Man's physical universe

xanabras

UNIT IX

SECTION 9

NATURAL AND SYNTHETIC RUBBERS ARE VERY

IMPORTANT INDUSTRIAL MATERIALS

Introduction.

Rubber is obtained by coagulating the latex obtained by tapping

rubber trees. Originally the best grades of rubber were prepared from

latex obtained from wild rubber trees {Hevea braziliensis) in the Amazon

region of Brazil. Other grades were obtained from Landolphia

and Funtumia plants in Africa and from the Castilloa tree of Central

America. In 1876 Sir Henry Wickham smuggled 70,000 seeds obtained

from the best rubber trees along the Rio Tapajoz, which furnished the

start for the cultivated rubber plantations in the East Indies. The

production of plantation rubber rose from 11,000 tons in 1910 to

nearly a million tons in 1940, while the production of wild rubber

decreased from 54,000 tons in 1900 to about 10,000 tons in 1940.

High prices maintained by a combination of British and Dutch planters

caused the United States Rubber Company and the Goodyear Tire

and Rubber Company to establish plantations in the Far East. Later

Harvey Firestone started plantations in Liberia, while Henry Ford,

after ten years of costly research, developed a large plantation in

Brazil.

The Discovery of Vulcanization Enabled Man to Put Rubber to Work.

The desirable properties of natural rubber were early recognized,

but products made from it had the disadvantage that they became

soft and sticky when warmed and also became very stiff at winter

temperatures. In 1839 Charles Goodyear discovered that hardness and

resistance to deterioration could be imparted to rubber by mixing

sulfur with it and heating the mixture. This process, called vulcanization,

was but the beginning of a long series of researches which have

resulted in the improvement of natural rubber for many purposes

from year to year.

The long, chainlike molecules of rubber are responsible for its

extensibility, while the pronounced unsaturation of these molecules

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