NEOPRENE, THE CHLOROPRENE RUBBER E. R. BRIDGWATER,
I
E. I. du Pont de Nemours & Companq-, Inc., Wihnington, Del
XSPIRED by the prevailing high prices of natural rubber
and presumably in part by the prospect of war, intensive research on synthetic rubber was carried out in Germany, England, and Russia during the years 1908 to 1914. The only tangible result was the production in Germany during World War I of 2350 tons of an admittedly inferior product. With the return of peace, production was stopped, and to the best of our knowledge research was discontinued throughout the world until 1925 when du Pont took up the problem. While the object of previous work had apparently been to duplicate as closely as possible the properties of natural rubber, our goal was quite different. It was recognized that rubber could not be synthesized as cheaply as it could be grown in the Far East, but it was also recognized that rubber was being pressed into service for many industrial uses for which it was not a t all well adapted, merely because no better product was available. Accordingly, our objective was to create a synthetic product which would be outstandingly superior for some of these industrial uses and hence capable of finding a commercial market in free competition with natural rubber even though its price were much higher. Out of this research which extended from 1925 to 1931 was developed the previously unknown chemical compound /3chlorobutadiene, and a process for polymerizing this into the material now known as neoprene. Since this rubberlike product is chemically different from natural rubber, it is not, of course, synthetic rubber in the strict sense of the term. No one has ever made a synthetic product that is chemically identical with natural rubber, but the term “synthetic rubber” is now frequently applied to products with properties even remotely like those of natural rubber. The first plant for the manufacture of neoprene was constructed in 1931. Commercial production began in 1932, and our sales in each year since have been more than double the sales of the preceding year, with the exception of 1938. However, in 1939, our sales were again more than double the sales for 1938, and a t present we are shipping about 550,000 pounds a month of neoprene, which represents an increase of fully 100 per cent over the past 12 months. The steady increase in the consumption of neoprene is due in part to the fact that the selling price has been steadily reduced from $1.05 a pound to the present price of 65 cents. A more important factor is the continuous progress that American rubber manufacturers have made in developing the art of using neoprene so as to make from it the best possible products. It must be remembered that since neoprene is quite different from natural rubber, i t requires different formulations for its most effective use. The art of compounding natural rubber has been developed over a period of many years to such a point that rubber manufacturers today are making products that are many times more serviceable than those of 20 or 30 years ago. The art of compounding neoprene is still very young, and although remarkable advances have been made in the past 9 years, it is anticipated that the rubber industry will make equally important advances in the future; hence, the quality of neoprene products has been and will continue to be improved, independent of any improvement that may be made in neoprene itself aq a result of further research.
Xeoprene is now being sold to about two hundred and fifty American rubber manufacturers, who are making from i t practically all types of products that were previously made solely from natural rubber. Because of its higher price, neoprene is now used only when conditions of service are such that natural rubber is relatively short-lived. The fact that neoprene is almost completely immune to sunlight deterioration accounts for many of its uses, such, for example, as sealing strips around the windows on high-altitude airplanes. Other properties of neoprene that account for many of its commercial uses are its superior heat resistance and oil resistance as compared with natural rubber, and the fact that it does not support combustion. It can be burned when a direct flame is applied to it, but the fire goes out as soon as the flame is removed. Neoprene is also more resistant to oxidation than natural rubber. It does not become either soft and sticky or hard and brittle due to the action of the oxygen of the air. Because of these unusual properties, neoprene parts are used in the automobile, airplane, shipbuilding, machine tool, electrical, and petroleum industries. Neoprene is also used for garments, shoes, gloves, hospital equipment, etc. There is hardly an industry that does not depend upon neoprene to do a job that cannot be done with natural rubber. Neoprene is used commercially in solid tires for industrial trucks and experimentally in pneumatic tires for highway service. It is not used commercially for that purpose because its cost is still too high. Commercial use in pneumatic tires is expected to develop as the price of neoprene is reduced by reason of increased production and consequent lower cost. Neoprene is preferable to natural rubber for the outer surface of a tire because of its resistance to sunlight deterioration. This is a factor of particular importance in tractor and other types of tires not protected by fenders. Despite the industry’s present limited experience with tires from neoprene, i t is possible to produce tire tread compositions having abrasion resistance approximately equal to that of the best natural rubber tire treads. Neoprene has required 8 years to grow from the pilobplant stage to its present commercial maturity. Today the process for its large-scale commercial production is well developed; more than two hundred American rubber manufacturers have become familiar with its properties and have acquired the technique of fabricating i t into practically every type of product that can be made of natural rubber. More than $2,000,000 is being spent this year for additional production facilities which will be completed in the late fall and will increase production capacity t o 1,000,000 pounds a month. With this background of experience in the large-scale production and use of neoprene, it will be possible to expand production of neoprene rapidly if it should be necessary to do so. The rubber industrywould also be able to multiply its consumption of neoprene many times on short notice on the basis of the experience it has gained during these 8 years of development. How rapidly production could be expanded depends upon the extent to which i t would be deemed advisable to give construction of neoprene plants priority over other elements of our rearmament program. Although greatly increased production would result in lower costs, there is no prospect of producing neoprene as
1155
1156
cheaply as natural rubber can be grown. The quantity of neoprene that can be sold in free competition with natural rubber a t a premium price is necessarily limited, although probably considerably greater than the amount now being produced. Hence, it would not be an attractive venture for private capital to build neoprene plants with sufficient capacity to supply a major portion of our national rubber needs so long as there is a possibility that it might have to be sold in free competition with unlimited supplies of the natural product.
SYNTHETIC RUBBERS BEVIS LONGSTRETH Thiokol Corporation, Trenton, N. J.
T
VOL. 32, NO. 9
INDUSTRIAL AND ENGINEERING CHEMISTRY
H E Department of Commerce reported that 175 rubber manufacturers purchased 1700 long tons of synthetic rubber in 1939, whereas in 1938, 168 companies purchased 814 long tons. The synthetic rubbers reported on were neoprene, Thiokol, and Perbunan. The reported consumption of crude rubber in 1939 was 592,000 long tons. Thus the synthetic rubber consumption in the United States in 1939 was less than 0.5 per cent of that of crude natural rubber. This was not entirely due to lack of productive capacity but to the fact that synthetic rubber does not compete in price with natural rubber. Where natural rubber is highly satisfactory, the synthetics are not used a t all, because their price ranges from two to five times that of the present price of natural rubber. The synthetics do a trick that natural rubber will not do, and in addition to replacing natural rubber have also been used in the place of cork, felt, leather, and metals. The figures given above show that while the total consumption is small in comparison with natural rubber, nevertheless the synthetic rubber industry has grown rapidly. Under the present emergency the subject of synthetic rubber is being examined from the opposite point of view; namely, regardless of cost can synthetic rubber be substituted for crude natural rubber? The answer is yes. All the products now being made of natural crude rubber in this country, I believe, could be made from the three synthetic rubbers being manufactured by du Pont, Standard Oil, and the Thiokol Corporation a t the Dow Chemical Company plant. The next question is whether these companies could quickly increase their production to take care of the huge output that would be necessary to replace rubber. Again the answer is yes. But, it cannot be done overnight. However, with units of certain sizes of production established, they can be duplicated rapidly. For instance, the Dow Chemical Company built a t Midland, Mich., a plant for the production of Thiokol synthetic rubber, with a capacity of 2,000,000 pounds per year, in approximately 3 months. But a problem of equal importance to that of production is the job that the rubber companies face in working out the infinite number of compounds and construction that are involved in producing finished synthetic rubber goods. While the rubber companies have had several years of experience with these synthetics, this experience has been limited to special items. Little work has been done, for instance, in the building of tires and many other types of rubber goods; there has been no incentive for such work since natural rubber has been highly satisfactory.
It appears that our Government, in its preparedness program, could well afford to give experimental orders to the rubber industry for synthetic rubber products of every type and kind used or needed by the Army and Xavy. This would cover almost the whole field of rubber goods. They could be bought on open bid from the rubber companies, and these orders would enable the rubber companies to work out the necessary compounds, constructions, processes, etc., which take such a long time. It mould also have the double advantage of allowing actual field tests of these products so that when they failed, improvements could be made in order to perfect the finished products. The Army and Navy have already, over a period of years, written specifications on synthetic rubber in special cases, such as airplane refueling hose, feed lines for airplanes, suction and discharge hose, where synthetic rubber has many advantages over natural rubber. But for most of the places where rubber is used by the Army and Navy, little attempt has been made to change from natural rubber. If these products could be worked out and actually put into service by the Army and Navy, it would be the greatest practical and useful single effort that could be made to advance the cause of synthetic rubber and enable the country to be independent of the supply of crude rubber from the other side of the world.
***
Photooraph from Wide World Photoe. Inc.
SETTLING TANKSOF THE SOCONY-VACUUM OIL COMPANY ASSUREPETROLEUM PRODUCTS FOR MARINEOPERATIONS THATARE FREEFROM DIRTAND WATER
