Science: Post-Baruch Report

With two big butadiene plants almost completed (at Baton Rouge and at Charleston, W.Va.), 22 others to be ready for production between now and next July, synthetic rubber begins to look real in the U.S. Last week two American Chemical Society journals celebrated its birth by a presentation of the technical factors involved in the new industry. Forgotten now are the pains of the prenatal period (TIME, July 20) and the desperate remedies of the Baruch Committee (TIME, Sept. 21). More than a million tons of good synthetic rubber are in sight—for 1944.

There are a dozen varieties. At least four—neoprene, butyl, Koroseal and Thiokol—are wholly American products. Each of the synthetics is superior to natural rubber in at least one respect and for at least one use. Yet none claims to be perfect. Each will improve with further research, and ought to supersede natural rubber in its special field. Rubber itself may never regain its pre-war place, may join natural dyes, lacquers, resins, and perhaps silk in limbo.

One thing the synthetics have in common : none is really rubber. Natural rubber has never been duplicated in the laboratory, probably never will be. Chemists prefer to call the synthetic rubbers “elastomers,” a new class of materials, and an industry as big and diverse as plastics and synthetic textiles. Special properties can be built to order in elastomers because their molecules are tailor-made. They are put together in different designs by combining various small unit groups of atoms into polymers (from the Greek: “many parts”). The chief units: butadiene, acetylene, ethylene, styrene.

Butadiene Polymers. The most useful of these units is butadiene, a liquid closely related to butane, hence easily made from natural gas, petroleum refinery vapors or (less easily) from alcohol. Buna, butyl, Ameripol and Perbunan are all based on butadiene.

Closely related to it is isoprene (also called methyl butadiene). Although isoprene is the basic unit in natural rubber, it is useless by itself. But when isobutylene and isoprene are polymerized together the result is Standard Oil’s butyl, tough, very elastic, now favored for inner tubes. It is to be made at a rate of 100,000 tons a year.

When butadiene is polymerized with styrene the result is Buna-S, developed in Germany but since improved by Standard Oil (of N.J.). Styrene itself has no relation whatever to natural rubber. It is made from benzene, principally by the Dow and Monsanto companies, and gives an excellent crystal-clear plastic when polymerized by itself. Combined with butadiene in Buna-S, the product is high in tensile strength and resistant to abrasion. In some tests it has proved distinctly superior to natural rubber in wearing qualities. (Some Buna-S truck tires have lasted over 50,000 miles.) The Baruch plan calls for an annual production of 845,000 tons, primarily for tires.

Four other elastomers are made from butadiene: Perbunan, Chemigum, Hycar and Ameripol. Perbunan is made with acrylonitrile but the formulas of the others have not been published. All are highly resistant to oil and are used for oil hose, gasoline hose and gaskets. Hycar makes an excellent ebonite, or hard rubber, when vulcanized. Ameripol is featured for tires by Goodrich. None of these is included in the Baruch program; they are in production without emergency Government financing.

Acetylene Polymers. Another group of elastomers is based on acetylene which is made from calcium carbide, hence from coal. These require no petroleum or natural gas. Acetylene is converted into chloro-prene—short for chloro-butadiene—and is polymerized to give Du Pont’s neoprene. This is a close match for natural rubber but is far more resistant to oil, heat, air and light. Because it holds gases well and is not affected by sunshine, neoprene is used for barrage balloons. The program calls for 69,000 tons annually.

Goodrich’s Koroseal is made by adding hydrogen chloride to acetylene, then polymerizing. Its distinction is resistance to chemical attack, hence it is used for tanks, waterproofing, linings. But it lacks elasticity and is not included in the Baruch program as a possibility for tires.

Ethylene Polymers. Simplest of all in chemical structure is Thiokol, made by Thiokol Corp. from ethylene gas obtained from petroleum or natural gas. Both chlorine and sulfur are added before polymerizing. Thiokol is excellent for recapping and retreading, and 60,000 tons are in the program.