Mineral and Clay Based textile bleaching

 

Now a days many commercial products based on innovative clay or mineral chemistry  are available for discontinuous bleaching of cotton and its blends with hydrogen peroxide. The clay or mineral technology have several advantages over conventional peroxide bleaching process.

What are these clay or mineral based products

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The clay or mineral based products are a composition of naturally occurring mineral or clays such as  montmorillonite and/or bentonite in combination with suitable wetting , sequestering agents  and viscosity control agents . The clay is finely dispersed in the form of a non settling, non separating emulsion which can be diluted with water and can be used easily. The clay structure is based on sheets. By separating these sheets e.g. by stirring, a very big surface is created This surface (till 800 M 2 per gram) makes it possible to absorb all kind of components like dirt, oil, greases etc. This gives an unique detergency effect .Two properties of montmorillonite crystals enable its use as a highly effective bleaching agent:

•On the one hand, impurities are adsorbed from the fabric and the liquor, due to the high specific surface area.

•On the other hand, montmorillonite has the property to replace disturbing heavy metal ions in the bleaching bath by Na-ions

The result is a dual effect as bleaching stabiliser and extractant.

How these products acts
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In water the clay particles are anionic charged and show a large adsorption effect for:

• Hydrophobic waxes and oils

• Metal ions (cation exchange capacity)

• Hydrophilic materials and polymers

It is believed that the clay component provides both a scouring and softening effect, in essence by adsorbing organic contaminants and acting as an ion exchanger, in effect having a contaminant-suspending capacity. The powder or agglomerate particles of the clay divide into primary crystal plates caused by the swelling of the clay. The average size of the primary crystal plates is approximately 1.mu.. After being dispersed in the treatment liquor, the contaminants detached from the treated textile material are adsorbed by the clay particles, resulting in a greatly reduced redeposition of the contaminants. Textile incrustation is reduced due to the hardness elements released during washing having either become attached to the dispersed clay crystals or having been deactivated by the sequestrant. Clay, a natural product, washes off the treated textile material and forms an effluent having low BOD and COD values. The clay does not contribute to the BOD or COD values at all.(Ref: Clay-containing textile material treating composition and method by Brown; Harold M. (Lyman, SC))

The higher whiteness index of the treated textile materials is attributed to the fact that in this bleaching system the hydrogen peroxide is consumed to the maximum extent ,resulting into very low or zero residual peroxide.

Advantages of these single-component multifunctional auxiliaries are

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1.No need of Organic peroxide stabilizers,

2.No need of Dye bath Lubricants,

3.No need of Wetting and scouring agents

4.No need of Emulsifiers in most applications,

5.No need of Antifoaming agent.

6.No need of Machine cleaning aids.

7.Very low or no need of peroxide killer treatment.

8.Shortened bleaching cycle , less water and steam consumption.

9. Low loss of degree of polymerisation, due to controlled peroxide degradation

10.Better tensile strength compared with conventionally bleached fabric

11.Lower weight loss.

12, Better removal of oil or silicone

And since these products are derived from clay or natural resources these are eco friendly in nature , having low COD and BOD values

A typical bleaching recipe for cellulosic material is

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Best suitable for package dyeing machines , jets and winches .

1-2 ml/l Clay product

2-3 g/l Caustic flakes

2-5 ml/l Hydrogen peroxide 35%

At 95 -98 oC for 45-60 min

Test the peroxide content at equal intervals and ensure maximum utilization of peroxide , to optimize the process timing.

Followed by hot and cold wash, do peroxide killing if necessary.

Machine Embroidery

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Embroidery

Embroidery is the art or handicraft of decorating fabric or other materials with needle and thread or yarn. Embroidery designs are the way to add excellence and creativity to the garments and several other form of products. It is a way to give a professional and sophisticated outlook to the textiles. Embroidery design is used to create eye-catching effects and striking images on the garments, clothing and several forms of outfits and home textiles.

Hand Embroidery

The craft of hand embroidery  has a long and interesting tradition and has bought many hours of creative pleasure to women for generations.

Machine Embroidery

Because the  hand embroidery is a time consuming process and depends largely on the human skills , at the same time it is not possible to go for large scale commercial production of the same design . These disadvantages of hand embroidery led to the development of machine and now digital or computerized machines for embroidery. There are two main types of machine embroidery. The first, free-motion sewing machine embroidery, uses a basic zigzag sewing machine. The second, computerized machine embroidery, uses an embroidery machine or sewing/embroidery machine. With the advancement of computer technology, machine embroidery is improving very fast in its look and quality

Dyed on Dyed Embroidery

When the embroidery is done on a previously dyed fabric or garment  either with in the same shade or in different shade or color combination.

Grieg on Greig embroidery

When the embroidery is done on either a greig or ready to dye fabric , which is then overdyed in different colors or shades , to produce articles of same embroidered patterns in different shades.

Selection of a good embroidery thread

Selecting the proper thread   is achieved by first determining the end-use requirements of the embroidered products. Other factors that are considered include the type of material being embroidered, the type of embroidery machines being used, conditions under which the product must perform, and cost effectiveness.

Types of threads used in machine embroidery

1.Soft cotton threads are used where dull look is required or in traditional articles to match the outfit designs.

Mercerized cotton threads

2.Mercerized cotton threads have  more lusture , more strength and clean finish , and higher dye pick up make them suitable to produce deeper and brighter shades.

3.Viscose rayon threads replace traditionally used silk threads . These have good shine, brighter shades  and clean finish .

4.Spun polyester threads give the look of a cotton thread, but provide superior strength and durability. Polyester is colorfast, resistant to chemicals, and can be washed or dry-cleaned with most common cleaning solvents.

Polyester filament threads

Trilobal polyester  is a multiple filament, twisted, high-sheen continuous fiber thread. It has the bright appearance of rayon or silk. If the desired effect is strength, durability, softness, and brightness, trilobal polyester is perfect for the job. It is wash, boil, and lightfast and also has a high resistance to chlorine and abrasion.

Others such as

1.      Metallic threads ,

2.      Aramid threads

3.      Silk threads

4.      Glowing or fluorescent threads in cotton and polyester.

5.      Multi colored or tie and dye effect threads in cotton and polyester.

6.      and polyester cotton core spun threads where core and sheath are dyed in different shades are used for specific needs and finishes.

Quality requirements for embroidery threads

1. It should have good strength
2. Good lubricity
3. Low on dry and wet shrinkage
4. Good  over all color fastness
5. Evenly dyed
6. Free from knots , fluffs and thick and thin places.
7. TPI and Twist direction of thread as per the embroidery machine requirement.
8. Non Metameric ie the shade of embroidery thread should match the base fabric in different light sources or remain same in different light sources.

Selection of dyed threads for dyed on dyed embroidery

1. Proper Shade matching
2. Even dyeing within lot
3. Lot to Lot shade matching of embroidery thread as well as Fabric.
4. No shade change from sampling to bulk production.

 

The dyed on dyed embroidery option is considered where

1. When the substrate of fabric and embroidery thread is different eg  polyester or rayon embroidery on cotton fabric and dyeing after embroidery is not possible.
2. When fabric and thread have same color but over dyeing is not possible due to smaller lot size etc.
3. A larger length of fabric is embroidered in multiple designs with same color thread in combination with others colors or qualities of thread.
4. In case of embroidery on finished garments .

Problems encountered in dyed on dyed embroidery fabrics

1.      Shade matching is not proper from sampling stage to bulk production due to shade change of embroidery yarn and /or fabric in bulk production.

2.      Shade mismatch in different light sources, due to metamerism.

3.      Poor colorfastness of thread or fabric resulting into cross staining.

4.      Lot to lot shade difference either in yarn or fabric or both.

5.      Unlevel dyeing of embroidery thread.

Types of threads mainly used in greig on greig embroidery

The greig on greig embroidery is mostly done for 100% cotton fabric ,with 100% cotton or rayon embroidery threads.

This is suitable when,

1. When the fabric and embroidery yarn are dyeable with same dyestuff to produce a same shade.
2. Larger quantities of fabric are required  with same shade of cloth and embroidery.
3. When a same embroidery pattern is repeated in different shades , the cloth is dyed in different shades after embroidery.

Problems encountered in overdyeing of greig on greig embroidery fabrics

1. Uneven dyeing if different qualities of embroidery threads are used simultaneously due to difference in dye pick up.
2. Shade difference in embroidery and fabric is observed when there is difference between fabric quality and thread quality is there , such as mercerized cotton fabric and soft thread or vice versa.
3. Shade difference between fabric and thread , due to difference in pretreatment of fabric and yarn such as greig fabric and RFD thread or vice versa.
4. Wrong quality of thread is used such as synthetic thread on cotton fabric.
5. Shade difference between embroidery due to mixing of different lots of embroidery thread such as different lots of mercerized threads.
6. Uneven dyeing of heavy embroidery patterns because if poor penetration of dyes in embroidered portions of fabric.
7. Uneven dye pick up of embroidered patterns due poor pretreatments such as scouring and bleaching and insufficient dyeing time for proper dye penetration and leveling .

Colorfastness requirement of embroidery threads

1. Good wash fastness :- The overall wash fastness properties of embroidery threads must be superior to the base fabric to avoid cross staining .
2. Good rubbing or crocking fastness
3. Good fastness to dry cleaning
4. High sublimation fastness in case of polyester threads
5. Good light fastness
6. Good chemical wash fastness :- fastness to chemicals such as chlorine or mild bleaching agents.

Problems in Garment Dyeing

With today’s exploding clothing markets of leisure , casual wear and sports wear , garment wet processing has emerged as one of the best production routes towards meeting the quick changing fashion markets.

Unlike fabric or yarn as a substrate , a garment is not a uniform in texture ,it is full of thick places like seams , multilayered sites like pockets , cuffs and shoulders. At times certain unevenness like puckered seams lend a distinct style often highly valued but it could result into rejection of goods at other times .

Here we will try to figure out certain key problems associated with garment dyeing and their possible causes, so that a garment can analyze and overcome these problems. 

Garment size control and appearance

• variations in yarn size / twist
• ends per inch
• picks per inch
• courses per inch in the knitted fabrics   

Spirality in Knitted Fabrics 

 

• Twist of the yarn
• Fibre parameters,
• Yarn formation system,
• Yarn geometry,
• Knit structure
• Fabric finishing.            

Poor tear strength of garment

• Degradation of cotton during
• pretreatment,
• dyeing and
• finishing  such as stone /enzyme washing.

Pilling

• Low twisted yarns.
• Use of low staple length, cheaper fibre in manufacture of yarns
• Surface friction of fabrics/garments during wet processing and handling
• Reworking of  goods
• Cylinder rotation is too high.
• Liquor ratio is too low.
• Excessive cycle time

Puckering of seams during dyeing

• Improper selection of stitching thread.
• Due to high twist in sewing thread
• High residual and wet  shrinkage of sewing threads
• High stitching tension and improper stitch length..

Poor Rubbing fastness

• Improper washing and soaping treatment after dyeing.
• Too much unexhausted dye in dyebath.
• Loosely held surface indigo dyes
• Considerable back staining in each step
• Exposure to atmospheric ozone

Poor light fastness  

• Use of reactive dyes which are not light fast
• Use of formaldehyde based dyefixing agents

White, undyed or light seams

• Use of improper thread such as polyester thread on cotton garments.
• Use of mercerized thread on unmercerized garments.
• Mixing of different types of threads such as mercerized and un mercerized .
• High tension stitching .
• Unmatched Shrinkage behavior of  garment and thread .

Dullness around Metallic fittings

• Corrosion and chemical reaction between metallic parts in
• Pretreatment
• Bleaching
• Dyeing
• Finishing

Streakmarks/ Lines / Creases

• Overloading of machine
• Friction between Garments
• Entanglement of garments.

Shade nonuniformity

• Differences in fabric preparation processes like
1. Desizing,
2. Scouring
3. Bleaching.
• Inconsistency in the garment assembly

Poor Dye Yield

•   Garments contain a finish, softener, or an optical brightener.
•    Garments were allowed to dry out after pretreatment stage
•    Liquor ratio is too high.
•         Agitation is too slow.
•         Excessive washing between cycles.
•         Excessive time spent in any cycle.
•         Too much/too little pretreatment.
•    Not pretreated for correct time and/or temperature.

Blotchy or Non-Uniformly Dyed Garments

• Garments contain a finish, softener, or an optical brightener.
•  Liquor ratio is too low (want 20:1). 
•  Excessive bath temperature at beginning of pretreat or dye cycle.
•  Dye bath temperature ramped too quickly .
•  Improper addition or dilution of dyes/chemicals.
•  Live steam injection into bath.
•  Hard water.
•  Garments not scoured properly
•  Garments were allowed to dry out after pretreatment stage 
•  Garments not allowed to wet-out sufficiently before adding pretreatment.
  

           

Patchy dyeing

• Starting temperature too high
• Heating rate too High
• Salt addition at high temperature
• Addition of dyes and chemical at once

Spotting

• Formation of foam
• Improper washing
• Machine not clean.
• Excess pretreat not rinsed from garment before dyeing.
• Dye not properly diluted or stirred before bath addition.
• Incompatibility of auxiliaries.

Harshness

• Insufficient size removal
• Use of high quantities of alkali
• Poor softner application

Smell

• Acetic acid,
• Residual chlorine,
• Cationic softners

Back staining

Improper maintenance of

• pH
• Temperature

Blotchy / unlevel dyeing in pigment dyeing

• Improper preparation
• Higher dosage of cationic reactant
• High rate of rise in temperature during Cationization
• Direct contact of steam with garment
• Too low MLR hence uneven build-up of Cationizer

Batch to batch shade reproducibility in Pigment dyeing

• Change in pH during cationization

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Related topics

1.Fabric spirality

2.Measurement of Fabric spirality

3. ComprehensiveView on Garment Dyeing and Finishing

4.Precaution in Garment Dyeing

5.Garment Washing Techniques for cottonapparels

6. Wrinkle-Resistant Finishing ofCotton Fabrics and Garments 

What is wrinkle free finish

7.Finishing of garments : slideshow

8.FUNCTIONAL FINISHES FORCOTTONPRODUCTS

9. Garment dyeing – Sewing thread and sewing recommendations

10.Garment Dyeing Machines

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Polyester dyeing in HTHP dyeing machines

Important factors: polyester dyeing in HTHP dyeing machines.
1.Water quality

Traces of soluble copper and iron salts can affect the shade of some disperse dyes quite markedly due to the formation of coordination complexes.The presence of calcium and magnesium cations can interfere with the anionic dye dispersing agents/leveling agents and wetting agents present in the dyebath. To overcome these problems a small amount of chelating agents might be added to the dyebath. 

2.pH of the dyebath

Ideally the pH of the dyebath should be buffered by use of a quality pH regulator, in the range of 4.5-5.5 to minimize the possibility of dye hydrolysis.

3.Use of Surfactants in dyeing

There are a multitude of purposes for which anionic surface active agents are used in dyebaths, such as wetting, penetrating and deareation etc. anionic surface active are also used to stabilize the diluted dispersions of the dye.This is necessary particularly when dyeing paler shades where dyebath concentration of surfactant introduced with the dye itself is small.

The non ionic surfactants are generally used to control the rate of exchange of dyebath to the fiber.

4.Temperature
For most cost effective dyeing of polyester depends on factors such as starting temperature ,rate of heating ,dyeing temperature and duration of dyeing which should result into well exhausted bath ,satisfactory color uniformity and batch to batch shade consistency.
A general rule of thumb , the starting temperature of dyeing is 70-80 degrees , the rate of rise of temperature is 1.5-2 deg.Celsius /min and the dyeing temperature is between 115-135 deg.Celsius.
5.Time

For an ideal dyeing time selection , one must take into account the exhaustion of dye bath , uniformity of the dye , satisfactory color penetration , for good color fastness and reproducibility of the dyeing results. Generally 15-60 minutes of dyeing time is followed and it is not necessary to prolong the dyeing long beyond the time of maximum exhaustion.

6.Dyes

The dyes with similar dyeing characteristics must be selected for particular formulation, it is important to identify the actual dyeing rate of each component will be dependent on the concentration present in the formulation.Care should be taken that the dyeing conditions allow the slowest dyeing component to reach the effective equilibrium.

7.Oligomers

Typically polyester fibres contain between 1.5 and 3.5% by mass of low molecular esters, the principal oligomer being cyclic tris(ethylene terephthalate) with smaller quantities of a dimer, pentamer as well as traces of other compounds.

when oligomers are released from the polyester fibre, after some time
at 130° C, if an efficient dispersing agent not present in the bath to prevent crystallization of the oligomers, and to prevent small particles of oligomers coming together to form larger agglomerates, oligomers will deposit on the yarn and the machine.

Dispersing will maintain the oligomers in a fine dispersion so that when the machine is drained more oligomer goes down the drain. Discharging the dyebath at high temperature if this is possible can also reduce oligomer deposition because any of the material soluble during dyeing at a high temperature can precipitate during cooling.
8.Reduction Clearing
Reduction-clearing treatment is necessary to remove any dye remaining on the fibre surfaces, If not removed, this surface contamination can undermine the brightness of shade as well as the wash, sublimation and crock fastness results.Commonly, the dyed polyester is cleared of surface-deposited dye as well as auxiliaries (e.g. carriers, surfactants) by means of treatment with detergent or reductive or oxidative treatments, in order to secure optimum fastness of the dyeing and also to improve the brightness of shade.
The usual treatment carried out, especially in heavy depth, is reduction- clearing, where the dyed fibre is treated in a strong reducing bath, usually made up of sodium dithionite and caustic soda. A treatment for 20 minutes at approximately 70-80 deg Cel, is often sufficient to clear
the fibre surface, but the ease of removal varies from chromophore to chromophore and dye to dye. This treatment acts to destroy loose azo disperse dye through chemical reduction of the azo link . Anthraquinone disperse dyes are not fully destroyed by such a treatment but a degree of removal of surface dye is achieved through temporary solubilisation of the disperse dye to the alkali-leuco form.

9.Stripping 
Stripping of disperse dyed material can be accomplished by treating goods
a. In a blank bath containing non ionic leveling agent at 130 deg.cel.
b.For chemical destruction of dye use 1-2 gpl NaOH and a reducing agent
or mild acidic treatment with zinc sulfoxlate-formaldehyde or sodium chlorite can reduce the shade to almost a off white back ground.

A New Study on Stripping for Polyester Fabrics

10.Prolonged treatment of polyester in alkaline solutions

Prolonged treatment of polyester goods in alkaline solutions will cause weight loss due to hydrolysis of polyester at the fiber surfaces, since the fiber surface has been eroded considerably  after a long alkaline treatment it is very difficult to rework the goods to give them originally anticipated appearance.

Watch Video on HTHP package dyeing machine

 

Useful Auxiliaries and Ingredients Used in Textile 

Q&A Session for Overview of Dye Classes and Methods of Coloration Webinar.

Problems with oligomer in dyeing polyester yarns and fabrics. 

Dyeing with Disperse Dyes

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Levelling agents

in every dye house ,levelness of the dyeing is a major criteria , since unlevelled    goods are usually not saleable ,causing loss to the manufacturer.

Leveling
Migration of applied dyes in a uniform manner throughout the dyed goods is called leveling and it may be a property of the dye or it may require some chemical assistance (of leveling agents which are dye bath additives
 to promote level dyeing)
Levelling agents are invariably surfactants ;they may be anionic ,cationic,non ionic or amphoteric in nature .some times combinations of these are also used ,There are two fundamental mechanisms that can contribute to a level dyeing:

1.Control of rate of exhaustion of the dye so that it is taken evenly and slowly.

2.Migration of the dye after initial uneven sorption on the fiber.

In complex formation the principle of leveling is usually the same ,irrespective of whether non ionic or ionic agents are used , although the mode of complexing is different.

The attractive forces between leveling agent and dye creates a counter balancing mechanism against dye fiber attractive forces,restraining the uptake of dye by the fiber.

As the temperature of the dyebath increases , the complex gradually breaks down ,progressively releasing dye for more gradual sorption by the fiber.

further reading :-Role of leveling agents in textile wet processing
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How to Test pH of Textile material

Testing of pH by water extraction method

Purpose of the test

The pH of the processed textiles must be neutral and within the prescribed limits for a particular end use. The textiles with higher pH value may exhibit yellowing tendencies ,create change of shade upon storage and during shipment, result into poor dye pick up , patchy dyeing and poor colorfastness. very high and very low pH results into degradation of textiles during storage and use , may result into poor softness and harsh feel. pH of apparel fabrics which are in direct contact with the skin or used for baby wear, must be controlled not to make the skin itchy. 

The pH control is very important for in process quality as well as quality of the finished material.

Test method

Boil 250 ml distilled water or deionized water for 10 minutes and put 10+/- 0.1 gm of test specimen in it boil for another 10 minutes. Allow it cool down to room temperature , remove the specimen and squeeze back the excess water in the beaker. 

Test the pH by using a calibrated pH meter within an accuracy of +/-0.1 on pH scale.

The pH of water extract must be tested after prior to dyeing if you are getting uneven dyeing and to be tested after completion of dyeing and soaping to avoid any problems in finishing such as softening and dye fixing etc.  

This information is generalized for day to day in house process control, for detailed information please follow AATCC 81-2006

and ISO-3071. 
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pH and pH buffers

pH

In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. definition: pH is the negative logarithm of the hydrogen ion concentration.  pH is a measure of the concentration of hydrogens ions ( H⁺ ions or protons) in a solution.

pH scale

The pH scale was defined by Sören Sörensen, Danish biochemist, in 1909The pH scale measures how acidic or basic a substance is. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic and a pH more than 7 is alkaline.

Measuring pH

Measuring pH is essential not only in finding the chemical characteristics of a substance but also as the first step toward managing chemical reactions.

Measuring pH involve either the use of pH measuring electrodes or indicators whose colors are dependent on pH. A pH meter measures the difference in potential between a reference electrode insensitive to changes in pH and an electrode sensitive to such changes.

pH indicators based on color changes are normally used in the form of pH papers. The paper is wetted with the solution being measured and the resulting color is compared with color standards to determine the pH.

In the textile industry, measuring pH is important in product testing, pretreatments,dyeing and finishing processes. 

pH buffers

A pH buffer is a substance that resists a change in pH when small amounts of an acid or a base are added to it. The pH of a buffer changes very little when small amounts of  an acid or a base is added to the buffered solution. A buffer consists of approximately equal amounts of conjugate weak acid/base pair in equilibrium with each other . Strong acids and their conjugate bases do not produce a buffer since in  strong acid ionization is complete and there is no equilibrium.

Why pH changes during a Textile dyeing process

1. Water quality
2. Reaction products
3. Additives during the process
4. Time
5. Temperature
6. Contaminants in the substrates.

Some pH  buffers systems useful in textile pretreatment , dyeing and finishing.

HCl and sodium citrate                                     pH 1-5

Citric Acid and sodium Citrate                          pH 2.5-5.6

Acetic Acid and Sodium Acetate                       pH 3.7-5.6

K₂HPO₄ and KH₂PO₄                                      pH 5.8-8.0

Na₂HPO₄ and NaH₂PO₄                                  pH 6-7.5

Borax and NaOH                                              pH 9.2-11

pH in textile coloration

Most of the dyeing processes requires a controlled pH , such as slightly alkaline in direct dyes , strong alkaline in reactive , vat and azoics , acidic in disperse and basic dyes strongly acidic in acid dyes etc.

The control of pH in textile processing is ensured by fundamentally three different techniques , such as

1. The maintenance of a relatively high degree of acidity or alkalinity .
2. The control of pH within fairly narrow tolerances mainly in near neutral regions.
3. The gradual shift  of pH as dyeing proceeds.

Many processes of textile processing are pH dependent.

1. Scouring of cotton in highly alkaline conditions
2. Bleaching  of different substrates where pH has to be maintained for proper bleaching action.
3. Solubilising the dyestuffs.
4. Exhaustion and fixation
5. Oxidation
6. Stripping
7. Finishing 

further reading
pH of textiles by water extraction method