Preamble
This is the thirtieth 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
The term "nylon" was derived from "no-run", the name originally considered by its inventors in order to emphasize the durability of ladies' hosiery which was manufactured from it.
Swiss dot pantyhose made from nylon.
Nylon is a man-made synthetic polymer, polyamide filament or staple fiber. Textile materials composed of nylon tend to be light in weight because the density of nylon filaments or staple fibers is 1.14 g cm-3.
The most important polyamide fiber in terms of the amount that is produced is nylon 6,6; that is, in chemical terms a polyhexamethylene adipamide. The notion 6,6 denotes that there are two monomers, each containing six carbon atoms, which are required to form the polymer of this type of nylon (see below).
Nylon stretchy fake tatto sleeve arm stockings.
Nylon 6 is the second most important polyamide fiber. It is extruded from polycaprolactam. The notation 6 denotes it has only one monomer containing 6 carbon atoms required to polymerize this type of nylon.
Cheese dyed nylon 6 textured yarn.
This post will focus on nylon 6,6 and nylon 6 fibers. The following descriptions and explanations of the properties of nylon will be based on nylon 6,6 as the two nylon fibers have similar properties unless otherwise stated.
History
In 1939 the first nylon hosiery for women was marketed in limited quantity. Women found them to be stronger and sheerer than silk hosiery they had been wearing. During World War II, the supplies of nylon was sufficient only for military purposes. Parachutes were made of nylon as were tents and many garments.
Thousands of nylon parachutes during the Arnhem landings in WW2.
After the war when nylon hose came on the market again, women were almost frantic to obtain them. Hours before opening time people would line up outside any store where nylon was sold. As the stockings were limited to one pair per customer in the USA, women would enlist their husbands and children to stand in line for them. If their size was sold out when they finally reached the counter, they would buy any size available, in order to give as gifts to friends or to barter.
Lines formed when nylons were finally available again in autumn 1945 after the end of WW2.
Courtesy of German Hosiery Museum.
Since then nylon has become plentiful and is in demand for clothing and industrial uses. Today it is made by many companies throughout the world. In Germany it is called Perlon; in Great Britain it is called Brinylon; in Mexico, Nyfil; and in Australia and the USA as nylon.
Source and Production
The term nylon refers to a whole group of fibers, not just one. Nylon is a generic term that is used for a group of protein-like chemical fibers. The method of fabrication depends upon the intended use. The chemical elements present in petroleum, air, water and natural gas are combined to form a nylon polymer, which is processed in molten form and them pumped through a spinneret, air cooled, and solidified into filaments.
Manufacture process of nylon 6.
Nylon can be made into both filament and short, staple lengths. Of course it can be drawn in different fiber shapes. The original nylon has a cross-section that was round.
Cross-section of conventional nylon.
The circular, featureless cross-section of nylon, magnified 500 times.
Note: the specks are that of a delustering agent.
A more recent nylon named antron has a trilobal cross-section. Hence it is more opaque and has a silk-like feel than regular nylon.
Cross section of antron nylon.
A cross-section of tri-lobal or profiled nylon, magnified 1000 times. Tri-lobal nylon is a man-made, readily available fiber whose cross-section has been purposely modified.
In summary nylons can be varied by both physical and chemical means to produce an enormous range of fibers with a wide spectrum of properties. However, if one property is changed (say pliability increased) then it is usually at the expense of another equally desirable property (e.g. strength decreased). So in spite of their variability, it is not quite possible to tailor-make synthetic fibers that are perfect for any application. Nevertheless, nylon fibers are used with great effect in many domestic and industrial applications.
General Properties of Nylon Polymers and Fibers
Fiber Density
The density of nylon filaments or staple fibers is 1.14 g cm-3, which makes them light weight fibers.
Micro Structure of Nylon Fibers
Nylon filaments or staple fibers do not have an identifiable micro-structure. Their longitudinal structure is very regular and essentially featureless, because of their almost circular cross section (see above). The nylon filament or staple fiber may, in fact, be likened to a glass rod.
The featureless longitudinal section of regular nylon magnified 500 times. Note the specks of a delustering agent.
A combination of factors is responsible for the rod-like, featureless microscopic appearance of nylon. These are the viscosity of the spinning solution, the nature of the polyamide material and the rate of coagulation in cold air of the extruded stream of polymers. These factors cause the coagulated filament to retain the round cords-section of the spinneret orifice.
A longitudinal section of the tri-lobal nylon (see above) magnified 600 times. The broad shadow line is due to the indentation between the lobes.
Macro Structure of Nylon
Nylon is a regular, translucent, fine filament or staple fiber. Staple fibers of nylon are usually crimped for reasons similar to those given by viscose (see past post). Nylon filaments are textured for reason given for crimping the staple fibers.
The length of nylon filaments is limited only by the yarn package onto which it is wound. The length of the staple fibers tends to be comparable to that of either cotton or wool, depending on end-use requirements. The fiber length to breadth ratio usually exceeds 2000:1. This ensures that even the shorter nylon staple fibers can be satisfactorily spun into yarn.
The descriptions and explanations given for viscose of fiber color, luster and translucency are also applicable to the nylon fibers.
The Nylon Polymer
Nylon is a linear, polyamide polymer. The nylon 6,6 polymer has a linear zig-zag arrangement of carbon (C) atoms. The carbon atoms can form four single covalent bonds, which are arranged about the carbon atom like vertices of a triangular pyramid (i.e. a tetrahedron). The tetrahedral arrangement of bonds causes the carbon atoms to form a zig-zag but linear polymer. The polymer configuration is partly responsible for the very good elastic properties of nylon.
The table below summarises the most relevant physical data for the two most common types of nylon fibers.
Physical data for nylon polymers.
Courtesy of reference[1].
The most important chemical group in the nylon polymer is the polar amide group, -CO-NH- (note: C is for carbon, O is for oxygen, N is for nitrogen and H for is for hydrogen). This owes its polarity to the slightly negative charge on the oxygen atom and is part of the carbonyl group (i.e. the -CO- group of atoms) and on the slightly positive charge of the hydrogen atom in the imino group (i.e. the -NH- group of atoms). These chemical groups are the ones which will form the hydrogen bonds in the nylon polymer system. The terminal groups on the nylon polymer provide the sites for the dye molecules.
The nylon 6,6 polymer system showing its zig-zag structure.The degree of polymerisation (labeled n) is of the order of 50-60.
Courtesy of reference[1].
The polymer system of nylon is about 65-85% crystalline and correspondingly about 35-15% amorphous. This gives nylon a very crystalline, very well aligned or oriented polymer system, with the inter-polymer distances on average about 0.3 mm This very short inter-polymer distance enables the nylon polymer to form an optimum number of strong, uniform hydrogen bonds.
Part of the crystalline portion of nylon 6,6. Note the nylon polymer systems are so close together that hydrogen bonds can be formed between them. The hydrogen bonds are represented by the black oval links between the O and H atoms of adjoining nylon polymers.
Courtesy of reference[1].
Reaction to Heat
Nylon is a thermoplastic fiber. The melting point of nylon 6,6 is 250oC, and that of nylon 6 is lower at 215oC. Ironing temperatures above 150oC should be avoided for both kinds of nylon, because of the danger of the fabric becoming glazed.
Because to their thermoplastic nature, fabrics made from nylon yarns can be heat set - either into pleats or into a stable flat form. Such heat setting helps with easy-care properties during laundering.
Polyamides which have aromatic groups (Kevlar, Nomex) have their molecular chains packed much closer together. This results not only in higher fiber density, but also in stronger forces of attraction between the molecular chains. When heat energy vibrates the molecules, these stronger attractive forces prevent the chains from separating from each other until much higher temperatures (350oC and more) are reached.
Flammability
When a material ignites (catches fire) its molecules react with the oxygen in air. The molecules break down to smaller components and release energy in the form of heat. On burning, hard tan beads remain.
As they burn, ordinary nylons give off acrid fumes and drip and melt away from the source of the flame. Nylon underwear worn under flammable garments can melt onto the skin and cause severe burns, without actually supporting the fire. After the Falklands war between Britain and Argentina (1982), the British navy banned nylon underwear because of terrible burns caused in this way,
Aromatic polyamides (aramids like Kevlar and Nomex) do not ignite or burn because of the very high energies involved in separating their molecules, and because the products of degradation of those aromatic molecules do not support combustion.
Fiber Strength
The strength of nylon can be regulated through the amount of cold drawing to which it is subjected. Where tenacity is very high, the extensibility and pliability are low. A special feature is that nylon has a very high strength even when knotted. This certainly is a help to fisherman and sailors since fishing lines and sails are made from nylon! As nylon does not absorb water, its strength is not greatly reduced on wetting.
The high strength of Kevlar allows the manufacture of lightweight and low bulk bullet resistant vests, which can be disguised as part of normal clothing. The vests, consisting of multiple layers of woven Kevlar, can convert a potentially lethal hand-gun attack into a severe bruise. Each successive layer of fabric serves to slow the bullet so that it stops before it can penetrate the body. Although other fabrics can confer a similar protection, many more layers (and so greater bulk) are needed. Bruising from the impact of the bullet may be severe enough to warrant hospitalisation, and the lightweight vests do not protect against high-powered rifles or against stabbing thrusts with weapons such as ice-picks.
Kevlar bullet proof vest.
Moisture Absorbency
Moisture is absorbed by nylon at the polar sites provided by the amide groups. The more crystalline the fiber the less moisture it absorbs.
Generally, at 65% relative humidity and 20oC, nylon absorbs only 4.2% of its mass in water. As it does not absorb a great deal of water on wetting, it dries rapidly - a useful attribute for laundering.
Static Electricity
The electrical conductivity of nylon is low. Unless the atmosphere is very humid, nylon fabrics are prone to generate static electricity.
The problem of static may be tackled in three ways. During manufacture the fibers may be coated with an electrically conductive film of polymer. The fibers may be given a "lifetime" conductivity by charged molecules added at the melt stage of the polymer. These molecules migrate to the surface during wear, and neutralise any charge, which may accumulate. If the fibers have not been treated during manufacture, or if these treatments have not proved satisfactory, nylon fabrics may be treated after each laundering by adding an anionic fabric conditioner to the rinse.
Drape
The drape of nylon fibers depends on the diameter of the filaments and the extent of crystallinity.
Qiana is a nylon fiber manufactured as fine filaments to produce a silk-like drape. Antron and Anso are nylon filaments for carpet pile. Because of their thickness and stiffness they have particularly poor drape properties.
The final drape of the fabric owes much to features of yarn and fabric construction as well.
Elasticity and Resilience
Nylon is a particularly resilient fiber. Fabrics made from nylon recover readily from creasing or wrinkling. If stretched as much as 8%, nylon will still have 100% elastic recovery, although it will take some time to return completely to its original dimensions. After an extension of 16% it has a 91% recovery.
Abrasion Resistance
The abrasion resistance of nylon is important in many industrial applications - belting, ropes, carpeting. In straight-forward rubbing tests, nylon withstands abrasion far better than any other fiber. For that reason, it is often blended with extremely resilient wool to yield excellent carpets.
Dye Affinity
Nylons have amide groups, as well as -NH2 and -COOH- end groups at the end of each polymer chain. This makes them quite similar to protein fibers.
Wool and other protein fibers are dyed with acid dyes. This involves converting the -NH2 end groups into -NH+3 by adding acid (H+) to the dye bath. These are the dyeing sites to which negatively charged dye molecules (Dye- unit) are attached.
Nylon can be dyed in the same way, with acid dyes. Since nylon is much more crystalline than wool, dye penetration is more difficult. On the other hand, the molecular chains of nylon polymer are shorter than those of natural protein fibers. Hence, in a given weight there are more end-groups and so more possible dye sites.
In summary, nylon can be dyed with acid dyes because it contains amine (-NH2) end groups. Like triacetate, it can also be dyed with disperse dyes because it is hydrophobic.
Effect of Sunlight
If white nylon fabric is exposed to sunlight, it becomes yellow. So while cotton shirts may be hung out in the sun to dry, the same treatment will yellow nylon garments. If a nylon garment is treated with an optical brightening agent, this will make the nylon even more susceptible to damage from light. A nylon garment may appear bright white in sunlight, where the optical brightening agent is active, but quite yellow in shadowy folds. For this reason, nylons should be dried in a tumble dryer or in shade.
In spite of this draw back (polyester for example is not yellowed by sunlight), nylon is still far more resistant to degradation by sunlight than is silk which it originally sought to replace. After a 16-day controlled test in which silk lost 85% of its original tenacity, nylon, under identical conditions, lost only 50% of its strength.
Care
Nylon fabrics can be machine washed unless they have a very delicate construction or decorative design. Machine washing in warm water may be necessary to remove soil thoroughly. Because of its heat conductivity, nylon should not be subjected to very hot water or high dryer heat. It is a so called scavenger of colors, that is, it picks up dirt and color from other fabrics. Therefore white or pastel nylons should not be washed with colored or heavily soiled garments. Thorough rinsing to remove soil and soap deposits will prevent greying. A water softener in the first rinse may be necessary in hard water areas. A fabric softener in the last rinse helps to eliminate static electricity.
Waterborne stains wash out easily. Oil or grease stains may be removed with a cleansing solvent. They may also be removed by rubbing liquid detergent into stained areas with fingers or a brush; let stand for 15 minutes before washing. Greyed or yellowed nylon may be whitened by using a commercial color remover and following the directions on the package.
Uses
Nylon is a leading yarn for lingerie and hosiery, as it is strong, sheer, stretches, and returns to shape, and dries easily. Because of its strength and ability to be made into warm, windproof fabrics, it is used for ski clothes. Its strength and quick drying properties make it ideal for swimwear. It is often blended with other fibers to add abrasion resistance. Only a small amount blended with wool or cashmere can improve the wear at such stress points as sleeve edges, buttonholes and collars.
Physical Properties
Tenacity
The good to very good tenacity of nylon is due to its very crystalline polymer system and the excellent potential of the nylon polymers to form hydrogen bonds.
Nylon 6,6 illustrates very well how relatively short polymers are aligned to form a very crystalline polymer system containing hydrogen bonds of the strongest kind; that is, those between hydrogen and oxygen atoms (see diagram above). The result is a strong, elastic and durable fiber.
The loss of tenacity by nylon when wet is due to water molecules hydrolyzing a significant number of hydrogen bonds in the amphorous regions of the polymer system.
Elastic-Plastic Nature
The very good elastic property of nylon filaments or staple fibers is due to the very regular grid of strong hydrogen bonds in the nylon polymer system. As these hydrogen bonds operate over very short distances, they are able to exert their optimum strength, preventing polymer slippage and causing the polymers to return to their original position in the polymer system, once the strain has been removed from the nylon textile material. This means that nylon textile materials return readily to their original configuration, shedding any wrinkles or creases. There is a limit to which this can occur. Severe straining of the nylon polymer will cause hydrogen bond breakage, resulting in polymer slippage. This may result in distortion, wrinkling or creasing of the nylon textile material.
It has been estimated that about 22% of the elasticity of nylon filaments or staple fibers is due to the zig-zag configuration of the nylon when a load is applied. The zig-zag configuration is only possible because of the very strong bonds, namely hydrogen bonds in the nylon 6,6, polymer system.
Weight for weight nylon 6,6 is the toughest textile fiber in common use. The toughness of nylon is due to its elasticity and is related to the grid of very strong hydrogen bonds. It is the strength of these hydrogen bonds plus the inherent strength of the nylon polymer itself which contributes to the toughness and durability of nylon textile material.
The loss in elasticity and the resultant increase in extensibility of nylon filaments or staple fibers when nylon is wet is due to water molecules hydrolyzing a significant number of hydrogen bonds in the amorphous regions of the polymer system.
The medium to hard handle of nylon filaments or staple fibers is due to nylon's very crystalline polymer system and the grid of strong hydrogen bonds. These two form a rather rigid polymer system, which does not permit the nylon filament or staple fiber to give or yield readily.
Hygroscopic Nature
Nylon filaments or staple fibers are not absorbent even though there is relatively strong attraction for water molecules by the polar amide groups. Nylon's very crystalline polymer system allows for few water molecules to be absorbed. The nylon fiber registered under the trade mark Qiana is claimed to be more absorbent than all other nylon types. The basis of this claim is that its nylon polymers contain hydroxyl groups; that is, -OH groups. These more polar groups attract more water molecules. In addition the Qiana polymer is somewhat more amorphous enabling a few more water molecules to enter the polymer system.
Nylon textile materials readily develop static electricity (see above) as they are unable to absorb sufficient water molecules to dissipate any build up of it. Nylon sold as "anti-static" nylon has had compounds containing hydroxyl groups (-OH) added to its spinning solutions. The addition of such compounds will attract an increased number of water molecules because of the polarity of the hydroxyl groups and will thus minimize the build up of static electricity.
Thermal Properties
There is no satisfactory explanation as yet for the poor heat conductivity of nylon and its low heat resistance. Heat causes the nylon polymers to become excited and this results in a breakdown of inter-polymer bonding. The fact that nylon becomes limp when warmed illustrates this. The handle is restored as soon as the nylon is cooled because most of the broken hydrogen bonds are reformed.
The application of excessive heat to the polymer system of nylon causes the polymers to become so excited that most of the nylon textile material melts. The application of even more heat will result in burning.
If heat is applied under controlled conditions so as to break a few of the inter-polymer hydrogen bonds, the nylon material can be heat set (see below). During heat setting of nylon, or any other thermoplastic textile material, the objective is to break those hydrogen bonds which are under strain to enable the material to assume the desired configuration.
The three steps involved in heat setting a fiber whose polymer system is mainly held together with hydrogen bonds (e.g. nylon) are as follows:
(i) The hydrogen bonds (shown as fine lines above) are formed in relaxed positions, across short distances, thus holding the fiber in a relaxed configuration.
(ii) The fiber is now bent. As it curves around the bend, its surface on the outside of the curvature expands, whilst the surface on the inside of the curve contracts. This strains the hydrogen bonds (marked with a dot) because they have reached across a relatively great distance.
(iii) Applying heat or kinetic energy causes the strained hydrogen bonds to rupture. On cooling, the hydrogen bonds reform but across the shortest possible distance. This will cause the fiber to retain the bent configuration. The fiber is now said to be heat set.
Chemical Properties
Effect of Acids
Nylon is less resistant to acids than it is to alkalis. The amide group in the nylon polymers are readily hydrolyzed under acidic conditions. Acid hydrolysis fragments nylon polymers with the result that the effectiveness of the inter-polymer hydrogen bonding is lost, and the nylon filament or staple fiber is weakened. Exposure to slightly acidic conditions, such as perspiration or polluted atmosphere, will cause some polymer hydrolysis on the surface of the filament or staple fibers. This changes their light reflection properties somewhat, with the result that white nylon textile materials will assume a yellow hue, whilst colored nylon may appear duller.
It should be pointed out that the yellowing of white nylon may also be due to the absorption of molecules of body oils and fats by the nylon polymer system. The presence of the molecules on the surface of the polymer alters the reflection of light and results in a yellowing of white nylon textiles or a dulling of colored materials.
Effect of Alkalis
Prolonged and frequent exposure to alkalis will cause significant alkali hydrolysis of nylon polymers. This is noticed as a weakening of the nylon textile material. The effect of alkalis on the nylon polymer is the same as for acid hydrolysis; namely, yellowing of the white fiber or dulling of colored nylon textiles.
Effect of Bleaches
Nylon textile materials are inherently white and do not require bleaching. On the few occasions when bleaching is necessary, the only bleaches that can be used under slightly alkaline conditions are oxidizing bleaches. These bleaches have the least detrimental effect upon the nylon polymer system. The most common oxidizing bleaches used on nylon are peracetic acid, hydrogen peroxide and sodium chlorite. The bleaching effect of these chemicals is not fully understood. It is considered that the oxygen from these bleaches reacts with the degraded surface polymers, which cause the discolouration of the nylon to form water soluble products, which are washed off the textile material by the bleach liquor.
Bleaching is not permanent. In fact, nylon that has been bleached may discolor more readily than nylon which has not.
Effect of Sunlight and Weather
Nylon has only a fair resistance to sunlight and weather. This is attributed to the ultraviolet rays of sunlight causing the imino groups of the amide group to react with the oxygen in the air. This produces groups that are more reactive and more water soluble. The groups that are produced react further causing polymer fragmentation and the breaking of inter-polymer hydrogen bonds resulting in the severe weakening of the nylon textile material.
In polluted atmosphere, which is acidic, these processes are accelerated.
Color-Fastness
The following classes of dye are most frequently used to dye or print nylon textile materials: acid, disperse and premetallized dyes.
Acid Dyes
Acid dye molecules are sodium salts and will dissociate in an aqueous dye liquor to form the acid dye anion. The dye anion is negatively charged and is attracted to the cationic or positively charged groups on the nylon polymer. The cationic sites are the terminal amino groups, which have acquired a hydrogen cation from the acid in the dye liquor.
The wash fastness of the acid dye or printed nylon textile materials is fair to good and depends on the specific acid dye. The strength of the bond between the dye molecules and the nylon polymer varies with different dyes. If the bond is relatively weak, alkaline detergents can cause color to be removed from the nylon textile materials.
Premetallized Dyes
The molecules of premetallized dyes contain a metal atom which is usually chromium (Cr). The presence of the metal atom provides the premetallized dyes molecule with enough stability to resist the degrading effects of the sun's ultraviolet radiation. The stable electron arrangement of the dye molecule is considered to be the main reason for the good light-fastness of premetallized dyed or printed nylon textile materials. As with acid dyes, breakdown of the nylon polymers in sunlight contributes towards the fading of premetallized dyed or printed textile materials. Premetallized dye molecules dissociate to produce a dye anion in an aqueous dye liquor, which is attracted to the cationic groups in the nylon polymers. The premetallized dye anion is larger than the acid dyes. This results in premetallized dyes and printed nylon textile materials having a very good wash fastness.
Disperse Dyes
The molecules of disperse dyes are non-polar and hydrophobic (water hating). Disperse dye molecules are more substantive to the hydrophobic polymer system of nylon than they are to the aqueous dye liquor. Disperse dyes have a fair to good light-fastness on dyed and printed nylon textile materials. This may be attributed to the aromatic (or ring) structures within disperse dye molecules. These aromatic structures provide the disperse dye molecules with a reasonably stable electron arrangement, which resists the degrading effects of the sun's ultraviolet radiation.
The good wash fastness of disperse colored nylon materials is mainly due to the insolubility in water of disperse dyes making it difficult for dye molecules to be washed out of the polymer system of the nylon filament or staple fiber.
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).
[3] E. J. Gawne, Fabrics for Clothing, 3rd Edition, Chas. A. Bennett Co., Peoria (1973).
This is the thirtieth 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
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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
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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
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Introduction
The term "nylon" was derived from "no-run", the name originally considered by its inventors in order to emphasize the durability of ladies' hosiery which was manufactured from it.
Nylon is a man-made synthetic polymer, polyamide filament or staple fiber. Textile materials composed of nylon tend to be light in weight because the density of nylon filaments or staple fibers is 1.14 g cm-3.
The most important polyamide fiber in terms of the amount that is produced is nylon 6,6; that is, in chemical terms a polyhexamethylene adipamide. The notion 6,6 denotes that there are two monomers, each containing six carbon atoms, which are required to form the polymer of this type of nylon (see below).
Nylon 6 is the second most important polyamide fiber. It is extruded from polycaprolactam. The notation 6 denotes it has only one monomer containing 6 carbon atoms required to polymerize this type of nylon.
This post will focus on nylon 6,6 and nylon 6 fibers. The following descriptions and explanations of the properties of nylon will be based on nylon 6,6 as the two nylon fibers have similar properties unless otherwise stated.
History
In 1939 the first nylon hosiery for women was marketed in limited quantity. Women found them to be stronger and sheerer than silk hosiery they had been wearing. During World War II, the supplies of nylon was sufficient only for military purposes. Parachutes were made of nylon as were tents and many garments.
After the war when nylon hose came on the market again, women were almost frantic to obtain them. Hours before opening time people would line up outside any store where nylon was sold. As the stockings were limited to one pair per customer in the USA, women would enlist their husbands and children to stand in line for them. If their size was sold out when they finally reached the counter, they would buy any size available, in order to give as gifts to friends or to barter.
Courtesy of German Hosiery Museum.
Since then nylon has become plentiful and is in demand for clothing and industrial uses. Today it is made by many companies throughout the world. In Germany it is called Perlon; in Great Britain it is called Brinylon; in Mexico, Nyfil; and in Australia and the USA as nylon.
Source and Production
The term nylon refers to a whole group of fibers, not just one. Nylon is a generic term that is used for a group of protein-like chemical fibers. The method of fabrication depends upon the intended use. The chemical elements present in petroleum, air, water and natural gas are combined to form a nylon polymer, which is processed in molten form and them pumped through a spinneret, air cooled, and solidified into filaments.
Nylon can be made into both filament and short, staple lengths. Of course it can be drawn in different fiber shapes. The original nylon has a cross-section that was round.
The circular, featureless cross-section of nylon, magnified 500 times.
Note: the specks are that of a delustering agent.
A more recent nylon named antron has a trilobal cross-section. Hence it is more opaque and has a silk-like feel than regular nylon.
A cross-section of tri-lobal or profiled nylon, magnified 1000 times. Tri-lobal nylon is a man-made, readily available fiber whose cross-section has been purposely modified.
In summary nylons can be varied by both physical and chemical means to produce an enormous range of fibers with a wide spectrum of properties. However, if one property is changed (say pliability increased) then it is usually at the expense of another equally desirable property (e.g. strength decreased). So in spite of their variability, it is not quite possible to tailor-make synthetic fibers that are perfect for any application. Nevertheless, nylon fibers are used with great effect in many domestic and industrial applications.
General Properties of Nylon Polymers and Fibers
Fiber Density
The density of nylon filaments or staple fibers is 1.14 g cm-3, which makes them light weight fibers.
Micro Structure of Nylon Fibers
Nylon filaments or staple fibers do not have an identifiable micro-structure. Their longitudinal structure is very regular and essentially featureless, because of their almost circular cross section (see above). The nylon filament or staple fiber may, in fact, be likened to a glass rod.
A combination of factors is responsible for the rod-like, featureless microscopic appearance of nylon. These are the viscosity of the spinning solution, the nature of the polyamide material and the rate of coagulation in cold air of the extruded stream of polymers. These factors cause the coagulated filament to retain the round cords-section of the spinneret orifice.
Macro Structure of Nylon
Nylon is a regular, translucent, fine filament or staple fiber. Staple fibers of nylon are usually crimped for reasons similar to those given by viscose (see past post). Nylon filaments are textured for reason given for crimping the staple fibers.
The length of nylon filaments is limited only by the yarn package onto which it is wound. The length of the staple fibers tends to be comparable to that of either cotton or wool, depending on end-use requirements. The fiber length to breadth ratio usually exceeds 2000:1. This ensures that even the shorter nylon staple fibers can be satisfactorily spun into yarn.
The descriptions and explanations given for viscose of fiber color, luster and translucency are also applicable to the nylon fibers.
The Nylon Polymer
Nylon is a linear, polyamide polymer. The nylon 6,6 polymer has a linear zig-zag arrangement of carbon (C) atoms. The carbon atoms can form four single covalent bonds, which are arranged about the carbon atom like vertices of a triangular pyramid (i.e. a tetrahedron). The tetrahedral arrangement of bonds causes the carbon atoms to form a zig-zag but linear polymer. The polymer configuration is partly responsible for the very good elastic properties of nylon.
The table below summarises the most relevant physical data for the two most common types of nylon fibers.
Courtesy of reference[1].
The most important chemical group in the nylon polymer is the polar amide group, -CO-NH- (note: C is for carbon, O is for oxygen, N is for nitrogen and H for is for hydrogen). This owes its polarity to the slightly negative charge on the oxygen atom and is part of the carbonyl group (i.e. the -CO- group of atoms) and on the slightly positive charge of the hydrogen atom in the imino group (i.e. the -NH- group of atoms). These chemical groups are the ones which will form the hydrogen bonds in the nylon polymer system. The terminal groups on the nylon polymer provide the sites for the dye molecules.
Courtesy of reference[1].
The polymer system of nylon is about 65-85% crystalline and correspondingly about 35-15% amorphous. This gives nylon a very crystalline, very well aligned or oriented polymer system, with the inter-polymer distances on average about 0.3 mm This very short inter-polymer distance enables the nylon polymer to form an optimum number of strong, uniform hydrogen bonds.
Courtesy of reference[1].
Reaction to Heat
Nylon is a thermoplastic fiber. The melting point of nylon 6,6 is 250oC, and that of nylon 6 is lower at 215oC. Ironing temperatures above 150oC should be avoided for both kinds of nylon, because of the danger of the fabric becoming glazed.
Because to their thermoplastic nature, fabrics made from nylon yarns can be heat set - either into pleats or into a stable flat form. Such heat setting helps with easy-care properties during laundering.
Polyamides which have aromatic groups (Kevlar, Nomex) have their molecular chains packed much closer together. This results not only in higher fiber density, but also in stronger forces of attraction between the molecular chains. When heat energy vibrates the molecules, these stronger attractive forces prevent the chains from separating from each other until much higher temperatures (350oC and more) are reached.
Flammability
When a material ignites (catches fire) its molecules react with the oxygen in air. The molecules break down to smaller components and release energy in the form of heat. On burning, hard tan beads remain.
As they burn, ordinary nylons give off acrid fumes and drip and melt away from the source of the flame. Nylon underwear worn under flammable garments can melt onto the skin and cause severe burns, without actually supporting the fire. After the Falklands war between Britain and Argentina (1982), the British navy banned nylon underwear because of terrible burns caused in this way,
Aromatic polyamides (aramids like Kevlar and Nomex) do not ignite or burn because of the very high energies involved in separating their molecules, and because the products of degradation of those aromatic molecules do not support combustion.
Fiber Strength
The strength of nylon can be regulated through the amount of cold drawing to which it is subjected. Where tenacity is very high, the extensibility and pliability are low. A special feature is that nylon has a very high strength even when knotted. This certainly is a help to fisherman and sailors since fishing lines and sails are made from nylon! As nylon does not absorb water, its strength is not greatly reduced on wetting.
The high strength of Kevlar allows the manufacture of lightweight and low bulk bullet resistant vests, which can be disguised as part of normal clothing. The vests, consisting of multiple layers of woven Kevlar, can convert a potentially lethal hand-gun attack into a severe bruise. Each successive layer of fabric serves to slow the bullet so that it stops before it can penetrate the body. Although other fabrics can confer a similar protection, many more layers (and so greater bulk) are needed. Bruising from the impact of the bullet may be severe enough to warrant hospitalisation, and the lightweight vests do not protect against high-powered rifles or against stabbing thrusts with weapons such as ice-picks.
Moisture Absorbency
Moisture is absorbed by nylon at the polar sites provided by the amide groups. The more crystalline the fiber the less moisture it absorbs.
Generally, at 65% relative humidity and 20oC, nylon absorbs only 4.2% of its mass in water. As it does not absorb a great deal of water on wetting, it dries rapidly - a useful attribute for laundering.
Static Electricity
The electrical conductivity of nylon is low. Unless the atmosphere is very humid, nylon fabrics are prone to generate static electricity.
The problem of static may be tackled in three ways. During manufacture the fibers may be coated with an electrically conductive film of polymer. The fibers may be given a "lifetime" conductivity by charged molecules added at the melt stage of the polymer. These molecules migrate to the surface during wear, and neutralise any charge, which may accumulate. If the fibers have not been treated during manufacture, or if these treatments have not proved satisfactory, nylon fabrics may be treated after each laundering by adding an anionic fabric conditioner to the rinse.
Drape
The drape of nylon fibers depends on the diameter of the filaments and the extent of crystallinity.
Qiana is a nylon fiber manufactured as fine filaments to produce a silk-like drape. Antron and Anso are nylon filaments for carpet pile. Because of their thickness and stiffness they have particularly poor drape properties.
The final drape of the fabric owes much to features of yarn and fabric construction as well.
Elasticity and Resilience
Nylon is a particularly resilient fiber. Fabrics made from nylon recover readily from creasing or wrinkling. If stretched as much as 8%, nylon will still have 100% elastic recovery, although it will take some time to return completely to its original dimensions. After an extension of 16% it has a 91% recovery.
Abrasion Resistance
The abrasion resistance of nylon is important in many industrial applications - belting, ropes, carpeting. In straight-forward rubbing tests, nylon withstands abrasion far better than any other fiber. For that reason, it is often blended with extremely resilient wool to yield excellent carpets.
Dye Affinity
Nylons have amide groups, as well as -NH2 and -COOH- end groups at the end of each polymer chain. This makes them quite similar to protein fibers.
Wool and other protein fibers are dyed with acid dyes. This involves converting the -NH2 end groups into -NH+3 by adding acid (H+) to the dye bath. These are the dyeing sites to which negatively charged dye molecules (Dye- unit) are attached.
Nylon can be dyed in the same way, with acid dyes. Since nylon is much more crystalline than wool, dye penetration is more difficult. On the other hand, the molecular chains of nylon polymer are shorter than those of natural protein fibers. Hence, in a given weight there are more end-groups and so more possible dye sites.
In summary, nylon can be dyed with acid dyes because it contains amine (-NH2) end groups. Like triacetate, it can also be dyed with disperse dyes because it is hydrophobic.
Effect of Sunlight
If white nylon fabric is exposed to sunlight, it becomes yellow. So while cotton shirts may be hung out in the sun to dry, the same treatment will yellow nylon garments. If a nylon garment is treated with an optical brightening agent, this will make the nylon even more susceptible to damage from light. A nylon garment may appear bright white in sunlight, where the optical brightening agent is active, but quite yellow in shadowy folds. For this reason, nylons should be dried in a tumble dryer or in shade.
In spite of this draw back (polyester for example is not yellowed by sunlight), nylon is still far more resistant to degradation by sunlight than is silk which it originally sought to replace. After a 16-day controlled test in which silk lost 85% of its original tenacity, nylon, under identical conditions, lost only 50% of its strength.
Care
Nylon fabrics can be machine washed unless they have a very delicate construction or decorative design. Machine washing in warm water may be necessary to remove soil thoroughly. Because of its heat conductivity, nylon should not be subjected to very hot water or high dryer heat. It is a so called scavenger of colors, that is, it picks up dirt and color from other fabrics. Therefore white or pastel nylons should not be washed with colored or heavily soiled garments. Thorough rinsing to remove soil and soap deposits will prevent greying. A water softener in the first rinse may be necessary in hard water areas. A fabric softener in the last rinse helps to eliminate static electricity.
Waterborne stains wash out easily. Oil or grease stains may be removed with a cleansing solvent. They may also be removed by rubbing liquid detergent into stained areas with fingers or a brush; let stand for 15 minutes before washing. Greyed or yellowed nylon may be whitened by using a commercial color remover and following the directions on the package.
Uses
Nylon is a leading yarn for lingerie and hosiery, as it is strong, sheer, stretches, and returns to shape, and dries easily. Because of its strength and ability to be made into warm, windproof fabrics, it is used for ski clothes. Its strength and quick drying properties make it ideal for swimwear. It is often blended with other fibers to add abrasion resistance. Only a small amount blended with wool or cashmere can improve the wear at such stress points as sleeve edges, buttonholes and collars.
Physical Properties
Tenacity
The good to very good tenacity of nylon is due to its very crystalline polymer system and the excellent potential of the nylon polymers to form hydrogen bonds.
Nylon 6,6 illustrates very well how relatively short polymers are aligned to form a very crystalline polymer system containing hydrogen bonds of the strongest kind; that is, those between hydrogen and oxygen atoms (see diagram above). The result is a strong, elastic and durable fiber.
The loss of tenacity by nylon when wet is due to water molecules hydrolyzing a significant number of hydrogen bonds in the amphorous regions of the polymer system.
Elastic-Plastic Nature
The very good elastic property of nylon filaments or staple fibers is due to the very regular grid of strong hydrogen bonds in the nylon polymer system. As these hydrogen bonds operate over very short distances, they are able to exert their optimum strength, preventing polymer slippage and causing the polymers to return to their original position in the polymer system, once the strain has been removed from the nylon textile material. This means that nylon textile materials return readily to their original configuration, shedding any wrinkles or creases. There is a limit to which this can occur. Severe straining of the nylon polymer will cause hydrogen bond breakage, resulting in polymer slippage. This may result in distortion, wrinkling or creasing of the nylon textile material.
It has been estimated that about 22% of the elasticity of nylon filaments or staple fibers is due to the zig-zag configuration of the nylon when a load is applied. The zig-zag configuration is only possible because of the very strong bonds, namely hydrogen bonds in the nylon 6,6, polymer system.
Weight for weight nylon 6,6 is the toughest textile fiber in common use. The toughness of nylon is due to its elasticity and is related to the grid of very strong hydrogen bonds. It is the strength of these hydrogen bonds plus the inherent strength of the nylon polymer itself which contributes to the toughness and durability of nylon textile material.
The loss in elasticity and the resultant increase in extensibility of nylon filaments or staple fibers when nylon is wet is due to water molecules hydrolyzing a significant number of hydrogen bonds in the amorphous regions of the polymer system.
The medium to hard handle of nylon filaments or staple fibers is due to nylon's very crystalline polymer system and the grid of strong hydrogen bonds. These two form a rather rigid polymer system, which does not permit the nylon filament or staple fiber to give or yield readily.
Hygroscopic Nature
Nylon filaments or staple fibers are not absorbent even though there is relatively strong attraction for water molecules by the polar amide groups. Nylon's very crystalline polymer system allows for few water molecules to be absorbed. The nylon fiber registered under the trade mark Qiana is claimed to be more absorbent than all other nylon types. The basis of this claim is that its nylon polymers contain hydroxyl groups; that is, -OH groups. These more polar groups attract more water molecules. In addition the Qiana polymer is somewhat more amorphous enabling a few more water molecules to enter the polymer system.
Nylon textile materials readily develop static electricity (see above) as they are unable to absorb sufficient water molecules to dissipate any build up of it. Nylon sold as "anti-static" nylon has had compounds containing hydroxyl groups (-OH) added to its spinning solutions. The addition of such compounds will attract an increased number of water molecules because of the polarity of the hydroxyl groups and will thus minimize the build up of static electricity.
Thermal Properties
There is no satisfactory explanation as yet for the poor heat conductivity of nylon and its low heat resistance. Heat causes the nylon polymers to become excited and this results in a breakdown of inter-polymer bonding. The fact that nylon becomes limp when warmed illustrates this. The handle is restored as soon as the nylon is cooled because most of the broken hydrogen bonds are reformed.
The application of excessive heat to the polymer system of nylon causes the polymers to become so excited that most of the nylon textile material melts. The application of even more heat will result in burning.
If heat is applied under controlled conditions so as to break a few of the inter-polymer hydrogen bonds, the nylon material can be heat set (see below). During heat setting of nylon, or any other thermoplastic textile material, the objective is to break those hydrogen bonds which are under strain to enable the material to assume the desired configuration.
(i) The hydrogen bonds (shown as fine lines above) are formed in relaxed positions, across short distances, thus holding the fiber in a relaxed configuration.
(ii) The fiber is now bent. As it curves around the bend, its surface on the outside of the curvature expands, whilst the surface on the inside of the curve contracts. This strains the hydrogen bonds (marked with a dot) because they have reached across a relatively great distance.
(iii) Applying heat or kinetic energy causes the strained hydrogen bonds to rupture. On cooling, the hydrogen bonds reform but across the shortest possible distance. This will cause the fiber to retain the bent configuration. The fiber is now said to be heat set.
Chemical Properties
Effect of Acids
Nylon is less resistant to acids than it is to alkalis. The amide group in the nylon polymers are readily hydrolyzed under acidic conditions. Acid hydrolysis fragments nylon polymers with the result that the effectiveness of the inter-polymer hydrogen bonding is lost, and the nylon filament or staple fiber is weakened. Exposure to slightly acidic conditions, such as perspiration or polluted atmosphere, will cause some polymer hydrolysis on the surface of the filament or staple fibers. This changes their light reflection properties somewhat, with the result that white nylon textile materials will assume a yellow hue, whilst colored nylon may appear duller.
It should be pointed out that the yellowing of white nylon may also be due to the absorption of molecules of body oils and fats by the nylon polymer system. The presence of the molecules on the surface of the polymer alters the reflection of light and results in a yellowing of white nylon textiles or a dulling of colored materials.
Effect of Alkalis
Prolonged and frequent exposure to alkalis will cause significant alkali hydrolysis of nylon polymers. This is noticed as a weakening of the nylon textile material. The effect of alkalis on the nylon polymer is the same as for acid hydrolysis; namely, yellowing of the white fiber or dulling of colored nylon textiles.
Effect of Bleaches
Nylon textile materials are inherently white and do not require bleaching. On the few occasions when bleaching is necessary, the only bleaches that can be used under slightly alkaline conditions are oxidizing bleaches. These bleaches have the least detrimental effect upon the nylon polymer system. The most common oxidizing bleaches used on nylon are peracetic acid, hydrogen peroxide and sodium chlorite. The bleaching effect of these chemicals is not fully understood. It is considered that the oxygen from these bleaches reacts with the degraded surface polymers, which cause the discolouration of the nylon to form water soluble products, which are washed off the textile material by the bleach liquor.
Bleaching is not permanent. In fact, nylon that has been bleached may discolor more readily than nylon which has not.
Effect of Sunlight and Weather
Nylon has only a fair resistance to sunlight and weather. This is attributed to the ultraviolet rays of sunlight causing the imino groups of the amide group to react with the oxygen in the air. This produces groups that are more reactive and more water soluble. The groups that are produced react further causing polymer fragmentation and the breaking of inter-polymer hydrogen bonds resulting in the severe weakening of the nylon textile material.
In polluted atmosphere, which is acidic, these processes are accelerated.
Color-Fastness
The following classes of dye are most frequently used to dye or print nylon textile materials: acid, disperse and premetallized dyes.
Acid Dyes
Acid dye molecules are sodium salts and will dissociate in an aqueous dye liquor to form the acid dye anion. The dye anion is negatively charged and is attracted to the cationic or positively charged groups on the nylon polymer. The cationic sites are the terminal amino groups, which have acquired a hydrogen cation from the acid in the dye liquor.
The wash fastness of the acid dye or printed nylon textile materials is fair to good and depends on the specific acid dye. The strength of the bond between the dye molecules and the nylon polymer varies with different dyes. If the bond is relatively weak, alkaline detergents can cause color to be removed from the nylon textile materials.
Premetallized Dyes
The molecules of premetallized dyes contain a metal atom which is usually chromium (Cr). The presence of the metal atom provides the premetallized dyes molecule with enough stability to resist the degrading effects of the sun's ultraviolet radiation. The stable electron arrangement of the dye molecule is considered to be the main reason for the good light-fastness of premetallized dyed or printed nylon textile materials. As with acid dyes, breakdown of the nylon polymers in sunlight contributes towards the fading of premetallized dyed or printed textile materials. Premetallized dye molecules dissociate to produce a dye anion in an aqueous dye liquor, which is attracted to the cationic groups in the nylon polymers. The premetallized dye anion is larger than the acid dyes. This results in premetallized dyes and printed nylon textile materials having a very good wash fastness.
Disperse Dyes
The molecules of disperse dyes are non-polar and hydrophobic (water hating). Disperse dye molecules are more substantive to the hydrophobic polymer system of nylon than they are to the aqueous dye liquor. Disperse dyes have a fair to good light-fastness on dyed and printed nylon textile materials. This may be attributed to the aromatic (or ring) structures within disperse dye molecules. These aromatic structures provide the disperse dye molecules with a reasonably stable electron arrangement, which resists the degrading effects of the sun's ultraviolet radiation.
The good wash fastness of disperse colored nylon materials is mainly due to the insolubility in water of disperse dyes making it difficult for dye molecules to be washed out of the polymer system of the nylon filament or staple fiber.
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).
[3] E. J. Gawne, Fabrics for Clothing, 3rd Edition, Chas. A. Bennett Co., Peoria (1973).
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