Matter & Energy


Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Rubber

.
Rubber, natural or synthetic substance characterized by elasticity, water repellence, and electrical resistance. Natural rubber is obtained from the milky white fluid called latex, found in many plants; synthetic rubbers are produced from unsaturated hydrocarbons.

NATURAL RUBBER

In its natural state, rubber exists as a colloidal suspension in the latex of rubber-producing plants (see Colloid). The most important of these plants are the tree Hevea brasiliensis of the spurge family, and other species in the same genus, which were the sources of the original South American rubber, the commercially important Para rubber. The term Para rubber was then also applied to the product of H. brasiliensis trees cultivated in the rubber plantations of Indonesia, the Malay Peninsula, and Sri Lanka. These trees produce about 90 percent of all the new natural rubber consumed.

Crude rubber from other plant sources is generally contaminated by an admixture of resins that must be removed before the rubber is suitable for use. Such crude rubbers include gutta-percha and balata, which are products of various tropical trees in the sapodilla family, Sapotaceae. Other, nontropical sources of rubber, which were cultivated for economic reasons during World War II (1939-1945), include two shrublike plants: guayule, Parthenium argentatum, native to Mexico, and the Russian dandelion, Taraxacum kok-saghyz, native to Western Turkistan.