Vor.. 6,
Nos. 7 AND 8
COLLEGE ESSAYS
1259
THE RELATION OF CHEMISTRY TO THE RUBBER INDUSTRY* Rubber has been known to the civilized world since the beginning of the sixteenth century. In those dim and misty years there was no chemistry to analyze and put to use this new substance which was collected from the caoutchouc tree by the South American Indians. It is entirely to the chemist's credit that this crude and then practically useless material has heen brought t h r o u g h i t s earlier and doubtful stages of development to the vital position that i t now holds in the ranking industries of the world. The earliest mention of rubher is found in some old accounts of Spanish explorations, written about 1525 or 1530. Columbus is said to have found the natives of Santo Domingo playing with halls made from the gum of thecaoutchouc tree. Pizzaro's soldiers, when they conquered Peru, adopted the native custom of smearing caoutchouc juice over their coats to make them waterproof. The first practical use that was made of this new substance gave it its name. Magellan discovered in 1772 that i t was unequalled for removing pencil marks from paper. A lump was sent over from ~ r a n c e t oPriestley, that eminent English chemist who discovered oxygen. He cut the lump into small pieces and distributed them among his friends telling them that the little cubes were "India rubbers." The natives of Peru and Brazil had used rubber, or cauotchouc, for waterproof clothing, for shoes, and had also made jugs and bottles out of it. The articles were rather sticky and ill-smelling, especially in hot weather, and Europeans were averse to adopting them for this reason. It remained for the chemist, some centuries later, to discover and develop the method
* Prize-winning
college essay. 1928-29.
whereby rubber could be made to withstand heat and cold. A Scotch mannfacturer, Macintosh, made his name immortal by putting a layer of rubber between two cloths. Even this was not satisfactory and it was not until the year 1839 that rubber manufacture was made possible, when an American, Charles Goodyear, by his now-famous "lucky accident" discovered the means of making rubber articles that would not melt on a hot summer day and would not become as stiff as a board on a cold winter one. The life of Goodyear is one of unfaltering courage and conviction. It was a life of poverty, of high hopes followed by many failures and bitter disappointmentq. A friend of his, Hayward, told Goodyear that it bad been revealed to him in a dream that sulfur would harden rnbber. For ten years Goodyear worked on the chance that this "dream" had something back of it. He met with little or no success. One day he happened to drop a piece of sulfur together with a piece of rubber, which he was holding in his hand, on a hot kitchen stove. The sulfur and rubber a t once fused into a homogeneous mass. The secret was found, for the mass formed retained its properties in both heat and cold. When asked why he had persisted in his experiments in the face of such overwhelming odds and repeated failures, Goodyear replied: "I was encouraged in my efforts . . . . . by the reflection that that which is hidden and unknown and cannot be discovered by scientificresearch, will most likely be discovered by accident, if a t all, and by the man who applies himself most persistently to the subject and is most observing of everything relating thereto." Immediately after Goodyear's discovery rubber goods began to be manufactured on a large scale. Here was the field for the chemist. Some kinds of rubber were required to be soft and pliable, as in the manufacture of rubbers, boots, and raincoats, while others had to be hard and durable, such as combs, fountain pens, and insulating objects. The degree of hardness is determined by the amount of sulfur present in the rubber. This varies from 2% for soft, flexible articles to 35% for extremely hard articles. But sulfur is not the only substance used in the manufacture of rubber. Various pigments are used to color it, accelerating agents were found to speed up the reaction with sulfur, while other ingredients were discovered to give i t body and other qualities such as toughness and resistance to abrasion, non-conductivity, and resistance to heat. These were the things which the chemist discovered in his many experiments with both the raw and the finished product. The first pneumatic tires were invented by Robert William Thompson, of London, in 1846. They were known as "patent aerial wheels." But the pneumatic tire did not come into use until after 1888. John Boyd Dunlop, of Belfast, one day tied a rubber tube around the wheel of his little son's velocipede. Seven years later a $25,000,000 corporation was busy manufacturing Dnnlop tires.
VOL.6, Nos. 7 AND 8
COLLEGE ESSAYS
1261
With the advent of the automobile and the consequent demand for rubber, to be used in the manufacture of tires, the rubber "boom" of 1909-1910 came on. Men roamed the jungles of Brazil and Africa, madly in search of the valuable "Black Gold" and rnbber rose to the stupendous price of $3.00 a pound. This was the seed which started the development of the rubber plantation systems. Plantation rubber may he said to have started in about 1876 when Sir Joseph Hooker, then director of Kew Gardens near London, obtained a quantity of seeds from Brazil. Of all the seeds delivered to Kew Gardens only 2800 germinated. Of these seedlings a few were sent to the botanical gardens a t Singapore and the rest to Ceylon. In 1881 these trees seeded and distributions were made to Java, the Malays, and India. Thus the plantation systems originated with a few seeds. Again we owe to the chemist the credit for the development of the plantation systems. Studies were made of the trees and of the best ways to propagate them. The latex was analyzed in so far as it was possible. A new improved method for separating the rubber from the latex was discovered. Briefly, this consisted of adding acetic acid to the latex, after which the pure rubber coagulated, floated to the top, and could be removed. The rubber was then pressed into thin sheets and sent to be dried or smoked, after which it was packed in large bales. From the raw latex, coming from the tree, to the finished product, the rubber is almost entirely under the supervision of the chemist. Let us follow the process through from the latex to the completed rubber article. The latex is obtained from the rubber tree by making incisions in the bark and collecting the juice which runs out. The rubber may be obtained from the latex in either of two ways. The first, mentioned above, is by coagulation, that is, by treating thelatex with acetic acid. The coagulated rubber is separated, washed, and dried. The second method is by spraying the latex into a heated chamber. The latex flows upon an elevated disk which is revolving rapidly, thus hurling it into a stream of heated air. The water is evaporated by the heat and the rubber falls to the bottom of the chamber as fine particles which form a sort of sponge. This sponge is compressed into blocks for shipment. When plantation rubber arrives a t the factory it is usually ready for compounding or mixing. Wild rubber must first be washed and dried. The rubber to be washed is placed in tanks of warm water to soften it. It is then cut up into small pieces by powerful knives and put through the cracker. The cracker is a massive machine consisting of two corrugated steel rollers, rotating toward each other a t different speeds. The rubber is fed into this and comes out torn into ragged pieces. A stream of water is continually flowing on the rubber during this process. After this the rubber
is fed through a washer until it comes out a thin sheet resembling crbpe. A washer is a machine similar to a cracker except that i t has finer corrugations. After washing the rubber is ready to be dried. This is accomplished by hanging the sheets of rubber in a dark room through which is passed a current of warm air. The rubber is now ready for mixing. This consists of passing it through a mill made up of two heavy, polished rollers which rotate toward each other a t slightly differing speeds. As the rubber goes through the mill the filler is added and the process continues until a homogeneous mass is formed. The sulfur and accelerator are usually added after the fillers have been thoroughly mixed with the rubber. The next operation is that of calendering, by which the sheets of rubber of any desired thickness are procured. The temperature required for the particular compound to be made is regulated by means of steam and water connections to the calender. The next step in the process is the most important one, that of vulcanization or curing. This consists essentially of combining the rubber with sulfur and may be done in any one of several different ways. If the sulfur has been mixed with the rubber beforehand, any one of the methods employed in the curing simply involves heating in some form or other. There are a few methods of vulcanization which do not require heating and these are worthy of explanation. The cold cure consists in dipping the rubber article in a solution of one to three per cent sulfur chloride in either carbon bisulfide, carbon tetrachloride, naphtha, or benzine. This method is used only for thin articles. The bath cure consists in dipping the rubber articles in molten sulfur. In the vapor cure rubber articles are subjected to a treatment with sulfur chloride vapor. The gas cure is performed by exposing the rubber to hydrogen sulfide and sulfur dioxide successively a t room temperature. An active form of sulfur is liberated by the action of one gas on the other. This vulcanizes the rubber. Rubber articles are made in various ways. Some are molded and vulcanized while in the molds. Some, rubber hose for example, are first formed from the sheet rubber, wrapped on huge drums or put into a cage and then vulcanized. Still others, as pneumatic tires, are built up from a combmation of sheet rubber and fiber impregnated with rubber; an extra heavy sheet of rubber is put on the top; this is for the formation of the treads. The whole thing is then put into a mold and subjected to heat which vulcanizes it. The chemist has not only discovered ways of making natural rubber useful, but he has also discovered how to reclaim old rubber and how to make rubber synthetically.
VOL.6. NOS.7 AND 8
COLLEGE ESSAYS
1263
The process of reclaiming rubber is not as yet quite perfect, but every year the chemists are discovering new and better ways of extracting the rubber from old, worn-out articles. The rubber to be reclaimed is first sorted according to classification. It is then finely divided and passed through screens and magnetic separators. Rubber containing fiber is treated with dilute sulfuric acid which destroys the fiber. The rubber is then washed and passed over riffles to remove sand and metal. The mass is then softened by mixing with oils, tars, or other softening agents, after which it is passed into large digesters where i t is exposed to live steam a t a pressure of 100 to 150 pounds. This treatment removes a great part of the sulfur and plasticizes the rubber. It is impossible to remove all of the sulfur by any of the processes a t present known to man and this is one of the fields in which the chemist is now a t work. Reclaimed rubber, although not so good as new rubber, is still a very valuable material when properly compounded to meet the service required of it. The story of synthetic rubber is the story of what the chemist can do in the case of an emergency. Professor Tilden of England in 1892 discovered that isoprene is the basic constituent of rubber. Isoprene can he obtained from turpentine, but for a long time it was not known how to convert isoprene into rubber. Dr. Mathews, another English chemist, experimenting with isoprene in 1910, one day set a bottle of it to dry over sodium. Two months later he discovered that the bottle, instead of containing a colorless liquid was filled with real rubber. However, the discovery was not epochmaking, as one might think, for isoprene could only be obtained from turpentine which in turn was obtained from pine trees. Why cut down the pine trees instead of the rubber trees? After a number of experiments i t was found that isoprene could be obtained from starch. A process of fermentation was discovered by which a large amount of fusel oil could he obtained from starch. By the use of chlorine, isoprene can be prepared from fusel oil. The chain was complete and synthetic rubber was a fact. Synthetic rubber is still more expensive to produce than natural rubber and it is up to the chemist to discover more economical means for its production. Much use was made of synthetic rubber during the World War by Germany; but this was only because she could obtain no natural rubber. No matter how much synthetic rubber is made or how many rubber trees are planted the surplus will never go to waste. There are many things for which rubber might be used. It might he used to pave the streets (and I believe this has been tried in Scotland with great success) and side walks and give us added ease and comfort in walking or riding. Even the subway and elevated might be made almost noiseless and certainly much more comfortable by the use of rubber. There are still many things for the chemist to discover about rubber and there is a great amount of work to be done. There is the process of
reclaiming rubber t o be improved and perfected. Most of the reactions in the manufacture of rubber are not yet fully understood and the discovery of these would lead to new and better ways of production resulting in an improved product. Then there is the synthesis of rubber to be further investigated a t which, .even now, our own great chemist and inventor, Thomas A. Edison, is working. Chemistry today is battling, battling with the seen and the unseen, with the known and the unknown. The world looks on with eager eyes and keen criticism, nurturing greater realization of the impossible becoming possible. Chemistry is making everything possible and who knows that probability is not the next step forward? What end can there be? Where is the finality of life when men's minds are creating such wonders for the universe? Bibliography Hawe, H. E., Editor, "Chemistry in Industry," The Chemical Foundation, Inc., New York City, 1927. Slosson, Edwiu E., "Creative Chemistry," The Century Co., New York City, 1919. Sadtler, Samuel A., "Chemi&ry of Familiar Things," J. B. Lippincott Co., Philadelphia. Tilden. William A,, "Chemical Discovery and Invention in the Twentieth Century," E. P. Dutton Co., New York City, 1926. Porritt, B. D., "The Chemistry of Rubber.'' Circular of the Bureau of Standards, No. 38, "The Testing of Rubber Goods." Firestone, Harvey S., "Rubber, Its History and Development." Peirce, Bradford K., "Trials of an Inventor" (Life of Charles Goodyear).
