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FIGURE1. EXPANSION OF RUBBERINDUSTRY FROM 1850
ET
TO
1934
Rubber Industry at the Crossroads
HE year 1839 marks the birth of the rubber i n d u s t r y . Prior to that time the use of rubber was declining because the quality of the products made from it was poor. In that year Charles Goodyear, then living in Woburn, Mass., after a long series of experiments with a variety of different chemicals (including nitric acid for the use of which he obtained a patent in 1837), discovered what was subsequently termed ‘ ‘ ~ 1 canized” rubber. He mixed sulfur and white lead into rubber, heated the mixture, and arrived a t a product of improved strength. From this came vulcanWILLIAM ized rubber as we still know it. Shortly Ithaca, thereafter the Roxbury Rubber Company, subsequently known as the Boston Belting Company, began the nianufacture of articles by the Goodyear process a t Roxbury, Mass., now a part of Boston. From that time to recent years the ability of this industry to serve large and varied needs of mankind has been derived primarily from research-i. e., research in chemical laboratories, in the application of chemical data to rubber mixtures, in the design of rubber products, and in machine design. The industry grew slowly a t first. A few of its high spots are the invention of hard rubber in 1851 by Nelson Goodyear; the reclaiming of vulcanized rubber by Mitchell in 1881 and by Marks in 1899; the beginning of the plantation crude
rubber industry in the Far East in 1876; the start of the Akron industry, now the world’s great rubber m a n u f a c t u r i n g center, by Benjamin F. Goodrich in 1869; and theorganization of the United States Rubber Company in 1892, of the Goodyear Tire and Rubber Company in 1898, and of the Firestone Company in 1900. Figure 1 shows how the rubber manufacturing industry expanded from 1850 to 1934 and its widespread c h a r a c t e r today. It has grown within a period of less than 100 years from small beginnings to a mammoth industry which comprises over two hundred corporations manufacturing many thousands of articles of C. GEER vhich rubber is an essential part and of N. Y. which the total sales value in 1934 was nearly one billion dollars. By way of illustration the orginal Goodrich plant of 1869 (Figure 2) may be compared with its modern grandson of 1934 (Figure 3). In order to permit an easy appraisal of the scope of research in this industry, the following outline is offered to show the subjects which have engaged the rubber chemist and engineer and the relations of these subjects to each other: I. Crude rubber (CsHs), 1. Plantation practlce and control
362
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11. Crude rubber plus sulfur, heated, equals vulcanized rubber (C6Hs),S,. The rubber mixture or compound.
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APRIL, 193;
IADUSTRI\I, . O D ENGINEERING CHE\IISTRY
IRE FIQL FACT ’OR1
363
C‘ompanu
1. Materials mixed into crude rubber before vulcanizing
a. Sulfur b. Zinc oxide c. Accelerators d. Antioxidants e. Reenforcing pigments such as carbon black f. Plasticizers g. Colors h. Fatty acids i. Reclaimed rubber j. Deodorants 2. Product design, or new articles for specific uses: the compound in all its ramifications, such as tires, hose, shoes, ad infinitum; and fabric 3. The physics of vulcanized rubber: service tests, physical data, and values 4. Hard rubber (C6H.&3), 5. Mechanical coordination: mills, calenders, tubing machines, tire building machines 6. Latex with dispersed ingredients, then shaped, dried, and heated 111. Rubber plus sulfur monochloride. IV. Rubber derivatives: halides, hydrohalides, nitro derivatives, hydrogenated rubber V. Rubber isomers, cyclo rubbers VI. Synthetic rubber from isoprene or acet.ylene VII. The rubber molecule: fundamental properties, structure
Crude Rubber Naturally fundamental and outstanding is crude rubber, the essential raw material of the industry, which was formerly dirty, variable, and derived from hundreds of species of trees by crude irregular methods. There were, and still are, dozens of grades-Up River Fine Para, Camet’a, Coarse, Caucho, Kasai, etc. Although the plantations were conceived in 1876 through Wickham’s pioneer work, it was not until 1900 that plantation rubber achieved a “statistical position.” During 1934 the United States imported a total of 469,484 tons of crude rubber, of which wild rubber of all grades amounted t o only 0.92 per cent. Signscant, but of no moment as to tonnage, is the shrub rubber, guayule, now planted and harvested in California.
Plantation crude or raw rubber is a vegetable product taken from the sap of a tree. It exists in the markets in several grades and types. Nevertheless, because of excellent research work by the plantation chemists who have studied this colloidal suspension, this product has become marvelously clean, uniform, and useful. The creation and perfection of plantation rubber is a noteworthy achievement of the last fifty years. Rubber in the forin of cements finds a limited although useful place in industry, primarily as a n adhesive with limitations as to cost. In recent years rubber latex has undergone extensive investigation, and its uses have multiplied both in the condition as it comes from the tree and as more concentrated dispersions, until in 1934, out of a total of 465,000 tons of plantation rubber imported into the United States, some 10,726 tons (calculated as dry weight) of liquid latex and Revertex were imported. It is significant that the weight of this latex as dry rubber amounted to over 2.3 per cent of this total. Latex is successfully used for cement purposes, for there are no poisonous solvents to be wasted. It is mixed with the various pigments, accelerators, sulfur, etc., to be deposited then upon forms and subsequently vulcanized. The quality of the article thus obtained is higher than that when these materials are mixed into dry crude rubber by means of the usual mills. It is made into thread for fabric. Great stimulus has been given to the use of latex through the work of Hopkinson, Klein, Sheppard, and others since 1920. Is another revolution arising? Will liquid rubber (latex) displace the solid form? These are pertinent questions. It seems highly significant that so very large a proportion of the goods produced by the industry is still in the form of mixtures (“compounds’J as the rubber man terms them) of rubber with numerous other materials. Vulcanized rubber is a chemical substance and, whatever one’s theory may be as’ to the influence of sulfur in forming it, (CsH&Su is a fair expression of the material which is the essential part of over 99
364
Fl< GURE RriRtiEl I N FIGK
per cent of the dollar volume of the rubber industry. Fundamentally it is the same chemical as existed in Goodyear's first test.
cver, that with nearly every accelerator some portion ofziuc oxide is required. Only a few years later- -.froin 1910 to 1920--another vital problem in rubber quality and service v a s solved by research K d e of Hesearch chemists. Previously R. vital weakness in nilcanimd rubber in Improving was the ease Kith which it deteriorated because of oxidation. Rubber Rubber goods "perished" all too quickly. So the chemist C B G M I C A L 1 1 ~ - made a v a i l a b l e o r g a n i c compounds t o retard this SEANCW. Theaddition of s u l f u r t o r u b b e r oxidation and gave us anwas controlled up to tioxidants of many types, 1906 as to time, and as well as a w e a l t h of a certain degree as to literature about them. Vulcanized r u b b e r goods temperature, b y t h e may last in service, except use of a. limited number of substances, chiefly for wear, essentially as long o x i d e s of lead, calas the needs demand. c i u m , a n d niagneThe g r o w t h of t h e tire sirim. I n that year industry brought the Oenslager f o u n d cerchemist into action a,gain. 1Ie made what is ranked as coiiricry, n. R Goad,rch ~~m~~~~ tain organic coma third m a j o r research F ~ C ~ 4. W ONE OX THE E ~ R M K S T p o u l l ~ kn m t of them achievement-the use o i Fhtilrrc TIRES(34 X 3) RUILT E N containing n i t r o g e n , 1896 which would decrease reenforcing pigments. It this rate. >?as f o u n d t.hat t h o s e Itaoici develournents in the study and use of these ormnic powders which had the finest degree of subdivision accel&ators v e r i brought about by'a considerable nun& of !?hen dispersed into rubber chemists. Research laborstories flourished, and the patent Courleau. B. F. Qoodrich produced a supporting CWL9R"V Literature on accelerators has expanded to the proportions of a effect, with the result that P~GURE 5. A MODERNLowRood. Research work has developed orxanic accelerators to $'HBSSUBB COlrD 'FIRE 6ll practically every need. Some-activate only a t relatively the abrasive wear of such a compound was greatly imhigh temperatures-that is, in the order of 290" to 300" F., and others cause rubber to combine with sulfur over reasonproved. The most valualAe of these powders is carbon black, made from natural gas. Formerly used oiily as a coloring able periods of time at room temperatures. A tremendous quality improvement was brought about. The accelerator agent, it was found about 1915 that xvhen used in very much larger proportions the resistance of the treads of automobile not only speeded the time of vulcanization but it also notably tires to abrasive wear was notably improved. enhanced the service of rubher goods. It is significant, how-
At’RIl. I % l i
INDUSTRIAL ZRiU KNGINEERING CHEMISTItY
The rapid develol~ineritof ttccelerators, antioxidants, and carbon black, accompanied as it was by the introduction of tlie cord tire, led tu m e of the most amasing quality changes of all history. Tire service in 1910 was nieasured in terms of 3000 miles. Within t,he short period of 10 years the mileage lcaped fire to ten times. Whcreas the production planner f o r m e r l y could count upon t h e d e of five tires per car per year and even in 1920 he c o n s i d e r e d three tires per car per year a fair average, h e e s t i mates for 1935 a replacement d e mand of only 1.32 Picum 6. TEERUBBERSHOEOF 1800 tires P e r c a r . (Figures 4 and 5 illustrate the tires of 189Gand 1935.) Thesesimple figures hold a twofold meaning: Credit is due the research chemist and designer, good roads, and better automobiles: but the fa& show how blind we all were in the years 1915 to 1925 to the trend of tire service. Tire factories were built or enlarged t o care. for the apparent potential demand calculated from the mileage records of thme days, but we all failed to anticipate such radical service improvements. As a result the consumer of tires has enjoyed unprecedented price bargains and service values, but the owners of the common stocks of Nbher companies have suffered severely. Research in the rubber industry was badly timed. Had the chemist been ten years sooner in the perfection of organic accelerators, ailtioxidants, and carbon black, and had the cord tire been perfected as early, i t is doubtful if our rubber factoriev today would possess so large an overcapacity. Because of accelerators very small amounts of sulfur may be used without the appearance of surface “bloom” after vulcanization. Therefore, colored rubber goods have been made possible by t.he chemist, and beauty has entered the rubber industry. As a further refinement we now have perfumes to give agreeableodors to the finishedrubber. Theold-timemillroomforeman’s smells of Black Kasai, Red Masai, and Cametn Seem gone forever. Our rubber products, if you please, must possess the odors nf the drawing-room and the colors of lipstick and rouge1 API,I,IED ~ t E s E A R C I i . ‘fhe chemist has not been tho only research worker in the r u b b e r i n d u s t r y . His achievements were reduced to practice and pressed into service by R g o n p of men which the industry calls the ‘,compounders” and “designers.” The t h i r t y o r f o r t y thousand different articles through the range of automobile tires, shoes, belts and beking, soles and Iieels, water bottles a n d b a t h i n g cape, a u t om o b i I e engine suspensions, airplane deicers, sound-deadening devices for trolley cars, insulation for electrical and teieptione wires, fabric for balloons, liningsfor tanks, etc., havebeen hroiight about by the work of thesepracticallyrninded applied researchers. Figure G shows an originrtl latex-made shoe and Figure 7, for comparison, milady’s shophiv of today’s design.
365
In the study of these products tlie chemical and physical propert,ics o f vulcaiiized rubber have been reduced to exactly known terms. Where even thirty years ago a rubber mixture was designed primarily as to cost and tested by the plant superintendent by biting or snapping in his fingers, today the physical values of each new material are obtained and studied. MECHAN~CAL DEVELOPMENTR. In this appraisal of the present status of the ruhber industry we should not. overlook the mechanical developments. Mixing mills are no longer of the type of the original flaricock pickle, a sketch of which is shown in Figure 8. Its great-gmndsnn is tlie Ranbury internal mixer (Yigure 9) with its ceimcity of 2100 pounds per hour. T w o - r o l l
chinery and other automatic or high-speed apparatus used in forming articles, and the type of molds and vulcanizers have been radially improved over even twenty years ago. RECLAIMED ROBBER. What to do with old scrap rubber after the article itself bad ceased its usefulness was a problem as early as 1863. Could this tough, strong, nonthermoplastic substance be plasticized? Could sulfur be removed from this combination? An enormous amount of both practical and scientific research has been done upon the reclaiming of rubber. Mitchell in 1881 patented the acid process by which he removed cotton fabric from these articles by means of acid and then heated the vulcanized rubber to soften it. Marks in 1899 developed the alkali process by which lie simultaneously and by high temperature and pressure disintegrated the fabric and plasticized the rubber of old scrap tires so that onlv a washine oneration was necessa6. This s&kled alkali process istheonestillgreatlyused. Spence proved that sulfur could be completely removed, but the product was not useful. So r e c l a i m e d rubber, although important industrially to the extent in 1933of 64,964 long tons, from the chemical research standpoint still stands about as it did in 1900. It serves as an effective balance of power to keep the price of raw r u b b e r w i t h i n hounds. ISOMEILS In the tabular outline is a field of rubber research of considerable significance, although not of largetonnage industrial value. By the treatment of crude rubber with certain acids, Fisher in 1923 found that rubber was converted into a product isomeric with the original crude rubber hydrocarbon,
36h
INDL‘STIIIAL AND ENGINEERIRG CI-IEhlIS‘I’RY
brit harder, stiffer,a.nd with a lower percentage of chemical tinsaturation. These isomers made according to the several methods worked out by Fisher or by those of Bruson in 1925 have had considerable use. Fisher’s isomer in particular has a marked specific adhesion toward steel and other metals. UERIVATWES. The true derivatives of rubber have been studied by a number of chemists, with the result that several of them are available in the markets and rimy ijccoiiir of illdustrial importance. Although the halides of ruhber were known as early as 1859 a.nd the Iiydrohalides in the order of 1881, and despite the fact that many patents for the manufacture of them h a v e been issued, there has been no considerable use of these products in industry. Only within very recent years has industrial stimulus been given to their use as paints and varnishes in p l a c e s where chemical resistance is desired. The a d d i t i o n of nitrogen-containing r a d i c a l s to rubber, datiug back to Goodyear’s nitric acid addition a n d coming down to Bruni’s nitrone, has interested chemists, but no industrial vaiue can be giveri to this work. However, certain oxidizing agents were studied by Ostromuisienskii, who in 1917 patented new vulcanized rubbers in which sulfur was not used. 811 these “vulcanized” rubbers were lower in physical value than that possessed by the sulfurvulcanized rubbers, and even though they did possess certain other properties, such as longer life under certain practical conditions, nevertheless the Ostromuisleriskii schemes have not found quantity use. SYNTHETIC RUBBER. A world of meanimg, hard work, and dreams are suggested by that expression. From the days in 1860when Williams observed the stiffening of isoprene, through Perkins’observations, down to the work in Germany during the war when an isoprene synthetic rubber, and butadiene and dimethyl butadiene synthetic rubbers were made on a practical scale, much effort bas gone over this dam without large industrial use. Dame Nature still controls the rubber industry! Not, however, quit.e in the same order of magnitude is the recent work of Nieuwland, Carothers, and others of tlie du Pont organization, who make a ruhhery body called Duprene from acetylene as a starting point. The physical characteristics of products made from isoprene synthetic rubbers are in no sense equal t o those of natural rubber, but the case of Duprene is quite dserent. Not only bas the du Pont organization brilliantly brought about a chemical synthesis, but the product is of excellent strength value and differs peculiarlg from either crude or vulcanized rubber in that it is resistant to various oils and other chemicals which readily swell or destroy vulcanized rubber. Duprene, therefore, enters the rubber industry less as a competitor and more as a partner to fill needs and uscs nThich rubber cannot meet. It is of high value, although not yet involving a large tonnage.
VOL. 27, h0..1
Still another young brother of natural rubber is the synthetic product, Patrick‘s “Tliiokol,” made from ethylene dichloride and sodium polysulfide. It is a firm, rubbery product capable of improvement in strength when heated with such suhstances as zinc oxide. It too has oil resistant properties. THERuirue~MOLECULE.Even though not of industrial 5ignificance: rtdrniriiiilc work has beeii done both in this country and abroad in imp r o v i n g the knowledge of the chemical structure OS rubber. By x-ray anrslysisand other m e t h o d s , we come every year nearer t o a true picture of the nature of t h e p r o d u c t witli \r,Iiich we deal. Peculiarly, this substance s o l o n g considered only BS a noncrystalline or a m o r p h o u s colloid becomes crystalline when stretched and possesses a fiber structure. Most investigators, therefore, believe that the ultimate rubber molecule is a long narrow one and, when stretched, that these molecules orient t h e m s e l v e s more or less parallel to each other. This field of rubber r e s e a r c h is iu,dwiitodly due for a large stimulus.
Future of Rubber Chemistry What more is there to be done? Some stockholders think the rubher chemist arid designer might well be pensioned off to spend his remaining years on the golf courses of Florida and Lake Placid with ultimate improvement in corporation balance sheets. Members of the Rubber Division of the AMERICAN CHEMICAL SOCIETY, on the contrary, feel that the work of the chemist, a t least, has only just begun, and that he should continue his studies, even though the present achievements are great. It is conceivable that either of two courses may be taken by research in the rubher industry. The one is to continue along present lines and to extend our knowledge to answer specific and necessary questions. By this plan rubber plus sulfur should be improved and its uses extended. We need to know how to protect vulcanized rubber against the action of sunlight. The field of antioxidants isunhished. When rubber is softened by milling it is oxidized, but not all rubher products should be softened by that means. An antioxidant to permit mixing mill softening without oxidation should he an advantage. More work should be done in the field of reclaimed rubber, less, perhaps, to improve it as a material to be added to garden hose tubes than to make its re-use values approximately the Rame as those of the original crude. Some work has been done in the creation of vulcanized rubber with sulfur percentages as low as 0.25 per cent. The possibilities seem excellent. Undoubtedly there is wide opportunity for the study of reenforcing pign1ent.s. It is doubtful if carbon black is the last
APRIL, 1933
IXDUSTRIAL AND ENGINEERING CHEMISTRY
367
product which we now call “rubber.” We may dream of word, fmely divided as it ip. One ccn visualize white reenstrong, tough, elastic, alcohol-soluble substances, of tires forcing pigments, lighter in gravity then zinc oxide, a t least made from a thermoplastic material, the waste of which would as finely subdivided as carbon black and perhaps, because of be re-usable a t costs not radically greater than those of the peculiar interfacial tension relations between such new prodpresent. ucts and rubber, with greater reenforcing effects against As a part of this fundamental program a broad attack abrasion. should be concentrated on the structure of the rubber A vast territory for applied research still lies open; to ocmolecule. What is rubber? Some admirable work has been cupy it the compounder and designer must work together. done but a great deal more is needed. Even if nomore chemical knowledgeshould be given them, they This idea is really but a change of emphasis from the pracwill increase and improve vulcanized rubber products for factical to the fundamental, and ultimate useful results may tory, transportation, hospitals, and home. Rubber paints conceivably far transcend anything we now know. and varnishes, adhesives from crude, vulcanized, or isomeric With some justice it may be claimed that no one rubber rubber-these conceptions have not scratched the surface of company can afford to put, perhaps, 60 to 80 per cent of its its potential values. The comfort of automobiles may be research efforts upon a program from which profitable results enhanced by rubber instead of steel springs. Can tires be a t the moment seem so uncertain. Therefore, may not the made without fabric (a well-knom-n dream)? Latex use has time have come when the rubber lions and lambs may sit down only begun, and undoubtedly a larger tonnage will be emtogether and cooperate, if not in the control of competition ployed. No attempt is made to list the possibilities. and the making of prices, a t least in a future program based The growth of crude rubber in this country should, but unupon chemical research? Executives must face now the law fortunately probably will not, be extensively pursued. We of diminishing returns in research as conducted along present need a rubber Burbank as a successor to Edison in Florida. lines. Suppose, then, that a cooperative research laboratory Yet the potential production of Hevea rubber in the Far East is so enormous and a t so low a cost with profit to the grower were developed, a new building built, the present research brains of the industry concentrated in it, and its location that one cannot wax enthusiastic over the industrial outlook placed away from any present factory. With the pooled for American grown rubber. revertheless, goldenrod rubber is real and its study should be pursued. support of even a portion of the rubber industry, the burden Such undertakings would merely be a continuation of upon each corporation would be relatively insignificant. Stockholders of corporations may well ask, “What will I present methods. Shall this industry continue to occupy get from this scheme? Another and worse black eye because itself chiefly with rubber as (CsH~),Sv and its few unsolved of 50,000-mile tires?” They would, perhaps, be interested chemical but many applied problems? Great as have been the achievements with respect to vulcanized rubber, from a in a chemist who could change the surplus vulcanizers and chemical point of view they are comprised within a relatively buildings into rubber latex or cotton fiber but not into just narrow range, another new tire. t h a t of o n e They may be c h e m i c a l comright in a sense, pound. Indeed, b u t t h i s idea c o n t e m p lat es so thorough have these investigafundamental retions been that search which, in were the research t h e r u b b e r inlaboratories of dustry a t least, t h e r u b b e r incan p r o b a b l y dustry to be b e t t e r b e perclosed, the high f o r m e d if nonservice now competitive. rendered by vulThe results from canized r u b b e r it can b e m a d e could c o n t i n u e availab!e to those for many y e a r s who have conunchanged a n d tributed toward a f u r t h e r numCourtesy, Farrel-Birmingham Co. it, and a satisfacber of new prodFIGURE10. MIXINQMILL(21 X 81 INCHES)R I T H MOTOR-OPERATED ADJUSTMENT FOR t o r y control of ucts, d e s i g n s , THE FRONT ROLL i t s accomplisha n d construcments can surely tions perform useful service in human life be realized because industrial leaders will have worked toThis reasoning leads to the conviction that the rubber ingether in their development. dustry is a t the crossroads with two courses before it: either If a n ample appropriation were made and continued over a t o keep on along present lines or to branch out upon a broad, period of ten years, the entire scope, quality, and utility of intense program of fundamental research. Surely rubber the rubber industry might be revolutionized. Even though plus sulfur is not the only compound of value to be derived the worst were to happen and no practical results were to from rubber. The new plan is one by which the heavy excome from such activities, the industry would be dead certain penditures in money, time, and personnel should be given in the of its position in so far as research might influence it. field of derivatives, isomers, transformation products-call RECEIVED March 1, 1935. them what you will. Undoubtedly there are tremendous dificulties; perhaps methods must be developed, apparatus worked out, and new points of view imagined, in order to create and There is nothing which can better deserve your bring into use any one of the potentially large number of such patronage than the promotion of science. substances. Maybe from this type of investigation can come a new “Vulcanized rubber,” which will be far superior to any GEORGE WASHINGTON
