Man's physical universe

xanabras

NATURAL AND SYNTHETIC RUBBERS 713

tires are Butyl rubber, "Chemigum," and "Hycar," all of which have

their origin in petroleum. Butyl rubber is a copolymer of olefins

with diolefins, which are obtained from petroleum refinery gases.

By varying the composition of the raw materials, the properties of

the synthetic rubber may be controlled

to meet various specific

needs. "Hycar" rubber is used in

the manufacture of "Ameripol"

tires.

Butyl rubber is colorless, odorless,

tasteless, and more stretchable

than natural rubber.

Rubber molecules are extremely

polygamous, for even after being married

in the vulcanizing process, they

still want to join others. They will

combine with oxygen from the air, for

example, and this causes deterioration

of rubber with aging even though it

is not in use. The chemist calls this

willingness of the molecules to marry

others "unsaturation." The butyl

rubber molecules have just enough

saturation to permit them to combine

with sulphur for strength. Then they

are satisfied, and do not tend to react

further.^

Because these synthetic butyl t- ^^-r /-


, , , ,

rubber molecules,

. . . f IG. 307.

i i r

Cuttmg a block of raw

after vulcaniza-

Ameripol synthetic rubber. (Courtion,

are saturated, they possess a tesy of B. F. Goodrich Company.)

remarkable stability and durability.

The consumption of crude rubber in the United States is about

1,350,000,000 pounds per year, 97 per cent of which comes from the

Far East. In 1940 the production of all types of synthetic rubber was

only 50,000 pounds per day, or less than 2 per cent of the crude-rubber

imports, so it is quite evident that there is room for a great expansion

of the synthetic-rubber industry. The erection of the necessary plants

to produce enough synthetic rubber to

replace a substantial portion

of the natural rubber now used would require a number of years.

The

degree to which non-oil-resistant varieties of synthetic rubber will

replace natural rubber depends upon their relative prices.

Synthetic

rubber has been sold at a price as low as 65 cents per pound, while the

' Science News Letter, September 21, 1940, p. 179.

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