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The case for rubber.


It's hard to fight an effective war without rubber. Fan belts, gaskets, gas masks and, of course, tires are critical to the war effort. The young American army officer was well aware of this and welcomed his assignment in 1930 to search for alternative sources of rubber. The First World War had brought home the risks of being cut off from the rubber tree plantations of South East Asia, and it was becoming increasingly apparent that reliance on foreign sources was a dangerous business. His task was to investigate the possibility of using the latex of the guayule plant, which grew freely in Texas, as an alternate source of rubber. This was indeed viable, the officer found, and recommended that the plant be protected and reserved for emergencies. His advice was ignored.

Then came Pearl Harbor. Within weeks of the attack, the Japanese had advanced into the Asian rubber producing countries and the U.S lost about ninety percent of its supply. The very success of the Allied cause being at stake, a hastily appointed Presidential Commission reported. Luckily, American ingenuity came to the fore and by 1942, U.S. chemical companies were producing over 200,000 tons of synthetic rubber, twice the amount the Germans were cranking out. German scientists had begun research on synthetic rubber in the 1930s, their country also having learned its lesson during the First World War when the Allies cut off its supplies. They had a head start because of the pioneering ideas of Hermann Staudinger who had proposed that rubber was a polymer, a giant molecule made up of repeating units called monomers.

As early as 1826, Michael Faraday had distilled rubber and identified a small molecule called isoprene as one of its decomposition products. By 1879, the first synthetic rubbery materials had been produced by treating isoprene with hydrochloric acid, but chemists were unable to explain what was actually happening until Staudinger introduced the concept of polymers. Now it became clear that the secret of synthetic rubber lay in joining together isoprene units into long chains. But attempts to do this ended in failure. So the Germans experimented with molecules similar to isoprene and eventually found that a mixture of styrene and butadiene would yield a suitable rubbery "copolymer" when treated with a sodium catalyst. This "Buna-S" rubber (the name derives from butadiene, sodium (Na) and styrene) served Germany's needs, with massive amounts being produced, much of it by slave labor at a factory in Auschwitz.

Making Buna-S was not a simple business, as American scientists discovered. The polymerization worked best when the monomers were suspended in a solvent in the form of an emulsion, very much like fat droplets are suspended in water to form homogenized milk. Emulsifiers were needed to prevent the tiny droplets from coalescing and soap was an ideal candidate. After all, soap works by emulsifying oil and water. Ivory soap was selected because it was thought to be the purest such product available. Remember the 99 and 44/100 percent pure slogan? But there was a problem. While the soap was an excellent emulsifier, it somehow inactivated the sodium catalyst. Victor Mills, a chemist working for Proctor and Gamble, had an idea. Maybe the problem was the small amount of perfume that was added to Ivory to mask the soapy smell. He made a special batch of soap without any scent and found that it now did the job perfectly. Normally, such discoveries would have been tightly guarded as industrial secrets, but the 1940s were no ordinary times. President Roosevelt had created the Office of Rubber Director under William Jeffers and rubber manufacturers were asked to pool their resources. Petroleum had been the classic source of styrene and butadiene, but now methods were found to make butadiene and styrene from alcohol that was produced by the fermentation of grain, potatoes and molasses. By 1944 the U.S. was producing 700,000 tons of synthetic rubber, far out stripping German capacity. Victor Mills's discovery undoubtedly helped win the war!

Charles Goodyear would have been astounded by these developments. Just about a hundred years earlier he had produced the first practical samples of rubber. Of course, he did not "invent" rubber. This exudate of the Hevea Brasiliensis tree was already being used by South American natives when European explorers arrived. Columbus described the natives playing games with rubber balls and even coating fabrics with the latex to make primitive galoshes. Europeans found few uses for the substance. Joseph Priestley, the discoverer of oxygen, found it could rub out pencil marks on paper and coined the term "rubber." Charles Macintosh sandwiched a layer between sheets of fabric and created the first raincoat. But rubber got hard in winter and soft and tacky in summer. Goodyear dedicated his life to solving this problem. He tried mixing everything he could think of with the tree sap, including soup and cream cheese. Finances were a constant difficulty. Goodyear even sold his children's school books to help fund his research. Then came a happy accident. He had mixed the rubber with some sulfur and spilled the mix on the stove. When the rubber cooled, its elastic properties were maintained, but it was no longer sensitive to temperature. This "vulcanized" rubber eventually took the world by storm, but Goodyear, who had believed that God had given him the task of curing rubber, never benefited and died in debt.

The use of both synthetic and natural rubbers has increased dramatically in recent years. So have allergies to rubber. Research into this received a boost when Everett Koop, the former U.S. Surgeon General developed an allergy to the elastic in his underwear. We now know that certain proteins, present in small amounts in the latex, are responsible. This has renewed interest in extracting rubber from the guayule plant which apparently does not have allergenic proteins. Perhaps researchers should have listened when that army officer recommended the use of the guayule back in 1930. They would have listened 22 years later when that army officer was sworn in as president Dwight D. Eisenhower.

Joe Schwarcz, MCIC, is the director of McGill University's Office for Science and Society. He hosts the Dr Joe Show on Montreal's radio station CJAD and Toronto's CFRB. The broadcast is available at www.
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Title Annotation:CHEM FUSION
Author:Schwarcz, Joe
Publication:Canadian Chemical News
Date:Jun 1, 2009
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