Preamble
This is the one hundredth and thirteenth 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, we need to have some understanding of the general theory of printing. We have basically covered color, color systems, optical properties of textiles and fibers. We have also discussed the general theory of the dyeing of textile materials.
Today, we shall focus on the general theory of printing.
The printing of textile materials is the application of color according to a pre-determined design. Generally, a printing paste, consisting of dye, water, thickener and hydrocarbon oil or solvent is applied to the textile material. After the printing paste is applied, the textile material is steamed in order to ensure that the dye molecules migrate from the surface of the fabric and penetrate deeply into the fiber polymer system. Steaming swells the voids in the fiber polymer system and in particular, enlarges those in the amorphous regions of the fiber polymer system, thereby ensuring that the dye uptake of the polymer system is greater and held more securely, and so improving the color fastness of the textile material.
The general theory of printing explains the interaction, on steaming, between the dye, fiber, water, thickener and hydrocarbon solvent. More specifically, it explains how within the printing paste:
(i) Forces of repulsion are developed between the dye molecule and the constituents of the printing paste, and;
(ii) Forces of attraction are developed between the dye molecules and the fibers of the textile material to be printed.
We have already covered the general theory of dyeing and so we will not regurgitate many of those concepts that we covered in that blog.
The Role of Elements in the Printing Process
The Role Of Water
A relatively small amount of water is used; enough to dissolve the dye into a paste. Water is used as a convenient and readily available medium to mix, or to disperse the dye molecules into the thickener.
The Role of a Thickener
The printing paste is an emulsion of the thickener, hydrocarbon (such as a white spirit or a very light hydrocarbon oil) and a surface-active agent. The thickener acts as a medium for the dye paste. The surface-active agent enables emulsification of the thickener with the hydrocarbon imparting a uniform consistency (i.e. uniform viscosity) to the printing paste. The viscosity (i.e. ease with which the paste will flow) of a printing paste is very important since it influences the clarity and appearance of the printed pattern. The thickener therefore influences the clarity of the printed pattern. The physical-chemical properties of the thickener must be such that immediately after printing, it will form a film of sufficient plasticity and elasticity not to flake, crack or peel when dried. The thickener also prevents the dye to run via a capillary action.
The success of printing textile materials depends very much on the type, quality and characteristics of the thickener. Thickeners can be constituted from any of the following:
(i) Natural gums, such as gum arabic, acacia gums or gums prepared from starches and other polysaccharides.
(ii) Man-Made, natural polymer based gums such as water-soluble cellulose ethers, such as carboxymethyl cellulose, methyl and ethyl cellulose, and sodium alginate.
(iii) Occasionally man-made, synthetic compounds such as polyvinyl alcohol.
When selecting a thickener, it is important to select one that does not compete with the fiber for the dye. For example, if a cellulosic textile material is to be printed, the paste must not be mixed with a cellulosic-based thickener, because both polymer systems have similar characteristics and so the thickener, which initially houses the dye, will not release it since it may be similar and if not more substantive to the dye molecules than the fiber polymer system.
Textile printed with cellulose thickeners.
The Role of Steam
After printing, it is usual to steam the textile material in order to achieve color-fastness. Steaming ensures the adequate penetration of the fiber by dye molecules for the following reasons: it generates sufficient kinetic energy to the dye molecules to enter the fiber polymer system at speed, which is further assisted by the fact that steaming swells the fiber, enlarging the entry voids and the internal voids within the amorphous system of the fiber polymer system that will house the dye molecules. Hence steaming assists in dye uptake by the fiber polymer system.
The Role of Dry Heating
Thermoplastic fibers tend to be hydrophobic (water hating) and so will not swell sufficiently in water (which it tries to repel) or when subject to steaming. However, dry heating softens the fibers by pushing the fiber polymers in the amorphous region further apart, enlarging the voids in that region and so this promotes dye molecule entry and uptake. Note: Once the dry heating is turned off these voids shrink, trapping the dye molecules within the fiber polymer system.
The above process of fixing or setting of printed patterns on the textile materials is particularly important when using pigments, since they have little substantivity for the fiber polymer system, but by the above mechanism are nonetheless trapped in the amorphous regions of the fiber polymer system.
Washing Off
This has to be done to remove the thickener and other printing paste constituents, which have not entered the fiber polymer system. There will always be some dye molecules on the surface of the fibers, which must be removed in the washing off process.
Desirable Fastness Properties
Fading
Fading is a color loss due to dye molecules being removed over a length of time from the fiber polymer system. It is the result of some change in the structure of the dye molecule due to the absorption of light, reaction with air pollutants, laundering, dry-cleaning and/or due to some other degrading agency. To completely understand the cause of fading requires a map of the structural changes to the dye molecule, which at present is difficult to do.
Fastness To Sunlight
There is actually no hard and fast chemical explanation for fading of textile materials in the presence of UV sunlight. The most likely explanation is the UV light can ionize chromophores of the dyed molecules and so initiate reactions with the dye molecules, accelerating their structural damage. Moisture assists such processes.
Flags have to be color-fast to sunlight.
Wash-Fastness
The loss of color during laundering is referred to as a lack of wash-fastness or “bleeding". Dyes are held by weak forces in the amorphous region of the fiber polymer system by hydrogen bonds or even by the weaker van der Waals forces. If dyes bleed from the fiber they generally have not penetrated deeply enough in the fiber polymer system. Furthermore, voids, which are enlarged by the warm-to-hot laundering processes, the agitation of laundering may be sufficient to break these weak bonds, thereby allowing dye molecules to escape through the larger sized voids.
Fitness T-Shirts need to be wash-fast.
Note:If bleaches are used at some stage during the laundering process, then fading might also be due to chemical degradation of the dye by the bleach.
Dry Clean-Fastness
The loss of color due to the dry cleaning process is called the lack of dry cleaning-fastness. This is probably due to the same mechanism described above with an important proviso that the dye molecules are probably soluble in the dry-cleaning solvent. Loss of color during the dry cleaning process varies according to the particular dye and the particular dry-cleaning solvent used. Generally, loss of color during the dry cleaning process is a rare occurance.
Business shirts need to be dry clean-fast.
Fastness To Perspiration
Perspiration is a complex combination of body oils, fats, and saline solution. The perspiration process is further complicated by the addition of perfumes and under arm deodorants on the skin or even the addition of insect repellents. Perspiration is slightly acidic, and so the loss of color may result for similar reasons as given above for wash-fastness and dry cleaning fastness.
As perspiration is acidic it may be possible for it to chemically react with the dye molecule, causing its chemical degradation, but this is a somewhat rare occurrence as well.
Sports outfits need to be perspiration fast.
Fastness to Compounds and Bleaches containing Chlorine.
With the presence of swimming pools with chlorinated water (calcium hypochlorite) and with chlorine bleaches (sodium hypochlorite) being used in the laundering process, the chemical degradation of dyes sensitive to both these reagents is due to their oxidizing effect.
Fastness To Seawater
The main constituent of seawater is sodium chloride (NaCl) or more commonly known as table salt. When a textile material is subject to seawater, intense sunlight will hydrolyze it, producing hydrochloric acid, which degrades the dye molecules. Seawater also contains other oxidizing agents, which also degrades dye molecules (e.g. seawater will bleach the hair of professional surfers).
Dye molecules that provide good color-fastness to seawater are those, which can resist prolonged exposure to dilute hydrochloric acid and/or other oxidizing agents, ultraviolet radiation and heat.
Gucci swimwear is resistant to fading from seawater and has fastness to bleaches containing chlorine (see above).
Fading Due To Other Causes
Inorganic acids, alkalis, and fruit juices etc. can cause fading. It occurs because the dye molecule reacts with the degrading agent causing the chemical degradation of the dye.
Fading, due to dry ironing may be attributed to the dye molecule being heat sensitive and so it degrades with applied heat, whereas fading due to steam pressing is due to the inability of some dye molecules to resist the hydrolytic effects of steaming.
References:
[1] E.P.G. Gohl and L.D. Vilensky, Textile Science, Longman Cheshire, Melbourne (1989).
[2] E.P.G. Gohl and L.D. Vilensky, Textile Science, Longman Cheshire, Melbourne (1989).
This is the one hundredth and thirteenth 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, we need to have some understanding of the general theory of printing. We have basically covered color, color systems, optical properties of textiles and fibers. We have also discussed the general theory of the dyeing of textile materials.
Today, we shall focus on the general theory of printing.
The printing of textile materials is the application of color according to a pre-determined design. Generally, a printing paste, consisting of dye, water, thickener and hydrocarbon oil or solvent is applied to the textile material. After the printing paste is applied, the textile material is steamed in order to ensure that the dye molecules migrate from the surface of the fabric and penetrate deeply into the fiber polymer system. Steaming swells the voids in the fiber polymer system and in particular, enlarges those in the amorphous regions of the fiber polymer system, thereby ensuring that the dye uptake of the polymer system is greater and held more securely, and so improving the color fastness of the textile material.
The general theory of printing explains the interaction, on steaming, between the dye, fiber, water, thickener and hydrocarbon solvent. More specifically, it explains how within the printing paste:
(i) Forces of repulsion are developed between the dye molecule and the constituents of the printing paste, and;
(ii) Forces of attraction are developed between the dye molecules and the fibers of the textile material to be printed.
We have already covered the general theory of dyeing and so we will not regurgitate many of those concepts that we covered in that blog.
The Role of Elements in the Printing Process
The Role Of Water
A relatively small amount of water is used; enough to dissolve the dye into a paste. Water is used as a convenient and readily available medium to mix, or to disperse the dye molecules into the thickener.
The Role of a Thickener
The printing paste is an emulsion of the thickener, hydrocarbon (such as a white spirit or a very light hydrocarbon oil) and a surface-active agent. The thickener acts as a medium for the dye paste. The surface-active agent enables emulsification of the thickener with the hydrocarbon imparting a uniform consistency (i.e. uniform viscosity) to the printing paste. The viscosity (i.e. ease with which the paste will flow) of a printing paste is very important since it influences the clarity and appearance of the printed pattern. The thickener therefore influences the clarity of the printed pattern. The physical-chemical properties of the thickener must be such that immediately after printing, it will form a film of sufficient plasticity and elasticity not to flake, crack or peel when dried. The thickener also prevents the dye to run via a capillary action.
The success of printing textile materials depends very much on the type, quality and characteristics of the thickener. Thickeners can be constituted from any of the following:
(i) Natural gums, such as gum arabic, acacia gums or gums prepared from starches and other polysaccharides.
(ii) Man-Made, natural polymer based gums such as water-soluble cellulose ethers, such as carboxymethyl cellulose, methyl and ethyl cellulose, and sodium alginate.
(iii) Occasionally man-made, synthetic compounds such as polyvinyl alcohol.
When selecting a thickener, it is important to select one that does not compete with the fiber for the dye. For example, if a cellulosic textile material is to be printed, the paste must not be mixed with a cellulosic-based thickener, because both polymer systems have similar characteristics and so the thickener, which initially houses the dye, will not release it since it may be similar and if not more substantive to the dye molecules than the fiber polymer system.
The Role of Steam
After printing, it is usual to steam the textile material in order to achieve color-fastness. Steaming ensures the adequate penetration of the fiber by dye molecules for the following reasons: it generates sufficient kinetic energy to the dye molecules to enter the fiber polymer system at speed, which is further assisted by the fact that steaming swells the fiber, enlarging the entry voids and the internal voids within the amorphous system of the fiber polymer system that will house the dye molecules. Hence steaming assists in dye uptake by the fiber polymer system.
The Role of Dry Heating
Thermoplastic fibers tend to be hydrophobic (water hating) and so will not swell sufficiently in water (which it tries to repel) or when subject to steaming. However, dry heating softens the fibers by pushing the fiber polymers in the amorphous region further apart, enlarging the voids in that region and so this promotes dye molecule entry and uptake. Note: Once the dry heating is turned off these voids shrink, trapping the dye molecules within the fiber polymer system.
The above process of fixing or setting of printed patterns on the textile materials is particularly important when using pigments, since they have little substantivity for the fiber polymer system, but by the above mechanism are nonetheless trapped in the amorphous regions of the fiber polymer system.
Washing Off
This has to be done to remove the thickener and other printing paste constituents, which have not entered the fiber polymer system. There will always be some dye molecules on the surface of the fibers, which must be removed in the washing off process.
Desirable Fastness Properties
Fading
Fading is a color loss due to dye molecules being removed over a length of time from the fiber polymer system. It is the result of some change in the structure of the dye molecule due to the absorption of light, reaction with air pollutants, laundering, dry-cleaning and/or due to some other degrading agency. To completely understand the cause of fading requires a map of the structural changes to the dye molecule, which at present is difficult to do.
Fastness To Sunlight
There is actually no hard and fast chemical explanation for fading of textile materials in the presence of UV sunlight. The most likely explanation is the UV light can ionize chromophores of the dyed molecules and so initiate reactions with the dye molecules, accelerating their structural damage. Moisture assists such processes.
Wash-Fastness
The loss of color during laundering is referred to as a lack of wash-fastness or “bleeding". Dyes are held by weak forces in the amorphous region of the fiber polymer system by hydrogen bonds or even by the weaker van der Waals forces. If dyes bleed from the fiber they generally have not penetrated deeply enough in the fiber polymer system. Furthermore, voids, which are enlarged by the warm-to-hot laundering processes, the agitation of laundering may be sufficient to break these weak bonds, thereby allowing dye molecules to escape through the larger sized voids.
Note:If bleaches are used at some stage during the laundering process, then fading might also be due to chemical degradation of the dye by the bleach.
Dry Clean-Fastness
The loss of color due to the dry cleaning process is called the lack of dry cleaning-fastness. This is probably due to the same mechanism described above with an important proviso that the dye molecules are probably soluble in the dry-cleaning solvent. Loss of color during the dry cleaning process varies according to the particular dye and the particular dry-cleaning solvent used. Generally, loss of color during the dry cleaning process is a rare occurance.
Fastness To Perspiration
Perspiration is a complex combination of body oils, fats, and saline solution. The perspiration process is further complicated by the addition of perfumes and under arm deodorants on the skin or even the addition of insect repellents. Perspiration is slightly acidic, and so the loss of color may result for similar reasons as given above for wash-fastness and dry cleaning fastness.
As perspiration is acidic it may be possible for it to chemically react with the dye molecule, causing its chemical degradation, but this is a somewhat rare occurrence as well.
Fastness to Compounds and Bleaches containing Chlorine.
With the presence of swimming pools with chlorinated water (calcium hypochlorite) and with chlorine bleaches (sodium hypochlorite) being used in the laundering process, the chemical degradation of dyes sensitive to both these reagents is due to their oxidizing effect.
Fastness To Seawater
The main constituent of seawater is sodium chloride (NaCl) or more commonly known as table salt. When a textile material is subject to seawater, intense sunlight will hydrolyze it, producing hydrochloric acid, which degrades the dye molecules. Seawater also contains other oxidizing agents, which also degrades dye molecules (e.g. seawater will bleach the hair of professional surfers).
Dye molecules that provide good color-fastness to seawater are those, which can resist prolonged exposure to dilute hydrochloric acid and/or other oxidizing agents, ultraviolet radiation and heat.
Fading Due To Other Causes
Inorganic acids, alkalis, and fruit juices etc. can cause fading. It occurs because the dye molecule reacts with the degrading agent causing the chemical degradation of the dye.
Fading, due to dry ironing may be attributed to the dye molecule being heat sensitive and so it degrades with applied heat, whereas fading due to steam pressing is due to the inability of some dye molecules to resist the hydrolytic effects of steaming.
References:
[1] E.P.G. Gohl and L.D. Vilensky, Textile Science, Longman Cheshire, Melbourne (1989).
[2] E.P.G. Gohl and L.D. Vilensky, Textile Science, Longman Cheshire, Melbourne (1989).
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