All about Garments Washing Part- 4: Acid & Wet wash

Acid Wash, Stone wash and Enzyme Wash

Maruf Mahfuz

E-mail: maruf.txt@gmail.com

Department of Textile Engineering

World University of Bangladesh

Cell-  01738676060

Acid wash

Acid wash denim soared in popularity during the 1980s before dying out only to re-emerge, as a retro look, in the early 2000s. Despite the name, these splotch-faded denim products didn't get the look from a bath of acid. Instead, the jeans earned their distinctive look when manufacturers first stripped the denim of its resin finish then applied chlorine to remove the indigo that gives classic denim its traditional blue hue. The result Denim light in color with white splotches where the chlorine acted more aggressively.

Acid wash is again becoming popular on denim jeans and we are going to see more of acid washes in the coming seasons. Here, lets have a quick look at the acid washing process . An acid wash finish treatment creates significant contrasts in the color of the denim material. It can be done on Indigo & Sulphur base fabric garments. As the randomly faded, acid washed style came into vogue in 1980s, the process of treating denim in such a way began to become increasingly refined. Some tried to use a method similar to the stonewashing, yet the fading did not occur as dramatically or throughout the material. In 1980’s this washed being launched as first innovative finish on denim ever. This was being done by soaking stones in Bleach and making acid wash effect followed by neutralization. But this process was not so re find to get some how consistent & smooth effect on denim. In early 2000some laundry tried doing the same wash soaking thermocol bolls in bleach or pp solution to get this desired effect.

While this process can be done using either light bleach, chlorine , potassium permanganate etc. The most popular is PP Bleach and will produce the best acid washed results. Doing the process is very simple, but following all parameters in correct way to have right & repeatable results. Initially, the Acid Wash process involved soaking pumice in Industrial Strength Chlorine .However, it was discovered that potassium permanganate was more controllable and just as strong an oxidizer. They simply marinated pumice stone in it and then vacuum packed the stone to the required moisture level. Acid wash was a chemical process on  denim that stripped the top layer of color off to a white surface with the undertones of navy blue remaining in the jeans.

The Materials

The process of acid washing jeans involves porous pumice stones or small towel pieces and chlorine or Pp Bleach, such as you would put into a bucket or in drum for soaking process. Sodium-bisulfate is used in the second washing for Neutralization. Also recommended is access to two separate washing machines. One for Acid Washing & another one for further process i.e. Neutralization etc.

The Acid Washing Process On Denim Jeans

The process of acid washing jeans used chemicals, stripping off the color of the top layer, leaving the white fabric exposed. The color remained in the lower layers of the material, giving it a faded look. 

Acid washing could be done overall or made to look splotchy.

Process of Acid wash:

1.Soak porous pumice rocks or pieces of towels in chlorine or PP bleach solution for about 20 minutes to an hour. The longer you soak the pumice or towel, the more prominent the effects will be.

2.Once the stones are saturated with chlorine/pp, remove excess water from stones/towel then put the stones in machine followed by the jeans in a washing machine for about 20 minutes. Make sure machine do not have single drop of water, open the drain during complete process.

3.At this time, check on the jeans to ensure they look acceptable, and then move them to another washing machine for a regular washing process. Too long in the first machine can totally bleach or ruin the jeans and too little time may not produce the desired results or can make patchy appearance. Check on the jeans once every 10 minutes or so during the second wash process of neutralization to ensure the desired look is achieved.

4. Next, fully dry the jeans in a dryer that gets nice and hot.

 Potassium permanganate (PP) Spray & PP Sponging:

PP Spray is being done on denim garments to achieve local abraded area to appear whiter than back ground indigo color shade. This can be applied by spray gun or by towel dipped in to PP Solution & rubbed on desired area followed by neutralization in wet process. This process can be done in rigid after doing hand scrape or in the middle of the wash. Doing after enzyme or bleach cycle will give more natural & white effect that doing in rigid. There are many additives can be added in order to achieve desired intensity and look.

The same way bleach solution also can be spray or rubbed on the garments on desired area. But this process is very complicated & needs highly skilled operators to execute it followed by immediate neutralization.

There are many parameters needs to be taken into control for doing PP or Bleach spray Spray gun pressure, width of spray, flow & way of spraying.

 Fig: Spray gun

Precautions

Any time we mess with chemicals such as bleach or chlorine or PP, be sure to protect workers by wearing mask & aprons, so it is best to be fully prepared. Also, protective rubber gloves and safety glasses are highly recommended. These products can burn skin and eyes pretty badly.

• Safety of operators must be taken in to consideration and it must be ensured that he should wear mask, gloves & eye glasses etc.
• PP Spray & PP Sponging is doing in denim, Twill, poplin, corduroy before wash & sometime middle of wash i.e. after enzyme wash, stone enzyme wash.
• If need some particular area move white then we are doing PP Spray & PP Sponging.
• If we want more white effect in some particular area of garments by blasting then it high risk of damage. PP Spray & PP Sponging which is chemically action.
• After PP Spray & PP Sponging need to neutralize the garment per sodium metasulphite, then whitish effect come on respective area of garments. 
• Stock solution is 5% i.e. 40 liter water 200 gm potassium permanganate & phosphoric acid.
• PP Spray is done by nozzle and has a switch to start & stop.
• For Spray on garments need dry air which is supplied from screw compressor and PP stock solution tank.
• PP Sponging is done manually.
• By foam / fabric pcs wet in PP stock solution and rubbing particular area of garment by hand as a result fading affects on garments.
• PP Spray & PP Sponging operator must be used hand Gloves, Helmet, Musk, Ear flag & Uniform for their safety.

PP Spray & PP Sponging stock solution:

Potassium permanganate (KMno4 + H3Po4 + H2O) solution applied or stray on the garments so oxidizes the cellulose & color is partially removed according to the intensity & solution.

Solution.

Example:

• 1% PP Stock solution.  H2O = 40 Lit KMno4 = 40 gm H3Po4 = 40 gm
• 2% PP Stock solution.  H2O = 40 Lit KMno4 = 80 gm H3Po4 = 80 gm
• 3% PP Stock solution.  H2O = 40 Lit KMno4 = 120 gm H3Po4 = 120 gm
• 4% PP Stock solution.  H2O = 40 Lit KMno4 = 160 gm H3Po4 = 160 gm
• 5% PP Stock solution.  H2O = 40 Lit KMno4 = 200 gm H3Po4 = 200 gm
• 6% PP Stock solution.   H2O = 40 Lit KMno4 = 240 gm H3Po4 = 240 gm
• 7% PP Stock solution.   H2O = 40 Lit KMno4 = 280 gm H3Po4 = 280 gm
• 8% PP Stock solution.   H2O = 40 Lit KMno4 = 320 gm H3Po4 = 320 gm
• 9% PP Stock solution.   H2O = 40 Lit KMno4 = 360 gm H3Po4 = 400 gm
• 10% PP Stock solution. H2O = 40 Lit KMno4 = 360 gm H3Po4 = 400 gm                                     

Normal wash:

• This is a simplest type of industrial garments wash
• The main aim is to remove starch dust and dirt from the garments.
• Sometimes softening and bringing a used look is also a reason of normal wash.
• For color garments removal of unfixed dyes can also be achieved to improve color fastness.
• In special cases intentional shrinkage in garments can be achieved.
• Precautions are required to be taken for unwanted shrinkage issue and back staining.

 Sample recipe for normal wash:

If lot size 100 kg cotton shirt

M: L              = 1: 5

Water            = 500 liter

Detergent      = 1 % (basis on the weight of the garments).

Temp            = 40-60 degree Celsius

Time             = 15- 30 minutes.

 Back staining chemical is used if required.

Stone wash

Stone wash denim gained popularity in the 1960s and remain popular to this day. This type of denim is characterized by a lightly distressed, vintage look. The name comes from the fact that the original processing method involved rubbing pumice stones over the denim to wear down the fabric. But that method proved problematic due to environmental concerns over use of pumice and the fact that the stone often weakened the fabric too much, causing too much wear and tear. A newer stone wash method developed with the help of science. Special enzymes took the place of the pumice stone and work on degrading the material of the denim enough to look vintage but not to the point of destruction.

In order to accelerate the garment wash effect and to give garments an even more unique appearance and softer hand; abrasive stones were introduced to the wash bath. A variety of natural and synthetic stones are available for stonewashing with perhaps the most widely used being pumice or volcanic rock. As the stones are used, they slowly disintegrate, reducing the severity of the stonewash effect over a period of time. The stones not only abrade the fabric but also gradually abrade the inside of the rotary drum. A machine used for stonewashing should not be used to dye delicate articles or when abrasion would be detrimental to the fabric.

The demand of stone wash apparel now has encouraged a number of venues to offer the clothing. Stores are including stone wash as a part of their selection. Here are steps to begin a wardrobe of stone wash clothing.

Pumice stone

Pumice stones were the original technique to create the stone wash look. Clothes that are desired to be altered are placed in a washing machine, pumice stones are added, and the wash begins.

  

           

                                                             Fig: pumice stone                                                                         

Typical Chemical Properties of pumice stone

Silica	(SiO2)	71.75	70.90
Aluminum Oxide	(Al2O3)	12.33	12.76
Ferric Oxide	(Fe2O3)	1.98	1.75
Ferrous Oxide	(FeO)	0.02	0.64
Magnesium Oxide	(MgO)	0.12	0.09
Calcium Oxide	(CaO)	0.70	1.36
Sodium Oxide	(Na2O)	3.59	3.23
Potassium Oxide	(K2O)	4.47	3.83
Manganese Oxide	(MnO)	0.07	0.09
Titanium Dioxide	(TiO2)	0.11	0.14
Phosphorous Pentoxide	(P2O5)	0.008	0.015
Sulphur Trioxide	(SO3)	0.18	0.21
Combined Water	(H2O+)	3.71	3.88

Typical Physical Properties

Refractive Index	1.5
Hardness (Mohs Scale)	6.0
Melting Point	15000°C
pH Value	8.0
True Density (ISO 787.10)	2.313(g/cm3)

Procedure       

1. Load stones into machine.

2. Load garments into machine (ratio usually 0.5 - 3.0 part weight stones:1 part weight

garments).

3. Desize with alpha amylase enzyme and detergent. Liquor ratio approximately 5-8:1.

4. Rinse.

5. Refill and tumble with stones 30 to 90 minutes, depending upon desired effect. Liquor ratio

5-8:1 at 50-70◦C.Scouring additives can also be used.

6. Drain. Separate garments from stones (garments can be transferred to another machine).

7. Rinse.

8. Apply softener (garments can be transferred to another machine for softening).

9. Extract and unload.

10. De-stone and tumble dry.

11. Press, if required.

Softeners and/or lubricants can be added during steps three and five to reduce creasing potential.

Steps 8, 9, and 10 may vary depending upon individual mill arrangement.

Pumice stone usage in stone wash

One of such washing is known as stone wash. In stone-washing the worn-out look is given purposely. The fabric is washed along with pumice stones. The stones and denim are spun together in large industrial washing machines. The longer they are spun together lighter the colour of the fabric with better contrasts would result. The time duration of this procedure is set beforehand so as to avoid the tear and wear of the fabric. Thereafter, the fabric undergoes various other processes of rinsing, softening and finally tumble-drying. These stone-washed fabrics are used for different purposes -- garment making as well as for upholstery purpose.

Fig: Stone wash effect on Denim Pant

Disadvantages of pumice stone usage

Stone-washing the denim with pumice stones has some disadvantages. For instance, stones could cause wear and tear of the fabric; also it creates the problem of environmental disposition of waste of the grit produced by the stones. High labor costs are to be borne as the pumice stones and their dust particles produced are to be physically removed from the pockets of the garments and machines by the laborers. Denim is required to be washed several times in order to completely get rid of the stones. The process of stone-washing also harms big, expensive laundry machines.

Alternate methods for stonewashing

To minimize such drawbacks, stone-washing of denim is carried out with the aid of enzymes. The method of giving the denim a stone-wash look by use of enzymes like cellulase is known

as- ‘Enzymatic Stone-washing’. Here cellulases are used to provide that distressed worn out look to the denim fabric.

   

                                               Fig: Stone wash gives used look on denim

Americos Granofil is a Perlite which is introduced by Americos in two categories, one in powder and second in crystal foam. It gives a denim garment a casual look and uniform abrasion on garment without loss in fabric strength. It can be used for wide range of cellulosic fabrics such as cotton, viscose, and tencel.

Though Americos granofil stone wash has various applications but its introduction in garment processing has revolutionized the finishing of cellulosic and blended textile materials. This has been done by the modification of its physical form and making it suitable for garment processing industry. Americos granofil stone wash can be used on wide range of cellulosics as well as blended fabrics such as cotton, rayon, tencel etc. Americos granofil stone wash when applied on garments gives a gentle abrasion without disturbing the typical fabric properties viz., strength, colour and tone. The abrasion results in mild peach finish and removes extra gloss from the fabric to give it a casual look.

Moreover being a light weight material it does not damages the equipment as well as the garments, that is generally the problem in case of pumice stone application. It also has an excellent compatibility with acid cellulase as well as neutral cellulase enzymes as it is recommended to be used with the latter. Since it is not affected by the pH of the bath it could be used in any medium viz. acid, neutral and alkaline. It saves the enzyme dosages and the processing time that further results in saving of various resources like electricity, man power etc. 

Americos Granofil is currently available in three variants namely Americos Granofil 1.5G and Americos Granofil 2.4D. Where sold by Americos Granofil 1.5G is developed for light weight garments that weight maximum of 8 oz and Americos Granofil 2.4D for heavy garments that weight 8 oz and above. Americos Granofil 3.8F for powder grade and it works for abrasion on light/heavy garment.

Typical Dosage Table

S. No.	Fabric Type	Dosage (Gm/Kg of Garment)
1	Denim 03.0 OZ - 06.5 OZ	080 - 110
2	Denim 07.0 OZ - 12.5 OZ	100 - 120
3	Denim 13.0 OZ & above	125 - 150
4	Cottons 03.0 OZ - 06.5 OZ	070 - 080
5	Cottons 07.0 OZ - 12.5 OZ	075 - 090
6	Cottons 13.0 OZ & above	100 - 125

Application Procedure

Americos Granofil is to be added into the bath prior to any other chemicals including enzymes. The liquor ratio can be maintained as per the requirement of other chemicals. The machine should be run for a couple of minutes to ensure proper dispersion of Americos Granofil among the garments. The other chemicals can be then added including the enzymes. Process timings can be adjusted between 50 to 100 minutes depending upon the desired results. And temperature can also be maintained as required by enzymes in specific.

Cellulase method

Cellulase is environmental-friendly compared to pumice stones. It reduces the percentage of damage caused to denim caused by the rough effect of stones on them. As there is huge demand of garments with distressed jeans look, stone washing with enzymes is being used increasingly. It is also known as bio-stone-washing. Enzymatic treatment has become another substitute for kilograms of stones, also the jeans stonewashed by this method has more shelf-life. It ensures the same result with minimum amount of water, waste, time, volume and damage to machines.

As jeans are made up of cellulosic fibres, the use of cellulase enzyme is successful in giving the stone wash look. This enzyme breaks down the surface cellulose fibres and removes them without causing harm to the jeans. Better finishing and look is achieved even with indigo dyed denim. In cellulase enzymatic wash, the denim is given an enzyme bath. Here certain amount of indigo dye and cellulose fibres are removed from the surface of the fabric. As enzymes are like yeast in nature, they eat the cellulose present in denims. When the jeans get the preferred colour, enzymatic reaction is stopped by changing the alkalinity of the bath or else the water is heated. Thereafter, the fabric undergoes rinsing and softening process. The number of rinsing process after enzymes treatment is less than pumice stone-washing. There is reduced amount of waste produced and overall costs for stone-washing is also less.

Disadvantages of cellulase treatment

There are certain disadvantages of cellulase treatment. It could leave marks of backstaining like blue threads becoming more blue or white threads becoming blue. To get rid of such unwanted re-coloration of threads, the jeans are rigorously washed adding surfactants to it. This process could result in colour-fading of jeans and there is added usage of water for the washing. Thus wastage of water and certain amount of backstaining could be experienced. The primary target of stone-washing the denim with pumice stones or enzymes is to provide the garment worn-out, old and aged look. Sometimes both stones and enzymes are used for the purpose.

Latest process of stone wash – Perlite

A new process of stone-washing has been found by a series of laboratory testings – Perlite. Perlite is the form of naturally occurring silicon rock. It has the distinctive property of expanding to 4 to 20 times its initial volume when heated at a particular temperature. This happens because the raw Perlite rock consists of 2-6% of water content in it. The crude Perlite rock when heated at the temperature above 870º C it gets swollen up and tiny glass sealed bubbles are formed. Its original colour which is black or gray changes to grayish white or else white. This heated form of Perlite is used for stone wash purpose.

It does the same function of stone-washing as stones. Perlite treatment reduces the rate of harm caused to large washing machines by pumice stones and gives the denim better supple and softer finish. Many jeans manufacturing companies, in the place of enzymatic treatment, use Perlite, which reduces the rate of wearing out of jeans when used. It gives throughout uniform worn-out and old look to the denim and not just the upper part of the garment. There are many grades of Perlite differing in sizes are used for giving the stone wash finish to denim right from largest to finest grades; some are very tiny just like grounded earth.

Modern stone-washed jeans, bio stoning technique 

At first stone-washing involved using pea gravel, but pumice was discovered to float around with the jeans instead of lying in the bottom of the water and so manufacturers have switched. Turkish stone is commonly used for their porosity and cleanliness. There is beautiful pumice from Sicily but the supply is limited. Most of us are familiar with “Stone-washed” jeans. As the name implies, freshly dyed jeans are loaded into large washing machines and tumbled with stones. Adding pumice stones gives the additional effect of a faded or worn look. The pumice abrades the surface of the jeans like sandpaper, removing some dye particles from the surfaces of the yarn. Pumice has been used since the introduction of stone-washed jeans in the early 1980s. However, stone-washing with pumice has some severe drawbacks. The quality of the abrasion process is difficult to control: Too little will not give the desired look. Too much can damage the fabric, particularly at the hems and waistbands. The outcome of a load of jeans is never uniform, with a significant percentage always getting ruined by too much abrasion. The process is also non-selective. Everything in the washing machines gets abraded, including the metal buttons and rivets on the jeans as well as the drum of the washing machine. This substantially reduces the quality of the products and the life of the equipment, and increases production costs. 

Rinse (water) wash 

This speaks for itself mostly. Like in the good old days the jeans will be washed at about 50º C. There is high risk of colour bleeding, so ideal to use for brightening up your old faded jeans by washing them together. One should make certain to wash separately from other garments the first few times. Some Jeans brands will not even use sanforized fabric, so that you can shrink them to fit in a hot bath. This was (again) very popular back in the 80s. Stone wash effect.In traditional washing process, volcanic rocks or pumice stones are added to the garments during washing as abradant. Due to ring dyeing and heavy abrasion, fading is more apparent but less uniform. The degree of colour fading depends on the garment to stone ratio, washing time, size of stones, material to liquor ratio and load of garments. Normally, after desizing, stone wash process starts with pumice stone addition in rotary drum type garment washer. Process time varies from 60 - 120 min. Stone wash effect is one of the oldest but highly demanded washing effects.  Stone wash process gives “Used” look or “Vintage” on the garments, because of varying degree of abrasion in the area such as waistband, pocket, seam and body. There are many limitations and drawbacks associated with stone-washing process, which can be overcome by using new enzyme-based washing technology. This technology also helps to conserve water, time, energy and environment. 

 Enzyme washes:

An enzyme is a biological chemical compound that reduces complex organic compounds to simpler compounds. This is important to the enzyme wash because one of its main selling points is that it is different from other types of denim finishes because it is organic and non-harmful to the environment. A reason that enzyme washing is so ecologically friendly is the natural origins of enzymes biodegrade rather than lingering in the water supply in the environment.

There are four kinds of Enzymes available in market for Denim Laundry business.

1. Amylase …. Desizing

2. Cellulase …. For Salt & pepper effect, contrast

3. Laccase…. … bio bleaching

4. Catalase …… Peroxide killer

Now, the definition of enzyme wash is a fabric finish that uses cellulase enzyme to remove surface fuzz from cellulosic fabrics. The cellulases are used because they loosen up the indigo dye in the denim. The main purpose of the enzyme wash is to make the denim appear worn, rugged, broken in and used. The enzymes are used in denim finishing as an alternative to stonewashing, meaning that stonewashes and enzyme washes are very similar, but the enzyme wash still has its advantages. Jeans tend to be softer with the enzyme wash as a result of the organic enzymes that eat away at the fabric from the cellulose. Although this wash "eats away" at the fabric, it does not jeopardize its strength to hold up and it will make the fabric less likely to leave residue in drains or on other clothing. Stonewash damages fibers during the wash, which differs from the enzyme wash that creates a great vintage look without damage (Jeans and Accessories)

Enzyme is kind of protein that is obtained from fermentations method from naturally existing bacteria & fungi. The structure of Enzyme is a biological polymer and it can be found in every cell. Generally called as Cellulase & it works on cotton ( Cellulosic fiber ) only. Enzymes are living organisms which will attack a specific molecular group. There are mainly three kind of Cellulase being used for Denim washing, Neutral, Acid and Bio polishing Enzyme. Enzyme are very sensitive with parameters in washing cycle i.e, pH , Temperature & time. If any of these parameters are not up to the mark, result will not be accurate.The reaction of enzyme can be easily controlled, its biodegradable products, so they eco friendly.

Bio Polishing Cellulase are being used to have protruded fiber removal from denim & oven fabric. This is also widely known as Anti pilling enzyme. Any Cellulase used in process must be cleaned/killed after the process completion by simply disturbing the parameters ie. By raising high temperature or raising pH to alkaline where no Cellulase withstand.

Fig:  Enzymes are given to the wash liquor.

Cellulases are available in 3 categories

1. Neutral

2. Acidic &

3. Hybrid enzymes.

Neutral enzyme gives better salt & pepper effect with very less back staining & it’s generally comes from sin powder form & also retains better strength of fabric than acidic Cellulase. Where as acidic cellulase give faster results but with too heavy back staining & cuts down the indigo color, also affects the strength of fabrics.

Now a days laundry people needs faster results in less time & money hence chemical suppliers combined Neutral & acid cellulase in such way that it works faster & with better results than acid cellulase with cost effectiveness & known as Hybrid enzyme.

Laccase is bio bleaching agent & alternative for conventional bleaching agents. This impart greyer cast to blue denim & enhances salt & pepper effect. But due to high cost & low self life, laundries do not prefer it.

After finishing Enzyme wash it is must to add clean up process for better results & garments appearance & that can be done in various ways & methods. As clean up is a must process to be carried out after every chemicals steps done for any garments which allows next process to happen smoothly. 

All processes mentioned below kill/ deactivate the active enzymes process which is necessary in order to protect/retain garment strength

• Hydrogen peroxide in alkaline pH clean up enhances the brightness & rich blue tone of indigo.
• By using non ionic detergents in medium to high temperature.
• By doing two good hot water rinses etc.