16 From Natural Fibers to Man-Made Plastics 16.1.History and Classifications Fibers Natural fibers were utilized by mankind considerably earlier than metals,alloys,and ceramics.Indeed,it can be reasonably as- sumed that fibers were applied by humans long before recorded history.Moreover,even some animals use fibers,for example, when building nests (birds,mammals),webs (spiders),for pro- tection during pupation(caterpillars,silkworms),or for retriev- ing insects out of narrow holes (chimpanzees).In short,some animals produce fibers for their needs,whereas others collect them.The history of the utilization of fibers is,however,much harder to trace than that of metals and ceramics because fibers often deteriorate through rot,mildew,and bacterial action.In other words,only a few specimens of early fibers have been found so far. The first raw material that man turned into fabrics was prob- ably wool.Scholars assume that this might have occurred as early as during the Paleolithic period,that is,during the Old Stone Age, about 2 million years ago(see Chapter 1).Fabric from wool may have been produced by felting,a process that yields a nonwoven mat upon the application of heat,moisture,and mechanical ac- tion to some animal fibers,as will be explained in Section 16.2. That there was trade in wool can be inferred from documents and seals dating back to 4200 B.C.which have been found in Tall al- Asmar (Iraq).Breeding and raising wool-producing sheep appar- ently commenced in Central Asia and spread from there to other areas of the world.This was possible by the fact that sheep adapt easily to different climates.For example,it is reported that the Phoenicians brought the ancestors of the Merino sheep from Asia
16 Natural fibers were utilized by mankind considerably earlier than metals, alloys, and ceramics. Indeed, it can be reasonably assumed that fibers were applied by humans long before recorded history. Moreover, even some animals use fibers, for example, when building nests (birds, mammals), webs (spiders), for protection during pupation (caterpillars, silkworms), or for retrieving insects out of narrow holes (chimpanzees). In short, some animals produce fibers for their needs, whereas others collect them. The history of the utilization of fibers is, however, much harder to trace than that of metals and ceramics because fibers often deteriorate through rot, mildew, and bacterial action. In other words, only a few specimens of early fibers have been found so far. The first raw material that man turned into fabrics was probably wool. Scholars assume that this might have occurred as early as during the Paleolithic period, that is, during the Old Stone Age, about 2 million years ago (see Chapter 1). Fabric from wool may have been produced by felting, a process that yields a nonwoven mat upon the application of heat, moisture, and mechanical action to some animal fibers, as will be explained in Section 16.2. That there was trade in wool can be inferred from documents and seals dating back to 4200 B.C. which have been found in Tall alAsmar (Iraq). Breeding and raising wool-producing sheep apparently commenced in Central Asia and spread from there to other areas of the world. This was possible by the fact that sheep adapt easily to different climates. For example, it is reported that the Phoenicians brought the ancestors of the Merino sheep from Asia Fibers From Natural Fibers to Man-Made Plastics 16.1 • History and Classifications
16.1.History and Classifications 327 Minor to Spain several millennia ago.Today,Merino sheep are raised essentially on all of the continents.New Zealand,for ex- ample,with a population of only 3.5 million people,hosts some 50 million sheep of various breeds,whose forebearers were in- troduced there by British settlers about 150 years ago. Wild sheep have long,coarse fibers (called hairs)and a softer undercoat of short and fine fibers which provides thermal insu- lation.The Merino sheep has been bred to eliminate the outer coat and the annual shedding,allowing instead a continuously growing fine and soft fleece which can be repeatedly shorn off. Fibers retrieved from plants likewise played an important role in early civilizations because of their usefulness for clothing,stor- age,shelter (e.g.,tents),and cordage.It is,however,not fully known when specific plants were first cultivated for fiber pro- duction.Nevertheless,some records indicate that hemp was pre- sumably the oldest cultivated plant for this purpose.Hemp was first grown in Southeast Asia,from where it spread to China in approximately 4500 B.C.Flax was probably cultivated in Egypt before 3400 B.C.,at which time the art of spinning and weaving linen was already well developed.Woven flax and wool fabrics were found at the sites of the "Swiss lake dwellers"dating back to the seventh and sixth centuries B.C. Cotton was spun in India as early as 3000 B.C.,as some finds in tombs of that time indicate.A Hindu hymn written around 1400 B.C.describes the fabrication of cotton yarn and the weav- ing of cotton cloth.In contrast,the Egyptians seem to have started the cultivation of cotton much later,that is,at about A.D. 600-700.From there cotton spread to the Greek mainland and to the Romans. The production of silk,that is,the cultivation of the larva of Bombyx mori(commonly called mulberry silkworm)is attributed to the Chinese empress,Hsi-ling Shih,who,in 2640 B.C.,discov- ered that the silk filament from a cocoon could be unwound. (Other sources claim that Japan,at about 3,000 B.C.,was the first country in which silkworms were domesticated.)The technique of silk-making (called sericulture)was kept a secret by the Chi- nese for about 3,000 years but eventually spread to Persia,Japan, and India.Legend has it that two Persian monks smuggled some silkworm eggs and seeds of the mulberry tree (on whose leaves the larva feed)out of China.This triggered a silk industry in Byzantium during the reign of emperor Justinian(A.D.527-565) and in Arabic countries beginning with the eighth century A.D. Eventually,the art of sericulture spread in the twelfth century to Italy and thus to Europe.Silk was and still is regarded even to- day as a highly esteemed,luxury fabric because it is the finest of
Minor to Spain several millennia ago. Today, Merino sheep are raised essentially on all of the continents. New Zealand, for example, with a population of only 3.5 million people, hosts some 50 million sheep of various breeds, whose forebearers were introduced there by British settlers about 150 years ago. Wild sheep have long, coarse fibers (called hairs) and a softer undercoat of short and fine fibers which provides thermal insulation. The Merino sheep has been bred to eliminate the outer coat and the annual shedding, allowing instead a continuously growing fine and soft fleece which can be repeatedly shorn off. Fibers retrieved from plants likewise played an important role in early civilizations because of their usefulness for clothing, storage, shelter (e.g., tents), and cordage. It is, however, not fully known when specific plants were first cultivated for fiber production. Nevertheless, some records indicate that hemp was presumably the oldest cultivated plant for this purpose. Hemp was first grown in Southeast Asia, from where it spread to China in approximately 4500 B.C. Flax was probably cultivated in Egypt before 3400 B.C., at which time the art of spinning and weaving linen was already well developed. Woven flax and wool fabrics were found at the sites of the “Swiss lake dwellers” dating back to the seventh and sixth centuries B.C. Cotton was spun in India as early as 3000 B.C., as some finds in tombs of that time indicate. A Hindu hymn written around 1400 B.C. describes the fabrication of cotton yarn and the weaving of cotton cloth. In contrast, the Egyptians seem to have started the cultivation of cotton much later, that is, at about A.D. 600–700. From there cotton spread to the Greek mainland and to the Romans. The production of silk, that is, the cultivation of the larva of Bombyx mori (commonly called mulberry silkworm) is attributed to the Chinese empress, Hsi-ling Shih, who, in 2640 B.C., discovered that the silk filament from a cocoon could be unwound. (Other sources claim that Japan, at about 3,000 B.C., was the first country in which silkworms were domesticated.) The technique of silk-making (called sericulture) was kept a secret by the Chinese for about 3,000 years but eventually spread to Persia, Japan, and India. Legend has it that two Persian monks smuggled some silkworm eggs and seeds of the mulberry tree (on whose leaves the larva feed) out of China. This triggered a silk industry in Byzantium during the reign of emperor Justinian (A.D. 527–565) and in Arabic countries beginning with the eighth century A.D. Eventually, the art of sericulture spread in the twelfth century to Italy and thus to Europe. Silk was and still is regarded even today as a highly esteemed, luxury fabric because it is the finest of 16.1 • History and Classifications 327
328 16.From Natural Fibers to Man-Made Plastics all natural fibers and its production is cumbersome,as will be described later.Chinese silk textiles manufactured during the Han dynasty (206 B.C.-A.D.220)have been found in Egypt,in graves located in northern Mongolia,and in Chinese Turkistan. During the years of the industrial revolution,that is,in the eighteenth and nineteenth centuries,a number of machines were invented and put into service which transferred spinning,weav- ing,and other fiber-processing techniques from individual homes to centralized factories with consequential economic hardships for some people and concomitant social upheavals.These ma- chines which produced relatively inexpensive fabrics triggered, however,an increase in fiber demand and production. In the 1880s,it was eventually learned how to dissolve cellu- lose (from soft wood)and to extrude the resulting substance through narrow nozzles to form regenerated cellulose fibers such as artificial silk,which was later called viscose or rayon (see Section 16.3).Actually,the first artificial silk is said to have been made in 1879 by J.W.Swan in England for filaments of light bulbs even before Edison came up with his version!The first rayon stockings for women were manufactured as early as 1910 in Germany.(In France,viscose was called "mother-in-law silk"because of its extremely high flammability.)From there it was only one more (but not so easy)step to create completely synthetic fibers(from coal or oil)such as nylon.2 These new prod- ucts challenged the monopoly of natural fibers for textile and in- dustrial uses.Still,even today,more than one-half of the world's fibers stem from natural sources,among which cotton consti- tutes the most important part (Figure 16.1).We shall return to these topics in Sections 16.3 and 16.4. Natural fibers are generally classified by their origin.The plant or vegetable fibers are mostly cellulose-based,that is,they con- sist of polymers derived from carbohydrates (i.e.,CnH2nOn) which are manufactured by the plant from water and carbon dioxide gas through photosynthesis.They include bast fibers from stems of plants (jute,flax,sunn,hemp,ramie),leaf fibers (sisal, New Zealand flax,henequen,abaca,istle),palm-type and brush fibers (coir,raffia,palmyra,piassava),seed and fruit-hair fibers (cotton,kapok),and,of course,wood from trees.Table 16.1 con- tains usage,price,and origin of some of these fibers. Among the animal fibers,which are protein-based,are wool, mostly from sheep.Specialty animal fibers include mohair from Actually,the first useful light bulb was invented by the German H. Goebel who,in 1854,inserted a carbonized bamboo fiber into an evac- uated glass flask exactly like Edison 25 years later. 2Generic name for polyamides
all natural fibers and its production is cumbersome, as will be described later. Chinese silk textiles manufactured during the Han dynasty (206 B.C.–A.D. 220) have been found in Egypt, in graves located in northern Mongolia, and in Chinese Turkistan. During the years of the industrial revolution, that is, in the eighteenth and nineteenth centuries, a number of machines were invented and put into service which transferred spinning, weaving, and other fiber-processing techniques from individual homes to centralized factories with consequential economic hardships for some people and concomitant social upheavals. These machines which produced relatively inexpensive fabrics triggered, however, an increase in fiber demand and production. In the 1880s, it was eventually learned how to dissolve cellulose (from soft wood) and to extrude the resulting substance through narrow nozzles to form regenerated cellulose fibers such as artificial silk, which was later called viscose or rayon (see Section 16.3). Actually, the first artificial silk is said to have been made in 1879 by J.W. Swan in England for filaments of light bulbs even before Edison came up with his version!1 The first rayon stockings for women were manufactured as early as 1910 in Germany. (In France, viscose was called “mother-in-law silk” because of its extremely high flammability.) From there it was only one more (but not so easy) step to create completely synthetic fibers (from coal or oil) such as nylon. 2 These new products challenged the monopoly of natural fibers for textile and industrial uses. Still, even today, more than one-half of the world’s fibers stem from natural sources, among which cotton constitutes the most important part (Figure 16.1). We shall return to these topics in Sections 16.3 and 16.4. Natural fibers are generally classified by their origin. The plant or vegetable fibers are mostly cellulose-based, that is, they consist of polymers derived from carbohydrates (i.e., CnH2nOn) which are manufactured by the plant from water and carbon dioxide gas through photosynthesis. They include bast fibers from stems of plants (jute, flax, sunn, hemp, ramie), leaf fibers (sisal, New Zealand flax, henequen, abaca, istle), palm-type and brush fibers (coir, raffia, palmyra, piassava), seed and fruit-hair fibers (cotton, kapok), and, of course, wood from trees. Table 16.1 contains usage, price, and origin of some of these fibers. Among the animal fibers, which are protein-based, are wool, mostly from sheep. Specialty animal fibers include mohair from 328 16 • From Natural Fibers to Man-Made Plastics 1Actually, the first useful light bulb was invented by the German H. Goebel who, in 1854, inserted a carbonized bamboo fiber into an evacuated glass flask exactly like Edison 25 years later. 2Generic name for polyamides
16.1.History and Classifications 329 50 spunod 40 Cotton 30 Polyester 20 FIGURE 16.1.World textile fiber production 1980-2000.Note:Poly- ester means here "noncel- 10 Rayon and acetate lulosic synthetic fibers." Silk≈0.15×109 pounds. Wool 可ax Hemp (Source:U.S.Department of Agriculture Outlook 808182838485868788899091929394Sil9798992000 Board/Economic Re- Year search Service/Nov 2002.) the fleece of the Angora goat (named after the ancient province of Angora,today's Ankara,in Turkey),cashmere wool(stemming from the fine and soft undercoat of Kashmir goats which live in the mountains of Asia),and camel hair (which is collected dur- ing molting).Other specialty animal fibers stem from the llama and the alpaca,which are close relatives of the camel and live predominantly in the high grasslands of the Andes in South America.Further,one uses hair from horses,cows,and angora rabbits.The highest regarded animal fiber,however,is silk,which is spun by a caterpillar as already mentioned above. The third category of natural fibers is comprised of those made from minerals.Asbestos3 is the major member of this group of about 30 crystalline magnesium silicates,of which chrysotile ac- counted for 95%of the world production.Asbestos is no longer utilized for general applications because of its health hazards to the lungs.The fire-resistant property of asbestos was apparently known already to the Greeks and was documented during the first century A.D.by a Roman historian.The Chinese knew about asbestos as Marco Polo reported in the thirteenth century A.D. 3Asbestos (Greek)=indestructible
the fleece of the Angora goat (named after the ancient province of Angora, today’s Ankara, in Turkey), cashmere wool (stemming from the fine and soft undercoat of Kashmir goats which live in the mountains of Asia), and camel hair (which is collected during molting). Other specialty animal fibers stem from the llama and the alpaca, which are close relatives of the camel and live predominantly in the high grasslands of the Andes in South America. Further, one uses hair from horses, cows, and angora rabbits. The highest regarded animal fiber, however, is silk, which is spun by a caterpillar as already mentioned above. The third category of natural fibers is comprised of those made from minerals. Asbestos3 is the major member of this group of about 30 crystalline magnesium silicates, of which chrysotile accounted for 95% of the world production. Asbestos is no longer utilized for general applications because of its health hazards to the lungs. The fire-resistant property of asbestos was apparently known already to the Greeks and was documented during the first century A.D. by a Roman historian. The Chinese knew about asbestos as Marco Polo reported in the thirteenth century A.D. 16.1 • History and Classifications 329 80 81 82 83 84 85 86 87 88 89 Year Wool Flax Rayon and acetate Polyester Cotton 50 40 30 20 Textile fiber production in billion pounds 10 0 Hemp 90 91 92 99 2000 93 98 94 Silk 97 FIGURE 16.1. World textile fiber production 1980–2000. Note: Polyester means here “noncellulosic synthetic fibers.” Silk 0.15 109 pounds. (Source: U.S. Department of Agriculture Outlook Board/Economic Research Service/Nov 2002.) 3Asbestos (Greek) indestructible
330 16.From Natural Fibers to Man-Made Plastics TABLE 16.1.Major sources of natural fibers,usage,and raw and retail prices Raw world market price (U.S.cents/pound) Principal growing Fiber Usage 1995/96 2000 countries Flax/linen Fine textiles,cordage, 18.5 58.2 Belgium,Netherlands, raw,retted yarn Russia,France,China Ramie Garment blend with 28.3 51.8 China,Taiwan,Korea, farm price cotton Philippines,Brazil Cotton Garments,paper, 75.6 51.8 China,USA,Pakistan, farm price explosives,oil,padding India,Uzbekistan,Brazil Wool Knitting yarn,tweeds, 192.5 75 Australia,New Zealand, 3"and up flannels,carpets, China,South Africa, blankets,upholstery,felts Russia,Argentina Retail price Fiber Retail price Fiber ($/1 pound,Sept 2003) Almost white cashmere $130.00 Superwash Merino wool $16.33 Fine baby camel 46.00 Ramie 14.10 Baby llama 40.80 Goat hair 11.88 Cultivated silk 40.80 Fine Shetland wool 11.14 Water retted flax 24.76 Moorit English wool 9.28 White alpaca 19.68 Dew retted flax 8.17 Fine mohair 17.45 Source:Department of Commerce,U.S.Census Bureau,Foreign Trade Statistics. Rubber Probably the most fascinating natural material,however,is rubber, also known by the Maya name caoutchouc.4 Knowledge of the elas- tic properties of rubber was brought to Europe in 1496 by Christo- pher Columbus,who observed inhabitants of Haiti playing with bouncing balls.Considerably later,in 1615,a Spanish explorer re- ported how"milk"(latex5)gathered from incisions made on specific tropical trees was brushed on cloaks,rendering them waterproof af- ter drying,or on earthen,bottle-shaped molds to produce contain- ers.It was not until 1735 that a French geographical expedition iden- tified caoutchouc as the condensed sap of the Hevea brasiliensis tree, today called the rubber tree,because rubber has the capability to erase (rub off)pencil marks.Hevea trees grow only about ten de- grees north or south of the equator and need heavy annual rainfalls of about 250 cm,that is,a tropical climate.The rubber tree is cul- tivated at present particularly in Malaysia,but also in Ceylon,South- east Asia,and West Africa.Wild rubber is still harvested in South America(Brazil,Peru). HCaa wood and o-chu weeping,i.e.,weeping wood. 5Latex (Latin)=fluid
Probably the most fascinating natural material, however, is rubber, also known by the Maya name caoutchouc. 4 Knowledge of the elastic properties of rubber was brought to Europe in 1496 by Christopher Columbus, who observed inhabitants of Haiti playing with bouncing balls. Considerably later, in 1615, a Spanish explorer reported how “milk” (latex5) gathered from incisions made on specific tropical trees was brushed on cloaks, rendering them waterproof after drying, or on earthen, bottle-shaped molds to produce containers. It was not until 1735 that a French geographical expedition identified caoutchouc as the condensed sap of the Hevea brasiliensis tree, today called the rubber tree, because rubber has the capability to erase (rub off) pencil marks. Hevea trees grow only about ten degrees north or south of the equator and need heavy annual rainfalls of about 250 cm, that is, a tropical climate. The rubber tree is cultivated at present particularly in Malaysia, but also in Ceylon, Southeast Asia, and West Africa. Wild rubber is still harvested in South America (Brazil, Peru). 330 16 • From Natural Fibers to Man-Made Plastics 4Caa wood and o-chu weeping, i.e., weeping wood. 5Latex (Latin) fluid. Rubber TABLE 16.1. Major sources of natural fibers, usage, and raw and retail prices Raw world market price (U.S. cents/pound) Principal growing Fiber Usage 1995/96 2000 countries Flax/linen Fine textiles, cordage, 18.5 58.2 Belgium, Netherlands, raw, retted yarn Russia, France, China Ramie Garment blend with 28.3 51.8 China, Taiwan, Korea, farm price cotton Philippines, Brazil Cotton Garments, paper, 75.6 51.8 China, USA, Pakistan, farm price explosives, oil, padding India, Uzbekistan, Brazil Wool Knitting yarn, tweeds, 192.5 75.0 Australia, New Zealand, 3" and up flannels, carpets, China, South Africa, blankets, upholstery, felts Russia, Argentina Retail price Fiber Retail price Fiber ($/1 /2 pound, Sept 2003) Almost white cashmere $130.00 Superwash Merino wool $16.33 Fine baby camel 46.00 Ramie 14.10 Baby llama 40.80 Goat hair 11.88 Cultivated silk 40.80 Fine Shetland wool 11.14 Water retted flax 24.76 Moorit English wool 9.28 White alpaca 19.68 Dew retted flax 8.17 Fine mohair 17.45 Source: Department of Commerce, U.S. Census Bureau, Foreign Trade Statistics
16.1.History and Classifications 331 Latex is only workable when freshly tapped from the rubber tree.Thus,Europeans struggled considerably to find solvents for caoutchouc to make it spreadable after it arrived in Europe in its "dried"(actually,coagulated,i.e.,solid)state.Efforts utilizing ether,turpentine,or naphtha (a waste product from coal-gas plants)were only partially successful since the waterproofed items,produced from rubber,remained sticky particularly when warm,and turned to dust in hot summers.Moreover,these rub- ber items were odorous,perishable,and became brittle and even cracked upon the slightest use during extremely cold winters. Nevertheless,a large number of products were manufactured in the early 1800s,such as air mattresses,portable bath tubs,wa- terproof mailbags,boots,and,notably,"mackintoshes"(named after their Scottish inventor).The latter material consisted of a mixture of naphtha and rubber which was sandwiched between double layers of cloth.This procedure alleviated the exposure of a tacky surface which was so annoying in earlier products. A different(nonchemical)approach was applied in the 1820s by Thomas Hancock in England.He built a machine that rapidly cuts rubber into small pieces which generated heat and thus fa- cilitated the fusing of rubber scraps into blocks.This process is called masticationo and is still used in the rubber industry. Riding on the rubber boom of the 1830s was Charles Goodyear of Boston(USA)who,in the cold winter of 1839,after considerable experimentation,accidentally dropped a piece of rubber coated with sulfur and lead?onto a hot stove.Both white lead (a common pig- ment)and sulfur were used before by others in this context,but it was Goodyear who recognized the transformation(curing)process that occurred during heating.The new substance did not melt(as untreated rubber would do);it was durable and retained its plia- bility and elasticity when cold.This technique of vulcanization is still used today with very little modification.However,Goodyear's discovery was made at a time when rubber had a bad reputation because many rubber products had failed in extreme weather.As a consequence,potential investors were reluctant to risk money for the support of additional experimentation.Further,Goodyear was imprisoned for debt more than once,which required him to sell even his children's school books at one point.Nevertheless,in 1842, Goodyear received a U.S.patent which became probably the most litigated one in history (about 150 suits were filed in the first 12 years).Goodyear received a gold medal for excellence at the inter- national exhibitions in London and Paris in the 1850s,at which he displayed his entire vision about the future of rubber products,in- 6Mastikhan (Greek)=to grind the teeth. 7Other sources say zinc
Latex is only workable when freshly tapped from the rubber tree. Thus, Europeans struggled considerably to find solvents for caoutchouc to make it spreadable after it arrived in Europe in its “dried” (actually, coagulated, i.e., solid) state. Efforts utilizing ether, turpentine, or naphtha (a waste product from coal-gas plants) were only partially successful since the waterproofed items, produced from rubber, remained sticky particularly when warm, and turned to dust in hot summers. Moreover, these rubber items were odorous, perishable, and became brittle and even cracked upon the slightest use during extremely cold winters. Nevertheless, a large number of products were manufactured in the early 1800s, such as air mattresses, portable bath tubs, waterproof mailbags, boots, and, notably, “mackintoshes” (named after their Scottish inventor). The latter material consisted of a mixture of naphtha and rubber which was sandwiched between double layers of cloth. This procedure alleviated the exposure of a tacky surface which was so annoying in earlier products. A different (nonchemical) approach was applied in the 1820s by Thomas Hancock in England. He built a machine that rapidly cuts rubber into small pieces which generated heat and thus facilitated the fusing of rubber scraps into blocks. This process is called mastication6 and is still used in the rubber industry. Riding on the rubber boom of the 1830s was Charles Goodyear of Boston (USA) who, in the cold winter of 1839, after considerable experimentation, accidentally dropped a piece of rubber coated with sulfur and lead7 onto a hot stove. Both white lead (a common pigment) and sulfur were used before by others in this context, but it was Goodyear who recognized the transformation (curing) process that occurred during heating. The new substance did not melt (as untreated rubber would do); it was durable and retained its pliability and elasticity when cold. This technique of vulcanization is still used today with very little modification. However, Goodyear’s discovery was made at a time when rubber had a bad reputation because many rubber products had failed in extreme weather. As a consequence, potential investors were reluctant to risk money for the support of additional experimentation. Further, Goodyear was imprisoned for debt more than once, which required him to sell even his children’s school books at one point. Nevertheless, in 1842, Goodyear received a U.S. patent which became probably the most litigated one in history (about 150 suits were filed in the first 12 years). Goodyear received a gold medal for excellence at the international exhibitions in London and Paris in the 1850s, at which he displayed his entire vision about the future of rubber products, in- 16.1 • History and Classifications 331 6Mastikhan (Greek) to grind the teeth. 7Other sources say zinc
332 16.From Natural Fibers to Man-Made Plastics cluding "hard rubber,"which he and his brother Nelson created by extending the heating and sulfurization of caoutchouc.Goodyear died in 1860 and left his widow and six children with $200,000 in debts.In contrast,John B.Dunlop,a British veterinarian,fared much better after he patented and developed (in 1888)the pneu- matic rubber tire based on Goodyear's invention,which eventually made the bicycle popular and had an impact on the automobile in- dustry several decades later.High-performance tires such as for trucks are still produced from this exceptional material. The demand for natural caoutchouc has not decreased in this century despite fierce competition from synthetic rubber,for ex- ample,Buna,neoprene,and methyl rubber.(The latter was al- ready produced in Germany in the 1910s.)We shall return to syn- thetic rubber and other synthetic materials in Section 16.3. Other Organic There is a large number of other natural materials-not neces- Materials sarily fibers-which have been used by mankind over the mil- lennia.Among them is cork,which is harvested from cork oaks (quercus suber)by stripping their bark,boiling it,and scraping off the outer layer.(The trees need to be at least 20 years old but can be stripped again at 8-10-year intervals.)Cork was utilized as early as 400 B.C.,for example,by the Romans for sandals,float anchors,and fishing nets.Bottle stoppers made of cork were in- troduced in the seventeenth century.Today,cork is used for heat- and-sound insulation,linoleum (by mixing cork powder with lin- seed oil and spreading it over burlap),gasket seals,buoys,and household goods.The cork oak is native to the Mediterranean area and is cultivated in Portugal,Spain,Italy,and India. Sponges have been utilized by the ancient Greeks and Romans for applying paint,as mops,and as substitutes for drinking ves- sels.In the Middle Ages,burned sponges were used as medicine. Sponges are primitive,multicellular sea animals which attach to surfaces.They are removed by skin divers from tidal levels to depths of about 70 meters,particularly in the Eastern Mediter- ranean area and on the West coast of Florida. The list of natural materials is not complete with the brief sketch given above.Indeed,it is estimated that in the Western Hemisphere alone,more than 1000 species of plants or parts of plants are utilized in one way or another to create utilitarian products.Most of them,however,are consumed locally or in such small quantities that their mention is not warranted here.Other organic materials,such as animal skin,animal guts,horns, ivory (from elephant or mammoth tusks),straw,bark,reed, shell,amber(fossilized tree resin),etc.,likewise have been used by mankind for millennia and complement the variety of mate- rials which are at our disposal for a more comfortable living
cluding “hard rubber,” which he and his brother Nelson created by extending the heating and sulfurization of caoutchouc. Goodyear died in 1860 and left his widow and six children with $200,000 in debts. In contrast, John B. Dunlop, a British veterinarian, fared much better after he patented and developed (in 1888) the pneumatic rubber tire based on Goodyear’s invention, which eventually made the bicycle popular and had an impact on the automobile industry several decades later. High-performance tires such as for trucks are still produced from this exceptional material. The demand for natural caoutchouc has not decreased in this century despite fierce competition from synthetic rubber, for example, Buna, neoprene, and methyl rubber. (The latter was already produced in Germany in the 1910s.) We shall return to synthetic rubber and other synthetic materials in Section 16.3. There is a large number of other natural materials—not necessarily fibers—which have been used by mankind over the millennia. Among them is cork, which is harvested from cork oaks (quercus suber) by stripping their bark, boiling it, and scraping off the outer layer. (The trees need to be at least 20 years old but can be stripped again at 8–10-year intervals.) Cork was utilized as early as 400 B.C., for example, by the Romans for sandals, float anchors, and fishing nets. Bottle stoppers made of cork were introduced in the seventeenth century. Today, cork is used for heatand-sound insulation, linoleum (by mixing cork powder with linseed oil and spreading it over burlap), gasket seals, buoys, and household goods. The cork oak is native to the Mediterranean area and is cultivated in Portugal, Spain, Italy, and India. Sponges have been utilized by the ancient Greeks and Romans for applying paint, as mops, and as substitutes for drinking vessels. In the Middle Ages, burned sponges were used as medicine. Sponges are primitive, multicellular sea animals which attach to surfaces. They are removed by skin divers from tidal levels to depths of about 70 meters, particularly in the Eastern Mediterranean area and on the West coast of Florida. The list of natural materials is not complete with the brief sketch given above. Indeed, it is estimated that in the Western Hemisphere alone, more than 1000 species of plants or parts of plants are utilized in one way or another to create utilitarian products. Most of them, however, are consumed locally or in such small quantities that their mention is not warranted here. Other organic materials, such as animal skin, animal guts, horns, ivory (from elephant or mammoth tusks), straw, bark, reed, shell, amber (fossilized tree resin), etc., likewise have been used by mankind for millennia and complement the variety of materials which are at our disposal for a more comfortable living. Other Organic Materials 332 16 • From Natural Fibers to Man-Made Plastics
16.2.Production and Properties of Natural Fibers 333 16.2.Production and Properties of Natural Fibers Animal Fibers Animal fibers (wool,silk,etc.)are composed mostly of proteins, as already mentioned in Section 16.1.(Proteins are highly com- plex substances which consist of long chains of alpha amino acids involving carbon,hydrogen,nitrogen,sulfur,and oxygen.)All taken,animal fibers do not contain cellulose.They are therefore more vulnerable to chemical damage and unfavorable environ- mental conditions than cellulose. After extraction of the fibers as described above,they need to be spun into yarn.For this the individual fibers are arranged in parallel to overlap each other,yielding a ribbon.These rib- bons are then softened with mineral oil,lubricated,and even- tually drawn down to the desired sizes and twisted for secur- ing the position of the fibers.The yarn is eventually woven into fabrics. Wool consists mainly of the animal protein keratin,which is common in the outermost layers of the skin,nails,hooves,feath- ers,and hair.Keratin is completely insoluble in cold or hot wa- ter and is not attacked by proteolytic enzymes (i.e.,enzymes that break proteins).Keratin in wool is composed of a mixture of pep- tides.When wool is heated in water to about 90C,it shrinks ir- reversibly.This is attributed to the breakage of hydrogen bonds and other noncovalent bonds. Wool fibers are coarser than those of cotton,linen,silk,or rayon,and range in diameter between 15 and 60 um,depending on their lengths.Fine wool fibers are 4-7.5 cm long,whereas coarse fibers measure up to 35 cm.Unlike vegetable fibers,wool has a lower breaking point when wet.The fibers are elastic to a certain extent,that is,they return to their original length after stretching or compression and thus resist wrinkling in garments. The low density of wool results in light-weight fabrics.Wool can retain up to 18%of its weight in moisture.Still,water absorp- tion and release are slow,which allows the wearer not to feel damp or chilled.Wool deteriorates little when properly stored and is essentially mildew-resistant.However,clothes moths and carpet beetles feed on wool fibers,and extensive exposure to sun- light may cause decomposition.Further,wool deteriorates in strong alkali solutions and chars at 300C. Felting shrinkage,that is,compaction,occurs when wet,hot wool is subjected to mechanical action.Thus,washing in hot water with extensive mechanical action is harmful.On the other hand,felting produces a nonwoven fabric,as already mentioned in Section 16.1.This is possible due to the fact that
Animal fibers (wool, silk, etc.) are composed mostly of proteins, as already mentioned in Section 16.1. (Proteins are highly complex substances which consist of long chains of alpha amino acids involving carbon, hydrogen, nitrogen, sulfur, and oxygen.) All taken, animal fibers do not contain cellulose. They are therefore more vulnerable to chemical damage and unfavorable environmental conditions than cellulose. After extraction of the fibers as described above, they need to be spun into yarn. For this the individual fibers are arranged in parallel to overlap each other, yielding a ribbon. These ribbons are then softened with mineral oil, lubricated, and eventually drawn down to the desired sizes and twisted for securing the position of the fibers. The yarn is eventually woven into fabrics. Wool consists mainly of the animal protein keratin, which is common in the outermost layers of the skin, nails, hooves, feathers, and hair. Keratin is completely insoluble in cold or hot water and is not attacked by proteolytic enzymes (i.e., enzymes that break proteins). Keratin in wool is composed of a mixture of peptides. When wool is heated in water to about 90°C, it shrinks irreversibly. This is attributed to the breakage of hydrogen bonds and other noncovalent bonds. Wool fibers are coarser than those of cotton, linen, silk, or rayon, and range in diameter between 15 and 60 m, depending on their lengths. Fine wool fibers are 4–7.5 cm long, whereas coarse fibers measure up to 35 cm. Unlike vegetable fibers, wool has a lower breaking point when wet. The fibers are elastic to a certain extent, that is, they return to their original length after stretching or compression and thus resist wrinkling in garments. The low density of wool results in light-weight fabrics. Wool can retain up to 18% of its weight in moisture. Still, water absorption and release are slow, which allows the wearer not to feel damp or chilled. Wool deteriorates little when properly stored and is essentially mildew-resistant. However, clothes moths and carpet beetles feed on wool fibers, and extensive exposure to sunlight may cause decomposition. Further, wool deteriorates in strong alkali solutions and chars at 300°C. Felting shrinkage, that is, compaction, occurs when wet, hot wool is subjected to mechanical action. Thus, washing in hot water with extensive mechanical action is harmful. On the other hand, felting produces a nonwoven fabric, as already mentioned in Section 16.1. This is possible due to the fact that Animal Fibers 16.2 • Production and Properties of Natural Fibers 333 16.2 • Production and Properties of Natural Fibers
334 16.From Natural Fibers to Man-Made Plastics HOOL 4.0KU x286824mm X2500 (a) (b) 度K X58 39m前 (c) (d) FIGURE 16.2.Scanning animal fibers (except silk)are covered with an outer layer of electron micrographs unidirectional overlapping scales,as depicted in Figure 16.2(a). of (a)wool fiber(note Mechanical action in conjunction with heat and moisture the scales on the sur- causes the fibers to slide past each other and interlock.Felt is face that overlap each other;the tips point to widely used in the hat industry and for making slippers and the free end of the polishing materials. hair),(b)silk fibers Silk is spun by the larva of Bombyx mori,as was mentioned (note the thin syn- in Section 16.1.The proteins of silk contain about 80%fibroin thetic fiber that has (which makes up the filament)and about 20%sericin or silk gum been smuggled in),(c) (which holds the filaments together).Minor constituents are plant fiber at low mag- waxes,fats,salts,and ash.Silk is a continuous fiber,that is,it nification,and (d) has no cellular structure.The life cycle of Bombyx mori includes plant fiber at high hatching of the disk-shaped eggs in an incubator at 27C,which magnification.(Cour- requires about 10 days.The"silkworm,"3 mm long and 3 mg in tesy of R.Crockett and mass,eventually grows into a 90-mm-long caterpillar which R.E.Hummel,MAIC, University of Florida.) needs five daily feedings of chopped,young mulberry leaves.Af-
animal fibers (except silk) are covered with an outer layer of unidirectional overlapping scales, as depicted in Figure 16.2(a). Mechanical action in conjunction with heat and moisture causes the fibers to slide past each other and interlock. Felt is widely used in the hat industry and for making slippers and polishing materials. Silk is spun by the larva of Bombyx mori, as was mentioned in Section 16.1. The proteins of silk contain about 80% fibroin (which makes up the filament) and about 20% sericin or silk gum (which holds the filaments together). Minor constituents are waxes, fats, salts, and ash. Silk is a continuous fiber, that is, it has no cellular structure. The life cycle of Bombyx mori includes hatching of the disk-shaped eggs in an incubator at 27°C, which requires about 10 days. The “silkworm,” 3 mm long and 3 mg in mass, eventually grows into a 90-mm-long caterpillar which needs five daily feedings of chopped, young mulberry leaves. Af- 334 16 • From Natural Fibers to Man-Made Plastics FIGURE 16.2. Scanning electron micrographs of (a) wool fiber (note the scales on the surface that overlap each other; the tips point to the free end of the hair), (b) silk fibers (note the thin synthetic fiber that has been smuggled in), (c) plant fiber at low magnification, and (d) plant fiber at high magnification. (Courtesy of R. Crockett and R.E. Hummel, MAIC, University of Florida.) (c) (d) (a) (b)
16.2.Production and Properties of Natural Fibers 335 ter about 6 weeks and four moltings,it stops eating,shrinks somewhat,and its head makes restless rearing movements,in- dicating a readiness to spin the cocoon.The silkworm is then transferred into a compartmentalized tray or is given twigs.There it spins at first a net in whose center the cocoon is spun around the silkworm.After 3 days,during which time the filament is wound in a figure-eight pattern,the completed cocoon has the shape and size of a peanut shell. The silk substance is produced by two glands and is discharged through a spinneret,a small opening below the jaws.The spin- neret is made up of several chitin plates which press and form the filament.The filament (called bave)actually consists of two strands(called brins)that are glued together and coated by silk gum(sericin),which is excreted by two other glands in the head of the silkworm.The liquid substance hardens immediately due to the combined action of air exposure,the stretch and pressure applied by the spinneret,and to acid that is secreted from still another gland.Under normal circumstances,the chrysalis inside the cocoon would develop into a moth within 2 weeks and would break through the top by excreting an alkaline liquid that dis- solves the filament.Male and female moths would then mate within 3 days and the female would lay 400-500 eggs,after which time the moths would die.The life cycle is,however,generally interrupted after the cocoon is spun by applying hot air or boil- ing water(called stoving or stifling)except in limited cases when egg production is desired.The filaments of 2-7 cocoons are then unwound (called reeling)in staggered sequence to obtain a ho- mogeneous thread strength;see Plate 16.1.The usable length of the continuous filament is between 600 and 900 meters.Shorter pieces are utilized for spun silk.It takes 35,000 cocoons to yield 1 kg of silk.[Note in this context the silk fibers depicted in Fig- ure16.2(b)]. The raw silk is usually degummed to improve luster and soft- ness by boiling it in soap and water,which reduces its weight by as much as 30%.(Sericin is soluble in water whereas fibroin is not.)The silk is subsequently treated with metallic salt solutions (e.g.,stannic chloride),called weighting,which increases the mass (and profit)by about 11%and adds density.Excessive weighting beyond 11%causes the silk to discolor and decom- pose.Likewise,dying adds about 10%weight.Silk fabric treated with polyurethane possesses excellent wet wrinkle recovery and dimensional stability during washing.Silk is more heat-resistant than wool (it decomposes at about 170C);it is rarely attacked by mildew but degrades while exposed extensively to sunlight. Silk can adsorb large quantities of salts,for example during per-
ter about 6 weeks and four moltings, it stops eating, shrinks somewhat, and its head makes restless rearing movements, indicating a readiness to spin the cocoon. The silkworm is then transferred into a compartmentalized tray or is given twigs. There it spins at first a net in whose center the cocoon is spun around the silkworm. After 3 days, during which time the filament is wound in a figure-eight pattern, the completed cocoon has the shape and size of a peanut shell. The silk substance is produced by two glands and is discharged through a spinneret, a small opening below the jaws. The spinneret is made up of several chitin plates which press and form the filament. The filament (called bave) actually consists of two strands (called brins) that are glued together and coated by silk gum (sericin), which is excreted by two other glands in the head of the silkworm. The liquid substance hardens immediately due to the combined action of air exposure, the stretch and pressure applied by the spinneret, and to acid that is secreted from still another gland. Under normal circumstances, the chrysalis inside the cocoon would develop into a moth within 2 weeks and would break through the top by excreting an alkaline liquid that dissolves the filament. Male and female moths would then mate within 3 days and the female would lay 400–500 eggs, after which time the moths would die. The life cycle is, however, generally interrupted after the cocoon is spun by applying hot air or boiling water (called stoving or stifling) except in limited cases when egg production is desired. The filaments of 2–7 cocoons are then unwound (called reeling) in staggered sequence to obtain a homogeneous thread strength; see Plate 16.1. The usable length of the continuous filament is between 600 and 900 meters. Shorter pieces are utilized for spun silk. It takes 35,000 cocoons to yield 1 kg of silk. [Note in this context the silk fibers depicted in Figure 16.2(b)]. The raw silk is usually degummed to improve luster and softness by boiling it in soap and water, which reduces its weight by as much as 30%. (Sericin is soluble in water whereas fibroin is not.) The silk is subsequently treated with metallic salt solutions (e.g., stannic chloride), called weighting, which increases the mass (and profit) by about 11% and adds density. Excessive weighting beyond 11% causes the silk to discolor and decompose. Likewise, dying adds about 10% weight. Silk fabric treated with polyurethane possesses excellent wet wrinkle recovery and dimensional stability during washing. Silk is more heat-resistant than wool (it decomposes at about 170°C); it is rarely attacked by mildew but degrades while exposed extensively to sunlight. Silk can adsorb large quantities of salts, for example during per- 16.2 • Production and Properties of Natural Fibers 335
