Properties and Uses of Rubber
Rubber is not only elastic, but is also waterproof and is a good electrical insulator. Natural rubber is resilient and is resistant to tearing. Some types of rubber are resistant to oils, solvents, and other chemicals.
In a raw state, natural and synthetic rubber become sticky when hot and brittle when cold. The vulcanization process modifies rubber so that these changes will not occur. In the typical vulcanization process, sulfur and certain other substances are added to raw rubber and the mixture is then heated. The process tends to increase rubber's elasticity and its resistance to heat, cold, abrasion, and oxidation. It also makes rubber relatively airtight and resistant to deterioration by sunlight.
The molecules that make up rubber are long, coiled, and twisted. They are elongated by a stretching force and tend to resume their original shape when the force is removed, giving rubber the property of elasticity. Vulcanization sets up chemical linkages between the molecules, improving rubber's ability to return to its original shape after it is stretched.
Rubber is made into articles as diverse as raincoats and sponges, bowling balls and pillows, electrical insulation and erasers. People ride on rubber tires and walk on rubber heels. Rubber is also used in toys, balls, rafts, elastic bandages, adhesives, paints, hoses, and a multitude of other products.
The single most important use of rubber is for tires. Most tires contain several kinds of rubber, both natural and synthetic. Radial automobile tires contain a greater percentage of natural rubber than other types of automobile tires because radial tires have flexible sidewalls that tend to produce a buildup of heat, to which natural rubber has a superior resistance. Either natural or synthetic rubber is suitable for most uses, and price determines which is used.