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stretched condition (a sharp line in addition appears for isoelectric ash-free gelatin), give definite evidence of the appearance of a crystal-like phase when stretched. The interferences are so few and diffuse, however, that so far it is impossible t o establish the crystal system. Xevertheless, the dimensions of the unit cell must be of the same order as for rubber, and consequently the cell must contain far less mass than that corresponding to such formulas (for gelatin) as C3jHS;0,31C’n.
Vol. 18, No. 11
Striking x-ray results have been obtained in the writer’s laboratory in following the polymerization of shellac, other resins, and linseed oil. Ordinary shellac shows a diagram consisting of sharp rings and a weak “amorphous” ring. As heating in an inert atmosphere proceeds the crystal rings become weaker and the “amorphous” ring more intense, until in the completely polymerized state only the latter appears. These experiments and others related to the problem of rubber will be the subject of later communications.
Future Commercial Prospects for Synthetic Rubber’ By William C. Geer FORMERLY VICE PRESIDBST, THEB F GOODRICH Co , AKRON,OHIO
I
N AN analysis of the future commercial possibilities of
any commodity or of the extent to which research should be undertaken to produce a new or to improve an old one, we are faced .with a coldly practical problem. Research work from which financial gain or useful products are expected must indicate a hope of commercial success from the outset. The field of rubber is no exception to such a judgment. From a scientific standpoint, synthetic rubber is well known. The admirable paper of Richard Weil has shown clearly the experience of the Germans, and the chemical procedure by which they produced that substance. Others, however, began with turpentine, starch, and acetone and arrived a t approximately the same end. Commercially, however, it has been a failure. None of it is in general use, either in this or any other country, so far as our evidence goes. The present situation, therefore, is that of a commodity which is pretty well known, but which has not enjoyed an extended development in the competitive markets. 1
Causes for Synthetic Rubber Failure
Let us analyze the causes for the failure of synthetic rubber i n practical affairs. These are several. The quality is poorer, perhaps because this chemically made substance .does not possess that intricate physical structure which recent researches have shown to be possessed by the natural product from the tree. Although the chemist has achieved a substance which has many of the chemical properties of rubber, he has not duplicated that peculiar structure of the natural product nor the physical quality of natural rubber. I n the second place, although we know something about the chemical structure of both synthetic and natural rubber (from the standpoint of the arrangement of the atoms and groups in the molecule), we do not know why rubber is elastic, and therefore i t is a safe assumption we do not yet know the complete chemical structure either of synthetic or natural rubber; and until this so-called elastic structure is known and can be duplicated in the laboratory, synthetic rubber will probabIy continue to be left out of commercial products. In other words, we have not yet worked out the right type of polymerization by which isoprene or butadiene molecules may be built u p into the precise structure of natural rubber. Of far more serious commercial significance is cost, which is too high to permit synthetic rubber to compete with natural rubber. These costs are high, because even if we lbegin from coal, or other of the original raw materials mentioned above, the yield of rubber is low. And again, the 1
Presented under the title “The Present Status and Future Prospects
of Synthetic Rubber.”
different steps required in the processes, from the raw material to the finished product, are so many that the labor and overhead multiply too rapidly to permit us to gain an economical product. I n other words, the isoprene, or butadiene, or its derivatives, does not seem capable of sufficiently cheap production to permit the polymerization productnamely. rubber-to be made economically. Commercial Prospects CHEMICAL S T A N D P O 1 N T - k t me not seem too pessimistic. The future prospects for synthetic rubber from the chemical standpoint are good. It has been produced in the laboratory, and it probably will be produced, sometime in the future, of a quality to be fully the equal, if not the superior, of natural rubber. There is no chemical or physical problem involved which, however intricate, cannot be solved. To investigate this problem further is by all means a wise procedure from a scientific, if not from a national, standpoint, because we should know through research, against a period of stress a t least, the means by which this substance can be made from raw materials to be found in this country. VuLcaxmmor\.-It would be well also to investigate the vulcanization methods of synthetic rubber which have not been fully developed. The vulcanization of natural rubber has been intensively studied during eighty years, and within the last decade these methods of vulcanization have become better understood and commercially efficient. It is highly probable, if thorough research were undertaken, not necessarily along the usual lines, that the methods of vulcanizing this substance could be improved considerably. RAW ~\IaTERiaI,-Regsrdless of the foregoing observations, although synthetic rubber will in my judgment remain an interesting theoretical problem, it may not attain a position as a substitute for natural rubber under normal commercial conditions. The raw materials from which rubber may be synthesized have other and vital uses. Starch is a foodstuff. Coal and oil are not replaceable when the present supplies are exhausted. It is a sound argument that we should not draw unnecessarily upon raw materials which cannot be replaced. The trend, broadly, therefore, of research work should be toward the growth from the soil of as many of our needs as possible. The time may come when motor cars will be driven, not by a petroleum product but, for instance, by a substance manufactured from cheap cellulose. Indeed, is i t not more logical to conceive of rubber being made into motor oils, rather than petroleum products being transformed into rubber? R a w RUBBERSHORTAGE-Much has been written and said during the past few years regarding the danger from a short-
November, 1926
INDUSTRIAL A N D ENGINEERING CHEMISTRY
age of raw rubber, and that we should produce synthetic rubber because it is not possible for the plantations in the Far East to supply a sufficient amount of crude rubber for our uses. There is no logic in these arguments, and an analysis of the situation leads us to believe precisely the reverse. Only seven thousand square miles of territory have been planted to rubber trees, and yet when one considers the possibilities the world over, he can conceive of something like seven millions of square miles of territory in which rubber trees can be grown. This may sound trite, but it is, nevertheless, significant. CosT-In this practical discussion we must again look a t the cost sheet. The cost of growing and producing crude rubber is not so low as it can be brought. Preswt indications are that it can be produced more economically on plantations of some kind than in the chemical factory. It mould seem that the planters can reduce their costs radically by an intensive labor-saving campaign. This, likewise, has been discussed a t length. Such elements of cost as the clearing of the jungle can un-
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doubtedly be reduced by taking advantage of proper machinery and methods. Tapping schemes, while greatly improved over what they were ten years ago, are still too costly. The handling of latex from the tree t o the go-down requires more labor than it probably should, and the coagulation, washing, and drying, which are today intermittent processes, may be made continuous, provided the rubber trade will be willing, and no doubt it will be, to accept, instead of special types of crude rubber, one grade of a scientifically manufactured, dried, and pressed type in the form either of blocks or sheets. Conclusion
So the world has little to expect, and the planters nothing to fear, from synthetic rubber; and in the inevitable cost competition which would arise, were synthetic rubber to be produced, the planter would be able to deliver crude rubber on board ship at a profit to himself, and a t a price t o which synthetic rubber could not be brought.
Alternative Materials for Rubber Principles of Tread Wear and Resistance to Abrasion By Ellwood B. Spear RESEARCH A N D DEYELOPXENT LABORATORY, THERMATOMIC CARBOSC o . , PITTSBVRGH, PA.
HE term “alternative,” in this connection, is meant
T
to include any material now known, or yet to be discovered, that may be used in the industry instead of rubber. At present, the technologist is familiar with many such substances, among which are iron, wood, cotton, wool, silk, leather, balata, gutta-percha, Bakelite, gums, resins, bitch, asphalt, porcelain, glass, shellac, and many others. It is obvious that no one of these substancw can be used universally in the place of rubber. For instance, shellac, porcelain, and glass are very good electric insulators, but cannot be employed where elastic properties are required. Balata is used successfully in belting and gutta-percha is employed in large quantities for insulation in submarine cables. The properties of rubber are so unique and in many cases so extraordinary that it is a fair question to mk whether or not it is wise to attempt to make a synthetic product that will hare properties identical with those of caoutchouc. Would it not be a more rational procedure to aim at the production of a synthetic product having properties suitable for a specific purpose? For instance, in the manufacture of insulated wire me do not require the high tensile, the estraordinary stretch, or the very great resistance to abrasion that are exhibited by rubber compounds. On the other hand, a low dielectric constant, a low power loss, and high electric insulation are essential. Many materials are used today for this purpose instead of rubber. Shellac, paper, asphalt, gutta-percha, and several other substances may he employed for certain types of insulated wire and cable. Why not synthesize a substance for use in insulated wire where especial attention is given to the dielectric constant, the power loss, the insulating properties, and chemical stability? One of the features of rubber with which the technologist has to contend is the poor aging properties in the presence of sunlight. Properly cured rubber will last for many years if protected from strong sunlight. The writer has used a rubber stopper in a wash bottle for over ten years and when circumstances forced him to part company with the wash
bottle the stopper was still in good condition. Inner tubes will last for years in pneumatic tires for passenger cars barring accidents, provided that the climate is moderate and the speed reasonable so that the tires never become very hot. Severtheless, if a portion of one of these tubes is exposed to sunlight for a few months, the material will be absolutely destroyed so that it may be easily torn with the fingers. Is it possible to make a synthetic product that will be suitable for inner tubes and have aging properties superior to those of rubber? Another weakness of rubber comes to light when we consider the short life in steam hose. Here it is essential that the substance be impermeable to hot water or steam and have a high resistance to the chemical effects of the two last mentioned. I n steam hose we do not require high tensile, high stretch, or very great flexibility. Heat aging coupled with impermeability and moderate flexibility are the prerequisite qualities. For use in rubber shoes, rubber has some strong and some objectionable properties. I t is waterproof, flexible, resists wear very well, but the impermeability is not wholly an advantageous factor. Rubber does not permit ventilation for the feet and therefore rubbers or rubber boots become uncomfortable in a short time so that many people refuse to wear them or even rubber-soled shoes. It is possible to make a substance reasonably waterproof and a t the same time more permeable to perspiration than rubber is. The writer made determinations some years ago showing that the permeability to perspiration could be very greatly increased without unduly impairing the water-proof qualities. If one is to stand in water all day, then rubber meets the requirements for footwear quite well. On the contrary, for winter wear or intermittent wet and dry use the waterproof quality is exaggerated and the permeability not great enough to make the shoes comfortable. Can a synthetic substance be made which will be reasonably waterproof when used in footwear and still be more comfortable than rubber? As a material for solid and pneumatic tires, we are obliged
