CHEMICAL INDUSTRY MEDAL T
H E Chemical Industry Medal of the Society of Chemical Industry was presented to Elmer K. Bolton, chemical director of E. I. du Pont de Nemours & Company, Inc., a t a joint meeting of the American Section of the Society of Chemical Industry, the New York Section of the AMERICAN CFIBMICAL SOCIETY, and the New York Section of the American Institute of Chemical Engineers on November 7, 1941, with Lincoln T. Work presiding. The medal is awarded for valuable application of chemical research to industry. The meeting was held a t The Chemists’ Club in New York. C. M. A. Stine, vice president of the du Pont company, spoke on the personal side of the medalist’s life and Roger Adams of the University of Illinois told of his technical accomplishments. Lammot du Pont, chairman of the du Pont
Board of Directors, expressed the company’s appreciation of Dr. Bolton’s services. The medal was presented by Wallace P. Cohoe, past chairman of the American Section, and then Dr. Bolton gave an address on nylon. The recipients of the Chemical Industry Medal (until 1933 the Grasselli Medal) are as follows: Allen Roger8 W. H. Fulweiler B. D. Saklatwalls E. R. Berry Charles R. Downa Harold J. Rose Bradley Stoughton Per K. Frolich L. V. Redman
1920 1922 1924 1925 1926 1928 1929 1930 1931
G. L. Clark J. Q. Vail F. J. Metzger E. R. Weidlein W. S. Landis E. J. Crane J. V. N. Dorr R. E. Wilson Elmer K. Bolton
1932 1933 1934 1935 1936 1937 1938 1939 1941
DEVELOPMENT OF NYLON E. K. BOLTON E. I. du Pont de Nemours & Company, Inc., Wilrnington, Del.
S FAR back as 1929 an objective of du Pont research was to create a distinctly new fiber. The result was nylon. Attention was first directed to a study of derivatives of cellulose, particularly the ethers and new types of esters. These materials, although capable of being spun into yarns, appeared to offer no significant advantages in cost or properties compared with the known types of rayon. During the course of this investigation, certain nitrogencontaining derivatives of cellulose were prepared with the thought that amino or substituted amino groups would modify the properties of cellulose, particularly its dyeing characteristics, and make it approach in this respect more closely to silk or wool. This investigation, however, was unsuccessful in reaching the desired goal. While this work was under way, a background of scientific work on linear polymers was being laid under the direction of Wallace H. Carothers and his associates, and this led eventually to the development of nylon yarn. In order to answer the question frequently,asked, “How did the du Pont Company ‘discover’ nylon?”, it may be of interest to describe the circumstances which led to the invention of this class of polyamides. In 1927 C. M. A. Stine, who was then chemical director, foresaw the need of a more active program of research to provide new developments which would ensure the future growth of the company and decided to set up fundamental research as an important activity of the Chemical Department. As contrasted with applied research, with which the research divisions of the manufacturing departments were fully occupied a t that time, this new category of research aimed a t filling in the gaps of knowledge affecting important chemical processes and products, and exploring new realms of chemistry to discover scientific facts which might be of value in laying a foundation for future applied research. This activity was under Dr. Stine’s direction until the middle of 1930, when he was appointed vice president and adviser on all du Pont
research. Fundamental research in the Chemical Department has grown consistently since its inception until it now constitutes a major part of the activities of the department. After the decision was made to carry out fundamental research in organic chemistry, Wallace H. Carothers, who had served two years as an instructor a t Harvard University, was persuaded to join the Chemical Department. He was surrounded by a small group of well trained organic chemists and was encouraged to work on problems of his own selection. Carothers chose the subject of polymerisation by condensation and the structure of substances of high molecular weigl This proved to be an unusually fertile field since there had been little exploration of polymers of this type, as evidenced by the meagerness of the literature. I n 1928 Carothers began the study of polycondensation whereby linear polymers are produced, and this led eventually to the invention of nylon. The research activities preceding the manufacture of nylon yarn snay be divided into three periods :
A
1. Fundamental research activities which provided]the foundation for the development. 2. Concentration of attention on polyamides, which led to the synthesis of a polymer having properties suitable for use as a new fiber. 3. The development of gractical processes for the manqfacture of intermediates an polymer and for the spinning of fibers.
Fundamental Research Time permits only reference to the high lights of the first period or the scientific background for the nylon development. Carothers first directed his attention to polycondensation involving the reaction of difunctional molecules. He chose as his first attack the condensation of dibasic acids with glycols and selected reacting materials which would preclude the formation of five- or six-membered rings. He obtained, with53
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out exception, polymers characterized by recurring structural units which might be crudely pictured as hooked together like a chain of paper clips. Dibasic acids (such as malonic, sebacic, maleic, fumaric, and phthalic acids) were condensed with glycols (such as ethylene, trimethylene, hexamethylene, and decamethylene glycols) and esters of a highly polymeric character were obtained as reaction products. By a study of their physical properties and molecular weights, Carothers proved that these esters were not monomeric large-membered rings. The lowest molecular weight observed for any of the solid esters was 2300 and the highest 5000. After investigating the preparation and properties of many different polyesters, Carothers next turned his attention t o the study of the amide of e-aminocaproic acid. Upon heating, molecules of this material reacted with one another to form, as the principal product, a polycondensation polymer containing a t least ten molecules of the amino acid. The polymer was a hard waxlike material, insoluble in most organic solvents. After work had been under way less than two years, a significant advance in the preparation of linear polymers, particularly the polyesters, was achieved through the use of the molecular still. This tool made it possible to carry polymerization more nearly to completion by the elimination of water formed by the condensation reaction. The molecular still proved to be a valuable tool in obtaining products of higher molecular weight than were heretofore attainable with ordinary vacuum distillation equipment. Without this technique Carothers might have failed in his search for superpolymers. From this time on, attention was concentrated on the socalled superpolymers. By placing the polymeric esters having molecular weights up t o 5000 in the molecular still, and heating by means of a bath a t 200” C. for a total of twelve days, Carothers and his associates were able to increase the molecular weights substantially, obtaining values from above 10,000 to 25,000. At this time he applied the term “superpolymer” to materials having a molecular weight of 10,000 or higher.
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The new superpolyesters derived from the condensation of glycols and dibasic acids were tough, opaque solids which, a t an elevated temperature, became transparent viscous liquids. The important observation was made that filaments could be obtained by pulling threads from the molten polymer with a rod. Of still greater importance, however, was the observation that, after the superpolyester filaments had cooled, they could be further drawn to several times their original length, and that such cold-drawn fibers were quite different in physical properties from the initial mass of polymer or from undrawn fibers, that is, fibers pulled from the molten polymer with a minimum of tension and not subjected to further stress. For example, cold drawing developed transparency and a high degree of luster. Furthermore, and this was the really significant difference, cold-drawn fdaments had a much higher tensile strength and elasticity than undrawn filaments. They were sufficiently pliable and tough to be tied into hard knots, whereas undrawn fdaments were inelastic and fragile. The further striking observation was made that, unlike the ordinary textile fibers, the wet tenacity or tensile strength of these superpolyester fibers was approximately equal to the dry tenacity. Moreover, drawn polyester fibers were very superior to rayon in elastic properties. X-ray diffraction patterns indicated that superpolyester fibers in the undrawn state were crystalline, but that the crystals had a random orientation. Cold-drawn filaments, on the other hand, gave a fiber pattern which indicated a considerable degree of orientation parallel to the fiber axis. The character of this pattern, incidentally, is similar to that obtained from natural silk fibers or from rayon filaments spun under tension. I n addition to forming filaments by pulling a thread of the molten polyester with a rod, it was later found that filaments might also be formed by dissolving the superpolymer in chloroform and dry spinning it like cellulose acetate rayon. Such fibers, like undrawn fibers pulled from the molten polymer, exhibited random orientation of the crystals, but again as in the case of melt-spun fibers, cold drawing produced orientation along the fiber axis. Up to the time that the above s u p e r p o l y m e r s were made, this study was wholly fundamental in character and was designed to throw further light on certain aspects of polymerization. The rather striking properties of fibers obtained from the superpolyesters aroused the hope that it might be possible to make a fiber of commercial utility from some type of synthetic linear superpolymer. Research was accordingly directed to this practical end. Continued investigation showed, however, that fibers from the polyesters were of only theoretical interest, as their melting points were too low for general textile purposes and their solubilities r e r e too great. When the above results were preCHEMICAL sented a t an AMERICAN SOCIETY meeting in Buffalo, a leading New York newspaper, referring to the superpolyester from ethylene Nylon’s First Bath. Molten Polymer, Extruded on This Huge Casting Wheel, glycol and sebacic acid, stated that I s Quickly Sprayed w i t h Water Which Helps It to Solidify Into a Strip KesemDr. Carothers had predicted the posbling Ivory. In Later Operations It Is Chopped, Melted, and Extruded Again sibility of making women’s stockings As Filaments.
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from antifreeze and castor oil, which, after all, was a reasonably accurate statement iv layman’s language. A linear polyamide had been made earlier from &-aminocaproic acid by the condensation of molecules by dehydration at atmospheric pressure or under diminished pressure in the usual distillation equipment. This material had, however, a low molecular weight. When this same polyamide was heated in the molecular still for 48 hours a t 200’ C., the product became harder and tougher than before this treatment. Like the low-molecular-weight polyamide, it was insoluble in common organic solvents with the exceptions of hot phenol and hot formamide. The change in properties indicated a considerable change in molecular weight but no actual measurements of molecular weight were made, owing to the lack of any sufficiently reliable method. It was concluded that the polyamide so formed was too infusible and insoluble to allow a ready test of its spinnability. Processing of Nylon Yarn on Machines Which Twist the “Bundle” of Slender Filaments for Ease in Handling I n the hope of obtaining a compromise between the properties of the polyesters and the polyamides, mixed polyester -polyamides of a survey of his scientific work in this field, he wisely decided were next prepared by heating together trimethylene glycol, to resume work on the superpolyamides. Polyamide formahexadecamethylene dicarboxylic acid, and eaminocaproic tion with 9-aminononanoic acid was selected for study. The acid. On account of the high solubility and the low meltpolyamide from this acid, after treatment in the molecular ing points of the mixed polyester-polyamides, they were still, was spun into fibers which had a melting point of 195” C. not, however, of practical interest from the standpoint of and, after cold drawing, were equal to silk in strength and textile fibers. pliability. These observations renewed the hope of making A brief summary of the work to this point shows that by an entirely new type of textile fiber from a synthetic material means of the molecular still Carothers was able to prepare of the polyamide type, and clearly indicated the possibility linear superpolyesters having molecular weights above 10,000 of obtaining from Carothers’ fundamental work on linear polyfrom which fibers could be formed. These fibers were only of mers a material for fibers of commercial utility. theoretical interest, however, because of their low melting Following these observations, Carothers prepared polypoints and wide solubility and had no utility as textile fibers. amides from a variety of amino acids and also from dibasic The mixed polyester-polyamides exhibited the same defiacids and diamines. On February 28, 1935 (a now historic ciencies. I n this early period Carothers had made a superdate), the superpolymer from hexamethylenediamine and polyamide from €-aminocaproic acid but no fibers were preadipic acid was first synthesized. The resulting polymer, pofypared from this polymer. The refractory qualities of the hexaniethylene adipamide, was called “66”, the first digit inpolyamide, in Carothers’ opinion, made it diacult to prepare dicating the number of carbon atoms in the diamine and the satisfactory fibers. second digit the number of carbon atoms in the dibasic acid. Just as in the case of the polyesters previously mentioned, Polyamide Synthesis fibers could be formed from this new 66 polyamide by melt spinning or by dry spinning from a solution of the polyamide The second period of the research leading to nylon was in a solvent such as phenol. Also, as in the case of the polycharacterized by a concentration of effort in the laboratory to esters, undrawn fibers of the polyamide underwent a remarksynthesize a polyamide which might form the basis for a comable change in physical properties on cold drawing. The mercial textile fiber. cold-drawn 66 fibers possessed a high tensile strength and In the earlier work Carothers had not been successful in elasticity. Moreover, these polyamide fibers were insoluble preparing a superpolymer having the necessary properties for in common solvents and melted a t 263” C., which gave a marthis purpose. Other research work on cellulose derivatives gin of safety above commonly employed ironing temperatures. to obtain a distinctly new fiber had reached a stage where Polymer 66 was selected for initial manufacture because it little hope was held of attaining the objective. A large had the best balance of properties and manufacturing cost amount of time and money had been spent on the various of the polyamides then known. phases of the fiber program, but the results were chiefly of theoretical interest. It was therefore a matter of considerable Although adipic acid was produced commercially in Germany, it mas necessary to develop a new process to meet the concern to determine what practical use could be made of the conditions at the du Pont Company’s plant a t Belle, W. Va., scientific information that had been acquired on superpolywhere, because of the catalytic technique involved, it was mers. The possibility of laying the foundation for a new decided to make this intermediate. Hexamethylenediamine commercial fiber development appeared to be remote, with was only a laboratory curiosity and a process for its commerthe result that research work in this field was discontinued cial production had to be worked out. It was felt, however, for a number of months. that it should be possible by new catalytic processes to make Carothers, however, was encouraged to direct his work on this material from adipic acid. After the polyamide to be superpolymers specifically toward the development of a product which could be spun into practicable fibers. On the basis made was selected, development of a practical manufacturing ~~~
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E. B. Benger, at that time general assistant chemical director, and A. P. Tanberg, director of the Experimental Station, contributed to the progress of this work by advice, encouragement, selection of personnel, and assistance in the organization of these activities. In view of the long experience of the Rayon Department in textile operations of this type, the development of procedures and equipment for the cold drawing, sizing, twisting and packaging of the yarn was under the direct supervision of G. P. Hoff, who was then assistant director of the Rayon Research Division. The Engineering Department, under E. G. Ackart, had the responsibility for the construction of the pilot and large-scale plants. Time does not permit recounting the difficulties in working out the process elements of all these operations on a laboratory and semiworks scale. No similar previous experience with the types of processes employed for these intermediates existed in the company. Nylon polymer was an entirely new Nylon in Large Diameters, Produced for Surgical Sutures, Fishing material with properties different from those Leaders, and Bristles for Toothbrushes, Hairbrushes, and Industrial of any previous synthetic product, and spinBrushes, Etc. ning it ‘from the molten pdymer Gas entiEely different from spinning either acetate or viscose rayon. Information was therefore acquired only by painsprocess was turned over to other groups and Carothers was taking experimentation a t each step. The ingenuity and encouraged to explore other types of polyamides inasmuch as talents of some of the best chemists and chemical engineers this selection of 66 was made when only a small number of the within the company were needed to bring the development many theoretically possible superpolyamides had been exwork to a successful conclusion. amined. He and his associates prepared and studied many different kinds of polyamides from diamines and dibasic acids, from amino acids, and from interpolymers of dibasic Final Process acids, amino acids and diamines, but polyhexamethylene adipamide continued to appear the most attractive for textile The process as finally developed for the manufacture of nylon and its fabrication into yarn may be briefly outlined as purposes. His further work therefore confirmed the wisdom of this selection. follows. For the present type of nylon, adipic acid and hexamethylenediamine are combined t o form a salt which is charged into an autoclave where polymerization is carried out, Development of Practical Processes Stabilizers are added to control molecular weight and viscosity. In this reaction a long-chain linear polymer is formed The third period of research covered the development on a with a molecular weight of 10,000 or higher. laboratory scale of the manufacturing processes for the interAfter polymerization, the molten nylon is extruded as a mediates, the polymer and nylon yarn, and the development ribbon onto a chilled roll, and the ribbon is cut into small on a semiworks scale of the chemical and engineering data for chips. This is a convenient form for storing, handling, and the erection and operation of a large-scale plant. The task subsequently blending various batches t o ensure uniformity of was enormous and the company’s Executive Committee dethe product. sired to have these processes worked out as quickly as possible; The nylon chips are charged into the hopper of the spinin the words of W. S. Carpenter, Jr., president of the du Pont ning unit and drop onto a specially designed heated grid where Company, to reduce to a minimum the “time between the the polymer melts. The melt is pumped and metered by test tube and the counter”, a large force of some of the most specially designed pumps and finally filtered through special competent chemists and chemical engineers available (some filter packs before passing through the spinneret to form filaof whom were temporarily transferred from the Engineering ments. All parts of the equipment must obviously be mainand Rayon Departments) was assigned to the project. tained a t a temperature above the melting point of the polyThe development of the process for the manufacture of mer, which is blanketed with an inert gas t o prevent any unadipic acid from phenol Fax under Roger Williams, chemical desirable effects from oxidation a t the elevated temperature. director of the Ammonia Department. The Chemical DepartBy the pressure of the pumps, the molten nylon is extruded ment had the responsibility for the laboratory work on hexathrough spinnerets. The filaments, which harden quickly on methylenediamine, but the semiworks investigation was striking the air outside the spinneret, are wound up on bobcarried out a t the company’s Belle plant. The Chemical Debins by special take-up and traverse devices operated a t a partment developed the laboratory and semiworks process for thread speed of over 2500 feet per minute. the preparation of the 66 polymer and the spinning of the At this stage the filaments are in an undrawn condition, and fiber. The work within the department was under the gendo not exhibit the excellent tensile strength and elasticity ineral supervision of C. H. Greenewalt. Associated with him herent in the superpolyamides. By the application of a suitwere TV. A. Lazier, who directly supervised the laboratory able force, however, the nylon filaments are drawn out to work on the process for hexamethylenediamine, and G. D. about four times their original length. During drawing each Graves, who directly supervised the work of a large group on filament “necks down” and takes a smaller diameter, and the polymer and the spinning.
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after drawing retains this new dimension permanently. The fiber has become highly oriented and has a different physical structure, as can be shown by x-ray diagrams. It now has extremely desirable textile properties, particularly a high degree of true elasticity, combined with a tensile strength greater than that of any of the commonly used textile fibers. This cold drawing of nylon yarn, as well as sizing for the protection of the yarn during subsequent processing, is done on equipment specially developed for the purpose. Twisting and packaging are carried out on equipment familiar in the textile industry. For the hosiery industry the application of a knitting size is important, since knitting methods developed for silk depend on the natural gummy sericin coating to protect the yarn. To prevent excessive snagging of the fine filaments during the fabrication of the hosiery, nylon yarn must have a suitable knitting size, and this size had to be developed. As in the case of silk sericin, the knitting size is removed from the finished garment. Nylon yarn of the various deniers and counts is wound on packages suitable for the purpose for which it is destined, such as the manufacture of knitted goods, particularly hosiery, woven fabrics, and sewing thread. No complete picture can be given here of the numerous chemical and engineering problems which had to be solved in this development. Many types of spinning-cell melting grids were designed and tried before one was finally accepted which overcame difficulties incident to the very poor thermal conductivity of the polymer, coupled with the requirement that heated surfaces be maintained a t the minimum operable temperature. Pumps for the molten polymer represent a development in their own right, inasmuch as they must be operated under severe conditions at the high temperature of 285’ C., with small clearances and with no lubricant other than the polymer itself. Special abrasion-resistant steels that do not soften or warp at the temperature of operation were required.
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The entire spinning assembly involved radically new engineering developments to produce fibers of the required uniformity and with the other necessary qualities. Five different spinning units, each one embodying the newest ideas, were constructed before the pilot plant was erected. The pilot plant, which consisted of a bank of five spinning units, was operated by the newly formed Nylon Division of the du Pont Rayon Department under the direction of E. K. Gladding, formerly assistant manager of the Rayon Technical Division.
Nylon Hosiery The first nylon hosiery turned out, made by ordinary silk hosiery techniques, showed marked defects. The most serious was excessive wrinkling of the stockings during the dyeing operation, and this wrinkling could not be overcome by any subsequent pressing or “boarding” operation. The wrinkles appeared to be permanently set in the stockings. A scheme developed to prevent the possibility of wrinkling in the dye bath consisted of an operation in which the stockings, before dyeing, were placed on a form and subjected to a steam treatment a t high temperatures. This treatment, known as preboarding, sets the stitch and the form of the stocking and permits subsequent dyeing without trace of wrinkling. After a number of hosiery manufacturers had evaluated the yarn and pronounced the stockings to be of commercial utility, the decision was reached to go ahead at full speed with the construction of a large-scale plant which was announced October 27, 1938, by Dr. Stine. The first plant, located a t Seaford, Del., was designed initially for the production of 3,000,000 pounds of yarn per year; but before the first unit was in operation, plans were changed to increase the output to 4,000,000 pounds. I n turn, this volume of production was doubled to 8,000,000 pounds before the first plant was completed. Except for size, the Seaford plant was practically a duplication of the semiworks plant in all details. Each step of the process and the equipment for it had been worked out thoroughly on a semiworks scale, and it was unnecessary to gamble with untried methods and equipment on a full-plant scale. Rapid progress could be made only by carefully working out all steps on a semiworks or pilot scale before the construction of the large plant. As evidence of the thoroughness of this work by the chemists and engineers, the Seaford plant started operation early in 1940, and from the first day practically all yarn produced was of commercial quality. The development of manufacturing processes for the intermediates, polymer, and yarn represents one of the largest cooperative projects within the experience of the du Pont company. From the inception of the laboratory work until the designs could be turned over to the construction engineers, about 230 chemists and engineers were a t one time or another engaged on this development. It is not possible to mention the names of all of the men who worked with the greatest enthusiasm on this development, and to whom the fullest credit is due for bringing it to a successful conclusion. Less than five years elapsed from the invention of the 66 polymer by Carothers until a manufacturing plant was producing yarn for the hosiery trade.
Properties
Instrument Panel Watching Over the Manufacture of Nylon Yarn in the New du Pont Plant at Seaford, Del. Precision is maintained b controls which record every activity. Lights, chimes, and varicoIored linea traced o n charts record the operations.
Nylon yarn is the first truly synthetic fiber and has a closer similarity in both constitution and properties to silk than has any other fiber. For the first time the age-old problem of making a material closely resembling silk appears to be solved. It has the appearance and luster of silk, although the degree of luster can be modified as desired by use of a delusterant. It possesses, however, the advantage of having greater uni-
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formity than silk; in addition, filaments of any desired size can be spun. Two outstanding characteristics which make nylon yarn of particular interest for hosiery are tenacity and elasticity. The tenacity or tensile strength of the commercial product is about 5 grams per denier dry and 4.5 grams wet. The dry tenacity of good-quality silk is about 4.5 grams and the wet tenacity is about 3.8 grams per denier. I n fact, nylon has a tensile strength higher than that of wool, silk, rayon, or cotton. The elasticity of nylon yarn is truly remarkable. It will elongate 20 per cent before breaking. When stretched 4 per cent, held for 100 seconds, and measured 60 seconds after the load is released, nylon recovers 100 per cent; under the same conditions silk recovers only 50 per cent and viscose rayon only 30 per cent. In addition to these important properties, nylon is tough. The loop strength, which is a common measure of toughness, is about the same as that of silk, but nearly three times that of viscose process rayon. As fibers are given a higher degree of orientation to achieve better tensile strength, they usually become more brittle. Nylon, on the other hand, has excellent properties in the transverse direction, as shown by the loop strength, and is not brittle in this state of high orientation. Nylon has a high degree of chemical stability; it is remarkably stable to alkalies and affected very little by animal and vegetable fats or by peroxides. Its resistance to mineral acids, however, is not outstanding. Nylon is soluble in very few reagents and is not readily swollen. The yarn is not affected by any of the common dry-cleaning solvents. Mildew and mold will not grow on nylon, and it is not attacked by moths. Enzymes will not digest nylon. Bio-
Formation of Nylon Filaments from Tiny Holes in a Spinneret
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logically, the material is inert. Extensive tests on over 400 persons show nylon yarn to be harmless t o the skin, and the material is actually used for surgical sutures. Naturally, harmless finishes must be chosen for nylon fabrics as for any other product. While it is not possible t o specify an exact temperature a t which damage to a fabric may occur because of several other important factors, the safe ironing temperature for nylon fabrics, based on current yarn production, is about the same as for silk, wool, and acetate rayon. At 60 per cent relative humidity the water absorption of nylon is 3.5 per cent as compared to 6.5 per cent for acetate rayon, 12 per cent for viscose rayon, 11 per cent for silk, and 13 per cent for wool. Because of its low water absorption, garments fabricated from nylon yarn dry rapidly. Although nylon possesses some definite advantages over silk, it has certain disadvantages in its present form. Best results in dyeing nylon are obtained with the so-called acetate colors, whereas silk can be dyed with a wider range of dyestuffs. Research, however, offers the encouragement that modification of 66 nylon can enhance its dyeing characteristics. Both silk and wool, moreover, have greater resilience than nylon (that is, more rapid recovery from wrinkling or mild deformation) which is important for certain types of dress fabric. Although the resilience of a woven nylon fabric can be greatly improved by special finishing processes, it has not yet been possible t o impart to it the high resilience characteristic of silk and wool. Nylon can be fabricated into many types of articles in addition to textile yarns. By methods somewhat similar to the extrusion of fine textile filaments, it forms monofilaments of larger diameter, which are superior in many respects to imported hog bristles. They are widely employed in both toilet and industrial brushes, and are also finding use as tennis and badminton racquet strings, surgical sutures, fishing leaders, and similar products where a high degree of strength, toughness, and elasticity are demanded. Special treatments developed by research are utilized t o bring out the particular properties desired in these products, such as stiffness, impact strength, and fatigue resistance. Many other applications for types of nylons of different properties and in various forms and in diverse fields are under development. Although nylon yarn has been manufactured commercially since early in 1940, we have so far obtained only a glimpse of its possibilities. For the first time the supremacy of silk in the full-fashioned hosiery industry is threatened. Nylon offers the fabric designer the possibility of creating fabrics of far greater wearing qualities than have heretofore been attainable with silk or any other fiber. It makes possible, moreover, the construction of fabrics of extraordinary sheerness. Nylon yarn is being currently produced in our Seaford plant a t the rate of about 8,000,000 pounds per year, but demand has been so great that a new plant is now under construction a t Martinsville, Va. When this new plant reaches capacity production in the summer of 1942, the total annual output of yarn from the two plants will be about 16,000,000 pounds a t the normal deniers, or more than five times as much as the initial capacity of the first plant unit. In addition, plans are now under consideration for a still further increase in production. In this period of national emergency, nylon may prove to be of value as a replacement for silk in certain uses connected with national defense. Only time will reveal the full possibilities of this versatile new family of synthetic polyamides. Already numerous articles fabricated from some form of nylon are on the market, yet the nylon industry is only in its infancy. The development of a material of such potentiality has proved to be a great adventure in research.
