Preamble
This is the ninety-eighth post in the "Art Resource" series, specifically aimed to construct an appropriate knowledge base in order to develop an artistic voice in ArtCloth.
Other posts in this series are:
Glossary of Cultural and Architectural Terms
Units Used in Dyeing and Printing of Fabrics
Occupational, Health & Safety
A Brief History of Color
The Nature of Color
Psychology of Color
Color Schemes
The Naming of Colors
The Munsell Color Classification System
Methuen Color Index and Classification System
The CIE System
Pantone - A Modern Color Classification System
Optical Properties of Fiber Materials
General Properties of Fiber Polymers and Fibers - Part I
General Properties of Fiber Polymers and Fibers - Part II
General Properties of Fiber Polymers and Fibers - Part III
General Properties of Fiber Polymers and Fibers - Part IV
General Properties of Fiber Polymers and Fibers - Part V
Protein Fibers - Wool
Protein Fibers - Speciality Hair Fibers
Protein Fibers - Silk
Protein Fibers - Wool versus Silk
Timelines of Fabrics, Dyes and Other Stuff
Cellulosic Fibers (Natural) - Cotton
Cellulosic Fibers (Natural) - Linen
Other Natural Cellulosic Fibers
General Overview of Man-Made Fibers
Man-Made Cellulosic Fibers - Viscose
Man-Made Cellulosic Fibers - Esters
Man-Made Synthetic Fibers - Nylon
Man-Made Synthetic Fibers - Polyester
Man-Made Synthetic Fibers - Acrylic and Modacrylic
Man-Made Synthetic Fibers - Olefins
Man-Made Synthetic Fibers - Elastomers
Man-Made Synthetic Fibers - Mineral Fibers
Man Made Fibers - Other Textile Fibers
Fiber Blends
From Fiber to Yarn: Overview - Part I
From Fiber to Yarn: Overview - Part II
Melt-Spun Fibers
Characteristics of Filament Yarn
Yarn Classification
Direct Spun Yarns
Textured Filament Yarns
Fabric Construction - Felt
Fabric Construction - Nonwoven fabrics
A Fashion Data Base
Fabric Construction - Leather
Fabric Construction - Films
Glossary of Colors, Dyes, Inks, Pigments and Resins
Fabric Construction – Foams and Poromeric Material
Knitting
Hosiery
Glossary of Fabrics, Fibers, Finishes, Garments and Yarns
Weaving and the Loom
Similarities and Differences in Woven Fabrics
The Three Basic Weaves - Plain Weave (Part I)
The Three Basic Weaves - Plain Weave (Part II)
The Three Basic Weaves - Twill Weave
The Three Basic Weaves - Satin Weave
Figured Weaves - Leno Weave
Figured Weaves – Piqué Weave
Figured Fabrics
Glossary of Art, Artists, Art Motifs and Art Movements
Crêpe Fabrics
Crêpe Effect Fabrics
Pile Fabrics - General
Woven Pile Fabrics
Chenille Yarn and Tufted Pile Fabrics
Knit-Pile Fabrics
Flocked Pile Fabrics and Other Pile Construction Processes
Glossary of Paper, Photography, Printing, Prints and Publication Terms
Napped Fabrics – Part I
Napped Fabrics – Part II
Double Cloth
Multicomponent Fabrics
Knit-Sew or Stitch Through Fabrics
Finishes - Overview
Finishes - Initial Fabric Cleaning
Mechanical Finishes - Part I
Mechanical Finishes - Part II
Additive Finishes
Chemical Finishes - Bleaching
Glossary of Scientific Terms
Chemical Finishes - Acid Finishes
Finishes: Mercerization
Finishes: Waterproof and Water-Repellent Fabrics
Finishes: Flame-Proofed Fabrics
Finishes to Prevent Attack by Insects and Micro-Organisms
Other Finishes
Shrinkage - Part I
Shrinkage - Part II
Progressive Shrinkage and Methods of Control
Durable Press and Wash-and-Wear Finishes - Part I
Durable Press and Wash-and-Wear Finishes - Part II
Durable Press and Wash-and-Wear Finishes - Part III
Durable Press and Wash-and-Wear Finishes - Part IV
Durable Press and Wash-and-Wear Finishes - Part V
The General Theory of Dyeing – Part I
The General Theory Of Dyeing - Part II
Natural Dyes
Natural Dyes - Indigo
Mordant Dyes
Premetallized Dyes
Azoic Dyes
Basic Dyes
Acid Dyes
Disperse Dyes
Direct Dyes
Reactive Dyes
Sulfur Dyes
Blends – Fibers and Direct Dyeing
The General Theory of Printing
There are currently eight data bases on this blogspot, namely, the Glossary of Cultural and Architectural Terms, Timelines of Fabrics, Dyes and Other Stuff, A Fashion Data Base, the Glossary of Colors, Dyes, Inks, Pigments and Resins, the Glossary of Fabrics, Fibers, Finishes, Garments and Yarns, Glossary of Art, Artists, Art Motifs and Art Movements, Glossary of Paper, Photography, Printing, Prints and Publication Terms and the Glossary of Scientific Terms, which has been updated to Version 3.5. All data bases will be updated from time-to-time in the future.
If you find any post on this blog site useful, you can save it or copy and paste it into your own "Word" document etc. for your future reference. For example, Safari allows you to save a post (e.g. click on "File", click on "Print" and release, click on "PDF" and then click on "Save As" and release - and a PDF should appear where you have stored it). Safari also allows you to mail a post to a friend (click on "File", and then point cursor to "Mail Contents On This Page" and release). Either way, this or other posts on this site may be a useful Art Resource for you.
The Art Resource series will be the first post in each calendar month. Remember - these Art Resource posts span information that will be useful for a home hobbyist to that required by a final year University Fine-Art student and so undoubtedly, some parts of any Art Resource post may appear far too technical for your needs (skip over those mind boggling parts) and in other parts, it may be too simplistic with respect to your level of knowledge (ditto the skip). The trade-off between these two extremes will mean that Art Resource posts will hopefully be useful in parts to most, but unfortunately may not be satisfying to all!
Introduction
In order to understand the coloring of textile materials, you need to have some understanding of the general theory of dyeing and printing. After reading this post, and if you are still unsure of definitions, terminologies or properties used of fabrics that this post assumes you should know but you don't, then consult the "Preamble" above and click on any art resource post or glossary that might provide that missing information for you.
This post will concentrate on the general theory of dyeing.
O,H & S Issues with Dyeing Fabrics and Textiles
In general, always get a Material Safety Data Sheet (MSDS) from the manufacturer on all dyes and auxiliary compounds you wish to use for any art/craft project. If you do not possess the MSDS you need, go to the retailer who you have purchased the product from and they should provide you with the MSDS. If they cannot, for some unknown reason, then go to Chemists (Commonwealth Countries) or a Drug Store (USA) and ask them for assistance. Usually they are friendly enough to give some advice or point you to where you might obtain the necessary information.
In general, always wear rubber gloves to prevent dyes from being absorbed through the skin. Protective clothing - smock or plastic apron - is also recommended to prevent damage to your clothes. Wear old or disposable shoes and ventilate your work area with a fan to dissipate or exhaust fumes. Remember, not all natural dyes are harmless and/or not all man-made dyes are toxic. Wearing face masks and eye googles might be a pain, but not wearing them when you should, might one day render you in far greater pain! There is only one you, and needless to say, you are special!
It goes without saying that any utensils used in the dyeing process should never be used for food preparation or for any other purpose, even if you have convinced yourself that the cleaning procedures you have employed were excellent.
I cannot keep stressing that all work should be performed in well ventilated areas that are not "common" areas shared by children and other adults, who are not directly involved in your project. Avoid inhalation of dyes and consult my previous posts, namely, Units Used in Dyeing and Printing of Fabrics and Occupational, Health & Safety.
An indigo dyer, using a natural dye in India. Poor legislative and regulatory oversight creates dyed skin for the untouchable caste dyers in India. Even natural dyes are harmful and are thoughtlessly used in countries that have not put in place or monitored the necessary legislative and regulative oversight to demand safety first procedures.
If by any chance, something went amiss and you have inhaled dyes or irritated your eyes or any part of your body because of them, seek medical advice as quickly as possible. Better to be safe then unsure!
Introduction to Dyeing
Dye baths of Cliff Rose, Wild Carrot, Navajo Tea, Ground Lichen and Rabbit Brush.
Dye molecules are organic compounds, which are responsible for the coloring of textile materials. The optical properties of textile materials depends on the incident light that are absorbed, reflected and/or transmitted. The color of textile materials is dependent on the light waves that are reflected and absorbed.
Generally, dyeing is the process of coloring textile materials by immersing them in an aqueous solution called dye liquor. The dye liquor normally contains the dye, water and auxiliary compounds. To improve the effectiveness and efficiency of dyeing, heat is usually applied to the dye liquor. The theory of aqueous dyeing (as explained below) needs modification if an organic solvent is involved instead of water.
The general theory of dyeing focuses on:
(a) Forces of repulsion, which are developed between the dye molecules and water.
(b) Forces of attraction, which are developed between the dye molecules and the fibers.
Dye molecules may be classified from two different approaches:
(a) According to the chemical constitution of the dye molecule itself.
(b) According to the method of application.
In this series, to make the chemistry as manageable as possible, we shall generally concentrate on classifying dyes according to the method of application. However, before we do it is instructive to define some basic chemical terminology. Hold your breath and read on!
Anions are negatively charged species, whereas cations are positively charged species. Hence, dye molecules generally are organic compounds (i.e. mainly composed from carbon, hydrogen, oxygen, nitrogen and sulfur) and so may be classified as:
(a) anionic – in which the color is caused by the negative part of the dye molecule.
(b) cationic – in which the color is caused by the positive part of the dye molecule.
(c) disperse – in which the color is caused by the whole molecule since it is non-polar (no negative or positive parts within it).
Dyes used for mass dyeing of t-shirts in India.
The Fiber
Textile fibers are also generally organic compounds and develop a slight negative charge on the surface of the fiber, when immersed in an aqueous solution. Since the dye molecule in an aqueous solution is also slightly negative, they will repel one another (i.e two likes repel) and so conditions within the dye liquor have to be developed in order to overcome this tendency for repulsion, thereby promoting the entry of the dye molecules into the polymer system of the fiber.
Just as a reminder, a simplified and exaggerated representation of a fiber’s polymer system is given below. Each polymer system tends to possess several amorphous (chaotic) and crystalline (structured) regions. This assists in the cohesion of the polymer system. Whenever several individual polymer units are aligned or orientated in more or less parallel order, they form the crystalline regions, which only have extremely small voids between them and so generally prevent dyes or water molecules entry into the crystalline regions. Amorphous regions occur whenever polymer units are not orientated or are completely disorganized in a random fashion. It is these regions that often are the entry points for dye and water molecules into the fabric. Generally, the most important forces of attraction between the polymer units are hydrogen bonds and van der Waals forces.
A schematic of the regions of a fiber polymer system.
Note: These regions of the fiber polymer system will be often referred to in the following posts on this blogapot on dyeing and printing of textile materials and so you should grab this image and place it on your desktop.
The Role of Water
Water in aqueous dyeing is critical since it must dissolve or disperse the dye and moreover, it acts as the medium through which the dyed molecules are transferred into the fiber.
Water is polar (i.e. possesses relatively negative and positive parts to it) and so any polar group in the dye molecule is attracted to water molecules and this is the reason why dyes that are polar dissolve in it. In the case of disperse dyes, which does not have negative or positive parts to it, and so are hydrophobic (water hating), they purposely disperse within the water (e.g. may be assisted by dispersing agents) rather than dissolving in it. Think of it as dye droplets suspended by the water molecules that move randomly to keep these dye droplets afloat and so prevent the dye droplets from accumulating at the bottom of the container.
Generally, if a dye molecule dissolves in water, the act of dissolution is undesirable to ensure effective and an efficient transfer of the dye into the fiber, unless this attraction can be negated. Nevertheless, in some instances the rate of dye uptake from the water to the fiber needs to be controlled in order to ensure a uniform coloration of the fiber.
To encourage the dissolved dye to leave the water and enter into the fiber, heat is usually required. This also ensures an adequate penetration of dye into the polymer system of the fiber. Heating the dye liquor promotes the dissociation of water into its polar parts and so the dye liquor becomes more ionic, which promotes the repulsion between water and dye molecules and so promotes dye uptake by the fiber polymer system.
Water, assisted by heat, also swells fibers that are hydrophilic (water loving) and in doing so enlarges the surface and internal voids of the fabric, which makes the fiber polymer system far more accessible to large dye molecules, that otherwise at room temperature would be confronted with small entry voids in the fiber and so the small entry points would prevent the dye molecule from diffusing into the fiber.
The Role of Electrolytes
Electrolytes (such as salts like sodium chloride) are ionic compounds that readily dissolve in aqueous systems as cations (e.g. Na+ is the cation of sodium chloride) and anions (e.g. Cl- is the anion of sodium chloride).
The addition of heat and an electrolyte to the dye liquor of an ionic dye increases the uptake of the dye by the fiber because of the following reasons:
(a) Heat promotes to charge ions in solution and so assists in the water-dye repulsion, thereby assisting in the dye-fiber attraction.
(b) Electrolytes dissociate into ions in water and so assist the dye liquor-dye molecule repulsion, thereby assisting the dye molecule-fiber attractions.
(c) The electrolyte ions neutralize any fiber surface charge and so assist the dye molecule - fiber attraction.
(d) Heat also enlarges the surface and internal voids of the fiber thereby, increasing and deepening the passage of large dyed molecules into the fiber.
The Role of Heating the Dye Liquor
Rather than repeat (a) and (d) above, we shall add that heating the dye liquor also imparts a greater translation energy to the dyed molecules and so reduces the time of dye uptake of a particular fiber, with all other factors being equal. It also enables a greater penetration of the dye into the fiber polymer system (i.e. dye molecules entering the amorphous regions of the fiber do so and at a greater depth).
When the dyed liquor cools and the fibers dry, the surface and internal voids of the polymer system will return to their original size, trapping and entangling the dye molecules that are now resident within it. In this environment, weak van Waals forces of attraction between the dyed molecules and the polymer system of the fiber assist to retain the dye molecules within the fiber's polymer system.
High Temperature Dyeing
Dyeing at temperatures from 100oC to 130oC under pressure of 170kPa (note: one atmosphere is 101.3 kPa) is termed high temperature dyeing. Hydrophobic fibers, such as polyester fibers, are commercially dyed in this way using dye liquors (as distinct from sublimation dyeing) because under normal atmospheric conditions, their extremely crystalline polymer system will not allow a good dye uptake.
When dyeing at high temperature, dye molecule penetration of the fiber polymer system is increased significantly. At temperatures above 100oC and under pressure, the heat generates a very large amount of energy in the constituents of the dye liquor. This swells the fiber, and so enlarges its surface and internal voids, enabling the dye molecules to penetrate into the fiber system more readily and deeper.
Dye Auxiliary Compounds
Dye auxiliary compounds assist the dyeing process and include: carriers or swelling agents, leveling agents, anti-foaming agents, dispersing agents, detergents and wetting agents. The way these auxiliary agents affect the dyeing process is chemically complex and so beyond this series. Nevertheless, their purpose and use will be explained below.
Carriers or Swelling Agents
The purpose of carriers added to the dye liquor is to improve the dye exhaustion for highly crystallized fibers such as polyesters. Due to their very crystalline nature, usually only pale colors can be achieved by aqueous dyeing without carriers (unlike sublimation dyeing). These carriers tend to swell the fiber, and so enlarge the size of the surface and internal voids of the fiber polymer system, thereby enabling greater dye uptake and penetration. In general, carriers are only used to dye polyester fibers in aqueous liquor baths with disperse dyes.
Disperse dye carrier: NSC.
Leveling Agents
The purpose of adding a leveling agent to the dye liquor is to produce a more uniform color in the textile materials. Leveling agents tend to slow down the dye uptake of the fabric and so they are also known as retarding agents or retarders. The use of retarders is essential in cases where dyes rush into the fiber and so produce uneven colored textile materials.
Leveling agents are surface-active agents and are chemically related to soaps, synthetic detergents and wetting agents. They may be anionic, cationic or non-ionic organic compounds.
High-temperature leveling agent, M214DD.
Anionic Leveling Agents
These molecules consist of large negatively charged or anionic organic radicals, with the corresponding cation usually a sodium cation, that assists the water solubility of the leveling agent.
These anionic leveling agent radicals are attracted to cationic or positive sites on the fiber. As the dye bath is heated, a two-fold process occurs:
(a) The anionic leveling agents are slowly removed from the positive sites of the fiber, due to the disruptive Brownian motion of the water molecules, which is greater the higher the temperature of the dye bath.
(b) The anionic dye molecules obtain sufficient energy to overcome the repulsive forces between the anionic dye molecules and the anionic nature of the retarder and moreover, its attraction to the positive sites on the fiber is stronger than any disruptive force due to Brownian motion.
Both these processes ensure a more uniform absorption of the dye by the polymer system of the fiber due to the slowing down of dye uptake by the fiber.
Cationic Leveling Agents
The molecules of these leveling agents consist of a large positively charged, or cationic organic radical, with an anionic radical, usually the chloride or bromide anion, which helps to assist the agent's water solubility.
Before dissolution in water both the cationic and anionic parts of the leveling agent are attached. However, on dissolution they are separated and the anionic dye portion has a greater attraction to the cationic part of the leveling agent in the dye liquor, thereby reducing the anionic dye radical substantivity for the fibers. The energy provided by heating the dye bath assists to dissociate very slowly the cationic radical of the leveling agent from the anionic dye radical. The slow release from the cationic leveling radical is why they are known as retardants. Moreover, the slow release of the dye anion ensures a more uniform absorption of the dye by the polymer system of the fiber.
Scouring after Dyeing
Dyeing always leaves some dye molecules on the surface of the dyed textile or cloth. It is essential that these dyed molecules be removed when dyeing is completed. If the dyes are not removed they may result in two problems, namely:
(a) Poor rub-fastness, which may result in the dye rubbing onto adjacent materials.
(b) Poor wash-fastness, which may result in other fabrics being colored by the excess dye resident on the fabric during the laundering process.
Block and roller printed Barege, Grenadine and Merino fabrics employing dyes in a variety of Paisley floral patterns.
Compiled by J. Claude Freres and Co, Paris, France, 1856.
Presented to the National Gallery of Victoria by the Australian Wool Corporation in 1982.
References:
[1] A Fritz and J. Cant, Consumer Textiles, Oxford University Press, Melbourne (1986).
[2] E.P.G. Gohl and L.D. Vilensky, Textile Science, Longman Cheshire, Melbourne (1989).
This is the ninety-eighth post in the "Art Resource" series, specifically aimed to construct an appropriate knowledge base in order to develop an artistic voice in ArtCloth.
Other posts in this series are:
Glossary of Cultural and Architectural Terms
Units Used in Dyeing and Printing of Fabrics
Occupational, Health & Safety
A Brief History of Color
The Nature of Color
Psychology of Color
Color Schemes
The Naming of Colors
The Munsell Color Classification System
Methuen Color Index and Classification System
The CIE System
Pantone - A Modern Color Classification System
Optical Properties of Fiber Materials
General Properties of Fiber Polymers and Fibers - Part I
General Properties of Fiber Polymers and Fibers - Part II
General Properties of Fiber Polymers and Fibers - Part III
General Properties of Fiber Polymers and Fibers - Part IV
General Properties of Fiber Polymers and Fibers - Part V
Protein Fibers - Wool
Protein Fibers - Speciality Hair Fibers
Protein Fibers - Silk
Protein Fibers - Wool versus Silk
Timelines of Fabrics, Dyes and Other Stuff
Cellulosic Fibers (Natural) - Cotton
Cellulosic Fibers (Natural) - Linen
Other Natural Cellulosic Fibers
General Overview of Man-Made Fibers
Man-Made Cellulosic Fibers - Viscose
Man-Made Cellulosic Fibers - Esters
Man-Made Synthetic Fibers - Nylon
Man-Made Synthetic Fibers - Polyester
Man-Made Synthetic Fibers - Acrylic and Modacrylic
Man-Made Synthetic Fibers - Olefins
Man-Made Synthetic Fibers - Elastomers
Man-Made Synthetic Fibers - Mineral Fibers
Man Made Fibers - Other Textile Fibers
Fiber Blends
From Fiber to Yarn: Overview - Part I
From Fiber to Yarn: Overview - Part II
Melt-Spun Fibers
Characteristics of Filament Yarn
Yarn Classification
Direct Spun Yarns
Textured Filament Yarns
Fabric Construction - Felt
Fabric Construction - Nonwoven fabrics
A Fashion Data Base
Fabric Construction - Leather
Fabric Construction - Films
Glossary of Colors, Dyes, Inks, Pigments and Resins
Fabric Construction – Foams and Poromeric Material
Knitting
Hosiery
Glossary of Fabrics, Fibers, Finishes, Garments and Yarns
Weaving and the Loom
Similarities and Differences in Woven Fabrics
The Three Basic Weaves - Plain Weave (Part I)
The Three Basic Weaves - Plain Weave (Part II)
The Three Basic Weaves - Twill Weave
The Three Basic Weaves - Satin Weave
Figured Weaves - Leno Weave
Figured Weaves – Piqué Weave
Figured Fabrics
Glossary of Art, Artists, Art Motifs and Art Movements
Crêpe Fabrics
Crêpe Effect Fabrics
Pile Fabrics - General
Woven Pile Fabrics
Chenille Yarn and Tufted Pile Fabrics
Knit-Pile Fabrics
Flocked Pile Fabrics and Other Pile Construction Processes
Glossary of Paper, Photography, Printing, Prints and Publication Terms
Napped Fabrics – Part I
Napped Fabrics – Part II
Double Cloth
Multicomponent Fabrics
Knit-Sew or Stitch Through Fabrics
Finishes - Overview
Finishes - Initial Fabric Cleaning
Mechanical Finishes - Part I
Mechanical Finishes - Part II
Additive Finishes
Chemical Finishes - Bleaching
Glossary of Scientific Terms
Chemical Finishes - Acid Finishes
Finishes: Mercerization
Finishes: Waterproof and Water-Repellent Fabrics
Finishes: Flame-Proofed Fabrics
Finishes to Prevent Attack by Insects and Micro-Organisms
Other Finishes
Shrinkage - Part I
Shrinkage - Part II
Progressive Shrinkage and Methods of Control
Durable Press and Wash-and-Wear Finishes - Part I
Durable Press and Wash-and-Wear Finishes - Part II
Durable Press and Wash-and-Wear Finishes - Part III
Durable Press and Wash-and-Wear Finishes - Part IV
Durable Press and Wash-and-Wear Finishes - Part V
The General Theory of Dyeing – Part I
The General Theory Of Dyeing - Part II
Natural Dyes
Natural Dyes - Indigo
Mordant Dyes
Premetallized Dyes
Azoic Dyes
Basic Dyes
Acid Dyes
Disperse Dyes
Direct Dyes
Reactive Dyes
Sulfur Dyes
Blends – Fibers and Direct Dyeing
The General Theory of Printing
There are currently eight data bases on this blogspot, namely, the Glossary of Cultural and Architectural Terms, Timelines of Fabrics, Dyes and Other Stuff, A Fashion Data Base, the Glossary of Colors, Dyes, Inks, Pigments and Resins, the Glossary of Fabrics, Fibers, Finishes, Garments and Yarns, Glossary of Art, Artists, Art Motifs and Art Movements, Glossary of Paper, Photography, Printing, Prints and Publication Terms and the Glossary of Scientific Terms, which has been updated to Version 3.5. All data bases will be updated from time-to-time in the future.
If you find any post on this blog site useful, you can save it or copy and paste it into your own "Word" document etc. for your future reference. For example, Safari allows you to save a post (e.g. click on "File", click on "Print" and release, click on "PDF" and then click on "Save As" and release - and a PDF should appear where you have stored it). Safari also allows you to mail a post to a friend (click on "File", and then point cursor to "Mail Contents On This Page" and release). Either way, this or other posts on this site may be a useful Art Resource for you.
The Art Resource series will be the first post in each calendar month. Remember - these Art Resource posts span information that will be useful for a home hobbyist to that required by a final year University Fine-Art student and so undoubtedly, some parts of any Art Resource post may appear far too technical for your needs (skip over those mind boggling parts) and in other parts, it may be too simplistic with respect to your level of knowledge (ditto the skip). The trade-off between these two extremes will mean that Art Resource posts will hopefully be useful in parts to most, but unfortunately may not be satisfying to all!
Introduction
In order to understand the coloring of textile materials, you need to have some understanding of the general theory of dyeing and printing. After reading this post, and if you are still unsure of definitions, terminologies or properties used of fabrics that this post assumes you should know but you don't, then consult the "Preamble" above and click on any art resource post or glossary that might provide that missing information for you.
This post will concentrate on the general theory of dyeing.
O,H & S Issues with Dyeing Fabrics and Textiles
In general, always get a Material Safety Data Sheet (MSDS) from the manufacturer on all dyes and auxiliary compounds you wish to use for any art/craft project. If you do not possess the MSDS you need, go to the retailer who you have purchased the product from and they should provide you with the MSDS. If they cannot, for some unknown reason, then go to Chemists (Commonwealth Countries) or a Drug Store (USA) and ask them for assistance. Usually they are friendly enough to give some advice or point you to where you might obtain the necessary information.
In general, always wear rubber gloves to prevent dyes from being absorbed through the skin. Protective clothing - smock or plastic apron - is also recommended to prevent damage to your clothes. Wear old or disposable shoes and ventilate your work area with a fan to dissipate or exhaust fumes. Remember, not all natural dyes are harmless and/or not all man-made dyes are toxic. Wearing face masks and eye googles might be a pain, but not wearing them when you should, might one day render you in far greater pain! There is only one you, and needless to say, you are special!
It goes without saying that any utensils used in the dyeing process should never be used for food preparation or for any other purpose, even if you have convinced yourself that the cleaning procedures you have employed were excellent.
I cannot keep stressing that all work should be performed in well ventilated areas that are not "common" areas shared by children and other adults, who are not directly involved in your project. Avoid inhalation of dyes and consult my previous posts, namely, Units Used in Dyeing and Printing of Fabrics and Occupational, Health & Safety.
If by any chance, something went amiss and you have inhaled dyes or irritated your eyes or any part of your body because of them, seek medical advice as quickly as possible. Better to be safe then unsure!
Introduction to Dyeing
Dye molecules are organic compounds, which are responsible for the coloring of textile materials. The optical properties of textile materials depends on the incident light that are absorbed, reflected and/or transmitted. The color of textile materials is dependent on the light waves that are reflected and absorbed.
Generally, dyeing is the process of coloring textile materials by immersing them in an aqueous solution called dye liquor. The dye liquor normally contains the dye, water and auxiliary compounds. To improve the effectiveness and efficiency of dyeing, heat is usually applied to the dye liquor. The theory of aqueous dyeing (as explained below) needs modification if an organic solvent is involved instead of water.
The general theory of dyeing focuses on:
(a) Forces of repulsion, which are developed between the dye molecules and water.
(b) Forces of attraction, which are developed between the dye molecules and the fibers.
Dye molecules may be classified from two different approaches:
(a) According to the chemical constitution of the dye molecule itself.
(b) According to the method of application.
In this series, to make the chemistry as manageable as possible, we shall generally concentrate on classifying dyes according to the method of application. However, before we do it is instructive to define some basic chemical terminology. Hold your breath and read on!
Anions are negatively charged species, whereas cations are positively charged species. Hence, dye molecules generally are organic compounds (i.e. mainly composed from carbon, hydrogen, oxygen, nitrogen and sulfur) and so may be classified as:
(a) anionic – in which the color is caused by the negative part of the dye molecule.
(b) cationic – in which the color is caused by the positive part of the dye molecule.
(c) disperse – in which the color is caused by the whole molecule since it is non-polar (no negative or positive parts within it).
The Fiber
Textile fibers are also generally organic compounds and develop a slight negative charge on the surface of the fiber, when immersed in an aqueous solution. Since the dye molecule in an aqueous solution is also slightly negative, they will repel one another (i.e two likes repel) and so conditions within the dye liquor have to be developed in order to overcome this tendency for repulsion, thereby promoting the entry of the dye molecules into the polymer system of the fiber.
Just as a reminder, a simplified and exaggerated representation of a fiber’s polymer system is given below. Each polymer system tends to possess several amorphous (chaotic) and crystalline (structured) regions. This assists in the cohesion of the polymer system. Whenever several individual polymer units are aligned or orientated in more or less parallel order, they form the crystalline regions, which only have extremely small voids between them and so generally prevent dyes or water molecules entry into the crystalline regions. Amorphous regions occur whenever polymer units are not orientated or are completely disorganized in a random fashion. It is these regions that often are the entry points for dye and water molecules into the fabric. Generally, the most important forces of attraction between the polymer units are hydrogen bonds and van der Waals forces.
Note: These regions of the fiber polymer system will be often referred to in the following posts on this blogapot on dyeing and printing of textile materials and so you should grab this image and place it on your desktop.
The Role of Water
Water in aqueous dyeing is critical since it must dissolve or disperse the dye and moreover, it acts as the medium through which the dyed molecules are transferred into the fiber.
Water is polar (i.e. possesses relatively negative and positive parts to it) and so any polar group in the dye molecule is attracted to water molecules and this is the reason why dyes that are polar dissolve in it. In the case of disperse dyes, which does not have negative or positive parts to it, and so are hydrophobic (water hating), they purposely disperse within the water (e.g. may be assisted by dispersing agents) rather than dissolving in it. Think of it as dye droplets suspended by the water molecules that move randomly to keep these dye droplets afloat and so prevent the dye droplets from accumulating at the bottom of the container.
Generally, if a dye molecule dissolves in water, the act of dissolution is undesirable to ensure effective and an efficient transfer of the dye into the fiber, unless this attraction can be negated. Nevertheless, in some instances the rate of dye uptake from the water to the fiber needs to be controlled in order to ensure a uniform coloration of the fiber.
To encourage the dissolved dye to leave the water and enter into the fiber, heat is usually required. This also ensures an adequate penetration of dye into the polymer system of the fiber. Heating the dye liquor promotes the dissociation of water into its polar parts and so the dye liquor becomes more ionic, which promotes the repulsion between water and dye molecules and so promotes dye uptake by the fiber polymer system.
Water, assisted by heat, also swells fibers that are hydrophilic (water loving) and in doing so enlarges the surface and internal voids of the fabric, which makes the fiber polymer system far more accessible to large dye molecules, that otherwise at room temperature would be confronted with small entry voids in the fiber and so the small entry points would prevent the dye molecule from diffusing into the fiber.
The Role of Electrolytes
Electrolytes (such as salts like sodium chloride) are ionic compounds that readily dissolve in aqueous systems as cations (e.g. Na+ is the cation of sodium chloride) and anions (e.g. Cl- is the anion of sodium chloride).
The addition of heat and an electrolyte to the dye liquor of an ionic dye increases the uptake of the dye by the fiber because of the following reasons:
(a) Heat promotes to charge ions in solution and so assists in the water-dye repulsion, thereby assisting in the dye-fiber attraction.
(b) Electrolytes dissociate into ions in water and so assist the dye liquor-dye molecule repulsion, thereby assisting the dye molecule-fiber attractions.
(c) The electrolyte ions neutralize any fiber surface charge and so assist the dye molecule - fiber attraction.
(d) Heat also enlarges the surface and internal voids of the fiber thereby, increasing and deepening the passage of large dyed molecules into the fiber.
The Role of Heating the Dye Liquor
Rather than repeat (a) and (d) above, we shall add that heating the dye liquor also imparts a greater translation energy to the dyed molecules and so reduces the time of dye uptake of a particular fiber, with all other factors being equal. It also enables a greater penetration of the dye into the fiber polymer system (i.e. dye molecules entering the amorphous regions of the fiber do so and at a greater depth).
When the dyed liquor cools and the fibers dry, the surface and internal voids of the polymer system will return to their original size, trapping and entangling the dye molecules that are now resident within it. In this environment, weak van Waals forces of attraction between the dyed molecules and the polymer system of the fiber assist to retain the dye molecules within the fiber's polymer system.
High Temperature Dyeing
Dyeing at temperatures from 100oC to 130oC under pressure of 170kPa (note: one atmosphere is 101.3 kPa) is termed high temperature dyeing. Hydrophobic fibers, such as polyester fibers, are commercially dyed in this way using dye liquors (as distinct from sublimation dyeing) because under normal atmospheric conditions, their extremely crystalline polymer system will not allow a good dye uptake.
When dyeing at high temperature, dye molecule penetration of the fiber polymer system is increased significantly. At temperatures above 100oC and under pressure, the heat generates a very large amount of energy in the constituents of the dye liquor. This swells the fiber, and so enlarges its surface and internal voids, enabling the dye molecules to penetrate into the fiber system more readily and deeper.
Dye Auxiliary Compounds
Dye auxiliary compounds assist the dyeing process and include: carriers or swelling agents, leveling agents, anti-foaming agents, dispersing agents, detergents and wetting agents. The way these auxiliary agents affect the dyeing process is chemically complex and so beyond this series. Nevertheless, their purpose and use will be explained below.
Carriers or Swelling Agents
The purpose of carriers added to the dye liquor is to improve the dye exhaustion for highly crystallized fibers such as polyesters. Due to their very crystalline nature, usually only pale colors can be achieved by aqueous dyeing without carriers (unlike sublimation dyeing). These carriers tend to swell the fiber, and so enlarge the size of the surface and internal voids of the fiber polymer system, thereby enabling greater dye uptake and penetration. In general, carriers are only used to dye polyester fibers in aqueous liquor baths with disperse dyes.
Leveling Agents
The purpose of adding a leveling agent to the dye liquor is to produce a more uniform color in the textile materials. Leveling agents tend to slow down the dye uptake of the fabric and so they are also known as retarding agents or retarders. The use of retarders is essential in cases where dyes rush into the fiber and so produce uneven colored textile materials.
Leveling agents are surface-active agents and are chemically related to soaps, synthetic detergents and wetting agents. They may be anionic, cationic or non-ionic organic compounds.
Anionic Leveling Agents
These molecules consist of large negatively charged or anionic organic radicals, with the corresponding cation usually a sodium cation, that assists the water solubility of the leveling agent.
These anionic leveling agent radicals are attracted to cationic or positive sites on the fiber. As the dye bath is heated, a two-fold process occurs:
(a) The anionic leveling agents are slowly removed from the positive sites of the fiber, due to the disruptive Brownian motion of the water molecules, which is greater the higher the temperature of the dye bath.
(b) The anionic dye molecules obtain sufficient energy to overcome the repulsive forces between the anionic dye molecules and the anionic nature of the retarder and moreover, its attraction to the positive sites on the fiber is stronger than any disruptive force due to Brownian motion.
Both these processes ensure a more uniform absorption of the dye by the polymer system of the fiber due to the slowing down of dye uptake by the fiber.
Cationic Leveling Agents
The molecules of these leveling agents consist of a large positively charged, or cationic organic radical, with an anionic radical, usually the chloride or bromide anion, which helps to assist the agent's water solubility.
Before dissolution in water both the cationic and anionic parts of the leveling agent are attached. However, on dissolution they are separated and the anionic dye portion has a greater attraction to the cationic part of the leveling agent in the dye liquor, thereby reducing the anionic dye radical substantivity for the fibers. The energy provided by heating the dye bath assists to dissociate very slowly the cationic radical of the leveling agent from the anionic dye radical. The slow release from the cationic leveling radical is why they are known as retardants. Moreover, the slow release of the dye anion ensures a more uniform absorption of the dye by the polymer system of the fiber.
Scouring after Dyeing
Dyeing always leaves some dye molecules on the surface of the dyed textile or cloth. It is essential that these dyed molecules be removed when dyeing is completed. If the dyes are not removed they may result in two problems, namely:
(a) Poor rub-fastness, which may result in the dye rubbing onto adjacent materials.
(b) Poor wash-fastness, which may result in other fabrics being colored by the excess dye resident on the fabric during the laundering process.
Compiled by J. Claude Freres and Co, Paris, France, 1856.
Presented to the National Gallery of Victoria by the Australian Wool Corporation in 1982.
References:
[1] A Fritz and J. Cant, Consumer Textiles, Oxford University Press, Melbourne (1986).
[2] E.P.G. Gohl and L.D. Vilensky, Textile Science, Longman Cheshire, Melbourne (1989).
No comments:
Post a Comment