edited by GEORGE6. KAUFFMAN California State Universily, Fresno Fresno, CA 93740
Wallace Hume Carothers and Nylon, The First Completely Synthetic Fiber George 6. Kauffman California State University, Fresno, Fresno, CA 93740 Nylon, the first completely synthetic polymer fiber, was first formally announced to the public on October 27, 1938 (I). In the intervening half century this versatile material, which laid the foundation for the synthetic fiber industry, has become indispensable for a multiplicity of uses. Today the production of synthetic fibers amounts to billions (lo9) of kiloarams ner vear (2). Althoueh taken for eranted todav by the';resent generation, news $this poly&ide burst l i k e a bombshell, despite prevalent earlier rumors that E. I. du Pant de Nemours and Company was at work on an "artifical silk" made from abundant raw materails-"air, water. and coal"-in the words of the popular press (2). Wallace Hume Carolhers Nylon was developed by the brilliant American chemist Wallace Hume Carothers (1896-1937) (Fig. 1) and a small group of intrepid colleagues, of whom Julian Werner Hill (born 1904) was the most outstandine. Carothers was horn in i3urlingtoi, lon,u, on April 27, 1896,;s the oldest of t h e four children of Ira Hume Carothers and Maw Evalina Carothers (nee McMullin) (3-8). In July 1915 he graduated with a major in accountancy and secretarial studies from the Capital City Commercial College of Des Moines, Iowa, where his father taught and was later Vice-President. He received his BS degree from Tarkio College, Tarkio, Missouri (1920) and his MA degree from the University of Illinois a t Urbana (1921). He taught analytical and physical chemistry for a year (1921-1922) a t the University of South Dakota (9,101 before returning to Urbana, where he earned his doctorate in organic chemistry under Roger Adams's(1889-1971) supervision with a dissertation on hydrogenations with modified platinum oxide-platinum black catalysts (11). He was Instructor in Chemistry a t the University of Illinois (19241926) and a t Harvard University (1926-1928). In December 1926 Charles Milton Altland Stine (18821954), Director of Du Pont's Chemical Department, pro-
Thls new Secondary School feature deals with the chemistry of specific everyday commercial items (foods, toilelries, cleaners, c o s metics, toys. etc.) readily recognizable to the high school and college studmt. Articles about these products may discuss Meir manufacture. the cheniical principles underlying their use, how they may be used to teach a specific concept, and ideas for modifying them for safe but Unusual purposes. Papers may provide background or supplemental information forteachers of high school or introductory college chemistry. Two types of contributions are solicited: (1)fdi-length articies(2-3 journal pages) and (2) short anecdotal notes (% to % journal page). which would be similar to the Bits and Pieces items of the Computer Series. Contributions should be sent to the feature editor.
Figure 1. Wailace Hume Carothers (1896-1937).
posed that the company undertake a program of fundamental research "with the object of discovering new scientific facts3'-commonplace today hut an innovative, radical departure from American industrial practice a t that time (12). In 1928, after heing assured by Stine that he could continue to work on whatever he pleased, Carothers reluctantly left academe to lead Du Pont's organic group in fundamental research a t its Central Laboratories in Wilmington, Delaware. During the remaining nine years of his short life he not only made major contributions to theoretical organic chemistry hut he also contributed to the founding of two industries-synthetic rubber (Du Pant began to manufacture neoprene (polychloroprene) in 1931) and completely synthetic fibers. His fundamental work on polymers (13) enabled Hermann Staudiuger (1881-1965) to convince skeptics that polymers were actually macromolecules held together by covalent bonds and not simply aggregates of small molecules held together by undefined forces (7,13). Within a short time Carothers had achieved a reputation as the outstanding researcher in high polymer chemistry. In 1936 he was elected to the National Academy of Sciences, the first industrial organic chemist to he so honored. A modest, shy person troubled from his youth by increasing periods of mental denression and obsessed with the idea that he was a failureasascientist, thefatherof~rnericanpolymerrhemistrv committed suicide in a I'hiladclr)hia hotrl room on April 29,1937, by drinking lemon juice laced with potassium cyanide. Volume 65 Number 9
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Blfunctlonal Esterlflcatlon H[O-R-0-CO-R'-CO]#-R-OH HO-R-OH
+
HOOC-w-COOH\
/ %60~o
Figure 2. Bifunctional esterification.
Development of Nylon During his last semester a t Harvard, Carothers began to consider research on oolvmers. and after arriving- in Wil. mington he defined his goal-to prepare organic molecules of known structure throuah the use of known reactions "and of these substances [were] to investigate how the dependent on constitution" (fib, 7,121. He began to synthesize long-chain molecules of high molecular weight (-5000) by esterification of glycols with dicarboxylic acids-compounds with functional groups at each end of the molecule (Fig. 2). In less than two years he achieved a significant advance by the use of a molecular still (Fig. 3), which allowed polymerization to oroceed more nearlvto cornoletion bv elimination of the watkr formed in the condensatibn reactions, resulting in molecular weights of 10,000-20,000. According to Elmer Keiser Boltou (18861968), who replaced Stine as Director of the Fundamental Research Program in June 1930, "without this technique Carothers m i g 6 have failed in his search for superpolymers" (14). Carother's work proved that polymers could be formed by using known organic reactions with reactants containing more than one reactive group per molecule and that the forces binding the individual monomers together are covalent bonds (7). He described his work in a series of papers and patents (15) (Fig. 4), including a land-
Figure 3. Carothers's molecular still (ref. 24. The molecular still, in which improvements by Carothers have been incorporated, is lirst highly evacuated. 8 isthecondenser containingwater leads for cooling. C is the glasssuppwt for the heater (D)and the distilling pan (E). The heater and distilling pan are contained in an outer capper pan. The heater leads (F) are brought up through the s u m m fC1. Carathers's imorovementsintraducedthe oan and its oroximity to tna canoenser The tncreased etfoc8sncy res~lteain tne complete r e m o w 01 the volstl e product as most of the mo scules that managed to escape hom ths evaporallng surlace were caught by the condenser w.m a negl g bls probability of return.
About the Edllor
I
George 8. KauUman, Protesof Cheme.1~ at Ca forna State University. Fresno, has been at CSUF since 1956. His interest in the history of chemistry was aroused during his undergraduate years at the University of Pennsylvania, where a strong badition In history was established by Edgar Fahs Smith, who organized the ACS Division of History of Chemistry. Receiving his BA with honors in chemistry from the University of Pennsylvs1118 in 1951 and his PhD from the University of Florida in 1956. Kauffman has been a research participant at the Oak Ridge National Laboratory, an instructor in Chemistry at the University of Texas, and a research chemist for the Humble Oil and Refining Co. and the General Electric Co. Long active in American Chemical Soclety affairs, including his invoivwnents with the ACS Division of Chemistry. NorHlwest Tour Speaker, and Editor of the History of Chemistry Series. ACS Audio Courses. He has been a Contributing Editor of The Hexagon. Polyhedron, and hdustrial Chemist. Kauffman is the author of 15 b w k s and more than 730 papers. reviews, and encyclopedia articles on chemistry, history of science. and chemical education, morethan 170 of which have appeared in this Journal. SO,
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Journal of Chemical Education
mark review article, which laid the foundation for much of organic polymer chemistry (16). Filaments of these so-called superpolyesters could be easily drawn like taffy from viscous melts, a process discovered by Hill, which, according to X-ray diffraction patterns, oriented the polymer chains along the fiber axis. This so-called "coId drawing" made the fibers more pliable, elastic, flexible, and tough and today is used in the production of most . lines. and tire cords. When these textiles. rue ~ i l e sfishine superpolye&s were found to melt below 100 "C, to be only moderatelv stable in water. and to he excessivelv soluble in various soivents, ~arothersturnedhis attention to the higher melting superpolyamides, produced from the reaction of diamines withdicarhoxylicarids, using the methods used for su~erpolyesters(66, 7, 12, 14, 17-21) (Fip. 5). These polymers were designated by iwo numbers-the first corresponding to the number of carbon atoms in the monomeric diamiie and the second corresponding to the number of carhon atoms in the monomeric dicarhoxylicacid. For several years, during which he considered abandoning the project, Carothers and his co-workers systematically meoared numerous nolvamides from various combinations bf iiamines and diiasic acids. By the spring of 1935 he decided that the oolvamide o r e ~ a r e dfrom oentamethvlenediamine and seb& acid ( j 1 0 j (Fig. 5) was the best Eandi-
Polyamldes
UNITED S T A T E S PATENT O F F I C E Lml.lm " W I U
C(IYDI"Sl~O*I rnL1rn11
HCI
+ (-RNHCOR'CONHR-),
Figure 5. Synlhasas of palyamldes.
Figure 4. Patent. "Linear Candensation Polymed"'
date for a textile fiber since its fibers were elastic, stronger than silk, and inert to moisture and solvents. However, Bolton insisted that the high cost of its starting materials and its still relatively low melting point (-196 "C) made it commercially unsuitable. Instead, he favored the polyamide prepared from hexamethylenediamine and adinic acid.. viz....oolv(hexamethvlene adioamide). (66) . . (Fia. .. 4).. .. insoluhle in common solvents and having a melting point of 263 ' C . first svnthesized bv Carothers on Februarv 28.1935. and becausk i t possessed the "best balance of manufacturing cost of the polyamides then known" (14). Production of Nylon
After the 66 polyamide had been selected as the most suitable candidate for commercial production, development of a practical manufacturing process was relegated to other groups, while Carothers continued to explore other possihle superpolyamides; none of these, however, was found to be more useful than the 66 polyamide, although some are now being produced commercially. The starting materials for the production of nylon-adipic acid and hexamethylenediamine-were mere laboratory curiosities at the time, and no manufacturing plants in the world could produce either of them in the large quantities required. Since processes had to be devised based on abundant raw materials, benzene and reactions involving six-carbon intermediates were chosen. By 1936 Roger Williams of Du Pont's Ammonia Department had developed a new catalytic process for the production of adipic acid from phenol to he
carried out at the company's plant at Belle, West Virginia. A new process for the commercial production of bexamethylenediamine from adipic acid was similarly developed. A journalist's view of the probable process of the production of nylon is shown in Figure 6 (17). In the production of nylon, hexamethylenediamine and adipic acid are reacted to form a salt, which, after purification via crystallization, is polymerized to long-chain polymers of molecular weight above 10,000 in an autoclave with stabilizers and monofunctional reactants added to control molecular weight and viscosity (14). The molten nylon is then extruded as a ribbon, which is cut into small chips that are convenient for storing, handling, and subsequent blending with other batches. The chips are melted, and the melt is filtered, before being extruded (melt spun) by pumps of special abrasion-resistant steel through spinnerets as filaments. All parts of the specially designed equipment are blanketed with an inert gas to avoid oxidation at the hieh temoeratures employed.-The filaments, which quickl; harden on contact with air, are wound up on bobbins and drawn out to about four times their original length (cold drawing) to attain the desirable properties associated with nylon (22-24). The entire spinning assembly involved radically new engineering developments. A pilot plant for production of what was then known as "66 polyamide" was completed in Wilmington in July 1938, the same month in which the material was introduced on the market as "Exton" bristles for brushes. On October 27,1938, Stine formally announced that construction of a large-scale plant designed initially to produce 3 million pounds of yarn annually would begin in January 1939at Seaford, Delaware. Before the first unit was in operation the planned capacity was increased to 4 million pounds, and before the first plant was completed this figure was doubled to 8 million pounds. In February 1939 nylon stockings were first exhibited a t the Golden Gate International Exposition in San Francisco and were first sold to Du Pont employees. In April 1939 they were displayed a t the New York World's Fair. On October 24,1939, they were sold to Wilmington, Delaware, residents only, and on May 15,1940, they went on sale throughout the country. In January 1940 the Seaford plant began full-scale production; less than five years had elapsed between Carothers' laboratory synthesis of the 66 polymer and commercial production of nylon yarn-a virtually unprecedented achievement in the history of American industrial enterprise. Volume 65 Number 9
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Figure 6. Haw nylon is made (ref 17).
Orlgln of the Name "Nylon" In his historic announcement of October 27, 1938, Stine used the term nylon publicly for the first time. According to E. K. Gladding, Director of the newly formed NylonDivision of Du Pont's Rayon Department, the name norun was first suggested because of the resistance of nylon stockings to snagging, but this name was not desirahle for numerous reasons. Gladding's daughter suggested that norun he spelled backward as nuron, hut the Naming Committee decided that this sounded like a nerve tonic. Someone suggest-
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Journal of Chemical Education
ed changing the r to 1 giving nulon, but the Legal Department thought this name was too similar to another registered trademark. Someone else suggested changing the u to i, giving nilon, hut it was feared that this name might he mispronounced. Finally, the i was changed t o y , and nylon entered the American language as a "generic name for all synthetic fiher-forming polymeric amides having a proteinlike chemical structure, derivable from coal, air, and water or other substances and characterized by extreme toughness and strength" (23).
Properties and Uses of Nylon
Before the advent of nylon, the United States and muchof the world was dependent on Japan for silk, and this first truly synthetic fiber arrived on the scene just in time to replace the supply of natural silk that was cut off during World War 11. More than any other fiber, natural or artificial, nylon is closer in both constitution and properties to silk. Possessine silk's anoearance and luster. it has the advantage of greGer uniformity and can be spun into filaments of any desired size (14). I t also possesses the outstanding comhination of great strength, elasticity, toughness, and resistance to abrasion (14.18.20.22.23) hecause of the great length, great flexibility, and relatively high polymeth;lene content of the polvmer chain, the strength of the forces between the amidegroups as well as stericfactors favorable to the efficient operation of these forres. Because of nylon's lower water absorption than cotton, nylon garments dry more rapidly than cotton ones. The ereat streneth and elasticitv of nvlon make it ewecially kitable forLhosiery.The reiativel; high hexamethylene. ( C H . ~ ~ . a tetramethvlene, nd (CHIJr,contentmakes the chain flexible and gives nilon fiber low elastic modulus (ease of stretch) regardless of the degree of orientation or crystallinity. Nylon possesses a high tensile strength; for fibers of the same size it is stronger than silk, cotton, linen, wool, or rayon. This strength results from the fairly strong hydrogen bonds (bond length -2.8 A) formed between carbonyl oxygen atoms on one chain and imino hydrogen atoms on adjacent chains, which resist slippage of the molecules when tension is applied (18,221. The strength of these bonds and the regularity of their location along the chain contribute to the close packing and crystallinity responsible for nylon's high melting point, which provides a safe ironing temperature, i.e., about the same as that of silk, wool, and acetate rayon. Until the development of nvlon yarn, silk was the only textile fiber posses& the combined elasticity and strength needed for hosiery, hut nylon issuperior to silk in itsstren~th-elasticity factor (18). ~urtherrnore,oriented nylon yarn can take a permanent set through simple treatments with boiling water or steam (22,23). Chemically, nylon is relatively inert, being unaffected by water, most organic acids, alcohol, halogenated hydrocarbons, cold dilute alkalis, soaps, aldehydes, ketones, cold bleaches, organic solvent mixtures, common dry cleaning solvents, or animal or vegetable fats (14, 18, 20, 23). I t is flame resistant and melts and burns onlv when held in a flame. Physiologically, nylon is completeiy inert, and it is used for surgical sutures. Mildew or molds do not grow on it, enzymes donot digest it, and moths do not attackit. Because of the properties enumerated above nylon has found a variety of applications. In addition to its use in hoisery, clothing textiles, brush bristles, and surgical sutures, it has been used in fishing lines, leaders, and nets, fishing reels, tennis and badminton racket strings, photoengraving printing plates, upholstery material, sewing thread, parachutes, injection-molded articles, balloon cloth, ropes, cables, tire cords, transparent wrapping film and films for boil-in-bag and other packaging, sa& aGd rigging, engineering plastics (as a metal substitute in gears, wheels, bearings, rollers, housings, casings, and oil seals), machinery parts, electrical appliances, hoses, tubing, automobile parts, combs, zip fasteners, hinges, propellers, furniture, syringes, catheters, spectacle frames, sausage sheaths, insulators, ski bindines. - . ciearette holders. saddles. aircraft comnonents. and miscellaneous plastic applicatio& (25, 26). ~ i l o nhas hecome an example of basic research that beeins with no practical end use in mind but that results & an almost endless array of new products that enrich our daily lives. T o foreigners it is a symbol of modern American industrial achievement. &.
a
u
Damonsirations and Experiments There is no scarcity of demonstrations or experiments for the synthesis of nylon. The acyl chloride instead of the free dibasic acid is used so that hvdroeen chloride rather than . water is eliminated, resulting in a more rapid reaction. A solution of hexamethvlenediamine (1.6-diaminohexane. NHz(CH2)6NHz) in water or aqueous N ~ O Hor NazC03 is mixed with either a solution of sebacoyl chloride (1,lO-decanedioyl chloride, CICO(CH2)&OC1) in CC4, CSHI~,or CbC=CCb for the nrenaration of nvlon 610 (27-30) or a solution of adipyl-cbioride (1,6&xanedioyl chloride, ClCO(CH2)aCOCI)in CsH14 for the preparation of nylon 66 (30,31). The nylon film can be wound as a fiber on a stirring rod or drawn out with a paper clip or forceps. Although nylon resists alkaline hydrolysis even after several hours of boiling, an experiment has been designed to demonstrate its hvdrolvsis in inoreanic acid solution (32). Nylon 66 hosiery in reflixed in 3 0 9 o i 2 ~ 0 , for six hours,and the adinic acid formed is recovered bv crvstallization. The hexamethylenediamine is isolated a s i t s dibenzoyl derivative. The experiment illustrates the hydrolysis of the -CONH- linkage, the separation of basic and acidic organic compounds from a mixture of the two, the liberation of a weaker base from its salt by a stronger base, and the esterification of an amine. In all the above demonstrations and experiments adequate safety precautions should be taken. Contact of reagents with the skin should he avoided, the work should be carried out in a well-ventilated hood, and safety goggles should be worn.
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Acknowledgments The author wishes to acknowledge the assistance of James D. Barhydt, Charles W. Carlson, and PatriciaL. Zebley of E. I. du Pant de Nemours & Co.. Wilmineton. DE: Mavnard Brichford, Archivist, ~ n i v e r s i tof ' ~1llin& ~ r b a i ~a i i r a r y ; David A. Hounshell. Universitv of Delaware. Newark: the late Carl S. Marvel, ~ n i v e r s i t y b fArizona, ~ " c s o n ;A. ~ r u man Schwartz, Macalester College, St. Paul, MN, George P. Scott, University of South Dakota, Vermillion; Raymond B. Seymour, University of Southern Mississippi, Hattiesburg; John K. Smith, Lehigh University, Bethlehem, PA; and D. Stanely Tarbell, Vanderbilt University, Nashville, TN. Llteratuie Cited 1. Mown, P. W. In History ol Polymer Seienes and Technology: Seymour, R. B., Ed.: Dekker: New York, 1982, pp49-67. 2. Anon. Business Weak 1938 (Oet. 29). 478.18. 3. Adams, R. Bioq. Mom., Nor. Aced. Sei. 1939.20.293; reprinted in abbreviated form in Cmof Chemiafs; Farher, E., Ed.; lnteneienee: New York, 1961:pp 1601-1611. 4. Johnson. J. R. In Dielionory of AmericonBiography; Schuyler, R. L., Ed.: Scribner's: New York, 1958:Vol. 22, Suppl. 2. pp 96-97. 5. H s ~ l e r ,W. W. Am. Hist. IUuatroled 1910, 5(7), 32; in American Chemist8 ond Chemical Enginera; Milpa, W . D.. Ed.: American Chemical Society: Washington, DC, 1976:pp 65-66, 6. Rill, J. W. (a) In Dictionary o f S & l i ~ i ~Biography; Gillispie, C. C., Ed.; Seribner'l: Near York, 1971: Vol. 3, pp 85-88: (b) Pmc. Robert A. Welch Found. Conf Chem. Res.
1977,20,232251.
7. Marvc1.C. S.;Carraher,C.E.,Jr. Chemlech 1984.14(12),716. 8. Monis, P. J. T.PolymerPionoors:Center for History of Chemistry Publication No. 5: Philadelphia. PA. 1986; pp 5860.
9. Smff,G.P.SovrhDnboroJ~Acod.Sci.Newa1966, (Feb.l.3. 10. Sehwartz. A. T. il Coli. Sei. Teach. 1981,10(4), 218. 11. Adams,R.:Carofhers, W. H. J. Am. Chsm. Sac 1923.45 1071: I924,46,167J;1925.47, 1047. 12. Smith, J. K: Hounshell, D. A. Science 1985,229,436,
13. Stahl, G. A. Chsmlech 19%. 14(8).492. 14. Bolton, E. K.Ind. Eng. Chem. 1942.34,53. 15. Forexample,Carothen. W.H.U.S.Pat.2,071,250 (Feb.16.1937); U S Pat. 2.071.251 (Feb.IS, 1937): U.S. Pat. 2,130,523 (Sepr 30,1938); U.S. Pat. 2,130,947 (Sept 20, 1938): U.S. Pat. 2,130,948(Sept. 20, 1938). The Rrst W o patents are reprinted in Chemlech 1978.8(9), 536,544. 16. Csrothors, W. H. Cham. Re". 1931.8.353: reprinted in Colipcted Papers of Wolloeo Hume Comlhors on High Polymwic Subaloncea: Mark, H.: Whitby, G. S., Ed.; Inteneience: New York, 1 9 4 t pp 61.140. 17. Anon. Fortune 1940,22(2),56. 18 Rutledge, H. T. Sci. Am. 194O.i62(2), 78. IS. Sehid:owitz, P. India-RubberJ. L941,18,322; reprinted in Chem. Age 1941,44,293. 20. Sh0r.M. J.Chem. Edur 1944.21.88.
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21. Monnieff. R. W. il Chem. Educ. 1954.31.213. 22. Heeke*. W.W. J. Chem. Edue. 1953,30.166. 23. Hoff, G.,P. lnd. E q . Chem 1940.32,1560. 94 nnree.w * I nvoatuff~soorter ~ 1942.31.373.
university of Wismnsin: Madisan, WI,1983; '
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Higgina, J. G.Erpwimenfol Olganic Chemistry: Barnes & Noble: New York. 1971: Exp. 13, PP 115-123. 19. Humphrey., D. A. Damonsfrnting Chemistry: 160 Experiments to Show Your Sfudenfs:Chemirtn.Department, MeMsster University: Hamilton, ON. Canada, 1983;
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30. Summer1in.L. R.;Ealy, J. L., Jr. Chemico1Dornonsfroliona:ASourcebwklor Teochera; American Chemical Smiaty: Washington, DC, 1985; PP 124-125. 31. Kinsinger, J. B. J. Chom. Educ. 1958.35, A607. 32. Bassert, R. C.; Croft, R. G.:Bwrd, C. E. J. Chem Educ. 1949,26,611.
