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S D A PHOTO BY FORSYTHE

Cotton-Yesterday, Today, and Tomorrow HENRY G. KNIGHT

Bureau of Agricultural Chemistry and Engineering, United States Department of Agriculture, Washington, D. C.

Up Tο the present the work of me-chanical and textile engineers has been more influential than that of

chemists in the development of the cotton-textile industry. Nevertheless, the con-tributions of chemistry have been most essential to this development.

The principal applications of chemistry in the cotton-textile industry have been in the bleaching, dyeing, and finishing of fabrics to make them more attractive, more useful, and more durable. The chemical treatments used to accomplish these ends may be classified into four groups, according to the manner in which they affect the fiber:

(1) Treatments that take undesirable substances out of the fiber, exemplified by scouring and bleaching;

(2) Treatments that add something to the fiber without altering the chemical composition of the underlying cellulose, exemplified by dyeing;

(3) Treatments that help to modify the form and density of the fiber, such as mercerization ;

(4) Treatments that actually change the chemical composition of the fibers, without changing their form, exemplified by acetylation.

Scouring or purification of cotton goods, an example of the first group of treat-ments, is accomplished by a process known as kier boiling, which removes natural fats and waxes, mineral matter, and protein and pectic substances, together with any

1 Abstract of an address before the general meeting at the 103rd meeting of the AMERICAN CHEMICAL SOCIETY, Memphis, Tenn., April 20 to 23, 1942.

oil or grease acquired by the yarn during spinning and any warp-sizing materials present in the woven fabrics. In the early days of the industry cotton fabrics were sometimes bleached by the method used for linen—that is, by exposure to air and sunshine. It was later discovered that chlorine dissolved in lime water was more effective and by 1830 chlorinated lime be-came available in the form of a fairly stable powder. Since then most cotton fabrics have been bleached for use as white goods and in preparation for dyeing and printing.

The dyeing of cotton goods and other fabrics was originally an empirical process limited to the application of one of a few natural dyestuffs, after mordanting with a heavy metal salt (sometimes over tannin extract) to set the color. The first direct cotton dye (Congo Red) was used in 1884 and the first important azoic dye (Para Red) in 1889. Synthetic indigo became available in 1880, and other vat colors during the first decade of the present cen-tury.

Today, dyeing is a carefully controlled chemical process for which a vast army of synthetic dyestuffs of different classes, with appropriate mordants and fixing agents, developers, or other dyeing assistants for each class, have been made available through chemistry. Dyestuffs and print-ing colors and methods for applying them are among the most important contribu-tions which chemists have made to the cotton-textile industry. The pleasing and

permanent colors we have today are no doubt among the most important f-governing utilization of clothing ano household fabrics.

In addition to dyeing and printing, other additive finishing treatments are often applied to cotton fabrics to impart properties that will make them more useful for special purposes or otherwise more acceptable to consumers—for example, mildewproofing, waterproofing, and fire-proofing treatments. Substances can now be added to cotton fibers to make them resistant to mildew and other microorgan-isms which destroy cellulose, and occa-sionally chemicals are added to retard burning. But unfortunately the more effective flameproofing or so-called fire-proofing agents are soluble in water and therefore easily removed by rain. Sub-stances have also been added to cotton fabrics to make them water repellent.

Besides the additive finishing treat-ments for imparting mildew resistance, flame resistance, and water repellency to cotton textiles, there are many treat­ments of this class designed for special purposes. Some are applied to fabrics used for wrapping silverware or lining silver chests to make them absorb sulfur gases from the air and thus protect the silver from tarnishing. Others are in­tended to make cotton fabrics useful as substitutes for leather. And still others are intended to impart softness, stiffness, smoothness, luster, or some other special property to cotton fabrics.

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The recent introduction of new chemical products, such as cellulose esters, cellulose ethers, synthetic resins, and other plastics, has made possible the development of new additive finishes for cotton clothing and household fabrics that are not removed by washing. Application of cellulose com-pounds to cotton fabrics has resulted in greatly improved materials for window shades and other uses. Another process, which prevents creasing and crushing of cotton fabrics, comprises the implication of synthetic resin in an intermediate stage within the fibers, the resin on the surface being subsequently removed as com-pletely as possible. By means of alkali-soluble cellulose ethers various perma-nent finishes have been imparted. One is a glossy finish like that of glazed chintz, and another is a finish having the appear-ance and feel of linen.

Mercerization is one of the most inter-esting and important of all the chemical treatments. The process, discovered by John Mercer in 1850, alters both the form and appearance of the cotton fiber. It causes the fabric to shrink considerably, but increases its strength and also the affinity of the cotton for dyestufTs. In this process the individual fiber, which ordinarily has the form of a flat twisted ribbon, swells, becomes almost cylindrical, and acquires a rough surface. One of the purposes of this treatment is to strengthen the fabric and permit dyeing to deeper shades. About 1890 it was discovered that under tension the fibers, which are distended and apparently softened by mercerization, are straightened and be-come smooth and lustrous. So today the mercerizing treatment is applied to cotton yarns and fabrics to give luster, as well as to increase strength and affinity for dyes.

There are only a few chemical finishing treatments for cotton of the fourth class— those that actually change the chemical composition of the fiber, without chang-ing its form. Examples of such treatments are: acetylation of the cellulose fibers to produce cellulose sulfonic acid or other cellulose ester on the fiber surfaces, and production of a mixed ether of cellulose on the fiber by treating with a substituted quaternary ammonium salt and sodium acetate and decomposing the intermediate product with moderate heat.

These treatments, which actually change the composition of the fiber by producing cellulose compounds on the surface, open up a new field of research in chemical finishing of cotton textiles which invites further investigation.

In the United States the growing, handling, manufacturing, and utilization of cotton are closely entwined with our daily lives; in truth, it is a part of our very existence. This being so, the answer to the question of what the future holds for the cotton industry is of deep concern to everybody.

It is difficult to conceive of an industry

so huge as the cotton-textile industry and producing such a wide variety of products, as not being prosperous during the extrava­gant years of the late 1920's. And yet the industry a-s a whole was not prosper­ous during that period.

The depression beginning in 1929 came when the industry was ill-prepared to do little more than try t o keep losses at a mini­mum and wait until our national economy should take a turn for the better. There were signs of revival in the middle thirties, but by then new factors had come into the picture. So-called artificial silk, today universally known a s rayon, was fast be­coming a textile fiber of importance. Paper had acquired a strong foothold in many important uses, such as bags for food products and cement, where cotton and its competitor, burlap, had once reigned supreme. In the offing were nylon, vinyon, fiberglas, and other man-made fibers ready to enter the textile field. And here is a significant fact and a broad hint to the cotton industry—all these com­peting textile materials are the outgrowth of research. The cotton industry might not have suffered such an economic set­back if it had put more faith in research and pushed it as hard as research was pushed by the developers of these com­peting synthetic fibers.

The present war prosperity, shared in full by the cotton-textile industry, tends to obscure the real condition of this indus­try. For decades leaders both in and out of the industry have pleaded strongly and worked tirelessly for an expanded research program to prepare the industry for the inevitable competition from textiles and other products which are better meeting the public needs for many uses. Many organizations of a private, public, and semipublic nature are now undertaking research on cotton. The Southern Re­gional Research Laboratory of the Bureau of Agricultural Chemistry and Engineer­ing, United States Department of Agri­culture, the national Cotton% Council, with headquarters in Memphis, the Cot­ton Textile Institute, the Textile Foun­dation, the United States Institute for Tex­tile Research, the American Association of Textile Chemists and Colorists, and many state and private universities, are either conducting or sponsoring research to increase the utilization of cotton. A few of the larger textile mills have organ­ized their own research departments to improve the quality and lower the cost of their products.

Obviously, the properties of yarns and fabrics depend ultimately on the physical and chemical properties of the individual fibers. AJthough man has been remark­ably ingenious in devising machinery for spinning and weaving cotton into fabrics with an almost unlimited variety of prop­erties, he has been making use of cotton's inherent fiber properties in only an em­pirical manner. B y trial and error he has found that cotton of certain varieties

grown in certain localities is suitable for, say, tire cord, while other varieties grown in other localities are not. Moreover, there are comparatively few fabric uses for which even an empirical relationship of this nature has been established. Such a condition has existed partly because use requirements, in general, have never been carefully and systematically studied, and partly because only a few of the relevant fiber properties have been known or measurable.

Various scientists who have studied the structure of the cotton fiber have reported that the cellulose wall is made up of layers of fibrils alternately spiraling in opposite directions, but roughly parallel to the axis of the fiber. Studies of the fiber with all available facilities have led to the belief that the cellulose of cotton fibers exists in two forms—amorphous and crystalline. The general concept of the submicroscopic structure of cotton cellulose is that in some places the long-chain cellulose molecules are arranged substantially parallel to each other in parallel groups, or micelles, which are crystalline in character, and that some portions of molecules cross from one group to another through regions of porous or amorphous matter. The proportion of the cellulose molecules arranged in crystalline alignment determines the relative strength of the fibers. The cause of lower strength of cotton fibers, as compared to flax, ramie, or hemp, is the lower proportion of cellulose in crystalline structural align­ment.

While the naturally poor alignment of cotton fiber is a fault from the tensile strength standpoint, it is advantageous from other standpoints. That cotton is one of the least brittle of vegetable fibers may be ascribed to the considerable proportion of amorphous cellulose, which in turn seems to be related to the poorer alignment of cellulose molecules. This lack of brittle-ness makes it possible for cotton fiber to withstand continued shock or impact— such, for instance, as in automobile tires— to a far greater extent than many other plant fibers.

Intensive and more comprehensive re­search is needed to explore the various physical and chemical properties of cotton fiber, to disclose their interrelationships, and to devise better means of measuring many of them, so that all these properties may be utilized in the best possible way. Sufficient research has already been done along this line to demonstrate its real value in connection with the development of new and improved cotton products. This is true not only from the standpoint of mechanical processing, but also from that of developing new and improved chemical treatments to alter or enhance the properties of cotton products.

There are many unsolved problems associated with the development of new and improved cotton products affecting mechanical processing machinery. Re­search on the development of cotton prod-

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ucts is not new. The cotton-textile in-dustry from its beginning has developed many hundreds of products. But very few of these have been developed by the use of scientific methods to determine the re-quirements for specific uses. This was only natural in an industry which during its growth period found markets for almost any type of staple fabric which could be produced. But today, considering that the present war demand for textiles is temporary, the industry is facing an entirely different problem. Competition from other fibers and products is keen and any further expansion of markets, or oven the holding of some of the present markets, can be accomplished only by in-tensive research aimed at developing new and improved cotton products for specific uses.

The procedure involved in this type of research is quite straightforward, and its effectiveness is limited only by the extent of man's ingenuity. Three principal steps are involved: first, the determination of permissible cost and the basic physical and other requirements of the particular use being studied; second, the experimental development of a cotton product designed to meet the requirement of the use; and third, laboratory and service testing to determine whether the experimentally developed product meets all use require-ments. Repetition of these steps, where necessary, finally leads to the development of a satisfactory cotton product or to a reliable conclusion that such a develop-ment is not feasible.

Although it may seem obvious that such a procedure is the one and only logical method to be followed in developing new and improved cotton products, this has not been the general procedure in the cotton industry. However, there have been a few notable exceptions which definitely establish the effectiveness of this type of research. Tire fabric is an outstanding example of a cotton product, which, during its entire history, has been developed into a better and better product by the use of scientific methods with attention focused directly on the use requirements. Open-mesh cotton bags for handling fruits and vegetables are another example of a widely used cotton product developed in this manner. Research of this nature must be both broadened and intensified. The re-sults obtained will be a major factor in determining the future of the cotton in-dustry.

Within recent years more research has been done on chemical finishes than in any other field. This does not mean, however, that more research of this nature is not needed or that opportunities for increas-ing the utilization of cotton in this manner have been lessened by the results already obtained. Precisely the opposite is true. Instead of lessening these opportunities, recent progress in the development of new and improved, chemical finishes has actually indicated new opportunities which

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10 years ago were only in the realm of speculation. T h e possibilities of some of these newly developed finishes have been only partially explored, and the introduc­tion of new types of finishes serves only as a stimulus for the discovery and develop­ment of other types.

The needs with regard to chemical finishing include more effective finishes for some purposes, and more permanent and less expensive finishes for most pur­poses for which finishes are now applied. Also, new kinds of finishes will be needed to produce new effects in cot ton textiles to adapt them to uses now served by other fibers or to other uses not ye t con­ceived. A few specific examples of re­search needed in chemical finishing might be mentioned. There is a need for more research on mildewproofing, especially for clothing fabrics where it is desirable that the appearance, feel, and draping proper­ties of the fabrics be unaffected. There is need, too, for improvement in making wearing apparel water repellent, and for new t rea tments to replace the rubber coating and rubber impregnation t reat­ments so extensively used in the past to make hospital sheeting and other fabrics impervious to water. Finally, since cotton is competitive with rayon, nylon, and other synthet ic fibers in many uses, finishes must be developed which will give to cotton fabric as many as possible of the properties of t he fabrics made from these other fibers.

The Southern Regional Research Labo­ratory a t New Orleans, one of the four laboratories recently established by Con­gress to develop larger industrial outlets for farm products, is giving most of its at tent ion to cotton. An extensive pro­gram of research has been planned to in­crease the utilization of cotton and cotton­seed products. The program for cotton includes research on the fiber, on me­chanical processing, and on chemical finishes. Fach branch of research is handled by a separate group or division.

The objective of the first group, the CV)tton Fiber Research Division, is to determine the relationships between the chemical and physical s t ructures and properties of cotton fibers and the char­acteristics desired in textiles for specific uses, and to learn how to improve cotton fibers for specific textile and o ther uses by changing them physically or chemi­cally.

One objective of the second group, the Cotton Processing Division, is to deter­mine the physical requirements of a textile for a specific use, regardless of the part icu­lar kind of fiber t ha t may have been used in the past , and then to learn how to meet these requirements as fully as possible with cotton, by controlling the properties of the yarns through necessary mechanical processing and those of the fabrics b y em­ploying suitable weaving pa t te rns . An­other objective is to improve and develop cotton-processing machinery through bet-

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ter application of basic mechanical prin­ciples in order to reduce cost and improve quality of products.

The objective of the third group, the Cotton Chemical Finishing Division, is to improve additive and modifying finishing methods which will impart the properties most desired in textile products for spe­cific purposes.

The research work on cotton at the Southern Laboratory and, in fact, all of the work of the Bureau of Agricultural Chemistry and Engineering of which it is a part, is now specifically directed toward aiding the Nation in the war effort. Most of the projects which would require several years to yield useful results have been deferred until the end of the war. Short-time special projects of a defense nature are given precedence over all others.

One accomplishment of this special war work is the development of means for cutting cotton to uniformly short lengths so it can be used with existing commercial equipment to supplement linters for mak­ing smokeless powder. Some of the ob­jectives of present war work are: plastic-coated or impregnated fabrics for replac­ing rubberized fabrics; an unlined cotton fire hose to replace linen hose of the same type; rotproofing treatments suitable for commercial application to cotton fabrics for sandbags and revetment covers; im­proved mesh fabric for use as a base for t ransparent plastic substitutes for window glass ; the development of cotton products to replace those made from imported fibers; and other projects which cannot be men­tioned on account of their defense nature.

Up until around a year ago there was a great deal of discussion about the future of the whole cotton industry. Because of low prices and mounting surpluses, the outlook was not very encouraging. But the war has changed the appearance of the picture almost overnight. Instead of the low prices that existed 18 months ago we are now enjoying the most favorable prices that we have had in years, with domestic consumption at the highest level in his­tory, ana some feel that because every­thing is all right now our cotton troubles are over.

But that is not the case. The tempo­rary relief and prosperity that we are now enjoying is like a shot in the arm, the effects of which will die out when the war is over. So instead of relaxing and feelinsç that our troubles are over we should take advantage of the present favorable situ­ation by pushing constructive research so that the throne which has been recently threatened by paper, rayon, and other synthetic fibers will be made safe for Kins Cotton.

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