The Story About Rubber

By “Awake!” correspondent in Brazil

AN ENORMOUS jumbo jet approaches an airfield. For a successful landing​—much depends upon the tires. They must bear tremendous shock and friction as the aircraft, with its immense weight, touches down and comes to a halt. The only natural substance that can take such a beating is rubber.

According to Rubber, a Firestone publication, world production for 1973 has been estimated at 3.25 million long tonsa of natural rubber and 5.8 million long tons of man-made rubber. The major share goes to the automobile industry. “Automobile tires,” notes the Encyclopædia Britannica, “absorb 60 to 70 percent of the available rubber.”

Where does rubber originate? A number of tropical and subtropical trees produce a milklike fluid, or latex, containing rubber. The best commercial source for natural rubber is a straight, handsome tree called Hevea brasiliensis, native to Brazil’s Amazon jungles. It grows wild to heights of 65 to 100 feet (20 to 30 meters). Cultivated on plantations, these trees attain a height of 60 feet (18 meters). As to the source of rubber-bearing latex, the Encyclopædia Britannica states:

“The trunk of a tree may be divided roughly into an inner portion of wood and an outer portion of bark. At the junction of the bark and the wood is a layer of cells about the thickness of a sheet of paper, known as the cambium, which appears as a slimy layer when the bark is torn away from the tree. This layer is the seat of growth, on the one hand adding new cells to the wood and on the other new cells to the bark. Next to the cambium and in the soft portion of the bark are found the latex tubes. Outside the soft bark is a hard portion where there are comparatively few latex tubes. The whole is protected by an external layer of cork. The diameter of the latex tubes is considered to be about 0.0015 inch [0.0038 centimeter].”

Rubber molecules are composed of five carbon and eight hydrogen atoms. A large number of such molecules linked together form long, chainlike giant molecules known as polymers (“many parts”). Says Rubber: “Scientists believe that the chainlike make-up of rubber may explain its ability to stretch. They think the long chains of rubber molecules may link and twist, somewhat like coiled springs. When the rubber is stretched, the coils pull apart. When released, they go back into place.”

Tapping Jungle Trees

Francisco da Silva is one of some 150,000 Brazilian family men who eke out a living by gathering natural wild rubber in the inhospitable forests near the Amazon River. Francisco’s daily routine starts at the crack of dawn near the jungle city of Rio Branco, Acre State, about 1,100 kilometers (680 miles) south of the equator. After a frugal breakfast, he sets out, carrying on his forehead a small lamp to illuminate the dense jungle. He also takes along a rifle to care for any dangers that might arise from wild animals or snakes.

Upon reaching the first tree, Francisco cleans the trunk. Then he uses a special knife to score the bark lightly, slanting the cut down from left to right. On each cut he places a tin cup. This serves to catch the milky juice that will ooze out from between the outside cork layer and the cambium during the next three to four hours. If a tree proves to be above average in producing, he puts up to four cups at the same level, about four inches (10 centimeters) apart.

Around noon Francisco stops to have a light meal. But soon afterward he begins collecting the latex. At about five p.m. he winds his way home with the day’s yield of some 66 pounds (30 kilograms) of latex. This will make about 22 pounds (10 kilograms) of crude rubber.

The next operation takes place in a thatched hut with no windows but with an opening in the roof. In the middle of the hut there is a slow-burning fire, with a forked branch on either side. Several times Francisco dips a pole into the latex and then rests it on the forks. As he turns the pole above the fire, more latex is poured on the pole. The heat evaporates water from the latex, and the rubber thickens. The process of adding latex continues and gradually a dark, solid ball of rubber takes shape around the pole. This continues until the ball weighs 20 kilograms (44 pounds) or more.

Periodically the heavy balls of raw rubber are brought to an agent, where they are weighed, classified and paid for. Then they are shipped out to industrial centers.

From Small Beginnings

The rubber tree was known to the Indians of tropical America. They called it caoutchouc, meaning “weeping tree.” From its latex they made shoes, coating for cloth, pear-shaped bottles, animal figures and balls for children’s play.

How did rubber get its name? This dates back to the eighteenth century, when British chemist Joseph Priestly used a piece of it to erase pencil marks. Since the substance was effective for rubbing out writing, what more apt name for it than “rubber”? This term has stuck.

It was in the nineteenth century that rubber appeared promising to commerce. At that time a Scottish manufacturing chemist, Charles Macintosh, applied the gum to cloth for waterproofing. From this came our raincoats, known by some as “mackintoshes.”

Back then, however, uses of rubber were very limited. This was mainly because pure rubber is adversely affected by heat and cold. In warm weather it becomes sticky, smelly and perishes easily, whereas it hardens and becomes brittle in the cold. In 1839, however, an American, Charles Goodyear, found a way of coping with these weaknesses. How?

During experiments Goodyear hit upon the idea of adding sulphur and lead to crude rubber and heating this compound to high temperatures. The resulting gum lacked the defects of pure rubber and, moreover, showed higher elasticity and resistance to friction. The process became known as vulcanization, after the Roman god of fire, Vulcan.

This invention signaled a turning point in the manufacture of rubber goods. Another forward step was the invention of rubber tires, including air-filled tires, for automobiles and other vehicles. Thereafter the demand for rubber soared.

Rubber “Plantations”

On the crest of a “rubber rush,” traders swarmed to the Amazon, and rubber barons amassed fortunes. Prices jumped to as much as a dollar a pound (454 grams). Manufacturers began to look for cheaper sources of rubber.

Hitherto, the sole supplier of crude rubber had been Brazil. Would it be possible to get rubber trees to flourish elsewhere? In 1876, Henry Wickham succeeded in taking to England about 70,000 seeds from Brazilian rubber trees. These were planted in greenhouses in the Royal Botanical Gardens at Kew, London. About 2,500 of the seeds germinated. The seedlings were rushed to Ceylon and Malaysia for replanting. With what result?

Nowadays, about 85 percent of the world’s supply of natural rubber comes from southeast Asia, with Malaysia being the biggest producing area. There are also some rubber plantations in Africa, especially in Liberia and Nigeria.

Man-made Rubber

The heavy demand for rubber during two world wars led to the invention of synthetic rubbers from sources such as coal and petroleum. The term “synthetic” means “put together.” Of these man-made products, some are better for certain uses than natural rubber.

Among the artificial rubbers are neoprene, which is particularly resistant to oil, gasoline, sunlight and ozone. “Arctic” rubber resists hardening and brittleness in cold weather. “Coral” by Firestone is said to be a virtual duplicate of natural rubber.

Rubber has been a constant servant of mankind for many years. It shows the wisdom and kindness of our Creator in furnishing the earth with an abundance of such natural resources that benefit mankind.

[Footnotes]

[Picture on page 25]

Rubber gatherer scoring rubber tree. Latex oozes from tree and is caught in tinplate cup

[Picture on page 26]

Ball of wild rubber being made over smoke. The carbonic acid helps to coagulate the rubber