All About Garments Washing part- 5

Bleach Wash, Pigment wash and Caustic wash

Maruf Mahfuz

Email: maruf.txt@gmail.com 

Department of textile Engineering 

World university of Bangladesh

Cell no: 01738676060 

Bleach wash:

This in one an important step in washing denim & can be done by various bleaching agents
a. Calcium hypo chlorite
b. Sodium hypo chlorite
c. Hydrogen peroxide
d. Potassium permanganate

First two chemicals are commonly being used for every medium to vintage denim but when it comes to super vintage & light shade its advisable to use potassium permanganate bleach to cut the color faster till half way & then neutralize it & go with Liquid ( Hypo ) bleach to adjust the desired shade. This process helps to get Greyer cast & also protects the lycra/spandex , retain elasticity.

Hydrogen Peroxide is rarely used as bleaching agent when very less color loss required or if fabric is sulphur top. As it takes longer time to give desired effect.
Potassium Permanganate is also being used on 100% sulphur black denim fabric for bleaching/reducing agent to get unique effects. As its not production friendly till laundry have very expertise team to handle this program, otherwise it will result in many shades & cast.

Recipe for bleach wash:

Lot size 100 kg
M: L = 100 kg
Water = 1: 5
Hydrogen peroxide = 5 ml/ liter
Stabilizer = 1 ml/ liter
Caustic soda = 5 ml/ liter
PH = 10- 11
Temp. = 80 degree Celsius
Time = 60-70 minutes
After completion of bleaching part couple of hot wash is done,then it required neutralizing the garments with acetic acid
Acetic acid = 2 ml/ liter
Time = 5 minutes
Proper Neutralizations of bleaching process is very essential in order to get rid of fabric strength, bad smell from garment, yellowing & skin irritation etc.
In this process, a strong oxidative bleaching agent such as sodium hypochlorite or KMnO4 is added during the washing with or without stone addition. Discoloration is usually more apparent depending on the strength of the bleach liquor quantity, temperature and treatment time.

Limitations

* Process is difficult to control, i.e., difficult to reach the same level of bleaching in repeated runs.
* When desired level of bleaching reached the time span available to stop the bleaching is very narrow.
* Due to harshness of chemical, it may cause damage to cellulose resulting in severe strength losses and/or breaks or pinholes at the seam, pocket, etc.
* Harmful to human health and causes corrosion to stainless steel.
* Required antichlor treatment.
* Problem of yellowing is very frequent due to residual chlorine.
* Chlorinated organic substances occur as abundant products in bleaching, and pass into the effluent where they cause severe environmental pollution.

3-E bleaching concept for denim

Intensive research is underway for the development of sodium hypochlorite bleaching alternative eg, glucose bleaching, bleaching with sulphinic acid derivatives, and recently with laccase (enzyme).
Laccase enzyme belongs to the oxidoreductase group. Laccase’s oxidative effect is complex, and it does not work independently. A mediator is necessary and a chemical mediator is employed between enzyme and indigo.

Advantages

* New Laccase based bleaching technique only affects the indigo and natural raw white of weft yarn is retained, giving the woven fabric a darker shade, which is not implicitly achieved with hypochlorite bleaching.
* The product is so specialised on indigo that it does not attack any other dyes.
* Laccases open up the door to bleach Lycra containing denim without losing the strength of the fabric. In case of hypochlorite bleaching Lycra containing product affects adversely by losing the tear and tensile strength.
* Finally, the process is based on enzyme so no risk of environmental pollution and harmful effluent discharge.

Limitations
* Expensive, compared to traditional process.
* Heavy faded look is difficult to achieve. 

Enzymatic anti-backstaining agent-protease

The use of an engineered oxidatively stable alkaline protease that can tolerate a range of operating temperature and pH conditions offers flexible and alternative processes for backstaining clean-up, improved contrast of denim finishes, and reduced residual cellulase of fabric. It is claimed that significant reduction in back staining can be achieved at much lower temperature than conventional process by using small amount of protease either at the end of the cellulase washing step or during the rinsing step. By adding the protease at the end of the cellulase wash step, one rinse step is eliminated offering savings in time and energy. This process at lower temperature also claims to achieve a significant reduction of residual cellulase.

Bleach Wash procedure:
Bleach wash or light stone wash refers to light blue shades of denim. The additional step is bleaching to stone wash. This bleaching is usually carried out by strong oxidizing agents. In industry, most widely used chemicals are sodium hypo-chlorite, calcium hypo-chlorite, hydrogen per oxide and potassium permangate.

Bleach Wash Process of Garments:

A process of bleach wash of 60 kg batch of Denim Long Pant as mentioned below

First Step: Pre-treatment/ Desizing

Batch size.......................         60 kg Denim Long Pant.

Add water @ L: R = 1: 9....540 litres.

Start the machine.

Temperature....................   60°c

Add Desizing agent @        0.6 gm / litre ............ 324 gm.

Add Detergent /Antistain @1 gm / litre..... 540 gm.

Time................................     15 to 25 mts.

Drop the liquor.

Second Step: Hot Wash

Add water @ L: R = 1: 9..............      540 litres.

Temperature....................................... 60°c.

Time................................................. .. 5 mts.

Third Step: Bleaching

Add water @ L: R = 1: 8................................. 480 litres.

Machine running.

Add bleaching powder (k.c.i) @ 10 gm/litre.. 4800 Gms.

Add soda ash @ 5 gm/litre ............................... 2400 Gms.

Temperature............................................................ 60°c.

Time (Depend upon the shade).................... …12 to 15 mts.

Drop the liquor.

Rinse twice, each 3 minutes.

Fourth Step: Neutral Wash

Add water @ L: R = 1: 9.......................... 540 litres.

Add sodium hyposulphite @ 3 gm/litre ....... 1620 Gms.

Temperature ......................................................... 40°c.

Time (Depend upon the shade).............. 10 to 12 mts.

Drop the liquor.

Rinse one.

Fifth Step: Soft W

Add water @ L: R = 1: 8..................................480 litres.

Add Acetic Acid @ 0.6 gm/litre ..................... 288 Gms.

Cationic softner @ 1 gm/litre ........................ 480 Gms.

Time................................................................. 5 mts.

Drop the liquor.

Unload the garments to trolley.

Sixth Step: Hydroextractor Machine

Hydroextraction the garment to remove excess water from the washed garments.

Seventh Step: Drying Machine

Load 40 kg garments

Set temperature ................ 75°c to 85°c.

Time ......................... ……35 to 40 mts.

Time ..................... ………10 minutes in cold dry.

Eighth Step: Delivery 

After quality checking garment will be delivery.

Patch & Repairs along with Bleach Spots

These are totally manual processes to give uniqueness to Denim and to make it look VINTAGE. First cut or damage the units intestinally to desired area & then make hand repairs or machine repair to look natural. Diluted bleach can be used to spot the desired area followed by neutralization in wet process.  These process are time consuming hence productivity is low & reproducibility is very difficult but similar aesthetics can be achieved.  When we talk about Vintage denim, every garment should look unique & not a photocopy. These garments are sold at very high prices so customer should have a feeling of uniqueness & feeling different from others. Vintage denim is signature/ autograph of a brand & its image.

Fig: Different wash effect on denim fabric

 Tinting/pigment dyeing /pigment wash

Tinting is a process where very less amount of tint is involved & mainly direct dye is being used to do this process. This is being done to change hue/cast/tone of indigo. As soon as quantity of tint color increases & it cover up indigo, reaches the level of dyeing. Tinting being used to give garments a used / vintage & muddy look. This process takes from 5 minutes to 15 minutes time for better results followed by dye fixing & cleans up of superficial dye. Dyeing is being done on very light shade of Indigo, Ecru/ grey denim & Ready for dyeing denim.

• There are various Types Of Dye . The comparison of these dyes is given in the chart here below:

1-Direct Dyes

2-Reactive Dyes

3-Pigment Dyes

4-Sulphur Dyes

Direct Dyes	Reactive Dyes	Pigment Dyes	Sulphur Dyes
Economical	Costly	Cost Efficient	Economical
Wide range of shades	Wide range of shades	Styling ( limited to dull shades)	Shades are dull
Short Cycles	Long Cycle	Short to long Cycle	Short to long Cycle, depends upon shade
Ease of application	Water Consumption High	Machine contamination, but hard to obtain consistency, harsh hand feel	Sulphur Odour & harsh hand feel
Smooth Appearance	Smooth Appearance	Smooth Appearance	Smooth Appearance

 Table: Introducing different Dyes

Need to choose right color of pigment or tint with binder or fixer to apply locally on denim to get vintage look. This process also needs an artist to execute it nicely to merge the tint with ground indigo color & should not look too artificial. Pigments & Local tint also can be applied through spray gun or rubbing on desired area of denim garment. After application its must be cured in order to have permanent effect on jean.
As we can see from all the dry denim processes mentioned above, they are mainly manual processes. The quality of the worker can make or break the garment. Hence, great care has to be given to select the right personnel for these jobs

Caustic wash

Chemical usually used  caustic soda wash
Now, we will discuss on chemicals those are used in pigment washing.

Caustic Soda (NaoH) :
Caustic created the role in bleach technique without colour change the garments.
Caustic has a cleaning power which is more powerful then soda Ash.
Fadding affect/old looking affect come rapidly on garments.

Soda Ash (Na2Co3) :
Soda ash created alkaline medium for the breakdown of pigment dye.
It has also a cleaning power.
It has also help colour fadding affect of garments.

Detergent:
Here detergent is used to remove impurities from the Garment fabric surfaces and temperature helps detergent to enhance its action. Detergent removes the impurities from the garments fabric surface. During coming these impurities, some pigment will be washed out from the pigment dyed or printed area of the garments. As a result fadding affect will be developed.

Acidic Acid (CH3COOH) : 

Acidic Acid is used to neutralize the garment from alkaline condition and to control the pH value in wash bath.

Flax Softner (Cationic, Nonionic) :

Softener is used to make the garments treated textiles is surface feel that is bath sickly and soft and also provides excellent lubricating properties.

Process of Caustic Wash:

To be continued.............