Preamble
This is the one hundredth and eigth 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
Direct dyes are also called substantive colors, because of their excellent substantivity for cellulose textile materials. Hence, the fibers most readily colored with direct dyes are the man-made and natural cellulose fibers, such as cotton and viscose fibers.
Pots of Direct Dyes.
Direct dyes have excellent substantivity for cellulosic fibers.
Direct dyes are long flat ribbon like molecules – some are small, whilst others are larger in size. Hence, the classification of what constitutes a direct dye is based on its application and not on its chemical structure.
Direct Dye - blue 81 (C.I. 34215).
Courtesy of reference [1].
Many of the direct dyes are in fact natural colorants (e.g. from onion skins, lichens, flowers etc.) All direct dyes have enough charged groups (e.g. –SO3- sulfonic groups) to make them water soluble, even though for the larger direct dyes they may possess hydrophobic components (water hating).
Many direct dyes are sodium salts of sulfonic acids (see above) and so in this respect are similar to acid dyes. In fact, some dyes that are applied as direct dyes have the same formula as acid dyes and so both are one of the same.
All direct dyes have a special affinity for cellulosic fibers, since their ribbon like shapes align effectively within the cellulosic fibers. The dye-fiber interactions form many van der Waals bonds or forces of attraction and hydrogen bonds along the length of the cellulosic fibers, thereby holding the dye molecules firmly in place within the fiber structure.
The ribbon like shape of Direct Dyes fit smugly within the cellulosic fibers.
Courtesy of reference [1].
Direct Dyes fall into two categories depending on their size and shape:
(a) Those that are able to move around the dye bath, rapidly absorbing and desorbing easily from the fiber, and so enable an even distribution over the fabric. These are termed level dyeing Direct Dyes.
(b) Those that are strongly attached to the fiber and so cannot distribute themselves evenly (without further action by the dyer) thereby producing a streaky or unlevel dyeing result.
Dyeing with Direct Dyes
Direct Dyes are applied to cellulosic fibers from an aqueous liquor to which is added an electrolyte, which is usually sodium chloride (table salt) or Glauber’s salt (Na2SO4). The addition of the electrolyte to the dye liquor is essential to obtain adequate exhaustion of the dye molecules by the fiber polymer system.
The addition of sodium salts assists in the fiber polymer system uptake of the Direct Dye. For example, once the salt is dissolved it produces sodium cations, Na+, which are attracted to the negative sites of the cellulosic fiber and so neutralizes these sites, thereby allowing the negatively charged dye molecule to approach the fiber molecules and finally to bond to them via van der Waals forces and polar attractions. That is, the negative sites on the fiber are first neutralized by the Na+ ions of the dissolved salt, thereby allowing the negative dye molecule to approach the fiber and to create bonds with the fiber molecule and in doing so displacing the original Na+ ions. The dye molecules being much larger than Na+ ions, take a much longer time to reach the fiber sites.
The sodium cations (Na+) neutralizes the fiber surface enabling the dye anion to enter the fiber polymer system.
Courtesy of reference [1].
The application of heat to the dye liquor increases the kinetic energy of all the constituents of the dye liquor, as well as enlarges the voids in the amorphous regions of the fiber polymer system. Both processes accelerate and increase the rate of dye uptake.
Printing with Direct Dyes
The application of Direct Dyes by printing is in principle the same as in dyeing, with the proviso that a thickener is added to restrict the dye and so ensure that the color does not run. Dye fixation is achieved through the application of steam heating and the addition of an electrolyte, which assists the dye molecule to leave the printing paste and penetrate into the fiber polymer system (as described above for heating the dye liquor in the dyeing process).
Properties of Direct Dyes
Light-Fastness
Dyed and printed direct color has a moderate light-fastness, which is rated at about 3. A relatively short exposure to direct sunlight is enough to initiate degradation of the dyed and printed color due to the gradual breakdown of their chromophores, resulting in a gradual fading of color.
Wash-Fastness
Direct dyed or printed cellulosic fibers have a comparatively poor wash-fastness, which is rated at about 2-3. Both forces of attraction (i.e. hydrogen bonds and van der Waals forces) between the dye anion and the fiber polymer system are essential and so under the alkali conditions of laundering, these weak bonds are hydrolyzed by the water, resulting in the gradual removal of the dye from the cellulosic polymer system and so resulting a noticeable fading of color.
Direct Dyes are easy to apply, comparatively low in cost, they have a wide range of available colors and so these factors alone provide more than enough motivation to develop after treatments in order to increase their wash-fastness. As the Direct Dye anion uptake is in the amorphous regions of the fiber polymer system, then the application of heat to enlarge the voids in this region, would suggest that making the direct dye anion larger in size, would trap and entangle them more effectively when these voids reduce in size as the fiber cools, thereby increasing their wash-fastness rating.
Four such methods based on the above concept have been developed and they are as follows.
(i) Diazotisation
Certain direct dyes possess a chemical structure so that should be classified as azoic dyes. This means that these type of Direct Dyes can be treated with naphthol and the dye anion would be enlarged, which improves their wash-fastness from poor to good. Diazotisation, however, causes an alteration in the hue and this factor must be considered when this method is used to improve this class of Direct Dye.
(ii) Copper After-Treatment
When certain Direct Dyes are treated with copper sulfate, the copper forms a metal complex with the Direct Dye, resulting in a Direct Dye molecule larger in size. However, this only slightly improves the wash-fastness of the Direct Dye.
(iii) Cationic Agents
In aqueous solution the Direct Dye molecules situated in the fiber polymer system ionizes slightly, and so the color component of the molecule is negatively charged (i.e. it is called an anion). As soon as a positively charged (or cationic) agent is added to the solution, it will be attracted to the negatively charged dye component and so form a much larger complex Direct Dye molecule, thereby improving its wash-fastness. However, it does this at a cost, by reducing its light-fastness, since the electronic configuration of its chromophores have now been lowered in energy, thereby decreasing their resistance to UV sunlight.
(iv) Formaldehyde After-Treatment
Certain (but not all) Direct Dyes will react with formaldehyde (HCHO) when heated between 70oC to 80oC, under slightly acidic conditions. The resulting Direct Dye molecules now appear to be joined together by methylene (-CH2-) cross links, generating a much larger in size Direct Dye molecular complex, thereby increasing its wash-fastness.
In summary, all the above four methods have been employed to improve the wash-fastness of Direct Dyes. Nevertheless, while after-treatment improves wash-fastness to some extent, improvements that have been achieved still leave much to be desired.
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 one hundredth and eigth 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
Direct dyes are also called substantive colors, because of their excellent substantivity for cellulose textile materials. Hence, the fibers most readily colored with direct dyes are the man-made and natural cellulose fibers, such as cotton and viscose fibers.
Direct dyes are long flat ribbon like molecules – some are small, whilst others are larger in size. Hence, the classification of what constitutes a direct dye is based on its application and not on its chemical structure.
Courtesy of reference [1].
Many of the direct dyes are in fact natural colorants (e.g. from onion skins, lichens, flowers etc.) All direct dyes have enough charged groups (e.g. –SO3- sulfonic groups) to make them water soluble, even though for the larger direct dyes they may possess hydrophobic components (water hating).
Many direct dyes are sodium salts of sulfonic acids (see above) and so in this respect are similar to acid dyes. In fact, some dyes that are applied as direct dyes have the same formula as acid dyes and so both are one of the same.
All direct dyes have a special affinity for cellulosic fibers, since their ribbon like shapes align effectively within the cellulosic fibers. The dye-fiber interactions form many van der Waals bonds or forces of attraction and hydrogen bonds along the length of the cellulosic fibers, thereby holding the dye molecules firmly in place within the fiber structure.
Courtesy of reference [1].
Direct Dyes fall into two categories depending on their size and shape:
(a) Those that are able to move around the dye bath, rapidly absorbing and desorbing easily from the fiber, and so enable an even distribution over the fabric. These are termed level dyeing Direct Dyes.
(b) Those that are strongly attached to the fiber and so cannot distribute themselves evenly (without further action by the dyer) thereby producing a streaky or unlevel dyeing result.
Dyeing with Direct Dyes
Direct Dyes are applied to cellulosic fibers from an aqueous liquor to which is added an electrolyte, which is usually sodium chloride (table salt) or Glauber’s salt (Na2SO4). The addition of the electrolyte to the dye liquor is essential to obtain adequate exhaustion of the dye molecules by the fiber polymer system.
The addition of sodium salts assists in the fiber polymer system uptake of the Direct Dye. For example, once the salt is dissolved it produces sodium cations, Na+, which are attracted to the negative sites of the cellulosic fiber and so neutralizes these sites, thereby allowing the negatively charged dye molecule to approach the fiber molecules and finally to bond to them via van der Waals forces and polar attractions. That is, the negative sites on the fiber are first neutralized by the Na+ ions of the dissolved salt, thereby allowing the negative dye molecule to approach the fiber and to create bonds with the fiber molecule and in doing so displacing the original Na+ ions. The dye molecules being much larger than Na+ ions, take a much longer time to reach the fiber sites.
Courtesy of reference [1].
The application of heat to the dye liquor increases the kinetic energy of all the constituents of the dye liquor, as well as enlarges the voids in the amorphous regions of the fiber polymer system. Both processes accelerate and increase the rate of dye uptake.
Printing with Direct Dyes
The application of Direct Dyes by printing is in principle the same as in dyeing, with the proviso that a thickener is added to restrict the dye and so ensure that the color does not run. Dye fixation is achieved through the application of steam heating and the addition of an electrolyte, which assists the dye molecule to leave the printing paste and penetrate into the fiber polymer system (as described above for heating the dye liquor in the dyeing process).
Properties of Direct Dyes
Light-Fastness
Dyed and printed direct color has a moderate light-fastness, which is rated at about 3. A relatively short exposure to direct sunlight is enough to initiate degradation of the dyed and printed color due to the gradual breakdown of their chromophores, resulting in a gradual fading of color.
Wash-Fastness
Direct dyed or printed cellulosic fibers have a comparatively poor wash-fastness, which is rated at about 2-3. Both forces of attraction (i.e. hydrogen bonds and van der Waals forces) between the dye anion and the fiber polymer system are essential and so under the alkali conditions of laundering, these weak bonds are hydrolyzed by the water, resulting in the gradual removal of the dye from the cellulosic polymer system and so resulting a noticeable fading of color.
Direct Dyes are easy to apply, comparatively low in cost, they have a wide range of available colors and so these factors alone provide more than enough motivation to develop after treatments in order to increase their wash-fastness. As the Direct Dye anion uptake is in the amorphous regions of the fiber polymer system, then the application of heat to enlarge the voids in this region, would suggest that making the direct dye anion larger in size, would trap and entangle them more effectively when these voids reduce in size as the fiber cools, thereby increasing their wash-fastness rating.
Four such methods based on the above concept have been developed and they are as follows.
(i) Diazotisation
Certain direct dyes possess a chemical structure so that should be classified as azoic dyes. This means that these type of Direct Dyes can be treated with naphthol and the dye anion would be enlarged, which improves their wash-fastness from poor to good. Diazotisation, however, causes an alteration in the hue and this factor must be considered when this method is used to improve this class of Direct Dye.
(ii) Copper After-Treatment
When certain Direct Dyes are treated with copper sulfate, the copper forms a metal complex with the Direct Dye, resulting in a Direct Dye molecule larger in size. However, this only slightly improves the wash-fastness of the Direct Dye.
(iii) Cationic Agents
In aqueous solution the Direct Dye molecules situated in the fiber polymer system ionizes slightly, and so the color component of the molecule is negatively charged (i.e. it is called an anion). As soon as a positively charged (or cationic) agent is added to the solution, it will be attracted to the negatively charged dye component and so form a much larger complex Direct Dye molecule, thereby improving its wash-fastness. However, it does this at a cost, by reducing its light-fastness, since the electronic configuration of its chromophores have now been lowered in energy, thereby decreasing their resistance to UV sunlight.
(iv) Formaldehyde After-Treatment
Certain (but not all) Direct Dyes will react with formaldehyde (HCHO) when heated between 70oC to 80oC, under slightly acidic conditions. The resulting Direct Dye molecules now appear to be joined together by methylene (-CH2-) cross links, generating a much larger in size Direct Dye molecular complex, thereby increasing its wash-fastness.
In summary, all the above four methods have been employed to improve the wash-fastness of Direct Dyes. Nevertheless, while after-treatment improves wash-fastness to some extent, improvements that have been achieved still leave much to be desired.
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).
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