Comparative Study of Cotton Fabric Quality Using Different Salts in Reactive Dyeing Process

Comparative Study of Cotton Fabric Quality Using Different Salts in Reactive Dyeing Process

Md. Fayez Ullah Bhuiyan & Md. Abdul Hannan Mia
Department of Textile Engineering
Dhaka University of Engineering & Technology (DUET)
Gazipur -1700, Bangladesh

ABSTRACT
The Buzz word which is dominating the present decade in the textile processing industry is “Environment aspect”. It could not survive without eco friendly approach at the same time could not change the existing textile processing system completely, which is taxing the environment heavily. However, it can modify processes in such a way that causes less pollution load and are reusable. In this study, emphasis is given on fabric dyeing by using glauber salt and its comparison with common salt and vacuum salt. Moreover, pollution load caused by addition of all salts are comparatively analyzed. After extensive experimental trials, got positive results not only in terms of environmental issues but also from fabric processing point of view. The key things like prevention of premature hardness of the dyestuff, low TDS level, less effluent load and better depth of dye shade are achieved during various trials.

CHAPTER 1
INTRODUCTION

1.1 Introduction
Salt used in textiles is an interesting and basic question in the area of textile processing, particularly in dyeing. The textile substrate and dye molecule, not necessarily should have of homogeneous characteristics to combine with each other. In such case, we require some catalyst to facilitate dyeing action on fabric. Salt plays this crucial role of catalyst. Salt has an extremely high affinity for water. Broadly speaking, Salt is necessary in three ways, firstly, to drive dye into textile during the dyeing process in textile. Secondly, use of salt leads to maximum exhaustion of dye molecules during dyeing process in textiles. Thirdly it is used as an electrolyte for Na₂SO₄·10H₂O white or colorless monoclinic crystals. Upon exposure to fairly dry air it effloresces, forming powdery anhydrous sodium sulfate. Johann Glauber’s was the first to produce the salt (from Hungarian spring waters). The naturally occurring salt is called mirabilite. Glauber’s salt is watersoluble, has a salty, bitter taste, and is sometimes used in medicine as a mild laxative; it is also used in dyeing.

Dyeing of cloth has the economic advantage of avoiding storage of fibers and yarns of varied colors. It makes easier to meet demands of the customer for a wide variety of shades, which are subject to rapid changes dictated by fashion. Reactive dyes are the only textile colorants designed to bond covalently with the substrate on application. These comprise a chromophore and a reactive group, and owe their excellent wet fastness to the formation of covalent bonds with the fiber. Accordingly, they differ fundamentally from other coloration products, which depend on physical adsorption or mechanical retention and in some ways can be regarded as the high tech end of the textile dyeing business. In knitwear industry, dyeing of cotton knitted fabrics is mostly done with reactive dyes, because of their good fastness properties and versatility of applications. The ease of application, wide shade range, high brilliancy and excellent wet fastness properties make the reactive dyes preferred choice for the dyeing of cellulosic fabrics.

In reactive dyeing, the dyeing process can be broadly divided into two phases, namely exhaustion and fixation. The process is lengthy, because much time is spent on the controlled heating of dye bath and portion wise addition of salt and alkali in order to avoid unlevel dyeing and maximizing the exhaustion and fixation.

1.2 Objectives of the projects & thesis:

• Comparative study of effect of Glauber salt, common salt and vaccum salt on the textile dyeing process.
• To study quality  of dyed fabric dyeing with various types of salts.
• To save the dyeing cost and Eco friendly aspect.
• To focus on the special role of Glauber salt in textile wet processing.

1.3 Structure different types of salt used in textile wet processing:

a) Common salt:
A colourless crystalline solid, NaCl, Inorganic compound of sodium and chlorine, a salt in which ionic bonds hold the two components in the familiar white crystals soluble in water and very slightly soluble in ethanol. It has the interesting property of a solubility in water that changes very little with temperature. Sodium chloride has a key role in in textile dyeing process in maintaining electrolyte balances in textile dyeing process.

b) Glauber’s salt:
Glauber’s salt, common name for sodium sulfate decahydrate, Na₂SO₄·10H₂O; it occurs as white or colorless monoclinic crystals. Upon exposure to fairly dry air it effloresces, forming powdery anhydrous sodium sulfate. Johann Glauber was the first to produce the salt (from Hungarian spring waters). The naturally occurring salt is called mirabilite. Glauber’s salt is water soluble, has a salty, bitter taste, and is sometimes used in medicine as a mild laxative; it is also used in dyeing.

The molecular formula for Glauber’s salt is Na₂SO₄.10H₂O.

c) Vacuum salt:
Vacuum salt is manufactured by recrystallization of purified brine.In vacuum crystallization process, raw salt is dissolved in water to make a saturated solution and sent to clarifier wherein bulk of insoluble impurities settles down and is removed from the bottom. Solution transferred from the clarifier is filtered and pumped to treatment vessels for precipitation to the extent required by means of chemical reaction. Precipitated mass is filtered out and the solution thus purified is pre-heated and subjected to continuous evaporation on being heated with steam. For economizing the steam consumption, multiple units are used in series, so that the steam coming out from one unit, be used in the next effect, thus eliminating the need for application of fresh steam at each stage. Vapour from the last effect is condensed in a condenser using water from cooling tower. The entire plant initially is under vacuum, and thereafter the pressure in the system is thermodynamically stabilized. Vacuum is generated by using a suitable Vacuum Pump. The number of effects depends upon the capacity of the plant, so that optimized economy is achieved at minimum investment.

1.4  Chemical Structure of Cellulose:
The molecular structure of cellulose has always been of great interest to scientists and over time several structures have been proposed. The linear polymer, β- Dglucop –yronose with 1,4-glycosidic bonds (1), is the widely accepted structure for cellulose. Consequently it may be considered as a polyhydric alcohol. Eachglucopyranose ring in the cellulose chain contains three hydroxyl groups, a primaryhydroxyl group in the 6- position and secondary hydroxyl groups in the 2- and 3-positions.

Cellulose forms a ribbon-like structure, which is capable of bending and twisting due to the oxygen bridges that connect the glucose rings. Six hydroxyl groups protrude from each cellobiose repeat unit in the chain. These groups aid the stability of the molecule by forming intermolecular (O-6-H and O-3 of another chain) and intermolecular (O-3-H and O-5’, O-2-H and O-6’) hydrogen bonds. The hydrogen bonds in the chains help connect the neighboring chains together in the structure. Intermolecular hydrogen bonds formed between the O-6 14 proton and the O-3 are to stabilize the structure of Cellulose I. The degree of polymerization (DP) for cellulose depends on the source. The DP can be as low as 100 for regenerated cellulose powders and as high as 14,000 for natural cellulose fibers such as cotton. Naturally occurring cellulosic materials have been evaluated with respect to their fine structure and morphology. The degree of crystallinity of the cellulose substrate depends on the origin and the pretreatment of the sample. It has been determined that the degree of order for cotton fibers is 2:1 crystalline regions to amorphous regions. In the cellulose structure the highly oriented molecules spiral around one another in the fiber. The spiral angle for cellulose depends on the source. Cotton has a spiral angle of 20°- 30°. Flax, jute and hemp have a smaller spiral angle of 6°, which provide these fibers with higher strength.

1.5 Role of Electrolyte on Reactive Dyeing:
Reactive dyes for cotton have negatively charged active groups, they are anionic. When cotton fiber immersed into water, its surface due to hydroxyl ions become also anionic, hence they- the dye particles and the cellulosic fiber-tend to repel each other.

The addition of salt, creates an electrical positive double layer which hides negative electrostatic charge of cotton surface. This allows the dye approach the fiber. If electrolyte is not spreaded –out uniformly on cotton surface , dye distribution will not be even also and patchy dyeing is unavoidable. After the addition of salt and dye, sufficient period of time should pass, fort the even distribution of salt and the dye. This levelling period us between 30 and 45 minutes, depending upon -circulation speed. -Flotte ratio-primary exhaustion property of dyes:

1.6 Salt Refining:
Common salt is a vital ingredient of human food and an important raw material for various industries. Salt, mainly, is produced by solar evaporation of sea water or saline water. Salt thus produced is called Raw Solar salt. The chemical name of pure salt is Sodium Chloride (NaCl) This salt contains a large percentage of physical and chemical impurities. Insolubles, like, dirt, clay and other extraneous material form part of physical impurities. Soluble impurities are mostly present as calcium and magnesium salts. The raw common salt also contains moisture varying from 4 to 6 %.

Common salt is recognized all over world as a stable vehicle in which to carry iodine. Iodine deficiency is one of the major nutritional problem. Its most simple manifestation is goiter, a swelling of the thyroid gland, which often grows to large proportion. But much more serious than goiter are the mental and other developmental disorders caused by iodine deficiency.

The success of salt iodisation, however, depends primarily on the quality of salt to be iodized. Moisture and impurities in salt tend to destroy its iodine content. So, mixing iodine compound with salt is not the solution. Salt has to be refined and dried to enable it to retain the iodine content put into it. So, refining and drying ensure.

• Iodine content in edible salt
• Purity and Hygiene
• Convenience in usage as it becomes free flowing
• Good visual appearance because of dryness and whiteness

The concept of salt being used as a carrier for imparting iodine is being extended to impart other micro nutrients and tasty flavors & ingredients. Only refined and dryed salt is capable of carrying and retaining such ingredients and flavours.

Refining of salt is also essential for its use as raw material in chlor- alkali industries. Use of dryed refined salt in place of dirty and unhygienic solar salt in industries, like, food processing, textile, detergent, dyes, chemicals and others, enhances quality and appearance of their products.

Refining of salt is done mainly by two processes :-

The basic difference in the two processes is that in a mechanical salt refining plant, raw salt is washed with saturated solution of salt whereas in a vacuum salt refining plant, salt is completely dissolved and then after purification is recrystallized.

Vacuum crystallization process can give the purest grade of salt, but the cost of setting up of a vacuum crystallization plant is many times higher than the cost of setting up of a mechanical refining plant of comparable capacity. Hence, the choice of salt refining & processing machinery would depend upon the purity requirement and end use of the refined salt.

CHAPTER 2
LITERATURE REVIEW

2.1 Physical and chemical properties of Common Salt:

• Molar mass: ……………..58.44 g mol⁻¹
• Exact mass: ……………….57.958622382 g mol⁻¹
• Appearance: ………………Colorless crystals
• Odor: …………………………..Odorless
• Density: ………………………2.165 g cm⁻³
• Melting point: …………..801 °C, 1074 K, 1474 °F
• Boiling point: ……………..413 °C, 1686 K, 2575 °F
• Solubility in water: …….359 g L⁻¹

It is dissolved in water and produced positive and negative ion

NaCl         ⇌     Na⁺   +  Cl^–

This is a reaction in which a salt reacts with water to form a solution which is either acidic or basic in nature.

NaCl + H₂O    ⇌    NaOH + HCl

In actual dyeing mechanism vegetable fibres contains cellulose which ionizes in the water

Cell – OH      →       Cell – O^– + H⁺

While reactive dye goes in the water, it is soubise giving dye anions and sodium cations

Reactive dye – SO₃Na + Water    →    Reactive dye – SO₃^– + Na⁺

(Dye anion) (Sodium cation)

During dyeing both the negative ions of dye and cellulose repels each other in the absence of salt and thus no exhaustion or very little exhaustion is done but in the presence of salt , it will ionize as follows,

NaCl     →      Na⁺ + Cl^– (Common Salt) or

Thus the salt neutralize the negative ion of the cellulose and facilating the exhaustion,

(Cell – O^– + H⁺ )+ (Na⁺ + Cl^– )      →     Cell – ONa

Cell – ONa + SO₃^– – Reactive dye      →      Cell – O – Reactive dye

Thus the presence of salt in the reactive dyeing increases the affinity of the dye towards the Cellulosic substrate.

2.2 Physical and chemical properties of Glauber Salt:
Sodium sulfate is chemically very stable – it does not decompose, even if heated, and it does not react with oxidizing or reducing agents at normal temperatures. At high temperatures, it can be reduced to sodium sulfide. It is a neutral salt, with a pH of 7 when dissolved in water, because it is derived from a strong acid (sulfuric acid) and a strong base (sodium hydroxide). In aqueous solution, some reactions are possible. Sodium sulfate reacts with an equivalent amount of sulfuric acid to give an equilibrium concentration of acid salts, such as sodium hydrogen sulfate:

Na₂SO₄(aq) + H₂SO₄(aq) → 2NaHSO₄(aq)

Na₂SO₄ is a typical ionic sulfate, containing Na+ ions and SO₄^2- ions. Aqueous solutions can produce precipitates when combined with salts of barium or lead which have insoluble sulfates:

Na2SO4(aq) + BaCl2(aq) → 2NaCl(aq) + BaSO₄(s)

Sodium sulfate has unusual solubility characteristics in water, as shown in the graph at the right. Its solubility rises more than tenfold between 0 °C to 32.4  °C,

where it reaches a maximum of 49.7 g Na₂SO₄ per 100 g water. At this point the solubility curve suddenly changes, and the solubility becomes almost independent of temperature. If sodium chloride is added, the solubility is markedly lower. Such changes provide the basis for the use of sodium sulfate in passive solar heating systems, as well is in the preparation and purification of sodium sulfate.

During dyeing both the negative ions of dye and cellulose repels each other in the absence of salt and thus no exhaustion or very little exhaustion is done but in the presence of salt , it will ionize as follows,

Na₂SO₄^–    →     2Na⁺ + SO₄– (Glauber’s Salt)

Thus the salt neutralize the negative ion of the cellulose and facilating the exhaustion,

Cell – ONa + SO^3- – Reactive dye    →      Cell – O – Reactive dye

(Exhausted dye on the substrate)

Thus the presence of salt in the reactive dyeing increases the affinity of the dye towards the Cellulosic substrate.

Since reactive dyes have low affinity for cellulose, the fixation can be increased by exhausting the dye bath by adding Glauber’s salt prior to fixation. The amount of the salts required to produce adequate exhaustion decreases with decreasing liquor ratio.

2.3 Physical and chemical properties of Vaccum salt:
Vacuum salt is manufactured by recrystallization of purified brine. Brine is a salt-water-solution. The term brine is used for a natural salt-water spring as well as for a solution where salt has been dissolved in water.Brine is used for a variety of applications, e.g. for de-icing purposes, in chemical industry, for water softening purposes, for swimming pools, sea-water aquariums and dolphinariums.By recrystallization of brine, vacuum salt is produced. Evaporated salt is – as well as rock salt – graded into the required size of grain through sieving, or pressed into tablets, compact salt or lickstones. Additional substances such as iodine, fluoride, nitrite or folic acid are added to it, according to requirements and intended use. Preservatives make the salt easier to pour and ensure even application. On the surface, the crude brine is carefully purified and freed of undesirable minerals. This is important in order to ensure the residue-fee solubility of salt products. The purified brine is boiled in crystallisers, and the resulting salt mass is then centrifuged, dried and processed into ready products. These are suitable, among others, for use as food-grade salt, in electrolysis plants or as regeneration salts for water-softening purposes.

2.4 Molecular structure of fibers:
The size of the molecules of most familiar chemical compounds may be deduced precisely from their chemical formulae. But many of the molecules forming the structural material of naturally occurring substances are so immense that simple chemical analysis is no longer an adequate guide to their true structure or shape. Such molecules are referred to as macromolecules.

The general concept of structure upon which modern macromolecular chemistry is based was first proposed by Staudinger, who envisaged such molecules as exceptionally long chains of repeating identical units. Each unit is a single simple molecule, but within the chain many such units are chemically linked in a head-to-tail arrangement, like the carriages on a train. His views have since been adequately confirmed, particularly by the work of Carothers, who was the first person to take simple compounds, synthesize a polymer and adapt its chemical structure to obtain a material with specified physical properties.

The molecule used as the building block in the construction of the long-chain molecule is referred to as the monomer and the long molecules themselves are polymer molecules, the word polymer being derived from the Greek poly (many) and meros (parts or segments). The chemical properties of the polymer chains are therefore governed by the monomer, so that a monomer with hydrophilic groups will produce a hydrophilic polymer and a hydrophobic monomer a hydrophobic polymer.

2.5 Role of electrolyte in the dye bath:
When a fibre is immersed in water, a negative electrostatic charge develops on its surface. This charge repels any dye anions present in the solution, so that the fibre cannot be dyed satisfactorily. If, however, the dyebath also contains an electrolyte such as sodium chloride or sodium sulphate, a diffuse layer of positive sodium ions forms at the fibre surface, neutralizing its charge. The dye ions are then able to approach sufficiently closely to the fibre for the inherent attractive forces between the dye and the fibre to operate.

2.6 Chemistry of reactive dyeing:
A fiber-reactive dye will form a covalent bond with the appropriate textile functionality.  This is of great interest, since, once attached, they are very difficult to remove.The first fiber-reactive dyes were designed for cellulose fibers, and they are still used mostly in this way. There are also commercially available fiber-reactive dyes for protein and polyamide fibers.  In theory, fiber-reactive dyes have been developed for other fibers, but these are not yet practical commercially.

Although fiber-reactive dyes have been a goal for quite some time, the breakthrough came fairly late, in 1954. Prior to then, attempts to react the dye and fibers involved harsh conditions that often resulted in degradation of the textile.

The first fiber-reactive dyes contained the 1,3-5-triazinyl group, and were shown by Rattee and Stephen to react with cellulose in mild alkali solution.  No significant fiber degradation occurred. ICI launched a range of dyes based on this chemistry, called the Procion dyes. This new range was superior in every way to vat and direct dyes, having excellent wash fastness and a wide range of brilliant colors. Procion dyes could also be applied in batches, or continuously.

The general structure of a fiber-reactive dye is shown below:

Note the four different components of the dye:

• The chromogen is as mentioned before (azo, carbonyl or phthalocyanine class).
• The water solubilising group (ionic groups, often sulphonate salts), which has the expected effect of improving the solubility, since reactive dyes must be in solution for application to fibers. This means that reactive dyes are not unlike acid dyes in nature.
• The bridging group links the chromogen and the fiber-reactive group. Frequently the bridging group is an amino, -NH-, group.  This is usually for convenience rather than for any specific purpose.
• The fiber-reactive group is the only part of the molecule able to react with the fiber. The different types of fiber-reactive group will be discussed below.

A cellulose polymer has hydroxy functional groups, and it is these that the reactive dyes utilize as nucleophiles.  Under alkali conditions, the cellulose-OH groups are encouraged to deprotonate to give cellulose-O- groups.  These can then attack electron-poor regions of the fibre-reactive group, and perform either aromatic nucleophilic substitution to aromatics or nucleophilic addition to alkenes.

2.6 a) Nucleophilic substitution:
Aromatic rings are electronically very stable, and will attempt to retain this.  This means that instead of the nucleophilic addition that occurs with alkenes, they undergo nucleophilic substitution, and keep the favorable p-electron system.  However, nucleophilic subsitutions are not very common on aromatics, given their already high electron density.  To encourage nucloephilic substitution, groups can be added to the aromatic ring which will decrease the electron density at a position and facilitate attack. For example:

But this requires harsh conditions. To improve the rate under mild conditions, powerful electron-withdrawing groups such as –NO₂ may be added.

However, this will only work if there is a good leaving group, such as -Cl or –N₂.

The major fiber-reactive group which reacts this way contains six-membered, heterocyclic, aromatic rings, with halogen substituent.

For example, the Procion dye:

Where X = Cl, NHR, OR.  Nucleophilic substitution is facilitated by the electron withdrawing properties of the aromatic nitrogen, and the chlorine, and the anionic intermediate is resonance stabilized as well.  This resonance means that the negative charge is delocalized onto the electronegative nitrogens:

One problem is that instead of reacting with the -OH groups on the cellulose, the fiber-reactive group may react with the HO- ions in the alkali solution and become hydrolyzed.  The two reactions compete, and this unfavorable because the hydrolyzed dye cannot react further.  This must be washed out of the fabric before use, to prevent any leakage of dye, and not only increases the cost of the textile, but adds to possible environmental damage from contaminated water.

2.6 b) Nucleophilic addition:
Alkenes are quite reactive due to the electron-rich p-bond.  They normally undergo electrophilic addition reactions. Again, nucleophilic additions are less favored generally, because of the repulsion between the Nu- and the electron-rich p-bond. However, they will occur if there are sufficient electron withdrawing groups are attached to the alkene, much as before, with aromatic substitution. In this case, the process is known as Michael addition or Conjugate addition.

For this reaction type, the most important dye class is the Remazol reactive dye.  This dye type reacts in the presence of a base such as HO-.

The mechanism for the reaction of one of these dyes is shown below:

As before, the intermediate is resonance stabilized, but this has not been shown.

CHAPTER 3
SELECTION OF RAW MATERIALS

3.1 Required Raw materials:

1. Fabric
2. Reactive Dye (Dyemarine Bifunctional)
3. Water
4. Wetting Agent (Surfacetants)
5. Sandoclean PCLF- (Detergent).
6. Centafoam SC (Anti-foaming agent).
7. Sirrix 2UD- (Sequestering agent).
8. Leveling Agent (Drimazin E2R)
9. Electrolyte (Common Salt)
10. Sodium Carbonate (Soda ash, Na₂CO₃)
11. Caustic Soda (NaOH)
12. Weak acid (acetic).
13. Sandoper Sp- RSK. (Soaping agent).
14. Sandofix EC-(Fixing agent).

3.2 Fabric:

3.2.1 Fabric Specification

1. Fabric Type: Single Jersey
2. Type of Cotton: 100% cotton combed yarn
3. Yarn Count: 26s
4. Gram/Square Meter (GSM): 180

The fabric was scoured, bleached and enzyme by following the standard scouring and bleaching agent.

3.3 Reactive Dye (Dyemarine Bifunctional):

Information about Ingredients
Sodium 4- Amino-5-hydroxy -3,6-bis[[4-[[-2(sulfoxy) ethy] sulfonyl] phenyl] azo] -2-7 naphthalenedisulfonate. (EC NO. 241-164-5) is remained about 70 – 80% and Disodium 3,5-diamino-2-[(2-sulphonyl)azo] benzoate, reaction product diazotized 2-[(4- aminophenyl)sulphonyl] ethyl hydrogen sulfate, sodium salts is remained about 15-20. Dyemarine Bifunctional dyes

3.4 Physical properties of the Dye:

General Information:

1. Appearance:

• Form: Powder
• Colour: Black
• Odour: None

2. Important health safety environmetal Information

• PH : 7-8
• Boiling Point :Not Applicable
• Flash Point : Not applicable
• Oxidising Properties : None
• Solubility in water :100 gm/litre

3. Dyeing Properties

• Final Exhaushion :85%
• Final Fixation :80%
• Washing off properties : Very Good

4. Fastness Properties

• Fastness to light is excellent
• Fastness to Wash Very good.

5. Adverse Influence

a. During Dyeing:

• Dye Reduction: Not Sensible
• Cu ion in dyebath: Not Sensible
• Fe ion in dyebath: Not Sensible
• Cl ion in dye bath: Not Sensible

b. During Aftertreatrment

• Shade Change: Not Sensible
• Reduction to light Fastness: Slight Sensitive

3.5. Final Exhaustion or Fixation:
This refers to dyeing on cotton, tricot produced at about 2/3 Sd and navy light or black light by the 600 c method using soda at liquor ratio 1:7 after 90 min dyeing. 3.3.6. Fastness Properties Dyemarine Bifunctional Light fastness was tested at the given standard depth (SD). Other fastness properties refers to dyeing about 1/1 SD and Navy blue. Light fastness were tested and assessed in accordance with International Standard (IS) ISO 105Issued by International Organization for Standardization (ISO). The effectiveness of the inorganic salt is not decided by the ratio of its quantity to the quantity of fabric (o.w.f.) but rather by its concentration in the dyebath (g/l). Hence, the effect of inorganic salt can be reduced by lowering its concentration.

3.6. Control parameters of reactive dyeing:

1. Process parameters:
2. Internal fabric PH
3. Working liquor ratio on the machine
4. Effective salt concentration (actual)
5. Effective alkali concentration (actual)
6. Rate of heating
7. Rate of cooling
8. Fixation temperature
9. Fixation PH
10. Fixation time

3.7 Water as a raw material:
A abundant supply of clean water is necessary in order to run a dyeing and finishing plant. Dye houses are usually located in areas where the natural water supply is sufficiently pure and plentiful. A knowledge of the impurities and how to remove them is important. This section will briefly discuss some of the more important water purification methods. Rivers, lakes and wells represent the major sources of fresh water available for use in wet processing. Rain inevitably finds its way into rivers, streams and lakes, all classified as surface water. Well water is surface water which has percolated through soil or rock formations. Subsoil water is usually free of suspended matter but is rich in dissolved carbon dioxide. Dissolved carbon dioxide will convert insoluble calcium carbonate (limestone) into soluble calciumbicarbonate. Presence of calcium and magnesium ions in process water is undesirablebecause these ions are responsible for hardness in water and lead into the formation of insoluble precipitates of soaps and dyestuffs. The bicarbonate salts of calcium and magnesium are called Temporary hardness because boiling will liberate carbon dioxide and precipitate calcium carbonate. Chloride salts of calcium and magnesium are called Permanent hardness because boiling will not cause a precipitate.

3.8 Wetting Agent (Surfactant):
The word Surfactant is coined from the expression “surface active agent”. As the phrase implies, a surfactant molecule possesses surface activity, a property associated with the chemical structure of the molecule. The characteristic feature of a surfactant molecule is its two ends attached by a covalent bond The two ends have diametrically opposed polarities. The non-polar end is lyophilic (strongly attracted to organic molecules) while the strongly polar end is lyophobic (having little attraction for organic molecules) yet strongly hydrophilic (water loving). Duality of polarity causes the molecule to align itself with respect to the polar nature of the surfaces it contacts.

3.9 Sequestering Agent:
The principles behind sequestration are the formation of a water soluble complex between a sequestering agent and a polyvalent metal ion. The technique can be used for softening water; however, it is more often used as a component in many textile wet processing steps to remove metallic ions that interfere with the process.

3.10 Role of alkali on Reactive Dyeing:
Dyeing Reaction and Role of Alkali. During the dyeing of cellulose with reactive dyes, Hydrogen ion of cellulose react with Chloro(Cl₂) or Sulfone(SO₃) of the reactive group and forms a strong acids like Hydrochloric Acid (HCl) or sulphuric Acid H₂SO₄. Alkali (Soda Ash or Caustic soda) is important to neutralize this strong acid which will otherwise cease the reaction. Addition of alkali controls rate of reaction of the dyeing mechanism. Therefore it is important to add the alkali slowly. If pH of dyebath increases at full speed, reaction to the right goes very fast and hence patchy dyeing is inevitable.

CHAPTER 4
METHODOLOGY

4.1 Dyestuff Selection in Reactive Dyeing:
The selection of reactive dyestuff for a tri-chromatic or bi-chromatic combination plays a very important role in the performance and reproducibility of reactive dyeing in textile processing. The following points are to be borne in mind, while selecting the dyestuff for a combination shade.

Solubility of individual dyestuff in grams liter without salt (straight) and with salt should be checked prior to dye selection for a combination shade. In a tri-chromatic combination, all the dyes should have almost similar solubility property. The dyestuff that gets affected by the presence of salt would

1. Produce tonally different shade,
2. Produce poor rubbing and wash fast dyeing and
3. Batch to batch difference in depth and tone would result.

4.2 Solubility test of a dyestuff:
It’s a simple regular test – the procedure is as below.

Requirements for this solubility Test:

• Whatman filter paper,
• a good digital micro-balance,
• an electric oven,
• distilled water,
• Measuring flask 500 ml capacity. 250 ml drying crucible.

Procedure:

1. Weigh accurately 100 grams of the dyestuff and note the exact balance reading as A grams.
2. Transfer this dyestuff in to a 500 ml clean beaker.
3. Slowly add hot distilled water (60^oC) and make it in to a paste and dilute it further with cold distilled water.
4. Transfer the dissolved portion of the dyestuff liquor in to the 500 ml standard measuring flask (SMF).
5. To the un-dissolved semi-solid mass of dyestuff remaining in the beaker add further quantity of distilled water and dissolve it. Again transfer the dissolved dye in to the standard measuring flask. Repeat the process until about 400ml of water is added into the SMF. Now make the remaining quantity of dyestuff in the beaker in to a slurry by adding further water and transfer the whole slurry in to the SMF flask
6. Make up the volume of water to 500ml in the SMF.
7. Shake well for about 10 minutes.
8. Weigh a whatman filter paper blank – let the weight be B grams.
9. Filter the dissolved dye-liquor through  a pre-weighed whatman filter paper-1 – do not add any water during filtration. make use of the solute only for all transfers.
10. After filtering dry the filter paper at 110C for 3 hours. cool it in a decicator and weigh the paper along with the content. Let the Weight be C grams.
11. Then the un-dissolved dyestuff in the filter paper (D) = C – B grams
12. The solubility of the dyestuff (S1) = (A -D)/500 x 1000 grams per liter.
13. To counter check this value, measure 100 ml of the clear dissolved dyestuff solution and transfer in to a 250 ml pre-weighed drying crucible. Evaporate and dry it at constant temperature of 95^oC for 3 hours.
14. Check for drying in to powder mass and cool the crucible; weigh it. Find the weight of dissolved dyestuff – x grams.
15. So 100 grams of the solution contain x grams of dyestuff – calculate for 1000 ml. let it S.
16. Compare S1 and S2 – if the difference is very small then average out the two readings or repeat until you get both readings are very close.

4.3 Some important Criteria to be considered while selecting dyestuffs for a tri-chromatic matching:

Use of Primary colors:
One should try to use the Basic Colors such as Red, G.Yellow and Blue. The secondary colors should be avoided as far as possible. The Red’s and Blue’s varies with shade and requirement of fastness properties.

Dyes with similar Exhaustion and Fixation values:
The Reactive dyeing takes place in three steps,

1. Exhaustion ( primary and secondary)
2. Fixation
3. Wash off

Normally two types of exhaustion take place while dyeing. These are primary and secondary exhaustion.

Primary Exhaustion is the amount of dyestuff migrated on the substrate in the presence of salt. While secondary exhaustion is the total amount of dye migrated on the substrate in the presence of salt and alkali.

While selecting a combination, one has to ensure that the Percentage Exhaustion (PE) and The Percentage Fixation (PF) of dyes should be similar.

In the case of

Reactive ME Dyes ……………….PE is 60 to 70%
Reactive HE dyes …………………PE is 70 to 80%
Reactive VS dyes ………………….PE is 40 to 50%

If is always preferable to use dyes with PE about 60 to 70%, i.e., ME dyes. Patchy dyeing may occur if proper care is not taken while using dyes with higher PE, or lower PE.

Dyes With Similar Affinity:
Generally the dyes are classified as Low, Medium, High and Very High affinity dyes. For Exhaust dyeing, high and very high affinity dyes are preferred. Whereas low affinity dyes are used in continuous dyeing.

4.4 Best Trichromatic combinations in Bifunctional Dyes:

Reactive ME dyes:

• Almost 100% bulk to bulk reproducibility
• Better chlorinated poor water fastness
• Least metamerism

Table 4.1: Bi-functional Reactive dyes

4.5 Stock Solution Preparation:
During the lab deep preparation a little amount of dyes and others chemicals are require. The measurement of a little amount dyes and chemicals are very complex. 4 gm of dye has take and soluble in 100 ml of warm water and make 4% dye stock solution. Similarly 20% of Na₂CO₃ (Sodium carbonate), 40% (NaCl) common salt, 2% (NaOH) Caustic Soda, and others auxiliaries are 2% stock solution have make. By the preparation of stock solution we can easily take required amount of dyes and chemicals from the stock solution by the following calculation.

………………………………………….Total liquor × recipe amount
Amount of Chemicals = ………………………………………………………………….
……………………………………………..1000×stock solution%

……………………………………Wt of material × Shade%
Amount of Dyes = ………………………………………………………………..
………………………………………..Stock solution%

4.6 Sample Preparation:
The single jersey (Scoured, Bleached and Enzyme) fabric has cut and make sample about 5 gm ± 5% by the precious electronic balance. There have to make an indicator on the sample to distinguish each to others by numbering on sample salves. The sample size has required as rectangular to take crocking fastness test. Now all samples are soak in distill water for few minute and squeeze well therefore the sample are ready for dyeing.

4.7 Dyeing Mechanism:
In actual dyeing mechanism vegetable fibres contains cellulose which ionizes in the water

Cell – OH –     →     Cell – O- + H+

While reactive dye goes in the water, it is soubise giving dye anions and sodium cations

Reactive dye – SO3Na + Water    →      Reactive dye – SO3- + Na +

(Dye anion) (Sodium cation)

During dyeing both the negative ions of dye and cellulose repels each other in the absence of salt and thus no exhaustion or very little exhaustion is done but in the presence of salt , it will ionize as follows,

NaCl      →     Na + + Cl – (Common Salt) or

Na₂SO₄       →      2Na + + SO₄ – (Glauber’s Salt)

Thus the salt neutralize the negative ion of the cellulose and facilating the exhaustion,

(Cell – O^– + H⁺)+ (Na⁺ + Cl^– )      →      Cell – ONa

Cell – ONa + SO₃^– – Reactive dye      →      Cell – O – Reactive dye

(Exhausted dye on the substrate)

Thus the presence of salt in the reactive dyeing increases the affinity of the dye towards the Cellulosic substrate.

Since reactive dyes have low affinity for cellulose, the fixation can be increased by exhausting the dye bath by adding Glauber’s salt prior to fixation. The amount of the salts required to produce adequate exhaustion decreases with decreasing liquor ratio. Thus for pale shades on cotton and viscose rayon 10 to 15 gpl may be used.

4.8 Dyeing process:
At first take all auxiliaries and dyes from the stock solution in the dye bath and take water to maintain 1:10 liquor ratios therefore fabric is added in dye bath at room temperature and run 10 minute. Common salts are added in dye bath and temperatures gradually increase (1.5^o/min) up to 60^oC. Now various concentration of alkali are added in dye bath for fixation of reactive dye from the stock solution of sodium hydroxide and calcium carbonate and measure pH of dye bath and run 60 minute at 60^oC. Complete dyeing the dye liquor has drain. The process diagram is following:

1. Wetting Agent
2. Levelling agent
3. Sequestering agent
4. Salt
5. Dyes

4.9. After treatment:
Hot wash at 80^oC,then the fabric is put into a bath containing 1% acetic acid,at 60^oC. Secondly the material is treated with a 1g/l soap solution which removes the unfixed dye from fabric surface, makes the surface clean.Thirdly material is treated with a hot water bath.Fourthly  material is treated with a cold –water bath.

4.10 Drying & Finishing:
The sample is squeeze well to remove the excess water and dry the sample in the oven dryer which made by England. The drying temperature is 100^oC for 20 minute. Now the sample is calendaring at about 150^oC for few minute to make smooth surface of the fabric.

CHAPTER 5
QUALITY ASSESMENT OF SAMPLE

5.1 Grey Scale for Assessing Change in Shade:

EN ISO 105-A03 / IUF 132 / VESLIC C 1211

This Grey Scale is for assessing the degree of change in shade caused to a dyed Textile fabric / yarn in color fastness tests. For example, the change of shade of wool and cotton fabrics in the wash fastness, perspiration fastness, etc.

The scale consists of nine pairs of gray color chips each representing a visual difference and contrast.

The fastness rating goes step-wise from:

Note 5 = no visual change (best rating) to Note 1 = a large visual change (worst rating).

The gray scale has the 9 possible values:

5, 4-5, 4, 3-4, 3, 2-3, 2, 1-2, 1.

It is now quite common to measure the Grey Scale change in color instrumentally. This is made using a suitable reflectance spectrophotometer according to the test method procedure, EN ISO 105-A05.

5.2 Grey Scale for Assessing Staining:

EN ISO 105-A03 / IUF 132 / VESLIC C 1211

This Grey Scale is for assessing the degree of staining caused by a dyed Textile / yarn  in color fastness tests. For example, the staining of wool and cotton fabrics in the wash fastness, perspiration fastness, etc.

The scale consists of nine pairs of gray color chips each representing a visual difference and contrast.

The fastness rating goes step-wise from:

Note 5 = no visual change (best rating) to Note 1 = a large visual change (worst rating).

The grey scale has the 9 possible values:

5, 4-5, 4, 3-4, 3, 2-3, 2, 1-2, 1.

It is now quite common to measure the Grey Scale for assessing staining instrumentally. This is made using a suitable reflectance spectrophotometer according to the test method procedure, EN ISO 105-A04.

5.3 Color fastness to rubbing:
There are two test methods for rubbing.

1. ISO-105-X12
2. AATCC-08

In ISO-105-X12 the wet pickup of the rubbing cloth is 100%
While in AATCC-08 the wet Pickup of the rubbing cloth is 65%.

We check rubbing by Dry and Wet methods. In wet rubbing we wet the rubbing cloth according to test method and give rating by comparing the Staining with the gray scale. Similarly for dry rubbing we check the rubbing with dry rubbing cloth and compare the staining with gray scale for ratings.

5.4 Considering Factors:
Color Fastness to rubbing is a main test which is always required for every colored fabric either it is Printed or dyed.

If the color fastness to rubbing is good then it’s other properties like washing fastness and durability etc improves automatically because the rubbing is a method to check the fixation of the color on the fabric. So if the fixation is good it’s washing properties will be good.

Rubbing Fastness depends on:

• Nature of the Color
• Depth of the Shade
• Construction of the Fabric

Nature of the color each color either it is pigment, Reactive, Disperse or direct has its own fastness properties to rubbing. There are some colors like black, Red, Burgundy, Navy blue which have poor Color fastness properties because of their chemical structure.

Like Black color is a carbon base color and the particle size of carbon is large than the other colors that’s why its rubbing properties are poor. Similarly red and blue are in the same case. So to improve the color fastness we add more binder to improve the fastness properties of these colors. It doesn’t mean that we cannot achieve the best results with these colors. The required results can achieve but production cost will be increase.

On the other hand the construction of the fabric also affects the fastness properties. If the rubbing fastness on 100.80/40.40 is 3 on the gray scale it will be 2-3 on 52.52/22.22 with the same printing parameters. So always keep in mind these effects during finalize the required parameters with your customer.

Always check:

• Quality construction
• Color
• Depth of the Color
• End Use of the product

Results which we can achieve in Normal Conditions with usually used brand dyestuff

5.5 Considering points to get maximum wet rubbing fastness:
Instrument used for checking is the standard crock meter. However, test is quite sensitive and for getting consistent result, it is necessary to use standard crock meter cloth, maintain uniform pressure for applying rubbing strokes and number of strokes. Besides, for wet rubbing, % moisture on the crock-cloth has to be kept to uniform level. For ISO-105 x 12 test methods, rubbing cloth that has been wetted with water has to be squeezed to contain its own weight of water. For AATCC 116-1995 methods, wet pick up is to be maintained between 65 ± 5% by squeezing the wet crock meter cloth using a AATCC blotting paper. Any variation in the moisture content can lead to deviation in the rating. With high amount of moisture i.e.., wet pick up, ratings will be lower. Degree of staining is visually assessed using Grey scale for change of color with grade of 1-5 where rating of 5 signifies negligible change and 1 maximum change.

In order to get maximum achievable wet rubbing rating, with reactive dyes, it is absolutely necessary to remove all unfixed hydrolyzed dyes by proper soaping/washing of the sample before evaluating the ratings. Extraction with pyridine can be done to check the removal of hydrolyzed dyestuff.

5.6 Equipment that needed for rubbing measurement:

1. Crock Meter.
2. Rubbing Cotton.
3. Grey Scale
4. Stop Watch
5. Color Matching Cabinet.

5.7 Color Fastness to Rubbing (Dry & Wet):

ISO 105 × 12:

Procedure:

1. Rubbing cloth: Take rubbing cloth at 5×5 cm Size.
2. Sample Size: Take the specimen at 15×5 cm at Wales wise and course wise.
3. Put the rubbing cloth on to the grating and stag by steel wire and run 10 times manually and assess the rubbing cloth with gray scale.
4. Place the rubbing cloth on the water and socked and squeeze. Place the wet rubbing cloth on to the grating and stag wit stainless steel
5. Wire and run 10 times manually. Then assess the staining on to the rubbing cloth by grey scale for wet rubbing.

5.8 Color fastness:

Definition:
Clothing is colorfast if its colors and dyes do not bleed or run from the clothing. Clothing should be tested for colorfastness before using any type of bleach or bleaching solution, or strong cleaning product.

How to Test:
To test for colorfastness, find a hidden seam of the garment or an hidden spot. Apply the cleaner to the garment and then dab the area with a clean cotton cloth. If the color removes itself from the garment onto the cloth, you should not use the cleaning product on the clothing.

5.9 Various color fastness method:

• Color Fastnesses To Wash
• Color Fastnesses To Rubbing
• Color Fastnesses To Perspiration

5.10 Color fastnesses to wash:
Wash Fastness: The wash fastness rating of vat dyes is about 4 – 5 .The excellent wash fastness of textile material, colored with vat dyes is attributed to the large vat dyes molecule as well as its aqueous insolubility. The large vat dye molecule is trapped within the polymer system of the fiber because of its size and aqueous insolubility and it is absorbed within the fiber system by vandarwals forces.

• Sample size- 10cm x 4cm
• Un dyed fabric size- 5cm x 4cm

5.11 Method of color fastnesses to wash:

1. Method -i (ISO 105 C01)
2. Method-ii (ISO 105 C02)
3. Method-iii (ISO 105 C3)
4. Method -iv (ISO 105 C04)
5. Method -v (ISO 105 C05)

5.12 Recipe of various wash fastness method:

Method – i (ISO 105 C01)

• Soap = 5 g/l
• Soda ash = 2 g/l
• M:L = 1:50
• Temperature = 40⁰c ±2⁰c
• Time = 30 min

Method – ii (ISO 105 C02)

• Soap = 5 g/l
• Soda ash = 2 g/l
• M:L = 1:50
• Temperature = 50⁰C ±2⁰C
• Time = 30 min

Method – iii (ISO 105 C03)

• Soap = 5 g/l
• Soda ash = 2 g/l
• M:L = 1:50
• Temperature = 60⁰c ±2⁰c
• Time = 30 min

Method – iv (ISO 105 C04)

• Soap = 5 g/l
• Soda ash = 2 g/l
• M:L = 1:50
• Temperature = 95⁰c ±2⁰c
• Time = 30 min
• Steel ball = 10

Method – v (ISO 105 C05)

• Soap = 5 g/l
• Soda ash = 2 g/l
• M:L = 1:50
• Temperature = 95⁰c ±2⁰c
• Time = 4 hours
• Steel ball = 10

5.13 Procedure of wash fastness:

1. Size of specimen: Cut sample & Multifibre at 10×4 cm and then Stitch.
2. Detergent: Detergent ECE /Soap + Soda-ash  / Anhydrous Sodium Car borate put in distilled water & cooled at 20⁰c and measure pH (where necessary)
3. Run the program according to the method
4. Rinse the sample twice with cold water.
5. Dry at 60⁰C by hanging or by flat iron pressing but Temperature should not be more than 120⁰C

5.14 Color Fastness to Perspiration Acid And Alkaline:

ISO 105 EO4:

Procedure:

a. Specimen size: Cut the specimen & Multifibre at 10×2 cm & sewn together.

b. Prepare Solution:

1. Alkaline Solution:

• L-histidine mono hydrochloride monohydrate (C₆H₉O₂N₃, HCL, H₂O) = 0.5 g/l.
• Sodium chloride (NaCl) = 5 g/l.

OR

• Disodium hydrogen orthophosphate dodecahydrate (Na₂HPO₄, 12H₂O) = 5 g/l .
• Disodium hydrogen orthophosphate dehydrate (Na₂HPO₄, 2H₂O) = 2.5 g/l.
• This solution is brought to pH 8 with 0.1 mole/L caustic solution.

2. Acid Solution:

• L-histidine mono hydrochloride monohydrate (C₆H₉O₂N₃, HCL, H₂O) = 0.5 g/l.
• Sodium chloride (NaCl) = 5 g/l.
• Disodium dihydrogen orthophosphate dehydrate (NaH₂PO₄, 2H₂O) = 2.2 g/l.
• This solution is brought to pH 5.8 with Acid.

c. Material : Liquor = 1 : 50

d. Wet the specimen in the flat dish containing with Acid or Alkaline solution and kept for 30 min. Then take the specimen & squeeze the excess solution by two glass rods.

e. Put the specimen in to the acrylic resin plates and put the weight on the plates.

f. Keep it in the oven at 37±02^oC for 4 hrs.

g. Opened the specimen and Multifibre and dry separately in the air by hanging not exceeding 60^oC Temperature.

Assess the staining & shad change with Grey Scale

CHAPTER 6
RESULTS AND DISCUSSION

6.1 Wash Fastness Test Report:

(a) Color Staining Scale:

Table 6.1 Color Staining Scale value of wash fastness test

(b)  Color Change Scale:

Table 6.2 Color Change value of wash fastness test

6.2 Perspiration Fastness Test Report:

(a) Color Staining Scale:

Table 6.3 Color Staining Scale value of Perspiration Fastness Test

(b) Color Change Scale:

Table 6.4 Color Change value of Perspiration Fastness Test

6.3 Rubbing fastness Test Report:

Table 6.5: Rubbing fastness usually found in normal condition

In this test report a comparison between Glauber salt, common salt & vaccum salt, were no show a great effect on various fastness property of textile dyed material.

Table 6.6 : Strength & color Value comparison for 2% shade.

6.4 Comparison between Common, Vaccum & Glauber Salt on Hardness / TDS & PH Values:

Table 6.7: Comparison of  PH value

The value from table indicates that of glauber salt in dye bath as an electrolyte reduces TDS levels to an approximately 15-20%. This reduces load on ETP in turn provides cost advantages. The hardness of water by using Glsuber’s Salt is least increased which is an important aspect from environmental issue.

As shown in graph 5, glauber salt maintains a normal PH value than common salt and vaccum salt. Following are the some of the values, which are noted down during distilled water test and dye liquor of dyeing machine.

Textile Processing causes more pollution in terms of its effluent, particularly in dyeing and finishing. Drinking water is a major concern, where tones of effluents discharged in water. Effluent is having salt 10 % of the total volume. Dye Effluent is pretreated first then passed through Multiple Evaporator followed by Salt Crystallizer and Primary, Secondary & Tertiary Treatment. During the Dyeing Process, it is better to use Glauber’s salt instead of common Salt because it is purer and easier to recover for Reuse. The concentrated Dye Effluent with Glauber’s salt is pre treated to remove Colour. It is passed through Multiple Evaporators and gets concentrated. The concentrated solution is chilled in Vacuum Crystallizer and the Glauber’s salt is crystallized the crystallized Glauber’s salt is centrifuged and taken for Reuse in the Dyeing Process. Technology of Salt Recovery using Glauber’s salt gives better Dyeing Results. Salt Recovery and Reuse in a Textile Dye House is a Technological

Break through. The combined Recovery & Reuse of Salt and Water will be amilestone in the Textile Dye House Effluent Treatment globally. The cost of Dyeing increases by about Rs 10 per Kg of Fabric but other Cost Benefit Results are firstly, 90 % of the Salt can be Recovered & Reused. Secondly, every day about 4,500 Kgs of Salt can be recovered and lastly, expected annual Salt Recovery is 1,350 Tons (3).

6.5 Distilled Water test:

CHAPTER 07
CONCLUSION

Conclusion
In this study, a comparison between Glauber salt, common salt & vaccum salt, were no show a great effect on various fastness property of textile dyed material, but it has been found that strength of shade is higher when glauber salt is used, irrespective of the type of the shade. The present study revealed that varying type of salt, their application process and concentrations of alkali, dye influenced wet rubbing fastness in the case of applying reactive dyestuffs to different structures of cotton knitted fabrics, excellent results for glauber salt.

• Fabric handle with glauber salt becomes smoother and the fabric handle with common salt becomes rough.

• Addition of glauber salt in dye bath as an electrolyte reduces TDS levels to an approximately 15-20%. This reduces load on ETP in turn provides cost advantages.

References:

1. Thesmarttime. textile processing. textile processing guide. [Online] May 15, 2010. http://www.thesmarttime.com.
2. Muhammad Iftikhar, Nisar Ahmad Jamil and Babar Shahbaz. Rubbing, Ironing and Dry Cleaning Fastness of Reactive Dyed Cotton Knitted Fabric as Influenced by Salt, Alkali and Dye., International Journal of Agriculture and Biology, Vol. 3,Issue 1, pp. 109-112,2001.
3. School of Chemistry. Fibre-Reactive Dyes. University of BRISTROL. [Online] May 20, 2010. http://www.chm.bris.ac.uk/webprojects2002/price/reactive.htm.
4. Huntsman Textile Effects. Technical Data Sheet. May 2007.
5. Clariant International Ltd. Technical Information. February 2006.

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Mazharul Islam Kiron

Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.

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