October, 1927
INDUSTRIAL AND ENGINEERING CHEMISTRY
covered the heat treatment of aluminum-copper alloys. The alloys of this type, chiefly used in this country for automobile parts, such as connecting rods, were developed here by Archer and Jeffries. The ease with which these alloys can be forged makes practicable the use of such forgings for anything from hood-latches to airplane propellers. Their development is a striking example of the value of a painstaking laboratory investigation of the cause of an obscure chemical phenomenon (precipitation of copper and Mg,Si from solid solution) and a careful study of the alloy systems involved. The present theory of the heat treat-
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ment is based on the careful researches of Merica, Waltenberg, and Scott, at the Bureau of Standards. Future Problems
The world’s chemists and metallurgists will be busy for a long time in speeding the development of this, the youngest of the common metals, reducing its cost, and increasing its field of usefulness. The automotive industry, on account of increasing fuel costs, is bound to receive more and more benefit from their labors, and its demands will furnish the incentive for many new researches.
Rubber Chemistry’ By William C. Geer2 150 VALLEY ROAD,N E W ROCHELLE, N. Y.
I
N T H I S age of automotive transportation one may well meditate for a moment upon the factors which have con-
tributed to its spectacular growth. Expanding as it has within our own generation, we are inclined perhaps to overlook its origins and the contributions to its success given by that ever necessary, usually comfortable, though at times exasperating, article called the rubber tire. And the world has heard but little of the rubber chemists, a quiet group of men, by whose efforts it and other rubber products have been brought to so high a degree of serviceability. An automobile. namely, a horseless carriage, is no new conception. There was such in China before 1600. Again, in the early part of the eighteenth century in France a mechanical vehicle was invented and for a day played its little part in the scheme of transportation. The period from 1800 to 1835 was a busy one for steam engineers, who created the first interurban passenger bus which made regular trips between London and Stratford. Why, the question may well be asked, did not the steam carriage extend its service and why did it soon leave the more convenient highways to run over iron and steel rails? One reason at least is definite. These early vehicles had no cushions on the wheels and they rapidly jarred themselves to pieces upon even the best of Roman roads. They were truthfully called “bone-shakers.” To be sure, a solid rubber tire was tried in those days, but it was made from crude rubber, a soft, rapidly wearing substance, for vulcanization had not been discovered and the rubber chemist was then unborn. So the steam vehicle took t o rails upon which its service expanded; and thus, perhaps, the railroad owes its early growth to the lack of rubber chemistry and the automobile, to its discoveries. Complex P r o b l e m s of t h e R u b b e r C h e m i s t
The business of the rubber chemist is confused by a loose terminology because the word “rubber” means three distinct groups of products. (1) Crude rubber, a plastic solid made from a milky sap which flows from certain trees which grow in the tropics. ( 2 ) When mixed with small amounts, say 3 t o 5 per cent of sulfur, and with other substances and heated or vulcanized, this material alters its properties, becoming stronger and more cerviceable, but the product, though radically changed, still is called This article is respectfully dedicated by,the author to I,. M. Dennis. I t will be reprinted as Article No 5 in the Louis Monroe Dennis Quarter Century Volume, to be published in 1928, in commemoration of the completion by Professor Dennis of twenty-five years of service as head of the Department of Chemistry at Cornell University. 2 Formerly vice president in charge of Research and Development, The B. F. Goodrich Company, Akron, Ohio, 1
rubber, or soft rubber. It has come into our economics in the form of numerous articles, among them certain essential parts of the automobile tire, inner tubes, bumpers, window trim or shackle blocks. Indeed, comprehended as soft rubber, is the major portion of what the world understands as rubber. (3) When, however, some 30 or more per cent of sulfur is mixed with this crude rubber and the mixture heated over longer intervals of time there results a hard, tough body known as hard rubber, or preferably by the word “ebonite.”
The rubber business presents to the rubber chemist intricate problems. To form rubber articles, mixtures of several substances are made. The tread, for instance, of an automobile tire must be composed of a number of different ingredients. I n the formulation of these mixtures, or “compounds” as they are termed, a large variety of materials may be employed. They may be grouped into ten classes. (1) Crude rubber of which there are many grades. Every mixture is supposed to contain some crude rubber. ( 2 ) Sulfur which is placed as a division by itself because it is the one known substance necessary to the process of vulcanization. (3) . Certain dry powders, or pigments, such as carbon black and zinc oxide which have a decided reenforcing or toughening effect in rubber mixtures. (4) A still larger number of pigments, usually neutral in character, diluents, if you will, whose purpose is for different applications. ( 5 ) Again there is a group of substances of an inorganic nature such as litharge, lime and magnesia, which stiffen mixtures as well as speed the time of vulcanization. (6) Colors of a large variety. (7) Oils and waxes which give definite and desirable properties. (8) A large group of organic substances discovered during the last twenty-five years, called organic accelerators, the purpose of which is to speed the time of vulcanization and to give to the vulcanized article desired characteristics, such as increased toughness and resiliency. (9) At the moment coming actively into the rubber chemists’ picture is a group of organic compounds known as antioxidants, the purpose of which is to prevent deterioration of the vulcanized rubber and thus extend its life from but a few months without such a substance to many years if it be used. (10) Finally, is the group of reclaimed rubber, namely, old scrap tires, hose, etc., which have been chemically treated in order to free them from cotton fabric and produce a plastic homogeneous material capable of mixing with advantage into rubber mixtures.
I n total, the number of chemical individuals in these ten groups of substances is several thousand. The task of the rubber chemist is not alone to know the chemical and physical nature of each of these materials. His business is complex in the extreme, for he must combine and select from these thousands, in order to create differing mixtures each of which after vulcanization may possess definite physical
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 19, No. 10
ratio fell to 24.4 per cent and the price to a low of 11.5 cents. During these years the chemist was decreasing his proportions of reclaimed and increasing those of crude. Are we not right in thinking that had he maintained a 56.7 per cent ratio in 1921 the price of crude would have been still lower and that, therefore, he saved the plantations from a greater calamity? We happen to know also that as early as 1923, when the price of crude began to rise, the rubber chemist stimulated again his studies of reclaimed that they might meet new and changed demands, and was ready with his tested mixtures to prevent a continuation of the high price of 1925 b y a n increase to 38.3 per cent in that year and 45.0 per cent in 1926. These changes were not the result of chance, but were possible only because of cool, far-sighted scientific efforts. By a computation which averages and weighs the rubber value, rubber content, specific gravity, and the proportion of the four more important grades employed, I have calculated that for every 100 pounds of reclaimed rubber used, 55 pounds of crude would be required to replace them. These figures indicate that if the same reclaimed ratio as in 1917 had continued in 1921, 58,300 tons less of crude would have Notable Achievements of the Rubber Chemist been demanded. The planters were sick enough in that PRODUCTION AND IMPROVEMENT OF RECLAIMED RUBBER- year. Such a further loss of tonnage would have been wellI n so far as they have influenced automotive transportation, nigh fatal. let me mention a few of his outstanding achievements, seOn the other hand, if the 1922 ratio, 19.2 per cent, had been lected because of the breadth of their influence rather than maintained in 1926, some 51,825 tons more of crude would from the details of the chemistry involved, of which not the have been used, and since the excess production of crude in ieast has been his ability to increase and decrease the propor- 1926 was only 31,000 tons a real physical shortage would tions of reclaimed rubber in rubber products with no loss of have been realized, and who knows to what loftier heights service value. Such flexibility in rubber compounding is the price would have risen. based upon the scientific knowledge of the rubber chemist and These latter 51,825 tons represent a saving to the industry, has been proved by thorough tests. figured against an average price of 48.5 cents3 for 1926, of The scope of this paper does not permit a description of $55,297,275. the origins of this material, its methods of manufacture, or So the rubber chemist has prevented two calamities-that the details of how it is employed in rubber mixtures. Like to the planter and that to the consumer. crude rubber, however, several grades are produced, the Nor were these striking increases in reclaimed rubber use chief source of which is the old vulcanized tires and tubes. confined to tires, for in 1926 the ratio to crude in them was A mixture containing proportions of it is homogeneous and 19.8 per cent, but in other rubber products it was 176.9 per definite. Although it cannot be used to replace crude rubber cent-an indication of how crude has been saved in other pound for pound, yet, when mixed with selected pigments commodities to permit the tire to have it. There is still a and accelerators, products of high value result and the con- long way to go before this commodity will be used to the sumption of crude rubber is noticeably altered. full in automotive transportation. Various have been the published statements to the effect IXCREASED SERVICEOF AUTOMOBILE TIRES-Another of that the recent fall in crude rubber prices was due to reclaimed the chemists’ successes has been the gain in service rendered rubber use, stimulated by influence from those in high places. the consumer by the automobile tire. A shape of tire as a n This point should be cleared and credit, if it be creditable, annular ring had been known as early as 1845, but the chemplaced where it belongs-at the feet of the rubber chemist. istry of rubber has evolved since 1906, without which knowlHe has understood reclaimed rubber these many yeais. If edge the tire would still wear out rapidly. Twenty-five years one will examine a table, recently published, showing the ago when an automobile tire ran 4000 miles without the tread relative consumption of crude and reclaimed rubber from having worn off, or the plies of fabric becoming separated, 1917 to 1926, prepared by the Rubber Division of the Depart- the user of the tire considered that he was well repaid for a ment of Commerce, and compare the high and low prices relatively large investment. Today, the tread of a cord of crude rubber for these years he may observe some signifi- tire is good a t 10,000 miles, and the plies of cord still hold cant facts. together a t 15,000 to 20,000 miles. To accomplish these improvements we have learned the Relative C o n s u m p t i o n of Crude a n d Reclaimed Rubbera OF CRUDE RUBRATIORE- PRICI~ chemistry of the rubber compound as a colloid dispersion CRUDE RECLAIMED CLAIMED TO BERb RUBBER RUBBER CRUDS High Low in rubber of the many materials mentioned earlier in this YEAR Long tons Long tons Per cent Dollars Dollars paper. It would be wholly possible to enter into a discussion 0.52 0.90 of the effect of these substances and to show data, in curve 0.39 0.57 0.55 0.16 form, to prove just the differences between the products of 0.115 0.20 0.285 0.135 1900, 1910, 1920, and the present. That would be a long 0.248 0.37 detailed story, for we have not been able to connect our knowl0.183 0.395 0.343 1.23 edge into mathematical generalizations from which predic0.365 0.90 tions are possible. a Dept. Commerce, Rubber Division, Special Circ. 1501. b India Rubber Tire Rev., 87, 40 (1927). However, it is well known that the tire tread is a firm, I n 1917 the ratio of reclaimed to crude was 56.7 per cent, tough product mixed to resist abrasive wear better than any 3 Courtesy of Henderson, Helm & Company. and the high price was 90 cents. From then to 1921 the and chemical properties, exactly realized for a wide series of diverse uses. Some thirty thousand rubber articles are said to be in current production. The tread of an automobile tire, for instance, is required to resist abrasion; it is quite a different mixture from the rubber between and around the layers of fabric that withstands repeated stretch. These two characteristics alone are diverse and call for different combinations of raw materials. Again, a rubber spring shackle block is subjected to repeated compression and the inner tube cannot leak or deteriorate unduly on account of the heat generated during service. Thus each article and often several compositions comprising different parts of a single article, require separate mixtures, each the result of chemical research aimed to sustain a specific service. This rubber chemist is discussed at length before a mention of his achievements for what seems a good reason. His efforts have not received the credit they have deserved. His results have not been patented; they have not as a rule been written up in the form of articles in the journals; and yet his contributions have been voluminous and far-reaching in point of technical and economic results.
October, 1927
I N D USTRI-4L A N D ENGINEERING CHEMISTRY
other known substance, Steel gives way in one-tenth the time; brass, leather, indeed any other known materials, wear far more rapidly than these rubber mixtures. Xor is it rubber alone, nor even rubber and sulfur, vulcanized, which shows this resistance. This property has been gained for rubber by the chemist who has learned to understand and to conquer it. On the other hand, the tread is quite unlike the soft, resilient friction compouhd which holds together the plies of fabric; the latter is soft, stretchy, and snappy. Used as a tread it would fail, but its life under heat and repeated strain is remarkable. KO two mixtures could be more different than the tread and this so-called friction and coat. They illustrate well the diverse nature of rubber products. So the rubber chemist has built compositions which give the consumer not less than a 300 per cent increase in serviceability over that of 1900. You may say that the road conditions have changed, but simultaneously with an improvement of roads has come an increase in the power of the car and in speed. There has also been a decrease in the diameter of the rims and tires SO that each section of the tire strikes the road and flexes more frequently than twenty years ago. The number of flexures sustained by tires varies from 4 million to 7.5 million per 10,000 miles. No other substance can resist such action. The non-rubberized cords under flexing tests give way a t about one-half the number of those rubber-coated. There may be those who will say that I draw an extreme picture of the part played by the rubber chemist in automotive transportation; that I do not give due credit to the designer; that I pay no attention to the marked change between the square woven fabric and the cord construction; and that no mention is made of those who increased the sectional size of the automobile tire. However, these factors have changed relatively little; 23/’5,3 cord is still standard; the cord tire was invented in 1892; and oversize tires have been made many years. Indeed, the balloon tire is a step backward to an early design now made possible because of the many new elements in the chemistry both of the tread and of the rubber between the layers of fabric. My sympathies, nevertheless, are with the tire designers who, during the past few years a t least, have had little chance to study the product because the engineers of the motor car companies have called for new size after new size, until upwards of one hundred and three4 sizes of pneumatic casingsalthough a lesser number of tube sizes-are in current production. Mold design has absorbed more energy than a study of internal tire structure. The chemists of the rubber industry are a cooperative group. They compete actively, yes, but upon matters of common interest they foregather cordially. May I be pardoned if I recommend to the automotive engineers a liberal portion of the same medicine-an active reduction of the number of tire sizes-in their own, their dealer’s, and the consumer’s interest? M y chief emphasis is that, although changes and advances have been realized in features of construction yet, relatively, evidence is clear that the chemistry of rubber has progressed more and has a greater effect upon tire life. I venture the statement that, other features remaining the same. if the old-time compositions of 1900 be used in conjunction with modern fabric and design the mileage rendered by such a tire would fall to one-third that of the present-day standard. These improvements in quality have given startling economies to the consumer. Although a figure of 300 per cent has been mentioned, a thoroughly conservative estimate of double value may be taken for purpose of calculation, for Rubber Association of America.
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records show that in 1910 over six tires per car were required; in 1916 it was 5.3; in 1926, after deducting four tires per new car produced, we are left with a figure of 45,672,000 casings used for replacement purposes or 2.9 tires per car. The bill for these casings and tubes may be assumed as 76 per cent (the ratio of 45,672,000 replacements to 61,472,000, the total tires produced) of the total sold, which were valued a t $871,649,000.4 Therefore, a t the present scale of prices, the chemist saved the consumer in 1926 a round 5662,453,000. Yet another and perhaps more startling bit of arithmetic is pertinent. Had 76 per cent more casings and tubes been needed, then probably the same additional proportion of crude rubber would have been demanded, and under such conditions the United States would have needed 640,000 tons, a volume wholly impossible, even had the Stevenson restriction plan been unknown. There could not have been rubber enough to have produced this estimated 111,914,000 casings in this country, let alone the added number of tubes. Without these achievements in rubber chemistry a physical shortage of rubber would have been faced and the production and sales of automobiles could not have expanded to the proportions so well recognized. ORGSIUC hccELERaTop,s-These are no idle statements. Each can be sustained by proof, and were I to mention no other contribution of rubber chemistry, it would suffice. But a few others may be described to round-out the story. Down to 1906, the time required to vulcanize a pneumatic tire ranged variously from 2.5 to 4 hours. Through the use of small quantities of organic substances, and of which a large number have been produced by the research chemist, this time of vulcanization has been reduced to approximately 30 to 45 minutes and the temperature a t which vulcanization may occur has been brought down to any desired practical point above that of the room. Researches have determined that the shorter the time and the lower the temperature of vulcanization, the better is the finished article. These organic accelerators, of which hundreds are in regular use, have played an important part in the improvement in quality, as well as in the economies of the rubber industry, for they give not only the shorter time of cure but greater uniformity to tires and other articles. The increased turnover in the rubber factory, made possible because of these cure-reducing substances, has saved the rubber industry fully $200,000,000 in investment in buildings, presses, molds, and power plants which would have been necessary to maintain the present volume of rubber goods production. The modern rapidity of operation of those factories has improved and not sacrificed the quality of the products. AwrIoxIDaiws-The fourth accomplishment in rubber chemistry has to do with other organic chemicals, those which have the peculiar effect of extending the life of the rubber articles. Small amounts-viz., 0.5 t o 1.5 per cent of them in a mixture-lengthen the period during which soft rubber articles remain strong and resilient. The precise chemical action of the deterioration of rubber, or perishing as the trade calls it, has been pretty exhaustively studied and chemists generally agree that that is caused by oxidation. So some years ago chemists set out, first to find accelerated aging tests to permit a quick study of the mixtures, and then to find substances to add to them which would retard the rate of decay. Success has been attained, until antioxidants are in growing demand and a prediction of the length of life of a given mixture may be made with considerable assurance. Nowadays, the antioxidant is as necessary as the accelerator. Where rubber goods formerly deteriorated on standing after, a t the outside, two years, now it is safe to say that if these antioxidants are used properly tires will be as good taken off the shelves after ten years as they used to be in
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
one. Better aging is of marked value to the consumer, although it is perhaps not capable of such a spectacular show of economies. R u b b e r Articles Used in Automotive Transport
SHOCKINSULATORS-Four major achievements of the chemist, each of far flung influence, have been discussed Let me mention now a few of the articles of rubber, other than tires, which have found acceptance in the automotive transport field. Shock insulators on the ends of springs have served not only to quiet automobiles but to render them more comfortable. For these the chemist has had to formulate the composition necessary to stand up under repeated compression, for which there seems to be a growing demand. One of the other types-that of the rubber fabric suspension disks by which the body of the car is suspended on strips of rubber and fabric-enjoys a wide popularity. BODYTRIM-we need not spend much time on the so-called body trim used in automobiles except to say that, where a few years ago the windows of closed cars continually rattled, now they have rubber channels with felt or velvet about them, through which the window glass may slide. Some 50 million feet of this material were sold to manufacturers in 1926. Of a windshield weather strip, which must not harden or oxidize but will stay soft for a period of years, some 60 million feet were sold in the same year. Further articles to add comfort and convenience are the windlace tubing, a thin wall, small size tubing used to form an edge on the doors to tighten the car and of which 100 million feet went into service in 1926; and over 12 million bumpers were used to prevent the windows breaking when the doors are slammed. Flexible couplings or rubber universal joint disks have long been used. There are sel-era1 types made of rubber and fabric. Even in the metal universal joints, rubber balls are frequently found. It is safe to say that not only does the automobile ride on rubber but also in many of them the power from the motor is transmitted through rubber to the rear wheels. Then the motor is less jarred if blocks of rubber are between it and the chassis, and the habit grows of supporting the motor itself upon nondistortable blocks of rubber. MISCELLA~EOUS-In passing I may point to rubber and fabric fan belts, of which many millions are in use; radiator hose which must be flexible and resistant to hot water and antifreeze solutions; hydraulic brake hose; floor-board mats; running-board mats; insulated wire in the electrical systems of the machine; and the storage battery of ebonite or hard rubber. These are other articles of specially designed rubber mixtures in service in this field. R u b b e r Used in Airplane T r a n s p o r t a t i o n
Shock and vibration absorbing rubber members assist over every mile of every flight, and the world will hear more about them as rapidly as the vast opportunities of air transport are realized. Risurne The rubber chemist during these past few years has achieved for the world unusual and spectacular attainments. From the product of a tree-a soft, plastic substance, in combination with many diverse materials-he has created numerous articles, each adapted for its own peculiar service. He has by this chemistry made possible the uninterrupted growth of a vast industry. I n the course of this enlargement of automotive transportation he has permitted the user to gain annual economies, ranging upwards of $7,000,000, and without his efforts restriction or stagnation would have been inevitable. He has saved to investors over $200,000,000. He has added service and length of life to rubber articles.
Vol. 19, No. 10
The Future
As he looks into the future he fears no rubber or reclaimed rubber shortage, for I venture the prediction that reclaimed rubber will be improved and larger amounts be used. The present producing capacity for reclaimed rubber is 227,000 tons per annum,s and because of a much larger and increasing tonnage of scrap available, it will for long years serve as an effective balance of power in the contpt between planter and consumer. He needs no call upon an imperfect synthetic rubber a t a high price to help in this problem of supplies to carry the automobiles of this country. The growth of rubber-bearing shrubs and plants-such as from the splendid botanical and chemical work with guayule rubber-will give us generous amounts of crude from our own soil, although one cannot entertain the thought that the English and Dutch plantations will cease to be powerful factors in the crude rubber situation. The tire may be improved through chemical research, but the engineers must need catch up with the chemist during the next decade. When the number of sizes and brands is reduced, we may undertake the task of further advance in service value. The accelerator is certain to show improvement and the antioxidant come into greater moment as a preservative to the life of rubber articles. And an extended new field will be in the use of rubber as a structural material; many parts of automobiles not now given consideration will be made of some rubber mixture worked out by the chemist for some particular use. The airplane is rapidly coming into its own, and those who fly place notable reliance upon vibration and shock-absorbing members, made of rubber. The light, strong, resilient tires and shock-absorber cord take up the heavy percussions of the start and the landing. Less noticeable, albeit perhaps more essential, are bits of rubber to prevent gasoline, oil, and water lines from shaking apart. Something a t least to the safety of transoceanic flights has been contributed by rubber. We are on the threshold of a new era. Will rubber play a prominent part as with the automobile? Without doubt. Rubber tubing insoluble in gasoline and oil will be produced; rubber paints to which water and ice will not cling; lighter and better tires; these are but random thoughts. We are sure, however, that the usefulness of rubber will be enhanced over the future only if those who construct the machine will take into their cohfidence the rubber chemist. These, then, in a spirit and reality of cooperation may work together t o draw from the infinite possibilities of rubber those special compositions which will fill the essential and changing need of the future. 6
Dept. Commerce, Rubber Division, Sgecial Circ. 1601.
New German Anesthetics German scientists in their search for improved anesthetics t h a t do not have t o be administered through inhalation, have developed a t least three narcotics that deserve more than passing notice according to a report t o the Department of Commerce by Trade Commissioner W. T. Daugherty, Berlin, Germany. E 107, known also as Avertin, owes its existence t o Willstaedter (Munich) and Sauerbruch (Berlin), and is produced by Willstaedter and Duisberg of I. G. Farbenindustrie A. G., Frankfort. It is a tribromal-alcohol, producing narcosis through the intestines. ;--Another new anesthetic is the so-called Pernokton, reported by Dr. Bumm a t the recent surgeons’ congress in Berlin. It is related to Verona1 and is injected into the veins, thus reaching sensitive parts through blood circulation. Lumbalanesthesia is another that is administered through the spinal cord and is capable of anesthetizing the lower half of the body particularly, b u t is reported not altogether harmless. Research continues t o seek anesthetics freed from the inconveniences of inhalation.
