One of the most fascinating and important raw materials is rubber. Because of its durability and elastic properties, it is the ideal material to use (Azomaterials). It is widely utilized throughout the world, in homes, schools, and factories. Shoes, Tupperware, doormats, and mattresses are just a few examples of household items that contain rubber. At school, there is rubber in the playgrounds, balls, stamps, rubber bands, and gym floor. Factories use rubber to create tires, hoses, battery boxes and conveyor belts. The material received its name in 1770 when Joseph Priestly, an English chemist, discovered that (rubber) could be used as an eraser to “rub” out pencil marks. Now, rubber is used for more than just erasing. What makes rubber unique is that it has the ability to hold air, keep out moisture, absorb shock and it doesn't conduct electricity. Most importantly, rubber can stretch to more than nine times its original size. Substituting it is not easy though, since no other material has as many varied characteristics. Rubber is classified into two different categories: natural and synthetic.
Natural rubber comes from the latex found in many different kinds of trees and plants. Pure rubber makes up 30-35% of that latex material. Because latex spoils quickly, it must be processed into crude rubber soon after tapping. To process latex into crude rubber, the rubber has to be separated from the water and other materials contained in the latex (“World Encyclopedia” Rubber 458-466). The Hevea brasiliensis tree produces the most natural rubber although it can also be extracted from varies trees of the Euphorbiaceae family (“Buzzle”). Hevea brasiliensis is more commonly known as the rubber tree. The rubber tree grows well in hot, moist climates. The trees can grow to about 60 to 70 feet tall. One of the most excellent rubber-growing regions is 700 miles on either side of the equator (“World Encyclopedia” Rubber 464-465). Rubber plantations in Malaysia, Indonesia, and Liberia are essential for their countries economic system (White 4). Today, Malaysia is the number one producer of rubber in the world (“Buzzle”). Botanists continually work to improve the hevea tree to produce more natural rubber. They have been able to graft and breed trees that produce six times as much as a wild hevea.
When collecting latex, workers will begin at daybreak because the latex flows freely in the chill morning air (“World Encyclopedia” Rubber 464). The worker will groove diagonal cuts halfway around the tree. At the bottom, the worker will attach a V-shaped spout with a cup, which is placed strategically to prevent waste (“Buzzle”). About three hours later the worker will return to the tree and collect a teacupful of latex (“World Encyclopedia” Rubber 464-465).
Although a large amount of natural rubber is produced, synthetic rubber is more broadly used. In the late 1920s, the United States was in great demand for rubber, which caused the prices to rise. Many countries had scientists continually working to develop synthetic rubber to satisfy the new demand (“Americanchemstry”). Synthetic rubber is divided into two classes: general-purpose and special-purpose. General-purpose rubber tends to replace natural rubber. Special-purpose rubber improves on the features of natural rubber. Synthetic rubber has distinctive properties such as immense resistance to grease, air, and extreme temperatures. Because of such properties, it is better than natural rubber for certain uses.
General-purpose rubber, or SBR (styrene-butadiene rubber), is produced four times as much as all other types of synthetic rubber combined in America. Styrene-butadiene, polybutadiene, and isoprene are types of general-purpose rubber. Tires, shoes, backings for rugs, air springs and rubber parts on automobiles are made from SBR. Special-purpose rubber is more expensive then natural rubber or SBR. It has greater resistance to extreme heat and cold. Unlike natural rubber, special-purpose rubber can resist contact with gasoline, oils, sunlight and air.
In 1839, rubber products dramatically improved after the discovery of vulcanization. Early rubber products would become sticky or brittle depending on the weather (“World Encyclopedia” Rubber 460-468). Because of those weather defects, Charles Goodyear, a Connecticut inventor, was trying to modify the current rubber to withstand weather conditions. He experimented with magnesia, bronze powder, nitric acid, and boiling the rubber in lime (“Azomaterials”). Nothing worked until Goodyear accidently made his discovery, which makes rubber stronger and give it resistance to heat and cold (“Kidcyber”). While conducting an experiment, he accidently spilled a sulfur, rubber and white lead mixture on a hot stove. The rubber mixture was preserved by the heat and stayed durable and firm. The process become known as vulcanization after the Roman god of fire, Vulcan (Azomaterials). The rubber industry grew rapidly because of the dependable products that resulted. Because the chains of atoms move quite freely in rubber, it gives a feeling of being soft and elastic. Vulcanized rubber is elastic, airtight, and watertight which made it great for moving parts of machinery (“World Encyclopedia” Rubber 467). Vulcanization is needed to prepare the majority of rubber used today (“Buzzle”). Isaac Asimov said, “The most exciting phrase to hear in science, the one that heralds new discoveries, is not ‘Eureka!' (I've found it!) but ‘That's funny…'.”
A substance that stretches easily is said to be “elastic”. Rubber is considered an extremely elastic substance. Materials like steel, glass and other familiar substances are only somewhat elastic. Rubber's elastic properties make it an ideal and interesting material to test (“Gale Encyclopedia” 1248).
Elasticity is when a material can return to its original shape after being twisted, bent or stretched. Elastic deformation lasts only as long as when a force is applied to the material. Permanent changes of shape or size can occur under great forces (“World Encyclopedia” Elasticity 112). When an object undergoes plastic deformation, or exceeds its elastic limit, it takes on a new permanent shape (“Gale Encyclopedia” 1248). The elastic limit is the maximum stress that can be placed on an object without causing permanent deformation (“Van Nostrand's Encyclopedia” 256).
Elasticity description is declared clearly in Hooke's Law. It states, “The stress is proportional to the strain.” This law was named after Robert Hooke, a British scientist, who first expressed this relation. To better study the concept, he placed weights on metal springs and measured how far the springs extended in response to the weight. In Hooke's Law, stress and strain have precise definitions. Stress is defined as a practical force divided by the area the force is affecting. Strain is the additional length divided by the initial length. The ratio of stress and strain relies completely on the materials; it is different for each substance. The ratio is called the elastic modulus or Young's modulus. Thomas Young was the first to describe it. Thousands of materials have been measured. If the elastic modulus is great, the material is stiffer (“Gale Encyclopedia” 1248).
The use of rubber has endless possibilities and potential in the future. The durability and strength of this material has improved over the years (“World Encyclopedia” Elasticity 112). Scientists and engineers are uncovering the benefits of rubber being used in earthquake-resistant building, law enforcement applications, medical gloves, military, and space travel (Azomaterials). The significance of rubber goes generally unnoticed even when it is used daily. Without rubber our culture and lifestyle would be very different.