Montshire Minute: Rubber

Originally aired during the week of November 8, 1999

Monday

We've all worn raincoats, boots and galoshes made from rubber. In fact, rubber has such unique flexibility, elasticity, and durability that you'll find it in hundreds of everyday products. Tires. Belts. Insulation. Surgical gloves. And lets not forget rubber chickens! Rubber was named two centuries ago by Joseph Priestley, a British scientist. He received an incredible bouncing ball from a friend. Among many other tricks, Preistly noticed the ball could rub out lead pencil marks - hence the name "rubber." Today, rubber also refers to many synthetic forms that, like the real thing, is a perfect waterproof material for galoshes, raincoats, and all manner of storm gear. You'll find out more about this amazing substance and how we humans use it to keep us dry at Montshire's new exhibit Clothing: Science from Head to Toe, which opens at the Museum on Saturday, November 6.

Tuesday

There are many tropical plants that produce a white, viscous sap called latex. One species in particular, the Hevea tree, produces a latex that can easily be converted into rubber. The Hevea tree is native to the Amazon region, but The British East Indian Company, understanding the commercial value of rubber, transported some seeds of the tree to greenhouses in England. The seeds were transplanted in other tropical regions of the British Empire, including Singapore. Today, rubber plantations in southeast Asia produce most of the world's rubber. To gather the liquid, workers slice off a strip of bark diagonally, about half way around the tree trunk. The latex flows down the cut and into a collection cup - fresh cuts are made progressively lower down on the trunk, and then the process is repeated on the other side of the tree.

Wednesday

The Brazilian Hevea tree has long been the traditional source of natural rubber, although plant-breeding research has produced trees that produce up to six times more rubber than the Hevea. Only about one third of the weight of liquid latex taken from the tree is rubber. After the latex is gathered, impurities are removed and an acid is added to help it coagulate. At the factory, the wet, solid rubber is rolled, dried, and then compacted into bales for transport. The raw latex can also be processed in a liquid form, to be used for coatings, adhesives, or carpet backing. However, figuring out how to do this was a long tortuous process. That's because early stuff made out of rubber tended to get soft and lose its shape in the summer, or become hard and crack in winter cold, or get sticky when it came in contact with almost any liquid besides water.

Thursday

If you could look at the basic structure of rubber, you'd see long chains formed by thousands of molecules. Chemists call these mega-molecules "polymers." Think of them as tiny, twisted strands of cold spaghetti. If a rubber band is stretched, the molecular chains uncoil and straighten. When it is released, the chains relax and bunch up again. This is the property that gives a rubber band its elastic "bounce." In order to make rubber really useful, someone had to figure out how to change its chemistry so it wouldn't get all soft and gooey in the heat or harden and crack in cold weather. In the early 1800s, Charles Goodyear took on this problem as his life's challenge. He was not a trained chemist, and had no financial backing for his experiments. Did he succeed? Well, I'm sure you've heard of the Goodyear blimp?

Friday

Charles Goodyear invented a process called vulcanization, which made it possible to use rubber as an ingredient for all sorts of useful things. Goodyear was so poor he did many of his experiments in debtors prison. He even sold his furniture and his children's school books to fund his work. One day he accidentally dropped a blob of rubber mixed with sulfur on a hot stove. The rubber didn't melt, and when he brought it outside in the cold, EUREKA! it retained its flexibility. After messing around some more, Goodyear showed that by steam heating rubber at around 270 degrees, and by changing the sulfur content, he could make a durable, waterproof rubber of varying hardness or softness. You'll find out more about this amazing substance and why it's so useful for raingear at Montshire's new exhibit Clothing: Science from Head to Toe, which opens at the Museum on Saturday, November 6.