712 CREATIVE CHEMISTRY Another new rubber substitute which, like "Thiokol," is unrelated to rubber, is " Koroseal." " Koroseal " is a polymer of vinyl chloride, CI CI CI —CH2—CH—CHy—CH—CHz—CH— , which, like neoprene, has its origin in acetylene or natural gas and salt. It finds application where absolvent- and corrosion-resistant product can be used to advantage. " Koroseal " compositions vary from materials similar to hard rubber to stiff jellies. They are used to line metal tanks, to make gaskets, to Fig. 306. A "Chemigum" tire, the raw material for which is essentially butadiene, to which is added other materials such as acrylonitrile or styrene. "Chemigum" products are oil and gasoline resistant. (Courtesy of the Goodyear Tire and Rubber Company.) coat papers, to insulate electrical conductors or cables, to join textile fabrics by heating with a warm iron, and to prepare acid-resistant paints under the name of "Koroplate." "Koroplate" is also oilresistant, and for that reason it is used to coat the inside of oilstorage tanks. "Koroseal" is made in a variety of beautiful colors. " Koroseal "-treated cloth has been used for clothing, shower curtains, and umbrellas. "Koroseal" has also been used extensively for wrist-watch straps, suspenders, garters, and trouser belts. A special composition containing aluminum is marketed in the form of ironingboard covers which enable the user to iron more pieces in a given time. Three new polymers which possess properties which should make them competitors of natural rubber for the manufacture of automobile
NATURAL AND SYNTHETIC RUBBERS 713 tires are Butyl rubber, "Chemigum," and "Hycar," all of which have their origin in petroleum. Butyl rubber is a copolymer of olefins with diolefins, which are obtained from petroleum refinery gases. By varying the composition of the raw materials, the properties of the synthetic rubber may be controlled to meet various specific needs. "Hycar" rubber is used in the manufacture of "Ameripol" tires. Butyl rubber is colorless, odorless, tasteless, and more stretchable than natural rubber. Rubber molecules are extremely polygamous, for even after being married in the vulcanizing process, they still want to join others. They will combine with oxygen from the air, for example, and this causes deterioration of rubber with aging even though it is not in use. The chemist calls this willingness of the molecules to marry others "unsaturation." The butyl rubber molecules have just enough saturation to permit them to combine with sulphur for strength. Then they are satisfied, and do not tend to react further.^ Because these synthetic butyl t- ^^-r /- • , , , , rubber molecules, . . . f IG. 307. i i r Cuttmg a block of raw after vulcaniza- Ameripol synthetic rubber. (Courtion, are saturated, they possess a tesy of B. F. Goodrich Company.) remarkable stability and durability. The consumption of crude rubber in the United States is about 1,350,000,000 pounds per year, 97 per cent of which comes from the Far East. In 1940 the production of all types of synthetic rubber was only 50,000 pounds per day, or less than 2 per cent of the crude-rubber imports, so it is quite evident that there is room for a great expansion of the synthetic-rubber industry. The erection of the necessary plants to produce enough synthetic rubber to replace a substantial portion of the natural rubber now used would require a number of years. The degree to which non-oil-resistant varieties of synthetic rubber will replace natural rubber depends upon their relative prices. Synthetic rubber has been sold at a price as low as 65 cents per pound, while the ' Science News Letter, September 21, 1940, p. 179.