Look around you. You can most likely see multiple things made of rubber: erasers, tires, shoe soles, rubber bands, bracelets, toys. The list goes on and on. We live in a mechanized world where rubber products are essential. This isoprene polymer presents many characteristics that are unique to it alone and this gives it its usefulness and necessity.
Natural rubber forms when multiple isoprene molecules connect, end-to-end. Isoprene molecules (which have a chemical formula of C5H8) only contain 5 carbon atoms which means that rubber is the simplest polymer that occurs naturally. Isoprene’s structure allows for rotation around any single bond between two carbon atoms. However, polymerization creates what is known as a cis double bond, which prevents rotation. This process creates two different forms of isoprene- the cis and trans forms. The only difference between the two lies in the position of the two hydrogen atoms and their complementary CH3 groups. In cis form, the two H atoms are on the same side of the double bond with the CH3 groups residing on the other half. But, in trans form, the two H atoms are on opposite sides of the double bond (meaning the two CH3 are as well). This seemingly minor alteration in arrangement has huge effects on the properties of the isoprene polymers.
The cis arrangement provides the characteristic elasticity of rubber. This elasticity is possible because isoprene polymers align themselves into randomly coiled chains. In the cis molecule, there are not many cross-links present. Therefore, when a stretching force is applied, the molecules are able to slip past one another and straighten out in the direction of the stretch. Once the tension recedes, they are able to reform their coils. Sulfur is added to this form to produce many of the types of rubber we use today. It is used to create cross-links and prevent slippage.
In contrast, the trans isoprene polymer creates a substance that can be molded but, once exposed to air for some time, becomes hard and inflexible. This occurs because many effective cross-links are present in the tight zigzag pattern of the trans form and the molecules are unable to slip past one another. This form was utilized in the production of golf balls as an improvement over the older wooden balls.
The production of this polymer is what truly led to its affect on history. In the 1800s, the rubber trade was focused around the Amazon Basin. Within these rainforest was the greatest supply of trees from the Havea species. These “rubber trees” were tapped to yield latex which was then cured over fires and shipped downstream. This created a significant flow of money to the area and built a major new industry, but there were problems. Often trees were felled in order to produce more latex. A felled tree could be drained of up to 100 pounds of latex as opposed to the three per year of a living tree. Apparently, this profit opportunity was too great to pass up. However, this practice greatly accelerated the process of deforestation within the Amazon rainforests that is still in effect today. Then, there was the labor. The merchants that ruled the rubber trade often hired Amazonian natives to work as indentured servants. The book states that this practice greatly resembled that of slavery. The work was tedious and exhausting. When they weren’t out in the forest, they lived in camps were they were watched by brutal overseers who wouldn’t hesitate to kill anyone who attempted an escape from these conditions.
Rubber production also led to the first formal colonial rule of central Africa. In 1880, Leopold II of Belgium gained interest in the area as one of the few that had not been conquered by his European competition. He secured the funds necessary for governing a colony via the rubber trade. He sold significant acreage of land to commercial rubber companies who used the natives as their work force. Leopold chipped in by supplying military forces to enforce the venture into the Congo basin to harvest the wild rubber vine. As in the Amazon, these people were forced to forget their way of life and labor as slaves for foreign overseers that saw them as merely tools necessary to secure a European profit.
Today, the need for rubber is just as influential. We live in a world that is constantly striving towards further mechanization. Rubber is essential to these new developments. It forms belts, joints, valves, tires, seals, etc. Transportation and industry itself would be nowhere without these tools.
Observing the questionable methods of production as well as the economic boost rubber has provided, it is extremely difficult to argue against its importance. It has brought many people pain while bringing others fortune. It has allowed developed societies to increase efficiency while actually decreasing the amount of man power put into the project. It has given us the cars, trucks, boats and planes that connect the world and push on globalization. All this is evidence that isoprene has truly played its role in molding our world.