleaching

- improving functional properties (e.g. wrinkle free)

-improving the quality (colour fastness, poor colour yield etc.)

Types of washingRegular washingBleach washingStone washingAcid washing

Enzyme washingDesizing

(Paul, Garment washing and finishing, 2015)

Environmental impact

→ most water consuming processes in denim production are dyeing and finishing/washing processes

→ dyeing operations: High levels of alkaline chemicals are used and these chemicals require more concern before discharging them to the receiving bodies

(Koppert, Leon, Luiken, Mulder, & Steen, Wet processing of textile fibers, 2016)

Reference ListErkens, L. (2017). Pre-treatments. Enschede.

Koppert, P., Leon, S., Luiken, A., Mulder, E., & Steen, N. (2016). Finishing. Zeist: Modint.

Koppert, P., Leon, S., Luiken, A., Mulder, E., & Steen, N. (2016). Garment dyeing and printing. In P. Koppert, S. Leon, A. Luiken, E. Mulder, & N. Steen, Sustainable Material Guide (S. 160). Zeist: Modint.

Koppert, P., Leon, S., Luiken, A., Mulder, E., & Steen, N. (2016). Pretreatment. In P. Koppert, S. Leon, A. Luiken, E. Mulder, & N. Steen, Sustainable Material Guide (S. 146). Zeist: Modint.

Koppert, P., Leon, S., Luiken, A., Mulder, E., & Steen, N. (2016). Wet processing of textile fibers. In P. Koppert, S. Leon, A. Luiken, E. Mulder, & N. Steen, Sustainable Material Guide (S. 146). Zeist: Modint.

levistrauss. (2015). levistrauss.com. Abgerufen am 13. december 2017 von http://levistrauss.com/wp-content/uploads/2015/03/Full-LCA-Results-Deck-FINAL.pdf

n.g. (2017). tellason.com. Abgerufen am 9. december 2017 von http://www.tellason.com/sanforized-denim-denim-dictionary

Paul, R. (2015). Continious dyeing techniques. In R. Paul, Denim Manufacture,Finishing and Applications (S. 75-76). Cambridge: Elsevier.

Paul, R. (2015). Continious dyeing techniques. In R. Paul, Denim Manufacture,Finishing and Apllications (S. 76-77). Cambridge: Elsevier.

Paul, R. (2015). Continious dyeing techniques. In R. Paul, Denim Manufacture,Finishing and Applications (S. 77-79). Cambridge: Elsevier.

Paul, R. (2015). Garment washing and finishing. In R. Paul, Denim Manufacture,Finishing and Applications (S. 575-577). Cambridge: Elsevier.

Paul, R. (2015). Indigo dye. In R. Paul, Denim Manufacture,Finishing and Applications (S. 567-568). Cambridge: Elsevier.

Paul, R. (2015). Indigo properties. In P. Roshan, Denim Manufacture,Finishing and Applications (S. 48). Cambridge: Elsevier.