Textile Chemistry for the Artist S a r a Butler a n d Sally Malott Home Economics and Consumer Sciences, Miami University, Oxford, OH 45056 A knowledge of the chemistry of textiles can he a valuable aid to any artist dealing with fihers or fabrics, including the fiber artist, the textile designer, and the weaver. The chemical nature of the fiber is the primary determinant of general oerformance . o r o.~ e r t i e simportant to all consumers. Fiber chemistry is also the criticd factor in relation to properties important to the artist, such as reactions to dyes, bleaches, and solvents. This paper will focus on the chemistry of fibers considered to be the most commonly used by artists. In addition to discussion of the characteristics of these selected fibers, information will be presented regarding their reaction to what may be considered the agents of design, such as dyes, bleaches, and solvents. Fiber Classification Critical to an understanding of textile performance is a fiber classification system. Prior to the production of manufactured fibers, clnwification uf the n n t ~ ~ rfiber* a l wns relatively simplt:. Howewr, with tht:;idvent of man-made fil~rrs,amorenmplvx wstem w;~snect.wJrv. In IYtitr. the Textile Fihrr Product-. ~,~~~ Identification Act became effective. In addition to requiring laheline established " statine " fiber content. the lerislation generic classes for all manufactured fibers. In general, the fihers within a "eeneric class Dossess the same essential properties. Tahle 1 below outlines the maior natural and man-made fibers. The natural fibers are categorized by their source, e.g., cotton fibers come from the seed hair portion of the cotton plant. The man-made cellulosic and protein fibers are so called because the fiber originates from a cellulose or protein base which is then altered. The synthetic fibers are generated chemically and are devoid of any natural base. The classification system in Tahle 1 includes the most commonly used fibers which are also those considered to he of interest to the artist and are most readilv available. Many of the natural fibers in Table 1are not used in commercial textile manufacture but may be of design interest to the craitiman. Kapok, milkweed, and c.~ttuil,lor indance, are not viahle alternatives in general textile productim becausc their lvw cohesiveness dors not allow efficient spinning into yarns. They may, howe\.er, he considend h y the hnnd weavvr as an intrrestine textural addition, Simil.trl\.. .. be~allrrof harjh textural properties, jute and hemp are not commonly used in apparel, but may be of interest to artists. The protein specialty fihers are very desirable aesthetically as a class, hut their high cost prohibits widespread use. These minor fibers will not he discussed in detail. Characteristics of these fibers, however, are similar to those of other fibers in the same general category, many of which will he discussed in more depth.
Table 1. Overvlew of Textile Fibers I. Natural Flbers A. Natural Cellulosic 1. Seed hair fibers
A.
kapok milkweed d. cattail Stem fibers
3. triacelate
b. C.
2.
B. Man-Made Protein-&Ion C.
a. flax
b.
jute
hemp d. ramie 3. Leaf fibers a. abaca b. pina (pineapple) C. sisal 4. Nut husk fibars-coir (coconut) 0. Proteh 1. Animal hair fibers a. w w l b. specially (1) cashmere
Man-Made CeMulosic 1, rayon 2. acefate
a. canon
C,
Synthetic 1. nylon 2. polyester 3. acrylic 4. modacrylic 5. olefin 6. spandex 7. synthetic rubber
8. vinyon 9. saran 10, nylril
11. vinal 12. la~trile 13. aramid 14, novoloid 0. Mineral
(2) mohair (3) camel (4) llama (5) guanaco (6) vicuna
~
~~~
11. Manulanured Flbers
1. glass 2. metallic
(7) alpaca C.
fur fibers (1) mink
(2) muskrat (3) angora rabbit 2. Animal secretion-silk 3. Feathers C. Natural Mineral-asbestos D. Natural Robber
Performance Properties Resulting from the Chemical Structure Fiber performance is primarily affected by three chemical characteristics: the length and arrangement of the molecular chain and the nature of the molecular bonds. Generally long chain fibers, or those with a high degree of polymerization, are stronger. Fibers with oriented chains tend to be stronger than amorphous fihers. Higher levels of orientation or crystalline areas nossess a greater ~otentialfor bondine. Strone-hvdroeen . . bonds providr the grentrst amount of strength in the lil~ers with Van d r r N'aals 1'0n.e~occurrin): in weaker fibers. Cross-
Volume 58 Number 4
April 1981
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Table 2. Characteristics and Chemical Formulas or FTC Definitions of Selected Fibers Chemical Formula andlor FTC Definition
Fiber Name
Chemical and Physical Characteristics
Ceilulose conon flax
The basic unit of the cellulose molecule is the glucose unit which is composed of carbon. hydrogen. and oxygen. me chemical reactivity is related l o the three hydroxyl (OH) groups. The molecular chains are in spiral form. Physically. cotton is characterized by convollrtions. or ribbon-like twists. Flax is identified by crosswise markings caiied nodes. Both have a Central canal.
Protein woo1 silk
Protein fibers are composed of amino acids which have been formed into polypeptide chains. They contain carbon, hydrogen, oxygen, and nitrogen. Wool also contains sulfur. Protein fibers are amphoteric. Silk possesses extended polypeptide chains while wool has folded polypeptide chains held together by crosslinks. Silk is a smooth, highly cry~tallinafiber, and woai is a crimped fiber with more amorphous areas. Physically, wool is identified by its scaley outer surface.
Rayon
Rayon is a manufactured fiber composed of regenerated cellulose, as well as a manufacturedfiber composed of regenerated cellulose in which substituents have replaced not more than 15% of the hydrogens of the hydroxyl groups.
The molecular structure is cellulosic in nature; however, the chains are shorter and do not form as many crystaliites, creating a generally amorphous fiber. Physically, rayon is characterized by lengthwise striations and a serrated cross-section.
Acetate and Triacetate
Acetate is a manufactured fiber in which the fiber forming Substance is cellulose acetate where not less than 92% of the hydroxyl groups ate acetylated. The term triacetate may be used also as a generic description of the fiber.
Acetate is an ester of cellulose. In triacetate all of the hydroxyl groups have been replaced by acetyl groups. In acetate, two of the hydroxyl groups have been replaced by acetyl groups. The acetyl groups cause less crystallinity. There is a lack of hydrogen bonding. Both acetate and triacetate are thermoplastic.
Nylon is a manufactured fiber in which the fiber forming substance is any long chain. synthetic polyamide
The nylons are poiyamides with recurring amide groups. They all contain CHON. The nylons vary in chemioai arrangement and dearea of oolvrnerization. The molecular chains are lono and
in which less than 85% of the amide linkages are anached to two aromatic rings. Polyester
the different nylons.
Polyester fibers are manufactured fibers in which the fiber forming substance is any long chain polymer composed of at least 85% by weight of an ester of dihydricalcohol and terephthalic acid. (p-HOOC-OsHrCOOH).
Polyester fibers are made hom different kinds of terephthalate polymers. Molecular chains are straight and packed closely together. Chains are wellariented with very strong hydrogen bonds. Physically, polyester fibers are rod-like with varying cross sectiondl shapes.
Acrvlic fibers are manufactured fibers in which the fibav forming substance is a synthetic polymer composed of at least 85% by weight of acrylonitrile units. H I
Most acwlics are ~ o. ~ . o l v m or e roran ~ DOlvmers with UD to 75% . . additives. The resulting structure is less compact and oriented. Physically, acrylics have a dog-bone shaped cross-section.
CH,-C-
-
I
CN Modacrylic
Modacrvlic fibers are manufacturedfibers in which the fiber form ng woslance 09an) ong cnam synlhet c PO )n el cornpoceu 01 less lhan 85). OLI more ln3" 35% acrylonitrile units.
linking ties molecular chains together in a bridge fashion whichiestricts movement between chains and prevents slipvaee. The length and arrangement of the chains can be inas nylon and polyester are generally drawn out as they are extruded which orients the chains and increases the potential for the stronger hydrogen honds to occur. In general, fibers with high molecular orientation and strong honds have high strength, low elongation, and low absorption. Amorphous fibers tend to have weaker honds and are characterized by high elongation, high absorbency, and relatively low strength. Table 2 presents the chemical formulas and/or Federal Trade commission definitions for the selected fibers. The Textile Fiber Identification Act also established the FTC definitions for the man-made fibers. A brief review of the chemical and physical characteristics is included. Of greatest importance to the artist, however, are the resulting fiber properties. A discussion of the outstanding properties which 296
Journal o f Chemical Education
Chemicals In modacrviic other than acwlonitrlle are vinvl chloride (CH,CHCI), vinylidene chloride (CHCC12)or vinyl~dene dicyanide (CH2CONz).
are a consequence of chemical and physical properties follows. Natural Cellulosic
The properties of cotton vary to some extent according to the length of the fiber and where it is grown. Because of the length of the molecular chains, cotton is characterized by moderate strength which increases when wet. Wet processing techniaues. such as dveine and laundering. are therefore easilv performed: ~ b s o r b e k c y i shigh due toyhe presence of thk hvdroxvl erouvs: this allows for r a ~ i ddve oenetration, comfort in weaiini apparel, and no st& buiidui. Cotton can withstand hieh temueratures which means that fabrics can be boiled and arc n d hwmed dur:ng ironing I)isndrilntage-. g r f sotron include a luw resilirncs, a high fl;~tnrnnl~il~tv pot(,nt~ul. and a propensity for fading anddamage by mildew. One hundred percent cotton fabrics such as muslin are widely used by textile designers for printing and dyeing because of the distinct performance advantages. Flax, also a cellulosic fiber, has many properties similar to cotton, hut its stem source allows for some quite different
As a manufactured fiher, the properties of rayon can be altered to some extent. During processing, the breakdown of the molecular chains of the cellulose material is quite severe. Regular rayon, therefore, possesses the characteristics of an amorphous fiber with a low degree of polymerization: low streneth. - . low elasticitv. " , and high - absorption. The low elasticity, in combination with high elongation when wet, allows for a dimensionallv unstable fabric. The amorphous nature also allows for weak hpnding, which in turn res;lts in low resiliency. High Wet Modulus rayon is a modified rayon which has different processing stages and has been stretched. The result is a more crystalline and oriented structure with greater strength, particularly when wet. High Wet Modulus rayon is also characterized hv ereater elasticitv and resiliencv. the lack of crystallinity and strong Acetate, because bonds, tends to he a weak fiher with low elasticity and poor abrasion resistance. Absorbency is also low due to the lack of hydroxyl groups. Triacetate is similar to acetate in durability and absorbency but has the advantage of a higher melting point, which allows for commercial heat-setting for permanent shape. Both burn readily. The chief advantages of the acetates are the low cost and good draping qualities.
Polyester possesses properties similar to nylon hecause of similar molecular characteristics. High orientation, crystallinity, and a high degree of polymerization accounts for the high strength and ahrasion resistance of polyester. Ahsorhency is also low in polyester, causing comfort and static problems. Polyester has excellent elastic recovery allowing for high levels of resiliency. Pilling is a problem with all of the synthetics, particularly polyester. The high strength of the synthetic fibers tends to hold the pills (small halls of fibers caused by ahrasion) rather than allowing them to break off. As with nylon, there are a variety of polyesters with varyin, crosssections and chemical arrangements. Acrylic, because of the copolymer structure, tends to be less durable than nylon and polyester. Acrylics are made as cofihers are so comDact oolvmers because 100% ~olvacrvlonitrile , . " " they would he virtually undyeable. The additives open the structure, assisting in dyeahility hut decreasing strength. The dog-hone cross-sectional shape contributes to hulk and resiliencv, which allows for properties similar to wool. Hirh bulk acryliis provide warmth without weight and are s i f t and non-allergenic. Acrylics are highly flammahle. The acrylics are used in many end uses similar to wool and in many cases perform as well as wool. The textile artist may find differences, however, in hand, texture, and dyeability. Modacrylic is similar to acrylic in properties but tends to occur in more limited end uses. Fur-like fahrics. wigs. - . and children's sleepwear are the primary product nses.~urahility is somewhat lower than acrylic, while comfort factors are similar. Modacrylics have good flame resistance accounting for their use in children's sleepwear. Thev do, however, melt a t relatively low temperatnies. Modac&lics can now be manufactured to be very fur-like and a t a cost much lower than genuine furs. The above discussion applies to fahrics constructed entirely of one fiher. Many fabrics today, however, are blends. Blending allows fahric manufacturers to capitalize upon the oositive ~rouertiesof each fiher. The resulting fahrics are often far superior in performance. Blends can he useful to the craftsman in creating unusual design effects, also. Artists must he aware, however, that blended fahrics do possess characteristics quite different from either fiber alone. In order for the textile artist to avoid bringing a harmful or inawpropriate substance into contact with a given fiber. he muBi he familiar with the reactions of generic fiher groups with substances commonly encountered in the processing, coloring, finishing and maintenance of textiles. Fiber reactions to acids, alkalis, bleaches, solvents, dyestuffs, and sunlight are summarized in Tahle 3. Knowledge of fiher reactions will also enable the artist to capitalize on these reactions to create special textile design effects including variations in fahric transparency, mixed color effects, and three-dimensional surfaces. The effect of environmental agents is also of importance in the practical consideration of display, use, and storage of textiles. Because each fiher, by its chemical nature, will respond uniquely to various substances, it is necessary to account for all fibers present in a textile product in order to achieve the desired effects and also prevent fiher damage. Specific uses of fiber reactions are discussed below.
Synthetics
Effects of Acids, Alkalis, and Solvents
Nylon was the first totally synthetic fiber. Since the first nylon, many varieties with a multitude of performance properties have been developed by altering the chemical arrangement andlor the length of the molecular chains. The
Natural fibers mav need to be cleaned (scoured) ~ r i o to r their utilization in textile products. Generally, weak alkalis cause little damage to most fihers except wool and silk. In preparing and processing protein fihers such as raw wool for use, carbonizing with a sulfuric acid solution will convert vegetable debris to carbon for subsequent removal with no harm to the fiher. Cellulosic and synthetic fihers may he safely scoured with alkaline detergents. Acids and alkalis are used also in creating textile designs. Parchmentizing to produce transparent cottons with permanent stiffness, such as organdy, is accomplished by immersion in strong sulfuric acid under controlled conditions. Such fahrics retain their crispness over many launderings
characteristics, as well. The fiher has a tough outer surface, which requires a great deal of hand processing, making flax one of the more expensive fihers. Flax is a strong fiher, but has relatively low elasticity and flexibility because of the tough outer surface. Like cotton, flax is absorbent and can withstand high temperatures. When woven into fahric, flax is referred to as linen, known for its desirable aesthetic qualities. Protein
Wool and silk, both protein fihers, have some properties in common of their chemical comwosition. hut the dif~ - ~ - - -hecause - ~ ferences outlined in Tahle 2 allow for distincti;e properties also. The folded polypeptide chains in wool account for higher levels of elasticity and resiliency than in silk fiber. Fiher and molecular c r i m ~in wool also aid in resiliency and increase thermal capacity. Silk, on the other hand, iismoother and more lustrous. Silk is a strong fiber because of its high degree of crystallinity. Because it is more amorphous, wool is weaker hut also more absorbent. Wool fabrics are considered durable, however, becauseof the excellent elastic recovery qf the fiher. When stress is put on the fahric, the crimped fihers elongate and the molecular chains unfold. The cross-links serve to wull the fiber into its original position when the stress is removed. Silk does not eloneate as much as wool, nor does it have as high . " of an elastic recovery. The scalev outer surface of wool is the cause of the felt in^ ability, which can be an asset in the construction of felt fabrics hut can be detrimental to the artist or consumer during care. Under conditions of heat, moisture, and agitation, thescales interlock causing felting. In contrast, silk has a smooth outer surface. The .------ sulfir ~ ~ in wool is the cause of attacks hv moths and beetles, a care problem not found in silk. Both wool and silk burn slowly and are self-extinguishing. ~
~
~
~
~
~
~~~~
~
Man-Made Cellulosics
.
nately, the tightly packed, long, straight chains also create ahsorhencv. orohlems. which in turn affect dve . . oenetration. . comfort and static build-up. The low ahsorhency aids in dimensional stahilitv and resiliency, however. Nylon, as a thermoplastic fibel, can he comm&ally heat-set for shape permanency.
.
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Volume 58
Number 4
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Table 4.
Characteristics of Dyestuffs
Direct or substantive
Sodium salts of sulpmnic acids, usually a m compounds No chemical reaction between dvestuff and fiber Laroest commercial group. Water soluble: salt used to control absorption rate. Good hghtfastness. poor washiastnes~unless developed with naphtholic compounds.
Aroic
lnsolubie pigments (naphthol 8 rapidogens) applied with a coupling agent. Chemical reaction between fiber and dlaro compound produces color. Low-cost. brilliant colors. Good fastness to laundering. bleach, alkali. and llght. Tendency to crock.
Acid or anionic
Sodium salts or carboxyllc acids applied in acia solutions. Sulfonic acidgroups or nitro groups react with nitrogenous basic radicals in fibers Complete color range with varying lightfastness and poor washfastness. Hydrochlorides or salts of organic bases. Chromophore is positively charged. Excellent fastness on acrylics. Used as "topping" colors to increase br8lliance of a fabric and where durability may not be a factor.
Disperse
Suspensions of organic compounds only slightly water soluble. Particles dissolve into the fibers. Suitability to fibers varies. Fume fading from exposure to nitrogen oxides in the atmosphere results in hue change.
Vat
Convened into soluble leuco compounds by action of sodium hydroxide 8 reducing agent. Reoxidation for color development produces excellent fastness. Limited color range.
S"1f"t
Oroanic comoounds containino sulfur. Fair
not been properly hleached prior to dyeing may ultimately return to its natural color. For example, wool bleached with a reducing agent will reoxidize in the presence of air and return to its natural grayish-yellow color. Hence, a blue wool would become green. The selection of an appropriate hleaching agent depends on the fiber. Hydrogen peroxide is an oxidation bleach which is effective as well as safe for use on all fihers. Many synthetic fihers are white as a result of processing, eliminatine- the need for bleachine. Bleaches can also be selected according to fiber type for use as discharre aeents on colored textiles to create interestinr design eff&ts.bischarge printing is a design method used ta attain dark rich grounds with light or bright color motifs. Vat dyes containing a reducing bleach which removes the ground color are printed on the previously dyed fahric. Hence, the ground shade is destroyed and simultaneously replaced with the design colors. Discharge prints are often dark fabrics with white desiens. such as small floral prints or nolka dots. or brilliantly colored designs on deep ground shades. Both sides of the fahric are totallv"penetrated hv color since the wroce. dure begins with a piece-dyed fabric. Bleached-out designs on previously colored fabrics can be created by experimenting with resist printing methods. Resist printing depends on the physical blocking of dye penetration by means such as sealing the design area with wax as in batik or tiehtlv constrictine the desien area as in tie-and-dve. The with a bleaching agent by &i& a resist method. ln-experimentinr with bleached-out designs, it is important to select an appropriate hleaching agentwhich will-not damage the fiber, affect the ground color, or allow for reoxidation of the ground color over time.
Color Application become tender. Reactive
Chrome or premelalized
Unites with fiber molecule by addition or Sub~titutionby means of a coupling agent. with excellent washfastness Bright CO~WS and good lightfastness. Susceptible to chlorine damage. Chromium, cobalt, aluminum, or nickel reacts With dyesluffs With im~rovedwetfastness and lightfastness.
esting burned-out effects. PlissB, a crinkled surface cotton lawn, results from the action of caustic soda on the cotton fiher. Caustic soda is printed on the fahric in a pattern of stripes. The action of the chemical causes the treated stripes to shrink. The untreated stripes will then pucker, resulting in a rather permanent crepe-like surface. All-over puckered surfaces on fabrics composed of other fihers can he achieved by application of chemicals selected to put fabric surfaces into partial solution. Phenol on nylon or polvester will result in shrinkare - durine- drvinr. . - creating- a &Ekered surface. Similarly, polyester, when treated with caustic soda, acquires a silk-like hand and greater structural mobility of the fahric. The resultant hand resembles the natural liveliness and suppleness of silk. Effects of Bleaches
Bleaching and whitening of fibers is an important step preliminary to the application of dyestuffs. A fiher which has
Each reneric fiher arouo has an affinitv for s~ecificclasses of dyes&ffs. A fiber's absorbency and'its agility to react chemically with dyestuffs will determine which coloring agents are suitable. Dyestuffs are classified by chemical composition, hue produced, method of application, and types of fihers to which thev can he anolied. For the textile artist. classification accordingto fiher compatahility is the most lelevant. The characteristics of the major groups of dyes according to classification by fiher compatability are given in Table 4. Suitahilitv of the various dvestuffs for swecific fibers is aiven in ~ a b l e 3In . addition, pigments can he used on any fiber since the color particles are held on the fahric surface mechanically by means of a bonding agent, resin, or adhesive. Because each fiher and each fiher variant has an affinity for one or several specific groups of dyestuffs, it is possible for the designer to achieve interesting.color effects by capitalizing on fiher-dyestuff reactions. Fiber-mix dyeing is a recent technology which is based on fiher affinities for dyestuffs and the implications for fiher blends. In the past, cross dyeing and union dyeing were piece dveine methods used for varn dved effects or solid colors with
~. .
~
dled this way. The concept has been extended today to color application not only on fahrics composed of two or more generically different fihers hut also on fabrics composed of several variants of a single generic fiber. For example, polyester variants have been engineered to accept only certain dyestuffs. By planning the location and arrangement of yarns within a given fabric structure, cross dyed effects such as plaids or stripes can he accomplished with a single dye hath. For example, a three-color woven plaid utilizing a single dye hath can he designed as follows: Volume 58 Number 4
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299
Fabric Blend Polyester
Dyehath Contains Blue Disperse
Effect Polyester takes Dye Blue Disperse Acrylic Acrylic takes Yellow Basic Polyester Yellow Basic Modified polyester Dye takes both Blue (cationic dyeable) Disperse and Yellow Basic for Green Result: three-color woven plaid of BluelYellowlGreen-piecedyed.'
Similarly, tone-on-tone designs comprisedof hues of varying intensities result from dye application to two or more fiber variants which differ in their affinity for a given dyestuff. Fiher-mix dyeing as a design alternative can greatly broaden the potential for creative color, especially when used in combination with the more common methods of fiher dyeing and yarn dyeing. The characteristics of dyestuff groups presented in Table 4 is also of importance in projecting end-use performance of specific textile products. For example, if an item is intended for use or display in an area with considerable exposure to direct sunlieht. " , direct. reactive. or chrome dves would be excellent choices where possible. Acid dyes do not launder well but would be an acceptable choice for decorative items which receive minimal maintenance. Azoic dyes, which tend to crack but have good washfastness, would he suitable for end-uses such as draperies which require laundering but are not typically subject to substantial rubbing against other surfaces which would result in color loss from the fabric surface. Effect of Sunlight
The effect of direct exposure of sunlight on fibers is also of importance in the practical considerations regarding display, end-use, and storage of textiles products. The natural fibers cotton, flax, wool, and silk are weakened and will eventually deteriorate from prolonged exposure to sunlight. Textile products which incorporate these fibers should he displayed or positioned for use in areas which receive no more than moderate sunlight exposure. Even so, some strength loss and discoloration is likely to occur. Similarly, rayon and acetate,
300
Journal of Chemical Education
the cellulose based man-mades, will weaken, split, and eventuallv deteriorate with sunlight exuosure. However. uolvester to sunlight damage-even though certain dyestuffs used on these fiherv could have poor lightfastness. The use of sunlight resistant backings or linings for textile items which are susceptible to sunlight damage is an efficient method of proloneine fiber life.
such as some acid dyes, could be bleached out of tbe exposed areas by exposing the fabric to controlled amounts of direct sunlight. Solar fading could result in unusual designs similar to photographic negatives or tie-and-dye techniques. However, consideration should he given to fiher choice and length of exposure time so that damage or weakening of the product will not occur. Experimentation with combinations of dyestuffs, fibers, and exposure periods would be advisable. Summary
Characteristics and classification of selected textile fibers have been presented as a basis for choosing design techniques suitable for snecific eeneric fiber erouos. The suitabilitv of u design techniques for fibers not discussed in this paper can be evaluated hv referring to that fiher's classification in terms of origin. The &portan& of textile chemistry to the artist has heen discussed in terms of preliminary fiber processing, burned-out effects, surface effects, color, and display or end use concerns. Advancing textile technology results in ever expanding design possibilities. u
.
'"The New Encyclopedia of Textiles, American Fabrics and Fashions Magazine." Prentice-Hall, h e . , Englewood Cliffs, New Jersey, 1980, pp. 448-449.
