Textile Dyeing

Textile Dyeing

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  A presentation on ‘Textile Dyeing’ AHMADMOSTAFA MASUD 2015131056 DEPARTMENT OF CHEMISTRY , SHAHJALAL UNIVERSITY OF SCIENCE & TECHNOLOGY , SYLHET
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  Basic Textile Terms andDefinition Some frequently used terms in textile dyeing are discussed in this Section
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  Dyeing Dyeing is theapplication of dyes or pigments on textile materials such as fibers, yarns, and fabrics with the goal of achieving color with desired color fastness. Dyeing is normally done in a special solution containing dyes and particular chemical material. Dye molecules are fixed to the fiber by absorption, diffusion, or bonding with temperature and time being key controlling factors. The bond between dye molecule and fiber may be strong or weak, depending on the dye used. Dyeing and printing are different applications; in printing, color is applied to a localized area with desired patterns. In dyeing, it is applied to the entire textile.
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  Pigment Pigment is atype of colour material, which has chromophore group. There are different chromophores, i.e. - N=O, -N=N- etc. Chromophores can absorb light of some wavelength and reflect some hence give us a sense of coloration. Pigments are water insoluble. They are typically used with binders in printing or mass coloration of synthetic fibers.
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  Dyestuff In dyestuff, thereare chromophore groups too. Dye stuff is a type of unsaturated complex compound. Characteristics of dye stuff are - • It must have the chromophore group. • This chromophore group may be different, i.e. -N=O, -NO2, -NH2 , =CO etc. • It must be soluble in water and produce saturated solution. • It must be substantive so that dye stuff can have the ability to enter into the from dye bath. • It must have the fastness property,
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  Classification of Dyestuff No SingleClass of Dyestuff can dye all type of fibre. A specific class of dyestuff can only applied to a given class of fibres. Type of dye stuff Fibre to apply Direct Cotton, viscous Acid Wool, nylon, silk Reactive Cotton, viscous, wool, nylon, silk Vat Cotton, viscous, wool, silk Basic Jute, acrylic Disperse Nylon, polyester, acrylic, diacetate triacetate Sulphur Cotton, viscous Pigment Cotton, manmade fibre Mordant Cotton, wool, silk Mineral Cotton, wool, silk
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  Dyeing Assistants Dyeing assistance a. Electrolytes:NaCl is an important electrolyte in dyeing with direct dye. It increases absorptivity of the cotton. b. Levelling agent: Retarding agent NarSO4 Used as levelling agent for dyeing wool. c. Carriers: Rate of dyeing is excellent for using carrier in dyeing with disperse dye. d. Solvents: Adding different solvents in dye bath increases dye uptake .i.e.; benzyl alcohol or urea is used for dyeing wool in room temperature. In the whole dyeing process apart from the dyestuff and pigments several other chemicals are required. They are commonly termed as ‘Dyeing Assistants’
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  Type of DyesVarious classes and types of dyes are discussed in this section
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  Vat Dyes A classificationof dyes that are converted from a water-insoluble pigment form to a soluble leuco form applied by immersion to fabric, then converted back to the insoluble form. The name comes from "vatting" which once meant using natural fermentation processes in a vat to produce the reducing conditions to make the dye soluble Dye class General Description Application Vat Difficult to apply. Requires reduction treatment to make soluble in water & oxidation to resume insoluble state after dyeing. One of the most expensive dye. incomplete colour range. Strong in blue & green but weak in red. Great all round fastness except indigo & sulphurised vat species. Tending to decrease in popularity due to increasing use of reactive dyes. Commonly used for high quality cotton goods, e.g. towel; specially used in the dyeing of denim fabric.
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  Working principle of Vat Dyes Vatdyes characteristically require a reducing agent to solubilize them. The most common reducing agent is sodium dithionite (Na2S2O4), which converts the dye to its "leuco" form that is soluble. Once attached to the fabric, the leuco dye is then oxidized to the insoluble state which is intensely colored. Chemical reactions such as oxidation, reduction, pH control are often necessary
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  Reactive Dyes Reactive dye attachesto the fibre by forming a covalent bond. Also called fibre reactive dye. Reactive dyes are known for their bright colours and very good to excellent light and wash fastness, though poor resistance to chlorine bleach. There are several broad classes of reactive dyes. Most are intended for cellulose fibres, but some are intended specifically for wool. DYE CLASS GENERAL DESCRIPTION APPLICATION Reactive Easy application. moderate price. complete colour range. good fastness due to direct reaction with fibres. Commonly used for all cellulosic goods especially in knitted fabric batchwise dyeing; selective dyes can also be applied on wool, silk & rayon. increasingly used in printing due to good fastness.
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  Working principle of ReactiveDyes Here the dye contains a reactive group and this reactive group makes covalent bond with the fibre polymer and act as an integral part of fibre .This covalent bond is formed between the dye molecules and the terminal –OH (hydroxyl) group cellulosic fibres or between the dye molecules and the terminal amino (- NH2) group of polyamide fibres.
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  Azoic Dyes "Azo" refersto a chemical compound which contains two nitrogen atoms with a double bond between them (- N=N-). "Azo" is use for a class of dyes based on (this) chemical structure. Azo dyes may be found among direct, acid, basic, reactive and disperse dye classes. Normally it is dyed in cold for all natural fibers. Azoic dyes are not sold in the form of a finished dye but in form of their components (Insoluble azo base & fast colour coupling compound) which combine on the fibre to produce a water insoluble azo dye of exceptional fastness properties. Dye class General Description Application Azoic Complicated application. Limited colour range (red, orange, navy among the best). Bright shade at moderate cost. Generally good wet fastness but moderate to poor on dry cleaning & rubbing fastness. Also called naphthol dye due to the use of naphthol or ice colour because of the usage of ice during Application . Mainly applied on cellulosic fibres, especially on brilliant red shade.
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  Working principle ofAzoic Dyes Azoic dyes are actually chemically synthesized inside the fibre, and are not truly dyes, but insoluble pigments. The soluble "naphthol" component applied to the fibre, and then a solution of "diazo salt" is used to develop the color. These dyes are used commercially especially for reds, but are not readily available for dyeing it needs to be synthesized inside the fibre. The components used can be very toxic before they react to form the pigment. The formation of this insoluble dye within the fabric makes it very fast to washing. The deposition of the dye on the surface of the fibre produces poor rub fastness but once the loose dyes are removed by boiling the fabric in soap the dyeing becomes one of the fastest and long lasting.
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  Acid Dyes Acid dyesare large class of dyes that applied from acidic solutions to polyamide fibres, these synthetic dyes are used for wool, silk and nylon. There are a great many acid dyes, in a number of major sub-groups, with a wide variety of properties. Included are "wash fast acid dyes". "milling dyes". "super milling dyes", "leveling acid, dves", "1:1 premetallized dyes". "2:1 premetallized dyes" and others (the premetallized dves are sometimes regarded as being in a class of their own, apart from acid dyes). The distinction between some of the groups is often vague, Acid dyes range from poor to excellent colour fastness and from dull tones to brilliant shades. Dye class General Description Application Acid Easy application. complete colour range with very good bright shades. fastness properties may vary among individual dyes. Commonly used for wool, silk & nylon.
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  Working principle ofAcid Dyes They typically applied in a bath that may range from strongly acidic to neutral and usually at temperatures approaching boiling. Bonding between the dye and fiber can be complex. Some form ionic bonds between basic groups of the fiber and acid groups of the dye occurs. The family of acid dye is very large & diverse, varying widely in their methods of dyeing, application & end use of the dyed fabric.
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  Sulphur Dyes These dyesare derived from the formulation of compounds containing Sulphur. These are water insoluble dyes and applied by exhaust dyeing method. Sulphur dyes are widely used for cellulosic fibres for darker shades. The exact chemical structure of sulfer dyes is not known, but these dyes contain sulfur as an integral of the chromophore as well as in the polysulphide side chains. These are produced by thionisation or sulphurisation of organic intermediates containing nitro and amino groups. Dye class General Description Application Sulphur Difficult to apply. Application similar to vat dyes. Cheap. particularly for dark shade. Incomplete black, navy, khaki colour range (strong in brown but no bright shade). Poor washing & rubbing fastness & sensitive to Chlorine. May cause fabric rendering of cellulose upon storage (aging). Mostly used for heavy cellulosic goods in dark shades.
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  Working principle of Sulphur Dyes Dyeing includesa few stages. Reduction, dyeing, washing, oxidation, soaping and final washing. The anion is developed on reducing and solubilizing at boil when it shows affinity for cellulose. Sodium sulphide (Na2S), the reducing cum solubilizing agent perform both reduction and solubilization producing thiols and then to sodium salt of thiols or thiolates, which are soluble in water and substantive towards cellulose. Higher rate of exhaustion occurs at 90-950C in presence of electrolyte. Dyed cellulosics exhibit tendering effect on storage under humid atmosphere due to presence of excess free sulphur and aftertreatment with sodium acetate is required to suppress that. H2S liberated during dyeing forms corrosive metal sulphide and this restricts use of metal vessels except those made of stainless s. The exact chemical structure of sulfer dyes is not known, but these dyes contain sulfur as an integral of the chromophoreteel.
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  Metal Complex Dyes Metal complex dyesor metallized dyes are that in which typically one or two dye molecules form a close permanent association or complex with a metal atom. The metal associated with the dye is held by what is more than one part of the dye molecule for the electrons of the metal atom. The metal is often copper, chromium or cobalt. Dye class General Application Metal Complex Relatively difficult to apply. Expensive. Complete colour range but duller shade than acid dyes. Good fastness due to high molecular size & metal complex structure. Mainly used for wool & Nylon..
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  Description of MetalComplex Dyes Metal-complex dyes are synthesized through coordination of bi- or polyvalent transition metal ions with selective acid dyes. They are mainly applied to wool, silk and nylon to achieve better wash fastness for dyed fabrics, compared to those obtained with the parent acid dye. These dyes may be produced on the substrate, during dyeing, through a one- or two-step process, which is known as mordant dye. Alternatively the metal is chelated in the dye structure by the manufacturer before application, which is called premetallised dye. Overall increase in the size of the acid dye molecules after coordination with metal is at the root of improved wash fastness. The extent of exhaustion, diffusion and levelling through migration, is utilized to promote build-up of shade.
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  Basic dyes Basic dyesare also known as cationic dyes. This a class of synthetic dyes, that act as bases and when made soluble in water, they form a colored cationic salt, which can react with the anionic sites on the surface of the substrate. The basic dyes produce bright shades with high tinctorial values, on textile materials Dye class General Description Application Basic (Cationic) Careful application required to prevent unlevel dyeing & adverse effect in hand- feel. Complete colour range with very good brilliant shades. . Mainly used for acrylic.
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  Working Process ofBasic Dyes Basic Dyes are cationic soluble salts of coloured bases. These dyes are applied to substrate with anionic character where electrostatic attractions are formed. They react on the basic side of the isoelectric points. Usually acetic acid is added to the dyebath to help the take up of the dye onto the fibre. . These dyes are mainly applied to acrylic fibers. The most common anionic group attached to acrylic polymers is the sulphonate group, -SO3-, closely followed by the carboxylate group, - CO2-. These are either introduced as a result of co-polymerization, or as the residues of anionic polymerization inhibitors. It is this anionic property which makes acrylics suitable for dyeing with cationic dyes, since there will be a strong ionic interaction between dye and polymer. Basic Orange 5
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  Disperse Dyes A classof slightly water-soluble dyes originally introduced for dyeing polyester, acetate, and related hydrophobic fibers and usually applied from fine aqueous suspensions. The negative charge on the surface of hydrophobic fibers like polyester can not be reduced by any means, so non-ionic dyes like disperse dyes are used which are not influenced by that surface charge. The dye has derived its name for its insoluble aqueous properties and the need to apply it from an aqueous dispersion. Of all the dyes, they are of the smallest molecular size. Dye class General Application Disperse Requires skill in application (either by carrier or under high temperature). Moderate price. Complete colour range. Limited solubility in water (normally dispersed in water for application). Good fastness after reduction clearing treatment; Posseses sublimation property. Mostly used for polyester & acetate. Can also be applied on nylon & Acrylic.
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  Working Process of Disperse Dyes Dispersedye have low solubility in water, typically less than 1 mg/L. They are applied to the article as an extremely fine suspension. Upon attachment to the article, the particles dissolve and, owing to their low molecular weight, migrate throughout.
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  Direct dye Direct dyeis a dye class based on application method, which is essentially by immersion of the fibre in a solution of dye without the need for other chemicals to adhere to the fabric molecules (though other chemicals may aid exhaustion). Direct dyes have high substantivity, but bond weakly to fibers, and therefore usually have poor wash fastness. Light fastness varies from poor to very good. A post-dyeing fixative is often used to improve wash fastness. Brightness can be limited in direct dyes, because brightness often is associated with small molecules and small molecules tend to make poor direct dyes. Dye class General Description Application Direct Simple application. Cheap. Complete colour range. Moderate colour fastness but can be improved by cationic aftertreatment. Mainly used for cellulosic fibres. Can also be applied on rayon, silk & wool.
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  Working Process ofDirect Dyes The dyeing process with direct dyes is very simple, Direct dyeing is normally carried out in a neutral or slight alkaline dyebath, at or near boiling point , but a separate aftertreatment such as cationic dye fixing , to enhance wet fastness has been necessary for most direct dyeing . An addition of alkali, usually sodium carbonate, may be made with acid-sensitive direct dyes and with hard water as well as to enhance the dye solubilization. When cellulose is immersed in a solution of a direct dye it absorbs dye from the solution until equilibrium is attained, and at this stage most of the dye is taken up by the fiber. The rate of absorption and equilibrium exhaustion vary from dye to dye. Direct dyes are used on cotton, paper, leather, wool, silk and nylon. They are also used as pH indicators and as biological stains.
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  Dyeing Parameters FACTORS WHICH INFLUENCE THE EFFECTIVE COLORATIONOF TEXTILE MATERIALS ARE DISCUSSED IN THIS SECTION
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  Liquor Ratio liquor ratioinfluences the dye solubility and the strength of the electrolyte effect. Lower liquor ratios are employed whenever possible, for ecological, economic, and technical reasons. However the correct liquor ratio for the recipe must be maintained otherwise the right shade will not be achieved first time
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  Electrolytes The electrolyte (i.e.,sodium chloride or sodium sulfate), its concentration, and the speed of addition, control the adsorptive behavior of the dyes and the degree of exhaustion. A high electrolyte content of the dye bath shifts the dyeing equilibrium toward the fiber.
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  pH The pH valueinfluences solubility substantively of the dyes, and their stability in the dye bath. Lower pH values improve exhaustion; however, leveling proceeds preferably at higher pH values.
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  Temperature Temperature of thedye bath plays vital role for dyeing. Rise in temperature has a large effect on an increase in the diffusion rate of dyes into fabrics. Increasing of temperature increases the rate of dyeing & of the dye migration. Higher dyeing temperature ensures the good leveling & better penetration of dye in to the fibers. But the temperature depends on the types of dye adapted in the dye bath. For Example-in case of hot brand dyestuff the dosing temperature of dye is 80ºC and for cold brand dye temperature is kept 60ºC.
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  Run Time The timefor dyeing also the vital one. A specific Time adjusted with the temperature, very much needed for better dyeing. For this reason color dosing takes place in 20 minutes (may vary process to process) & Specific run time is set for dyeing.
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  Theory of Dyeing THEORETICAL ASPECT OF DYEINGARE DESCRIBED IN THIS SECTION
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  Successive Stage in the Dyeing Thedyeing process is essentially a distribution process. The dye is distributed over at least two-phase systems, the dye bath and textile materials. The stages of dyeing are : (i) Dye dispersed in the dye bath (ii) Dye in the diffusion layer(boundary layer) (iii) Dye in the electrical double layer (iv) Dye absorbed on the fiber surface (v) Dye diffused in the fiber (vi) Dye physically or chemically bond in the fiber
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  1. Dye Dispersed in theDye Bath As we seen from the classification of dyes section , most of the dyes in solution are in molecular and partially ionized state or exist in the form of ionic micelles.
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  2. Dye inthe Diffusion Layer When a substrate is brought into a dye bath, a concentration gradient is created which will-make the dye molecules move or diffuse to the fiber. The dye which approaches the fiber surface must eventually diffuse through a thin liquid layer, the so-called diffusion layer, towards or onto the fiber surface.
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  3. Dye inthe Electrical Double Layer All textile fibers when immersed in water or aqueous solution, acquire an electrical potential after referred to as Beta potential. At the fiber surface the dye molecules must pass the electrical double layer, consists of non- solvated anions(mostly) and solvated cat ions. These positive and negative ions try to approach the fiber surface as close as possible. This layer is about 1nm thin.
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  4. Dye Absorbed on theFiber Surface The dye molecules reach the fiber surface ( and the first layer of the fiber ). This dye take-up at the fiber surface (absorption) occurs very rapidly and leads to a reduction of dye molecules in the immediate vicinity of this surface.
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  5. Dye Diffused in theFiber After absorption, dye diffused in the fiber. Owing to the high temperature , there is always an abundance of dye stuff molecules in the vicinity of the fiber and agitation has little effect upon the time of half dyeing.
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  6. Dye Physically or Chemically Bondin the Fiber The last step of dyeing is fixation. In case of reactive dyes, the fixation is one-way. Because here dye molecules become attached to the fiber polymer by strong co-valent bonds. In case of all other dyes this fixation is two ways. Because they are fixed with fiber by weak hydrogen or salt linkage.
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  The following factors are responsiblefor the anchoring of the dye molecules to the fiber 1.Salt linkage/ionic bonds for protein fibers. 2.Co-ordination linkage 3.Hydrogen bonds 4.Co-valent bonds ; for cellulose fibers 5.Physical forces 6.Dispersion forces.
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  Dyeing Process Cotton yarn dyeingprocess are briefly discussed in this section
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  DYEING PROCESS The whole dyeingprocess is separated into two part. 1. Lab Process 2. Floor Process
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  Lab Process Here inthe lab a spectrophotometer is used to analyze the color required for a certain fabric. Then lab technicians come up with a recipe for obtaining that color by mixing the available colors. This recipe is then tested in small scale and adjusted until a satisfactory result is obtained.
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  Floor Process The recipethat is obtained from the lab is transformed into bulk recipe keeping the same ratio and adjusting for the weight of the fabric to be dyed. Dyeing machines are used to carry out large scale dyeing of fabric and yarn.
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  Process flow chart for Cotton Yarn Dyeing
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  Process flow chart forCotton Yarn Dyeing
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  Process flow chart forCotton Yarn Dyeing
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  Chemicals Used in DyeingProcess Some commonly used chemicals in Dyeing Process are discussed in this Section
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  Basic Chemicals These are thego to chemicals for any dyeing process. Soda ash (Sodium Carbonate). Hydrochloric Acid. Hydrogen peroxide. Sulphuric Acid. Acetic Acid. Caustic soda (NaOH).
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  Acids Many acids areused in dyeing. Basically for pH control. They include acetic acid, citric acid, formic acid, hydrochloric acid and sulfuric acid. Acetic acid - Acetic acid is used in many dyeing processes. It is much less expensive than vinegar where large amounts are required. Often a 58% solution in water is called for. Citric acid - a solid organic acid; HOCCOOH(CH2COOH)2 , Citric is sometimes used in dyeing as an alternative to acetic acid. It is convenient to store and handle, but may be more expensive. It is a weak acid but can produce pH in the range of 3 to 6 Sulfuric acid – H2SO4 a very potent inorganic ("mineral") acid; a strong acid. Sulfuric acid is used in some preparation and dyeing process, most often with wool. Sodium bisulphate (not bisulphite) can sometimes be used as an alternative
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  Thickener "Sodium alginate" isused to thicken dye solutions for direct application. It is a preferred thickener for reactive dyes because it does not react with the dye. It comes in a number of variations that have somewhat different properties. "Low viscosity" types are appropriate for reducing migration of wet dye solutions for fine line work, while "high viscosity is more suitable for making printing pastes. It is extracted for seaweed. Sodium Alginate
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  Chelating Ageng Chelating agents aremostly used in dye baths, as they remove the hardness of water by bonding with heavy metal ion. Chelating agents form a stable complex compound that does not decompose over a prolonged processing period. The coordination of water with metal ions enhances the acidity of the dye solution, which is dependent on the physical and chemical characteristics of the metal ions. Inorganic chelating agents are also used as detergent by suspending and dispersing agents. They require less than the stoichiometric quantity predicted to keep ions in solution (threshold effect). EDTA and NTA are two of the widely used chelating agent.
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  Dispersing Agents Disperse dyes arenonionic chemicals that are barely soluble in water and often crystallize with varying particle size. These characteristics are inadequate for dispersing dyes of water and cause unleveled dyeing. To achieve the required particle size and distribution, the disperse dye is milled, usually in the presence of a dispersing agent. Generally, the dispersing agents are anionic, e.g., ligninsulfonates, or polycondensates of arylsulfonic acids with formaldehyde, which facilitate milling. Dispersing agents have shown a dual function role: breaking down aggregated dye particles and dispersing dyes in the dye liquor. Dispersing agents consists of high-molecular weight or polymeric compounds in which polar or ionizing groups alternate with nonpolar groups along the chain. The backbone of a dispersing agent is nonpolar, while the polar or ionizing groups are located in the side chains. Sodium dinaphthylmethane Sulfonate and Lingnosulfonates are some widely used dispersing agents.
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  Levelin g Agent To achieveuniform dyeing on fabric, it is essential to add a suitable leveling agent in the dye baths. However, it is quite difficult to explain the functions and actions of leveling agents. The effects of leveling agents are: (i) leveling agents tend to decrease the absorption of dyes by forming a dye-auxiliary complex with free dyes maintaining equilibrium; (ii) leveling agents act as retarding agents; and (iii) dye migration proceeds slowly, leads better leading to improved leveling of dye on the fiber.
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  Electrolytes During dyeing inthe dyebath, electrolyte serves as three important roles—driving dye into textiles causing, maximum exhaustion of dye molecules through the presence of salt, and fixing dyestuff to the cellulose material. Glauber’s salt is the common name for sodium sulfate decahydrates Na2SO4. 10H2O; it occurs as white or colorless monoclinic crystals along with common salt ( NaCl) these are the most commonly used electrolyte in the dyeing industry
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  Surfactants Surfactant molecules shouldhave surface active properties with the chemical structure of a hydrophilic (water loving) and hydrophobic (having little attraction for organic molecules) balance. These molecules get preferentially oriented at the interface between air and water, which lowers the surface tension of water substantially when dissolved in the concentration range of 0.1–10 g/l. Examples are alkyl benzene sulfonate and sodium lauryl sulfate
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  Anti Foaming Agents The dyeing processcan lead to the formation of macro and micro foams during circulation of dyes and auxiliaries in the dye bath. A macro foam is displayed with large bubbles, which are visible on the surface of the system and produce cosmetic imperfections. A typical list of anti-foaming agents is as follows: 2-ethyl hexanol (EH), tributyl phosphate (TBP), poly (dimethyl siloxane) (PDMS) amides, mineral oil, fatty acids, and their derivatives.
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  Reducing Agent Beginning of thenineteenth century, sodium dithionate (Na2S2O4) was introduced as a reducing agent for the vat dyeing process. Effective sodium dithionate, also called hydrose is till this date the most used reducing agent in dyeing industry.
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  Softeners A softeneris a chemical used to make the touch of fabric more pleasing. Softened fabrics are fluffier and have better drape ability. In addition to aesthetics, softeners improve abrasion resistance, improve tearing strength, and reduce needle cutting when the garments are sewn. Softeners are divided into three major chemical categories: anionic, cationic, and nonionic. Silicon based non ionic softener
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  Anti Creasing Agents Crease is formedin cotton fiber because of the intermolecular hydrogen bonding of primary and secondary hydroxyl groups of the polymer chains. The amorphous regions of the hydrogen bonds can easily break down by folding. In the folding state, the broken hydrogen bonds stabilize. Different durable press finishes have been used for many years for use in cotton fabric. N-methylol compounds such as dihydroxyethylene urea react readily with the hydroxyl groups of cellulose chains hence acting as anti creasing agent.
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  Bleaching Agent Hydrogen peroxide isextensively used in commercial bleaching of textiles, especially cellulose fibres and wool. It is effective and non-polluting. A 35-75% solution of H2O2 is used .
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  Others Diluents : Sodiumsulphate is a common diluent for dry dyes. Fixative : Chemicals that help improve wash fastness of dyed fabric. Lubricant : A material used to reduce friction between surfaces. Lubricants are often applied to yarns that are used for knitted fabrics such as jersey. They help protect the yarn from damage and the machinery from wear. Enzyme :. Enzymes are now extensively used in textile processing. Amylase enzymes are used for desizing, and cellulose enzymes are used for modification of cellulosic fabrics such as de-pilling or or permanent softening. Binder : A material that is typically used to attach a pigment to fabric. Antichlor : A chemical used to neutralize chlorine bleach. Anti Migrant : An additive used in dye or pigment mixtures to prevent undesired movement or spreading of the wet dye on fabric Restraining Agent :A dye bath auxiliary that is typically used to prevent one fibre in a blend from taking up dye intended for the other fibre, or to equalize the uptake.
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  Conclusion
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  Summing-up In this presentationI tried to discuss the dyeing process and other variables related with it along with its components as concisely as possible. The knowledge of Textile dyeing I gained from my industrial project at Sanzi Textile Mills Ltd was the key factor in preparing this presentation.