The document provides an overview of reactive dyes:
1) Reactive dyes chemically bond to fibers through reactive groups that form covalent bonds with hydroxyl or amino groups on fibers like cotton, polyamide, and wool.
2) They were first invented in 1956 and provided brighter colors and better fastness than previous dyes.
3) Reactive dyes are now widely used for cellulosic fibers due to their brighter colors, good fastness properties, and simpler dyeing process compared to other dyes.
Reactive dyes are organic dyes that form covalent bonds with cellulose fibers. They were first commercially produced in 1956 and have advantages like excellent color fastness and ease of washing. Reactive dyes contain three parts - a chromophore for color, a reactive group that bonds to fibers, and a bridging group connecting these. Dyeing involves exhaustion of dye onto fibers, fixation through alkaline conditions forming covalent bonds, and washing unfixed dye away. Reactive dyeing gives very colorfast results due to the strong covalent bonds formed.
The document discusses the production of denim fabric using slasher dyeing. It describes the slasher dyeing process which continuously passes warp yarns through indigo dye liquor troughs to dye the yarns on the warp beam. This allows for dyeing and sizing in a single operation. The document also provides details on the types of yarns, chemicals, and processes used, including scouring, dyeing with indigo and sulfur black, and sizing to strengthen and protect the yarns during weaving.
The document provides information about reactive dyes, including:
- Reactive dyes form covalent bonds with fiber polymers through reactive groups, giving excellent wash and light fastness.
- Important reactive groups include triazine, vinyl sulfone, and halogen groups.
- Reactive dyes were invented in 1956 and became popular for their bright colors, low temperature dyeing, and simple process.
- Common application methods are pad-batch and pad-dry processes at low temperatures. Proper pH, electrolyte, alkali, and time are required for effective dye fixation to the fiber.
This presentation provides an overview of disperse dyes. It was presented on November 27, 2016 at NUB by 4 students. Disperse dyes are organic compounds without ionizing groups that are insoluble in water but can be dispersed to dye synthetic fibers like polyester. The history and properties of disperse dyes are discussed. Disperse dyes are classified by chemical structure and fastness properties. Dispersing agents and carriers are used to aid disperse dyeing at high temperatures or through carrier methods. Examples of commercial disperse dyes and carriers are provided.
This presentation discusses direct dyes, which are water-soluble dyes used to dye cellulosic materials like cotton directly. There are two major types of direct dyes: anionic direct dyes, which are used for paper coloring and shade correction, and cationic direct dyes. Direct dyes have properties like water solubility and being anionic in nature. They dye materials through weak hydrogen and van der Waals bonding in alkaline conditions. The dyeing process involves dissolving the dye in boiling water with electrolytes before applying it to materials and boiling for 30-45 minutes. Direct dyes provide duller colors than reactive dyes and have lower wash fastness. They are used for applications where high fastness is
It has great effect of hot brand reactive dye on cotton fabric with exhaustion method. Migration method is more acceptable for proper color fixation in a dyeing process. Another way when we followed ISO method has create a lot of problem such as wash fastness variation rubbing fastness variation, uneven dyeing etc. If we want to get perfect dyeing than we must maintain migration method.
Special Instruction:
Fabric shrinkage must keep within ±5%
Color fastness should be 4-5 range
Pilling range 3 to 5
pH range 5.5 to 7
Fabric weight will be allowed ±02%
Fabric quality should be s per approved swatches & Lab-Dips.
Batch to batch color matching should be 4-5
Batch to batch “Shade Band Swatch” must be submitted for approval.
Chemicals and Auxiliaries used in Textile Wet ProcessingMashrur Wasity
This document discusses various chemicals and auxiliaries used in textile wet processing. It defines auxiliaries as chemicals that help processing operations like preparation, dyeing and printing work more efficiently. Some common auxiliaries mentioned include surfactants, wetting agents, sequestering agents, dispersing agents and emulsifiers. Basic chemicals used in wet processing like acids, bases, salts, oxidizing and reducing agents are also discussed. The roles and examples of various chemicals are provided in concise points.
Reactive dyes are organic dyes that form covalent bonds with cellulose fibers. They were first commercially produced in 1956 and have advantages like excellent color fastness and ease of washing. Reactive dyes contain three parts - a chromophore for color, a reactive group that bonds to fibers, and a bridging group connecting these. Dyeing involves exhaustion of dye onto fibers, fixation through alkaline conditions forming covalent bonds, and washing unfixed dye away. Reactive dyeing gives very colorfast results due to the strong covalent bonds formed.
The document discusses the production of denim fabric using slasher dyeing. It describes the slasher dyeing process which continuously passes warp yarns through indigo dye liquor troughs to dye the yarns on the warp beam. This allows for dyeing and sizing in a single operation. The document also provides details on the types of yarns, chemicals, and processes used, including scouring, dyeing with indigo and sulfur black, and sizing to strengthen and protect the yarns during weaving.
The document provides information about reactive dyes, including:
- Reactive dyes form covalent bonds with fiber polymers through reactive groups, giving excellent wash and light fastness.
- Important reactive groups include triazine, vinyl sulfone, and halogen groups.
- Reactive dyes were invented in 1956 and became popular for their bright colors, low temperature dyeing, and simple process.
- Common application methods are pad-batch and pad-dry processes at low temperatures. Proper pH, electrolyte, alkali, and time are required for effective dye fixation to the fiber.
This presentation provides an overview of disperse dyes. It was presented on November 27, 2016 at NUB by 4 students. Disperse dyes are organic compounds without ionizing groups that are insoluble in water but can be dispersed to dye synthetic fibers like polyester. The history and properties of disperse dyes are discussed. Disperse dyes are classified by chemical structure and fastness properties. Dispersing agents and carriers are used to aid disperse dyeing at high temperatures or through carrier methods. Examples of commercial disperse dyes and carriers are provided.
This presentation discusses direct dyes, which are water-soluble dyes used to dye cellulosic materials like cotton directly. There are two major types of direct dyes: anionic direct dyes, which are used for paper coloring and shade correction, and cationic direct dyes. Direct dyes have properties like water solubility and being anionic in nature. They dye materials through weak hydrogen and van der Waals bonding in alkaline conditions. The dyeing process involves dissolving the dye in boiling water with electrolytes before applying it to materials and boiling for 30-45 minutes. Direct dyes provide duller colors than reactive dyes and have lower wash fastness. They are used for applications where high fastness is
It has great effect of hot brand reactive dye on cotton fabric with exhaustion method. Migration method is more acceptable for proper color fixation in a dyeing process. Another way when we followed ISO method has create a lot of problem such as wash fastness variation rubbing fastness variation, uneven dyeing etc. If we want to get perfect dyeing than we must maintain migration method.
Special Instruction:
Fabric shrinkage must keep within ±5%
Color fastness should be 4-5 range
Pilling range 3 to 5
pH range 5.5 to 7
Fabric weight will be allowed ±02%
Fabric quality should be s per approved swatches & Lab-Dips.
Batch to batch color matching should be 4-5
Batch to batch “Shade Band Swatch” must be submitted for approval.
Chemicals and Auxiliaries used in Textile Wet ProcessingMashrur Wasity
This document discusses various chemicals and auxiliaries used in textile wet processing. It defines auxiliaries as chemicals that help processing operations like preparation, dyeing and printing work more efficiently. Some common auxiliaries mentioned include surfactants, wetting agents, sequestering agents, dispersing agents and emulsifiers. Basic chemicals used in wet processing like acids, bases, salts, oxidizing and reducing agents are also discussed. The roles and examples of various chemicals are provided in concise points.
Pigments are insoluble colorants that remain on the surface of fibers rather than penetrating inside. They are held in place mechanically by binders which are cured at high temperatures. For commercial use, pigments must have good heat resistance, dispersability, light/weather fastness, and be harmless and affordable. Binders are important as they bond pigment particles to fibers and form a clear film. The rubbing fastness of pigments depends on binder efficiency. Pigment dyeing involves padding dye paste onto fabric, drying, and curing at high heat to set the colors.
The document provides information about dyeing cotton with reactive dyes, including:
1. Reactive dyes form covalent bonds with cotton fibers through reaction groups, making them very colorfast.
2. The dyeing process involves an exhaustion phase where the dye adsorbs to the fiber, and a fixation phase where the dye chemically reacts with and bonds to the fiber.
3. Key factors that affect dyeing include salt, soda, temperature, pH, time, and other assistants; the optimal time for fixation of reactive dyes to cotton is around 60 minutes.
1. Dyeing polyester/cotton blend fabrics using reactive disperse dyes in supercritical carbon dioxide has several advantages over conventional dyeing methods.
2. Supercritical carbon dioxide acts as a solvent for the hydrophobic disperse dyes and allows for deep penetration and homogeneous dyeing of the polyester fibers.
3. The process is more environmentally friendly as supercritical carbon dioxide is non-toxic, non-flammable and can be recycled in a closed system without disposal issues.
The document discusses thermosol dyeing of PET/wool blended fabrics. It describes the process which involves padding the fabric with disperse dyes, drying, then applying heat in a stenter at 190-200 degrees C for 45-60 seconds. Dyes must be able to fix at this temperature range and minimally stain the wool. The thermosol conditions do not impair the mechanical properties of the wool. Faulty shades can be corrected by boiling the fabric in a solution containing levelling agents. Complete stripping is possible using a solution of formic acid, zinc sulphoxylate formaldehyde and other agents at elevated temperatures over time.
Direct dyes are water-soluble aromatic compounds that have an affinity for cellulose fibers like cotton. They are applied as aqueous solutions and bond to fibers physically through hydrogen bonding and van der Waals forces. Direct dyes generally have poor fastness properties but these can be improved through after-treatments using metallic salts like copper or chromium compounds, or formaldehyde, which increase the dye's molecular weight and bonding strength to the fibers. Key factors that influence direct dye uptake include electrolyte concentration, temperature, liquor ratio, and dye class.
Reactive dyes readily dissolve in water and form covalent bonds with cellulose fibers, providing good washing fastness. They are classified based on their reactivity - alkaline controllable dyes require gradual alkali addition, salt controllable dyes require portion-wise salt addition, and temperature controllable dyes react above boiling temperatures. Bifunctional reactive dyes contain two reactive groups, allowing for high exhaustion and fixation during dyeing of cotton which involves dyeing with salt, forming covalent bonds with alkali, and post-treatment processes like soaping and washing.
reactive Dyeing of cotton knitted fabricsOliyad Ebba
Exhaust dyeing is commonly used to dye cotton and cotton blend knitted fabrics. It involves dye migration from the dye liquor into the fabric batch using exhausting chemicals and circulation. Reactive and disperse dyes are most commonly used. Key parameters include temperature, speed, pressure, and cycle time. Proper preparation of dyes, salts, and chemicals is important to prevent issues. Checking points after dyeing ensure the required shade and pH are met before draining. An aftertreatment process includes neutralization, soaping, and fixing to improve wash fastness. Safety equipment and material safety data sheets are necessary in the dye house.
1. There are six main theories that explain the interaction between dyes and fibers: physical, chemical, physico-chemical, fiber-complex, solid solution, and mechanical or pigment theories.
2. The physical theory involves dyes being physically retained on fibers through hydrogen bonding and van der Waals forces, while the chemical theory involves chemical bonding between reactive groups on the dye and fiber.
3. The physico-chemical theory involves dyes first being attached physically and then chemically treated to further improve fastness.
Reactive dye (B.Sc in Textile Engineering)Mazharul Islam
This document provides information about reactive dyes used for dyeing cotton fabrics. It discusses the general structure and properties of reactive dyes, including that they form covalent bonds with fibers. The document also summarizes the dyeing process, which involves dye exhaustion, fixation in an alkaline environment, and washing off unfixed dye. Factors that affect dye hydrolysis are outlined, such as liquor ratio, salt concentration, and temperature. The role of salt and alkali in the dyeing process is also explained.
Styles of printing; Printing thickeners including synthetic thickeners; Printing auxiliaries; Printing of cotton with reactive dyes, wool, silk, nylon with acid and metal complex dyes, Printing of polyester with disperse dyes; Pigment printing; Resist and discharge printing of cotton, silk and polyester; Transfer printing of polyester; Inkjet printing.
The document discusses vat dyes, which are insoluble aromatic compounds containing quinone groups. Vat dyes are reduced to a soluble hydroquinone form using reducing agents like sodium dithionite and sodium hydroxide for application to cellulosic fibers. The reduced dyes are then oxidized back to the insoluble pigment form within the fibers. Vat dyes provide excellent fastness properties and can withstand various treatments. Common application methods include reduced vat dyeing in jigs or stock vats, and continuous padding and developing processes. Post-dyeing treatments may include oxidation, soaping, leveling, or partial stripping to correct any faults.
The document discusses various methods for dyeing polyester fibers, including:
1) Batch dyeing without carriers involves dyeing at a boil without additives to help penetration.
2) Carrier dyeing uses compounds to swell the fibers and allow deeper dye penetration.
3) High temperature, high pressure (HTHP) dyeing penetrates dye rapidly at over 120°C without carriers.
4) Continuous thermosol dyeing involves padding, drying, and fixing dye within fibers at 190-220°C.
This document provides information about reactive dyes and disperse dyes. It discusses the dyeing conditions for different types of dyes including acid, basic, direct, disperse, and reactive dyes. It also summarizes the types and properties of reactive dyes and disperse dyes, as well as the dyeing processes for polyester fibers using disperse dyes. Finally, it lists some of the author's textile-related Facebook pages for additional information.
Vat dyes are insoluble in water but can be converted to soluble leuco compounds using reducing agents like sodium hydrosulphite and caustic soda. These leuco compounds are applied to cotton and oxidized back to insoluble dyes. Vat dyes are classified by application temperature and chemical requirements, with IK requiring the lowest temperatures and chemicals and IN-Special requiring the highest. The vat dyeing process involves vatting to solubilize the dye, dyeing to apply it to cotton, oxidation to fix it, and after treatment including soaping to improve fastness.
Introduction of vat dye /Some knowledge for Vat dyes.TonmoyMollick
The document discusses vat dyes, which are water-insoluble dyes that must be chemically modified before use. It provides details on:
- The history and development of vat dyes, with the original being indigo obtained from plants.
- The chemical process of reducing vat dyes with sodium dithionite to create water-soluble leuco compounds that can be applied to fabrics.
- The dyeing process, which involves vatting, dyeing the fabric in alkaline conditions, oxidizing the dye, and soaping to improve fastness.
- Examples of common vat dyes like indanthrones and flavanthrones and their properties.
- The excellent fastness to light
Vat dyes are water-insoluble dyes that can be converted to a water-soluble form through chemical reduction. They were first developed in the 1850s as synthetic dyes and include indigo dye. The vat dyeing process involves three steps - vatting to convert the dye to its soluble leuco form, oxidation to convert it back to insoluble form in the fiber, and after treatment. Vat dyes have high color fastness but more limited shades than other dyes and their application process is complex and time-consuming.
This document provides information about acid dyes. It begins with an introduction to acid dyes, noting that they are large dyes containing sulfonic or carboxylic acid groups that dye protein fibers like wool from acid solutions. It then discusses the properties of acid dyes, including that they are water soluble and have affinity for protein and nylon fibers. The document also covers the classification, structure, and dyeing processes for acid dyes. In particular, it differentiates between types of acid dyes like levelling, fast, milling, and super-milling dyes based on their molecular size and dyeing characteristics.
Vat dyes are insoluble natural or synthetic dyes that are converted to their soluble leuco form using a reducing agent like sodium hydrosulfite. This allows the dye to penetrate cellulose fibers during the dyeing process. After penetration, the fabric is oxidized, converting the dye back to its insoluble form within the fibers. Key steps are vatting to solubilize the dye, dyeing to allow penetration, and oxidation to fix the dye in the fibers. Vat dyes provide excellent washing fastness due to being locked inside the fibers. However, they are more difficult and costly to apply than other dyes.
Batch dyeing involves dyeing fabric in a stationary dye bath. There are three main types of batch dyeing machines. Jigger dyeing machines transfer fabric back and forth between rollers through a dye bath, applying tension. Winch dyeing machines pass rope-formed fabric over rollers through a stationary dye bath with little tension. Jet dyeing machines eliminate rollers and use jet nozzles to circulate fabric through a closed tubular system at high temperatures and pressures.
This document discusses reactive dyes, including their classification, chemical properties, influencing dyeing factors, and application methods. Reactive dyes are classified based on their reactive groups and dyeing temperatures. They form covalent bonds with cellulose and protein fibers during dyeing. Key factors that influence dyeing include pH, temperature, electrolyte concentration, and time. Reactive dyes are applied using discontinuous, continuous, or semi-continuous methods. Their advantages include color permanence due to covalent bonding and easy washing without color transfer. Uneven dyeing can be difficult to strip due to the strong bonds formed.
Reactive dyes are popular for dyeing cellulosic fibers like cotton. They form covalent bonds with fiber polymers through reactive groups on the dye molecules. This allows for good wash fastness. Reactive dyes contain parts for color (chromophore), reactivity (reactive group), and solubility. Dyeing involves exhaustion of the dye from solution onto the fiber followed by fixation through a chemical reaction between the reactive group and fiber under alkaline conditions. Process parameters like pH, temperature and electrolyte concentration must be carefully controlled to maximize dye uptake and fixation while minimizing hydrolysis.
Pigments are insoluble colorants that remain on the surface of fibers rather than penetrating inside. They are held in place mechanically by binders which are cured at high temperatures. For commercial use, pigments must have good heat resistance, dispersability, light/weather fastness, and be harmless and affordable. Binders are important as they bond pigment particles to fibers and form a clear film. The rubbing fastness of pigments depends on binder efficiency. Pigment dyeing involves padding dye paste onto fabric, drying, and curing at high heat to set the colors.
The document provides information about dyeing cotton with reactive dyes, including:
1. Reactive dyes form covalent bonds with cotton fibers through reaction groups, making them very colorfast.
2. The dyeing process involves an exhaustion phase where the dye adsorbs to the fiber, and a fixation phase where the dye chemically reacts with and bonds to the fiber.
3. Key factors that affect dyeing include salt, soda, temperature, pH, time, and other assistants; the optimal time for fixation of reactive dyes to cotton is around 60 minutes.
1. Dyeing polyester/cotton blend fabrics using reactive disperse dyes in supercritical carbon dioxide has several advantages over conventional dyeing methods.
2. Supercritical carbon dioxide acts as a solvent for the hydrophobic disperse dyes and allows for deep penetration and homogeneous dyeing of the polyester fibers.
3. The process is more environmentally friendly as supercritical carbon dioxide is non-toxic, non-flammable and can be recycled in a closed system without disposal issues.
The document discusses thermosol dyeing of PET/wool blended fabrics. It describes the process which involves padding the fabric with disperse dyes, drying, then applying heat in a stenter at 190-200 degrees C for 45-60 seconds. Dyes must be able to fix at this temperature range and minimally stain the wool. The thermosol conditions do not impair the mechanical properties of the wool. Faulty shades can be corrected by boiling the fabric in a solution containing levelling agents. Complete stripping is possible using a solution of formic acid, zinc sulphoxylate formaldehyde and other agents at elevated temperatures over time.
Direct dyes are water-soluble aromatic compounds that have an affinity for cellulose fibers like cotton. They are applied as aqueous solutions and bond to fibers physically through hydrogen bonding and van der Waals forces. Direct dyes generally have poor fastness properties but these can be improved through after-treatments using metallic salts like copper or chromium compounds, or formaldehyde, which increase the dye's molecular weight and bonding strength to the fibers. Key factors that influence direct dye uptake include electrolyte concentration, temperature, liquor ratio, and dye class.
Reactive dyes readily dissolve in water and form covalent bonds with cellulose fibers, providing good washing fastness. They are classified based on their reactivity - alkaline controllable dyes require gradual alkali addition, salt controllable dyes require portion-wise salt addition, and temperature controllable dyes react above boiling temperatures. Bifunctional reactive dyes contain two reactive groups, allowing for high exhaustion and fixation during dyeing of cotton which involves dyeing with salt, forming covalent bonds with alkali, and post-treatment processes like soaping and washing.
reactive Dyeing of cotton knitted fabricsOliyad Ebba
Exhaust dyeing is commonly used to dye cotton and cotton blend knitted fabrics. It involves dye migration from the dye liquor into the fabric batch using exhausting chemicals and circulation. Reactive and disperse dyes are most commonly used. Key parameters include temperature, speed, pressure, and cycle time. Proper preparation of dyes, salts, and chemicals is important to prevent issues. Checking points after dyeing ensure the required shade and pH are met before draining. An aftertreatment process includes neutralization, soaping, and fixing to improve wash fastness. Safety equipment and material safety data sheets are necessary in the dye house.
1. There are six main theories that explain the interaction between dyes and fibers: physical, chemical, physico-chemical, fiber-complex, solid solution, and mechanical or pigment theories.
2. The physical theory involves dyes being physically retained on fibers through hydrogen bonding and van der Waals forces, while the chemical theory involves chemical bonding between reactive groups on the dye and fiber.
3. The physico-chemical theory involves dyes first being attached physically and then chemically treated to further improve fastness.
Reactive dye (B.Sc in Textile Engineering)Mazharul Islam
This document provides information about reactive dyes used for dyeing cotton fabrics. It discusses the general structure and properties of reactive dyes, including that they form covalent bonds with fibers. The document also summarizes the dyeing process, which involves dye exhaustion, fixation in an alkaline environment, and washing off unfixed dye. Factors that affect dye hydrolysis are outlined, such as liquor ratio, salt concentration, and temperature. The role of salt and alkali in the dyeing process is also explained.
Styles of printing; Printing thickeners including synthetic thickeners; Printing auxiliaries; Printing of cotton with reactive dyes, wool, silk, nylon with acid and metal complex dyes, Printing of polyester with disperse dyes; Pigment printing; Resist and discharge printing of cotton, silk and polyester; Transfer printing of polyester; Inkjet printing.
The document discusses vat dyes, which are insoluble aromatic compounds containing quinone groups. Vat dyes are reduced to a soluble hydroquinone form using reducing agents like sodium dithionite and sodium hydroxide for application to cellulosic fibers. The reduced dyes are then oxidized back to the insoluble pigment form within the fibers. Vat dyes provide excellent fastness properties and can withstand various treatments. Common application methods include reduced vat dyeing in jigs or stock vats, and continuous padding and developing processes. Post-dyeing treatments may include oxidation, soaping, leveling, or partial stripping to correct any faults.
The document discusses various methods for dyeing polyester fibers, including:
1) Batch dyeing without carriers involves dyeing at a boil without additives to help penetration.
2) Carrier dyeing uses compounds to swell the fibers and allow deeper dye penetration.
3) High temperature, high pressure (HTHP) dyeing penetrates dye rapidly at over 120°C without carriers.
4) Continuous thermosol dyeing involves padding, drying, and fixing dye within fibers at 190-220°C.
This document provides information about reactive dyes and disperse dyes. It discusses the dyeing conditions for different types of dyes including acid, basic, direct, disperse, and reactive dyes. It also summarizes the types and properties of reactive dyes and disperse dyes, as well as the dyeing processes for polyester fibers using disperse dyes. Finally, it lists some of the author's textile-related Facebook pages for additional information.
Vat dyes are insoluble in water but can be converted to soluble leuco compounds using reducing agents like sodium hydrosulphite and caustic soda. These leuco compounds are applied to cotton and oxidized back to insoluble dyes. Vat dyes are classified by application temperature and chemical requirements, with IK requiring the lowest temperatures and chemicals and IN-Special requiring the highest. The vat dyeing process involves vatting to solubilize the dye, dyeing to apply it to cotton, oxidation to fix it, and after treatment including soaping to improve fastness.
Introduction of vat dye /Some knowledge for Vat dyes.TonmoyMollick
The document discusses vat dyes, which are water-insoluble dyes that must be chemically modified before use. It provides details on:
- The history and development of vat dyes, with the original being indigo obtained from plants.
- The chemical process of reducing vat dyes with sodium dithionite to create water-soluble leuco compounds that can be applied to fabrics.
- The dyeing process, which involves vatting, dyeing the fabric in alkaline conditions, oxidizing the dye, and soaping to improve fastness.
- Examples of common vat dyes like indanthrones and flavanthrones and their properties.
- The excellent fastness to light
Vat dyes are water-insoluble dyes that can be converted to a water-soluble form through chemical reduction. They were first developed in the 1850s as synthetic dyes and include indigo dye. The vat dyeing process involves three steps - vatting to convert the dye to its soluble leuco form, oxidation to convert it back to insoluble form in the fiber, and after treatment. Vat dyes have high color fastness but more limited shades than other dyes and their application process is complex and time-consuming.
This document provides information about acid dyes. It begins with an introduction to acid dyes, noting that they are large dyes containing sulfonic or carboxylic acid groups that dye protein fibers like wool from acid solutions. It then discusses the properties of acid dyes, including that they are water soluble and have affinity for protein and nylon fibers. The document also covers the classification, structure, and dyeing processes for acid dyes. In particular, it differentiates between types of acid dyes like levelling, fast, milling, and super-milling dyes based on their molecular size and dyeing characteristics.
Vat dyes are insoluble natural or synthetic dyes that are converted to their soluble leuco form using a reducing agent like sodium hydrosulfite. This allows the dye to penetrate cellulose fibers during the dyeing process. After penetration, the fabric is oxidized, converting the dye back to its insoluble form within the fibers. Key steps are vatting to solubilize the dye, dyeing to allow penetration, and oxidation to fix the dye in the fibers. Vat dyes provide excellent washing fastness due to being locked inside the fibers. However, they are more difficult and costly to apply than other dyes.
Batch dyeing involves dyeing fabric in a stationary dye bath. There are three main types of batch dyeing machines. Jigger dyeing machines transfer fabric back and forth between rollers through a dye bath, applying tension. Winch dyeing machines pass rope-formed fabric over rollers through a stationary dye bath with little tension. Jet dyeing machines eliminate rollers and use jet nozzles to circulate fabric through a closed tubular system at high temperatures and pressures.
This document discusses reactive dyes, including their classification, chemical properties, influencing dyeing factors, and application methods. Reactive dyes are classified based on their reactive groups and dyeing temperatures. They form covalent bonds with cellulose and protein fibers during dyeing. Key factors that influence dyeing include pH, temperature, electrolyte concentration, and time. Reactive dyes are applied using discontinuous, continuous, or semi-continuous methods. Their advantages include color permanence due to covalent bonding and easy washing without color transfer. Uneven dyeing can be difficult to strip due to the strong bonds formed.
Reactive dyes are popular for dyeing cellulosic fibers like cotton. They form covalent bonds with fiber polymers through reactive groups on the dye molecules. This allows for good wash fastness. Reactive dyes contain parts for color (chromophore), reactivity (reactive group), and solubility. Dyeing involves exhaustion of the dye from solution onto the fiber followed by fixation through a chemical reaction between the reactive group and fiber under alkaline conditions. Process parameters like pH, temperature and electrolyte concentration must be carefully controlled to maximize dye uptake and fixation while minimizing hydrolysis.
This document discusses reactive dyes and disperse dyes used for dyeing textiles. It provides details on:
- Reactive dyes chemically bind to cellulose fibers and provide excellent wet fastness. Disperse dyes are used for synthetic fibers like polyester and acetate.
- Dyeing conditions like temperature, time and pH levels vary depending on the type of dye and fiber. Proper dye selection and process is needed to achieve good color fastness.
- Blends require multi-step dyeing using both reactive and disperse dyes in separate baths or a single bath approach to dye both natural and synthetic fiber components.
City University textile department, topic: cotton dyeing method with reactive...Anik Deb
The document discusses dyeing methods and processes at Keya Knit Composite Ltd. It outlines the organizational structure, with the general manager at the top and operators and helpers at the bottom. It then explains the basic concepts of dyeing, including what dyestuffs are, criteria for suitable dyestuffs, and how dyeing works through adsorption, penetration, and fixation. It also lists the types of chemicals used in the dyeing section and provides an overview of the dyeing machines and their processes at the company.
Reactive dyes were developed to improve the washing fastness of cotton dyes. Reactive dyes form covalent bonds with cotton fibers through reactive groups like chlorine or vinyl sulphone that react under alkaline conditions. This provides excellent washing fastness. Reactive dyes have structures like azo dyes but include a reactive group and sulfonate group. They are widely used for cotton dyeing due to their bright colors and versatile dyeing methods. Proper handling is needed as the reactive groups can hydrolyze over time reducing dye reactivity.
Reactive dyes, which are highly-coloured organic substances, are used to colour textile dyes. Reactive dyes are chemical reactions that occur when reactive dyes are applied to fiber. Covalent bonds are formed between the dye molecule and the fiber. This is one of strongest chemical reactions. It ensures that the colouring remains permanent.
1. Disperse dyes are organic coloring compounds that are insoluble in water but can be dispersed to dye hydrophobic fibers like polyester, nylon, and acrylic. They were developed in the 1920s and named "disperse dyes" due to their insoluble properties requiring dispersion.
2. Disperse dyes work by being dispersed in water using dispersing agents. They are then adsorbed onto the fiber surface and diffuse into the fiber structure. A series of equilibriums are established as the dye disperses, dissolves, is adsorbed, and diffuses.
3. Proper auxiliaries like dispersing agents, leveling agents, and wetting agents
This document provides an overview of dyes and pigments, with a focus on reactive dyes. It defines dyes and pigments, describes their classification and color-producing factors. Reactive dyes are discussed in more detail, including their classification based on reactivity and reactive groups. The process of reactive dyeing is summarized, including dyeing conditions, the approach of reactive dyes to fibers, and their chemical reaction with cellulose fibers. A sample process curve is also shown. Finally, the document provides a profile of a wet processing plant to illustrate dyeing operations.
Color fastness properties of different reactive dyesAzmir Latif Beg
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. The most important characteristic of reactive dyes is the formation of covalent bonds with the substrate to be colored, i.e. the dye forms a chemical bond with cellulose. Fiber reactive dyes are the most permanent of all dye types. Unlike other dyes, it actually forms a covalent bond with the cellulose or protein molecule. Once the bond is formed, what you have is one molecule, as the dye molecule has become an actual part of the cellulose fiber molecule.
The document summarizes the general structure and properties of reactive dyes. Reactive dyes have a D-B-G-X structure, where D is the dye/chromogen, B is the bridging group, G is the reactive group, and X is the actual reactive functional group. Reactive dyes form covalent bonds with cellulosic fibers and have good wash and light fastness as a result. They are classified based on the number of reactive groups and dyeing temperature. Factors like pH, temperature, electrolyte concentration influence the dyeing process. Defects can occur but are remedied by washing or chemical treatment.
Correlation between thermodynamic parameters andAlexander Decker
Nine carboxylated reactive dyes were synthesized and applied to silk fabric. The dyes showed high equilibrium exhaustion percentages between 80-97% on the silk. However, wash fastness was poor due to weak dye-fiber bonds. Aftertreatment with carbodiimide improved fixation and significantly increased wash fastness for dyes containing carboxylic acid groups by forming covalent bonds between the dye and silk fiber. Thermodynamic parameters like partition coefficient and standard affinity correlated with exhaustion percentage and were higher for dyes with stronger dye-fiber interactions.
This document provides an overview of different types of dyes used in textile dyeing, including their working principles and applications. It discusses vat dyes, reactive dyes, azoic dyes, acid dyes, sulphur dyes, metal complex dyes, basic dyes, disperse dyes, and direct dyes. For each dye type, it describes the general dyeing process, suitable fibers, advantages and limitations, and how the dye bonds to or reacts with the fiber on a molecular level. The document serves as an educational reference on the various classes of dyes and dyeing methods.
DEFINITION: Pigment is a substrate in a particulate form which is insoluble in water but which can be dispersed in this medium to modify its color and light scattering properties. They are organic or inorganic coloring materials. They have no affinity to textile materials. They are fixed on the textile material with the help of binding agent in form a thin invisible coating.
This document provides information about pigment dyeing. It begins with definitions of pigment and pigment dyeing. Pigments are insoluble in water but can be dispersed to modify color and light scattering properties. Pigment dyeing involves fixing pigments to textile materials with binders rather than a chemical reaction between dye and fabric. The document then discusses classification of pigments, trade names, properties, requirements, differences between dyes and pigments, examples of organic and inorganic pigments, binders, and the pigment dyeing process.
Dyeing of polyester with disperse reactive dyesIIT DELHI
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Reactive Dye (Full PDF)
1. 1
Reactive Dye
Introduction:
A dye, which is capable of reacting chemically with a substrate to form a covalent
dye substrate linkage, is known as reactive dye.
Here the dye contains a reactive group and this reactive group makes covalent bond
with the fiber polymer and act as an integral part of fibre. This covalent bond is
formed between the dye molecules and the terminal –OH (hydroxyl) group of
cellulosic fibres on between the dye molecules and the terminal –NH2 (amino) group
of polyamide or wool fibres.
History of Reactive Dye:
On the occasionof 100 year’s celebration of synthetic dye manufacturing, two
chemists of ICI company (UK) named Stephen and Rattee tried to manufacture a new
dyestuff. Thus they succeed to invent a new dye in 1956, which was named
REACTIVE DYE. This was manufacture for dyeing cellulosic fabrics. The first three
reactive dyes were PROCIONYELLOWR, PROCIONBRILLIANT RED 2B and
PROCIONBLUE 3G.for this effort they were awarded gold medal of the society of
dyes and colorists for the year 1960.
Reaction of Reactive Dye:
D-SO2-CH2-CH2-OSO3Na +OH-cell --- D-SO2-CH2-CH2-O-cell + NaHSO3
D-SO2-CH2-CH2-OSO3Na + NH2- wool ----D-SO2-CH2-CH2-NH-Wool+ NaHSO3
Here, D= dye part.
Wool= wool polymer.
Cell = cellulosic polymer.
2. 2
General structure of reactive dyes:
The general structure of reactive dye is: D-B-G-X.
Here,
D= dye part or chromogen (color producing part)
Dyes may be direct, acid, disperse, premetallised dye etc.
B = bridging part.
Bridging part may be –NH- group or –NR- group.
G = reactive group bearing part.
X= reactive group
Chemicalstructure of reactive dyes
Chemical structure of reactive dyes
Reasons for so named:
Reactive dyes are so called because this is the only type of dye, which has reactive
group, and that reactive group reacts chemically with fiber polymer molecules and
form covalent bond. This covalent bond is formed between the reactive group and
terminal –OH (Hydroxyl) group of cellulosic fiber or between reactive group and
terminal -NH2 (Amino) group of polyamide and wool fiber polymer. The strength of
3. 3
this covalent bond is more than ionic bond, hydrogen bond and Vander Waal’s force
of attraction. Thus the reactive group becomes an integral part of the fiber.
For this reasons the dyes are so called. They are also called ‘fiber reactive group’.
Fibers can be dyed with Reactive Dye:
By reactive dyes the following fibres can be dyed successfully:
1) Cotton, rayon, flax and other cellulosic fibres.
2) Polyamide and wool fibres.
3) Silk and acetate fibres.
It covers a wide range of color spectrum and includes shades varying from bright to
heavy dark like,
a. Violet
b. Blue
c. Green
d. Red
e. Black
f. Yellow
g. Etc.
Trade names:
Some trade names of this dye are mentioned:
Trade name Manufacturer Country
Procion I.C.I U.K
Cibacron Ciba Switzerland
Remazol Hoechst Germany
Levafix Bayer Germany
Reactone Geigy Switzerland
Primazin BASF Germany
Drimarine Sandoz Switzerland
4. 4
Popularity of reactive dye:
Reactive dyes are mostly used for dyeing cellulosic fibres. At past cellulosic fibres
were dyed with direct and vat dyes, but after the introduction of reactive dyes there
utility has become limited. Reactive dyes are superior to direct dye in the following
aspects:
1) Ability to producebright shade of wide range.
2) High leveling quality.
3) Good washing fastness.
4) Good light fastness.
And it is superior to vat dyes in the following aspects:
1) Simple dyeing method therefore one stage dyeing.
2) Low temperature dyeing(below 100•c)
3) Lower cost, i.e. cheaper.
Again its dyeing process is fast and gives brighter shades than metalized azo dyes.
For the above reasons reactive dyes are more popular.
Properties of reactive dye:
1) Reactive dyes are anionic dyes, which are used for dyeing cellulose, protein
and polyamide fibres.
2) Reactive dyes are found in powder, liquid and print paste form.
3) During dyeing the reactive group of this dye forms covalent bond with fibre
polymer and becomes an integral parts of the fibre.
4) Reactive dyes are soluble in water.
5) They have very good light fastness with rating about 6. The dyes have very
stable electron arrangement and can protect the degrading effect of ultra-violet
ray.
6) Textile materials dyed with reactive dyes have very good wash fastness with
5. 5
rating Reactive dye gives brighter shades and has moderate rubbing fastness.
7) Dyeing method of reactive dyes is easy. It requires less time and low
temperature for dyeing.
8) Reactive dyes are comparatively cheap
9) Reactive dyes have good perspiration fastness with rating 4-5.
10) Reactive dyes have good perspiration fastness.
Classification of reactive dyes:
Reactive dyes may be classified in various ways as below:
1) On the basis of reactive group:
Two types-
1. Mono-functional dyes
2. Bi-functional dyes
Monofunctionaldyes: The mono-functional reactive systems of
outstanding importance contain only one possible reactive centre, such as
the halogeno substituent in the aminohalotriazine dyes, or the activated
terminal carbonatom in the vinylsulphone system.
Two groups-
I. Halogenated heterocyclic compounds
II. Activated Vinyl compound
Halogenated heterocyclic compounds are - Three groups
i. Triazine group
a) Monochlorotriazine (MCT) dyes
b) Dichlorotriazine (DCT) dyes
c) Monofluorotriazine (MFT) dyes
6. 6
.
ii. Pyrimidine derivatives
a) Trichloropyrimidine (TCP) dyes
b) Difluorochloropyrimidine (DFCP)dyes
c) Chloromethylpyrimidine (CMP) dyes
iii. Quinaxoline dyes
II. Activated Vinyl compounds:
i. Vinyl Sulphone (D-SO2-CH˭CH2)
ii. Vinyl Sulphonamide (D-SO2-NH-CH2-CH2-)
iii. Vinyl Acrylamide (D-NH-CO-CH˭CH2)
2. Bi-functional Dyes:
The use of a reactive dye containing two reactive groups rather than its
analogue with only one reactive group per molecule increases the fixation from
a typical 60% to approximately 80% on average in exhaust dyeing. In pad
batch processes the correspondingfixation efficiency levels are about 75% and
95% respectively.
Bi-functional systems containing two different kinds of reactive group are
popular in exhaust dyeing and gaining ground, especially on account of their
relative insensitivity of fixation to fluctuations in dyeing temperature.
On the basis of reactivity:
a. Lower reactive dye: reactivity of these dyes is low. So highly alkaline
environment required for the fixation of these dyes with substrate. Here ph is
maintained 12-12.5 by using strong alkali such as NaOH in dye bath.
b. Medium reactive dye: Reactivity of these dyes is medium. Here ph is
maintained 11-12 by using Na2CO3 in dye bath.
7. 7
c. Higher reactive dye: Reactivity of this dye is high. So fixation of these dyes are
easy and lower alkaline medium is kept. Here ph is maintained 10-11 by using
NaHCO3 in dye bath.
On the basis of dyeing temperature:
a. Cold brand: These types of dyes contain reactive dye of high reactivity. So
dyeing can be done in lower temperature i.e. 32°-60°c
Forexample: PROCIONM, LIVAFIX E.
b. Medium brand: These types of dyes contains reactive group of moderate
reactivity. So dyeing is done in higher temperature than that of cold brand dyes
i.e. 60°-70°c.
Forexample: Remazol,Livafix are medium brand dyes.
c. Hot brand:These types of dyes contain reactive groups of least reactivity.
Sohigh temperature is required for dyeing i.e. 72-93°c is required for dyeing.
For example: PROCIONH, CIBACRON are hot brand dyes.
Characteristics of reactive group of reactive dye:
The characteristics of reactive group of reactive dye are mentioned below:
1) Reactive groups do not contribute to the color of dye. Chromogen group
imparts it.
2) The reactivity of vinyl sulphone group is less than that of halogen group.
3) If no of reactive group increases, binding also increases depending on dye
structure.
4) Reactive dye absorb up to 90%.
5) Molecular weight of reactive group 69-211gm/mole.
8. 8
6) Bond energy of halogen groups are as below:
F(Fluorine)- 102 kcal/gm
Cl(Chorine)- 74 kcal/gm
Br(Bromine)- 64 kcal/gm
I(Iodine) - 56 kcal/gm
7) If the molecular weight of reactive group increases, reactivity also increases.
8) Reactivity of iodine is high but its rate of hydrolysis is also high.
9) Chlorine imparts medium reactivity, but it is cheap and hydrolysis rate is
medium.
10) Reactivity of fluorine is the least and its rate hydrolysis is also less.
11) Reactivity of vinyl sulphone group increases with increasing temperature
and pH.
12) Sulphone group has more solubility but it is not stable
13) Generally low molecular weight dyes are of hot brand.
14) Less affinity dyes are used for pad dyes.
Criteria for a Suitable Dyestuff
1. Cheap
2. Non-toxic
3.Compatible to other dyes and chemicals
4.High color strength
5. Better brightness
6. Better fastness
7. Good levelness on the materials
9. 9
Assistants used for dyeing with reactive dyes:
The following assistants are used for dyeing in dye bath with reactive dyes.
1) Salt:
As a salt NaCl is widelyused. The salts do the following things-
Salts are used to increase the affinity of dye to fiber.
It decreases the hydrolysis rate of dyes.
It neutralizes the electro negativity of fiber surface when immersed
in solution.
It puts extra energy to pushthe dye inside the fiber polymer i.e.
increase absorptionof dye.
The amount of salt and used depends upon the shade to be produced.
For light shade – 10 gm/L salt is used.
For medium shade- 20 gm/L salt is used.
For dark shade – 30 gm/L salt is used.
2) Alkali:
Alkali is used for the following purposes:
Alkali is used to maintain properpH in dye bath and thus to create
alkaline condition.
Alkali is used as a dye fixing agent
Without alkali no dyeing take place.
The strength of alkali used depends on the reactivity of dyes.
As strong alkali caustic sodais used to create pH 12-12.5.
As medium alkali sodaash(Na2CO3) is used to create pH 11-12
when dye is of medium reactivity.
As weak alkali NaHCO3 is used to create pH 10-11 when dye is
highly reactive.
3) Urea:
Urea is used in continuous method of dyeing. It helps to get required shade
of dye. To get dark shade more urea is used and to get light shade less amount
of urea is used. Urea is also used in Printing to hold up the moisture.
4) Soaping:
By soaping, the extra color is removed from fibre surface. Thus washing
fastness I improved. Soaping increases the brightness and stability of the dye.
10. 10
Factors considered for selection of dyeing:
Dye selection depends upon the following factors:
1) Selection of dyeing method: Dye selection depends on dyeing method, which
may be-
1) Batch wise/discontinuous method
2) Semi continuous method i.e.
a) Pad-batchmethod
b) Pad-jig method
c) Pad-roll method
3) Continuous method i.e.
a) Pad- steam method
b) Pad-dry method
c) Pad-thermofix method
This dyeing method selection depends on:
1) Speed of dye diffusion on the fibre.
2) Affinity of dye to fibre.
3) Reactivity to dye stuff.
2) Selection of brand: Brand selection is important. It may be-
a) Hot brand- Less reactive dye (temp 72-93)
b) Medium brand- Medium reactive dye.
c) Cold brand- Most reactive dye.
3) Economy of production
4) Availability of dyes
5) Storage of dyes
6) Bond stability i.e. kind of bonding
7) Fastness of dye i.e. washes, light, rubbing fastness
8) Re-producibility.
11. 11
Reaction manner of dye and cellulose:
The bonding behavior of dye and cellulose are mentioned below:
1. Hydroxyl group of cottonpolymer takes part in reaction with reactive group of
dye.
2. Reactive group of dye react preferably with the hydroxyl group of cellulose
than that of water.
3. The activation energy of dye-water reaction is 16.4-26.2 kcal and that of dye
cellulose is 9.2-15.8 kcal. As the latter is less, so that occurpredominately.
4. Higher activation energy causes slower reaction.
5. The reaction with water and dye takes place in a smaller extent.
6. The strength of covalent bond formed between cellulose polymer and reactive
group is more than hydrogen bonding, Vander wall’s force of attraction and
metal co-ordination bonds.
7. Extreme acidic and alkaline condition should be avoided, otherwise hydrolysis
will take place resulting bond breakage and poorwash fastness.
Criteria for cellulose for attracting reactive dye:
The chemical structure of cellulose macromolecule is given below:
12. 12
Chemical structure of cellulose
In cellulose macromolecule glucose units are linked through oxygen bridges formed
between c1 position of one glucose and c4 position of adjacent glucose unit. Each
glucose unit contains one primary hydroxyl group(at c6 position) and two secondary
hydroxylgroup =CHOH(at c2 and c3 positions). Again one end of this glucose unit
has an additional secondary hydroxyl group at c4 position and the other end has an
aldehyde or hemiacetal group at c1 position. Now the following things are
considered.
1. Primary hydroxyl group(-CH2OH) at c6 position is more reactive then the
secondaryhydroxyl groups(-CHOH) at c2 and c3 positions.
2. C2 hydroxyl group is supported to be more acedic than c3 hydroxyl group
under suitable alkaline condition and hence is more reactive.
3. The hemiacetal group at c1 position is the most active while the additional
hydroxyl group of c4 position is the least reactive.
13. 13
4. The reaction between reactive group and cellulose takes place predominantly
with primary hydroxyl group to some extent.
5. Longer carbonchain lowers the rate of reaction.
6. Incase of monochloro triazinyl dyes, this reaction takes place 15 times more
frequently with c6 hydroxyl group than with the hydroxyl group at c2 or c3
position.
7. Incase of dichloro triazinyl dyes, this reaction takes place 3-7 times more
frequently with hydroxyl group at c2 position than that with hydroxyl group at
c1or c3 position.
The reactive rate of some compounds are mentioned below:
Compound Structure Reactive rate
Water H-OH 1.0
Iso-propanol CH3-CHOH-CH3 0.7
Ethanol CH3-CH2-OH 7.4
Methanol H-CH2-OH 12.3
Glucose C6H12O6 5.5
So from the above table it is obvious that secondaryhydroxyl group is the best
reactive while primary one is the most reactive.
Dyeing Mechanism of Reactive Dye
The dyeing mechanism of material withreactive dye takes place in 3 stages:-
1. Exhaustion of dye in presence of electrolyte or dye absorption.
14. 14
2. Fixation under the influence of alkali.
3. wash-off the unfixed dye from material surface.
Now they are mentioned below:
1. Dye absorption:
When fiber is immersed in dye liquor, an electrolyte is added to assist the exhaustion
of dye. Here NaCl is used as the electrolyte. This electrolyte neutralize the negative
charge formed in the fiber surface and puts extra energy to increase dye absorption.
So when the textile material is introduces to dye liquor the dye is exhausted on to the
fiber.
2. Fixation:
Fixation of dye means the reaction of reactive group of dye with terminal –OH or-
NH2 group of fiber and thus forming strong covalent bond with the fiber and thus
forming strong covalent bond with the fiber. This is an important phase, which is
controlled by maintaining properpH by adding alkali. The alkali used for this
purposedepends on brand of dye and dyeing temperature. Here generally caustic
soda, sodaash or NaHCO3 is used as alkali depending upon reactivity of dye. They
create proper pH in dye bath and do as the dye-fixing agent. The reaction takes place
in this stage is shown below: -
15. 15
3. Wash-off:
As the dyeing is completed, a good wash must be applied to the material to remove
extra and unfixed dyes from material surface. This is necessary for level dyeing and
good wash-fastness. It is done by a series of hot wash, cold wash and soap solution
wash.
Application method:
Application method of reactive dyes varies significantly with type of dyes,shade
required and available equipments in the mill. These are 3 application procedures
available:
1) Discontinuous method-
Conventional method
Exhaust or constant temperature method
High temperature method
Hot critical method
16. 16
2) Continuous method-
Pad-steam method
Pad dry method
Pad thermofix method
3) Semi continuous method-
Pad roll method
Pad jig method
Pad batch method
Stripping of reactive dyes:
The reactive dye cannot be satisfactory stripped from fiber due covalent bond
between dye molecule and fiber. Stripping becomes necessary when uneven dyeing
occurs. By stripping azo group(-N=N-)
From the dye is removed. Now the stripping processesare described:
1) Partial stripping:
Partial stripping is obtained by treating the dyed fabric with dilute acetic
acid or formic acid. Here temperature is raised to 70-100°c and treatment is
continued until shade is removed by desired amount. After that through
washing is necessary to remove the productof hydrolysis. The amount of acid
used is as below:-
Glacial acetic acid : 5-10 parts
Formic acid : 2.5 to 10 parts
With water : 1000 parts
Temperature : 70-100°c
Time : until desired shade is obtained.
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2) Full stripping:
For complete stripping the goods are first treated
with sodium hydrosulphite(hydrose) at boil then washed off and bleached
with 1% sodium hypochlorite(NaOCl) at room temperature. This is carried out
for 30 min.
The recipe is as below:-
Na-hydrosulphite : at boil
Na-hypochlorite : 1% at room temperature
Time : 30 min
Hydrolysis of Reactive Dye:
Under alkaline condition reactive dyes react with the terminal hydroxyl group of
cellulose. But if the solution of the dye is kept for long time its concentration drops.
Then the dye reacts with the hydroxyl group of water. This reaction of dye with water
is known as hydrolysis of reactive dye. After hydrolysis dye cannot react with fiber.
So hydrolysis increases the loss of dyes.
This hydrolysis occurs in two stages. At first the concentration of dye initially
increases and then begins to decrease. Where as the concentration of hydroxyl
compound increases continuously. Then the hydroxyl compound cannot react with
dye.
1. Hydrolysis of halogen containing reactive dye,
D-R-Cl + H-OH = D-R-OH + H-Cl
2. Hydrolysis of activated vinyl compound containing dye,
D-F-CH2-CH2-OSO3H + H-OH = D-F- CH2-CH2-OH + H2SO4
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For preventing hydrolysis the following precautions are taken
1. As hydrolysis increases with increasing temperature during dissolving and
application temperature should not be more than 40°C.
2. Dye and alkali solution are prepared separately and mixed just before using.
3. Dye and alkali should not be kept for long time after mixing.
Different methods of reactive dye application:
1) Pad-batch method.
Pad batch processesare of two types-
a) Pad (alkali)-batch (cold) process.
b) Pad (alkali)-batch (warm or hot) process.
2) Pad dry method
3) Pad steammethod.
1) Pad-batch method
a. Pad (alkali)-batch (cold) process.
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Figure: Pad-batch method
Steps:
1) The fabric is first padded in a padding mangle with reactive dye in presence of an
alkali.
2) The padded fabric is rolled in a batch and the batches are wrapped by polyethylene
sheets and stored in wet condition for 1-24 hours at 200-300C in a room.
3) During the storage period, the rolls may be kept slowly rotating to prevent seepage
of the dye liquor.
4) After storing time is finished fabric is washed in a rope washing machine to
remove the unfixed dye from fabric surface.
b. Pad batch (hot) process:
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Figure: Pad batch (hot) process
Steps:
1) The fabric is first padded in a padding mangle with reactive dye in presence of an
alkali.
2) The fabric is then passed in between infrared heater to preheat the padded fabric to
500C to 900C.
3) The fabric is then batched on a large diameter roller in a hot chamber. The
batching is done under controlled conditions of temperature and humidity for a
sufficient time to ensure diffusion and fixation of the dye in the fibre. During this
period the batch is kept slowly rotating to avoid the seepage of dye liquor.
4) The cloth is then washed in a rope washing machine to remove the unfixed dyes.
2) Pad dry method:
21. 21
Figure: Pad dry method
Steps:
1) Fabric is first padded in a padder with reactive dye in presence of an alkali.
2) Padded fabric is then passed through a squeezing roller into a dryer. As a dryer
cylinder, stenter etc may be used. During drying due to higher temperature fixation of
dye in fiber increases and at the same time water is removed by evaporation.
3) After drying fabric is washed in a washing machine to remove unfixed dye.
3) Pad steammethod:
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Figure: Pad steam method
Steps:
1) Fabric is first padded in a padder with the dye.
2) It is then passed through between two squeezing roller in a dryer. Drying should be
done slowly; otherwise precipitation of dye due to quick removal of water may take
place leading to lower color value.
3) After coming out from dryer fabric is padded in a paddercontaining salt and alkali.
Due to salt exhaustion of dye takes place and due to alkali fixation occurs.
4) Fabric then passed through a steamer where it is kept for 15-19 second. Due to
high temperature here fixation rate increases.
5) In this step fabric is washed in a washing machine to remove the unfixed dye.
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Important factors for dyeing cellulosic fibre with cold brand reactive dye in
batching process:
The Important Factors are as Follows:
1) pH of the Dye Bath:
The optimum pH for fixing cold brand reactive dyes on cottonand viscose rayon
depends on individual dyes, the temperature and time of dyeing. pH decreases with
increasing temperature and time of dyeing. For most of the dyes the optimum pH is
10.8 to 11 at 20o to 25oC. Sodaash has been the best alkali for dyeing at 30oC for
cotton, mercerized cottonand linen. Increased fixation (due to higher temperature)
and increased dye bath stability and better reproducibility are the advantages of soda
ash as the fixing agent.
For viscoserayon the optimum pH is 10.3 at 20o to 25oC.
2) Amount of Alkali:
The amount of alkali used for fixing depends on the depth of shade dyed and the
liquor ratio employed.
3) Dyeing Temperature:
Since increase in temperature affects the rate of physical and chemical processes
involved in dyeing, it is important in dyeing reactive dyes also. The affinity of the
dye for the fiber decreases with increases in temperature and at the same time the rate
of hydrolysis of the dye increases and adversely affects the fixation of color yield.
However the rate of diffusion of the dye in the fiber increases with increased
temperature. At temperatures lower than 20oc, the rate of fixation is very low. Hence
for most of the dyes a temperature of 20o to 25oC is the recommended temperature
while for some other dyeing at 50o to 60oC with sodium bicarbonate as the alkali
gives maximum color value.
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4) Electrolyte Concentration:
Since reactive dyes have low affinity for cellulose exhausting the dye bath by adding
common salt or Glauber’s salt prior to fixation can increase the fixation. The amount
of salt required producing adequate exhaustion decreases with decreasing liquor ratio.
Thus for pale shade on cottonand viscoserayon 15 and 10 g/l of common salt used.
The quantities may be increased to 30 and 20 to 30 g/l for medium and deep shades
on these fibres.
5) Time of Dyeing:
Generally the dye may be added in two portions. The salt may also be added in two
lots. The exhaustion takes place in 20 to 30 min. There is generally no advantage in
extending the period beyond 30 min. The alkali is then added and the dyeing
continued for 30 to 90 min. The depth of shade and reactivity of the dye decide the
time of dyeing. For deeper shades larger times are required.
6) Liquor Ratio:
With decreased liquor ratio, both exhaustion and fixation take place to increase exert.
However the rate of fixation of most of the dyes is not significantly affected. As the
liquor ratio is decreased, the effectiveness of increasing salt addition also decreases.
Hence lower amount of salt are sufficient to get optimum exhaustion.